Daily Archives: September 17, 2021

Newswise The novel design for a next-generation diamond sensor with capabilities that range from producing magnetic resonance imaging (MRI) of single molecules to detecting slight anomalies in the Earths magnetic field to guide aircraft that lack access to global positioning systems (GPS) will be developed by a collaboration of scientists led by the U.S. Department of Energys (DOE) Princeton Plasma Physics Laboratory (PPPL).

Leading the collaboration to develop a new quantum sensor, under a highly competitive three-year, $5.2-million award from the DOE, is David Graves, PPPL associate laboratory director for low temperature plasma surface interactions, who will work closely with co-designers Nathalie de Leon of Princeton University, a renowned expert in quantum hardware, and physicist Alastair Stacey of Australias Royal Melbourne Institute of Technology (RMIT).

"Technologies of tomorrow"

The award was one of 10 critically reviewed DOE microelectronic grants for national laboratories. Microelectronics are the key to the technologies of tomorrow, said Secretary of Energy Jennifer M. Granholm, and with DOEs world-class scientists leading the charge, they can help bring our clean energy future to life and put America a step ahead of our economic competitors.

The award brings PPPL, traditionally a fusion-focused research lab, fully into the often-bizarre world of quantum physics. This is the start of a whole new activity for the laboratory that will make us leaders in the use ofplasma to make diamond to improve sensors, said Steve Cowley, PPPL director. It is also a marvelous example of how the laboratory, under David Gravess leadership, iscollaborating with Princeton University and Professor Nathalie de Leon and physicist Alastair Stacey in Melbourne.

Creation of diamond sensors calls for the synthesis of designer diamond material that begins with a diamond seed that is built up through the gradual deposition of plasma-enhanced vapor. The trick is to replace carbon atoms of the growing material with nitrogen atoms and vacant spaces a combination referred to as NV centers in diamonds. This combination creates the sensor and is commonly called a color center since it glows red when a light shines on it.

Tricky materials design

The tricky materials design requires the exquisitely careful doping, or implantation, of nitrogen atoms together with the creation of vacant spaces in the color center. The doping is done with microwave reactors that produce the plasma-enhanced vapors that enlarge the diamond. These reactors are in some ways similar to the microwave ovens used in homes but are modified to enable them to ignite plasmas. Such reactors are very touchy and peculiar, Graves said. You have to do the process just right to get the doping to work.=

The PPPL venture will follow the pathway suggested by Stacey of Australias RMIT, who explained thatincreasing the number of color centers addressed at a time will make the sensor more sensitive.However, he said, the traditional methodofdoing this byincreasing the densityof the centerscreates defects in the diamond that degrade the color center properties and thus limit the sensor improvement.To avoid that problem, he proposed adding the innovative step of co-doping the diamond with phosphorus plasma to increase the density without electrical interference.

The plasma must be carefully controlled to successfully incorporate both dopants and that requires significant advances in plasma physics and chemistry. Key plasma researchers include PPPL physicists Yevgeny Raitses and Igor Kaganovich, leaders of PPPLs Laboratory for Plasma Nanosynthesis, who will examine plasma used in the synthesis of diamond sensors. Plasma, the fourth state of matter that makes up 99 percent of the visible universe, consists of free electrons and atomic nuclei, or ions.

Room-temperature plasmas

Kaganovich and his team will model the room-temperature plasmas and perform quantum-chemistry calculations of diamond growth, while Raitses will use state-of-the-art diagnostics to measure the chemical species, or substances, in the plasma. The plasma studies will help guide the choice of synthesis conditions. The low-temperature, or cold, plasmas studied compare with the million-degree fusion plasmas that have been the hallmark of PPPL research.

The basic idea is to combine plasma science with modeling the surface chemistry of the plasma and doing experiments to grow the diamond, Graves said. We also want to understand the science behind how you build and operate a plasma reactor to give you this highly specialized and defect-free material for useful quantum sensors.

The plan calls for buying two commercial reactors to co-dope the diamond at PPPL: one for light phosphorous doping and one for heavy phosphorous doping. The combination will enable a range of doping concentrations, Graves said.

The development process will bring all collaborators together. The group headed by Princetons de Leon will lead measurements that include what are called the coherence properties of the diamonds color centers. Such properties refer to the length of time that electrons in the color center spin in quantum superposition, or simultaneously up and down, to activate the sensor.

"Tight collaboration"

Having a tight collaboration between diamond synthesis, plasma modeling, and quantum measurement will enable a new frontier in quantum sensors, de Leon said. These research areas are typically completely separate research communities, and I am excited about what we can achieve together.

Meanwhile, Stacey will lead measurements of the doping characteristics and growth of the diamond crystal, beginning with the seed. The seed is a piece of existing high-purity single= crystal diamond, Stacey said. We often only add a tiny bit of new diamond, just as a new layer on the surface, but this new layer has precisely engineered properties [such as doping agents and increased densities] which the original seed did not have.

Graves notes the significance of the project for PPPL. This is a big step, he said. Its our first competitive [quantum] proposal. Its a pretty big deal for PPPL to get a grant in an area like this that is so different from our traditional research, and I think symbolically its important.

PPPL, on Princeton University's Forrestal Campus in Plainsboro, N.J., is devoted to creating new knowledge about the physics of plasmas ultra-hot, charged gases and to developing practical solutions for the creation of fusion energy. The Laboratory is managed by the University for the U.S. Department of Energys Office of Science, which is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visitenergy.gov/science(link is external).

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A gem of a lab will design next-generation diamond sensors, bringing the world of quantum physics into the light - Newswise

Electrons exhibit wave properties as well as particle properties, and can be used to construct images or probe particle sizes just as well as light can. Here, you can see the results of an experiment where electrons are fired one-at-a-time through a double-slit. Once enough electrons are fired, the interference pattern can clearly be seen. (Credit: THIERRY DUGNOLLE / PUBLIC DOMAIN)

At a fundamental level, we often assume that there are two ways of describing nature that each work well in their own regime, but that dont seem to play well together. On the one hand, we know that the matter and energy that makes up the Universe, from stars to atoms to neutrinos to photons, all require a quantum description in order to extract their properties and behavior. The Standard Model, the pinnacle of quantum physics, works perfectly well to describe every interaction weve ever measured in the Universe.

On the other hand, we also have General Relativity: our theory of gravity. However, this is fundamentally a classical theory, where the presence of matter and energy curves the fabric of space, and that curved space in turn tells matter and energy how to move through it. Although each one works quite well over its own range of validity, there are plenty of questions that require a thorough knowledge of both, together to answer. Due not only to their fundamental differences but their fundamental incompatibilities, many questions that we can imagine are currently beyond our ability to answer.

That doesnt necessarily imply that anything is broken with physics, but it certainly seems to indicate that our current understanding of matters is, at the very least, incomplete. In an attempt to uncover just what it is that we know, what we dont, and what the path forward might look like, I sat down in an interview with physicist Lee Smolin, wholl be appearing at the HowTheLightGetsIn festival in London this September 18 and 19. Lee is a pioneer in the field of quantum gravity and someone whose latest book, Einsteins Unfinished Revolution, details the search for what lies beyond whats presently known about the quantum Universe.

Ethan Siegel: What are the motivations behind why you would say quantum field theory and the Standard Model, and General Relativity for gravity, why can that not describe the Universe at a fundamental level?

Lee Smolin: Well it just cant. Its easy to think of experiments that that collection of ideas doesnt give consistent predictions for. More than that, there are reasons, in principle, why the principles that quantum physics is based on contradict the principles that General Relativity is based on, and we need to make these things fit together on a level of principle, because its supposed to be a fundamental theory of nature.

There are both experimental reasons and reasons of principle and between them there are also lots of technical problems that we see when we get to know them are a consequence of these conceptual clashes: clashes of principle.

ES: Can you give one example?

LS: Sure, what does collapse of the wavefunction, which is a part of quantum mechanics, look like in a spacetime which is dynamical, and which evolves according to some equations of motion in General Relativity?

ES: Einsteins original idea of unification was originally to geometrically add in classical electromagnetism to General Relativity, and we know that cant be right because we know the Universe is quantum mechanical in nature. You write about what you call Einsteins unfinished dream. Why is this dream important, even if Einsteins original ideas about it are no longer relevant?

LS: Well, I disagree with you about how relevant Einsteins original ideas were, for better or for worse. There are, in the history of science revolutions, where our understanding of nature changes profoundly and on every possible scale. When you go from being an Aristotelian scientist to a Newtonian scientist, your picture of the world changed drastically, on all scales, and there are many applications of that.

Heres what at stake. Einstein started two revolutions at the start of the 20th century: general relativity and quantum mechanics. He understood that they did not give a consistent picture put together. And in fact, he believed, and I agree with him, that quantum mechanics all by itself doesnt give a consistent picture. To put it directly, it just doesnt make sense: the quantum mechanics as it was formulated in the 1920s, by his friends and colleagues.

LS: So we have two tasks on the agenda. One is to make sense of quantum mechanics. And two is to fix that theory which is better than quantum mechanics, and to make that theory thats better than quantum mechanics also complete General Relativity. So I see it as a question of completion.

General Relativity covers very well, to a certain degree of approximation, certain phenomena. Quantum mechanics covers very well, to a certain degree of approximation, certain phenomena. Theyre both incomplete. Highly incomplete. At the level of experiments, you have to use some imagination, but its not all down at the Planck scale. There are experiments which involve timescales of minutes or seconds where we have no clear prediction. But this double revolution needs to be completed on both sides, and thats whats at stake: its to complete the revolution, because were living in a conceptual situation much analogous to that faced by Kepler and Galileo, who were contemporaries, they were each halfway between Aristotelian and Newtonian physics. They understood certain things very well, but they were deeply confused about other things. And thats our situation now.

ES: From the quantum side, Ive heard many people argue, counter to what youre arguing, that quantum physics works exactly fine for describing every quantum phenomenon in the Universe, so long as you dont also fold in quantum gravitational effects. If I can treat spacetime as being a classical or semi-classical background, then I can do everything that my quantum field theory predicts I should do without any errors or uncertainties. Do you disagree with that?

LS: Am I supposed to be impressed by that?

Aristotle worked with orbits and the positions of the planets that were accurate to a part in a thousand over a millennium. That was impressive, but it was bloody wrong. That simple-minded theory that youre describing why would somebody take such a little, little, low-ambitious thing? Of course you can make it work if you put in enough caveats and enough approximations, thats what were trained to do.

And there are some beautiful things that come out of it, like Steve Hawkings prediction of black hole radiation. So thats fine, but man, thats 1970s physics; do we want to do 1970s physics forever? Im being deliberately a bit provocative, but, you know, weve got to wake these people up!

ES: So I read, back in 2003, you co-wrote a paper [with Fotini Markopoulou] that showed what Ill say is an intriguing link between general ideas in quantum gravity and the fundamental non-locality of quantum physics. Now, maybe I should even ask you a setup question for this: we often state that quantum physics is fundamentally a non-local theory. And when we talk about quantum entanglement, we use that as sort of an illustration of that. But critics of that will say that no information ever travels faster than light from one quantum to another. Does this create any conflict in your mind? Would you say that quantum mechanics is fundamentally non-local?

LS: That quantum mechanics is fundamentally non-local, and therefore, making sense of quantum mechanics requires a strong modification in our understanding of what space is. And that General Relativity requires a strong modification in our ideas of what space is. And therefore, the things should go together. We shouldnt try to ignore that and do this and then ignore this and do that, we should fix them together, in one move. And thats what Ive been trying to do since 19 since I was in college.

That [paper], that was mostly [Markopoulous] idea, and that was a very clever demonstration of the principle that space could be is be emergent, so that time could be fundamental. And thats what she believed and she convinced me, and thats what Ive been working on, really, the last 20 years. Is the idea that time and causation are at the bottom, and are fundamental, and that space is a secondary, emergent quantity, like pressure of the air or temperature of the Earth. And so thats what weve been trying to do, and weve been having some moderate success along the road.

So that what we experience of the world, evolving in time event-by-event, event-by-event, is real, thats how the world really is. And out of that fundamental, active notion of time and causation, we make space as a derivative concept, the same way that out of the motion of atoms, you make a gas.

ES: Interesting. So you are very strongly an advocate that this classical notion of cause-and-effect, persists all the way down to the quantum level. I would assume that this means you are not a fan of quantum mechanics interpretations that do not maintain cause-and-effect as a fundamental tenet of all interactions?

LS: Mmm-hmmm, yes.

ES: I know that you have stated, and I dont know if its for ideological or physical reasons, that reality ought to be independent of us, the observer.

LS: Yes, of course.

ES: You say, yes, of course. And many people throughout the history of quantum mechanics have not thought, yes, of course. Can you explain why reality should be independent of the observer?

LS: Because Im a realist, and for me the goal of science is precisely the description of nature as it would be in our absence. Now, that doesnt mean that there isnt a role for the observer. For example, in the theories Ive been developing for the last five years its called the theory of views what is real in that Universe is a view of that Universe, looking back, causally, into the past. And thats exactly whats real. John Bell, who was very much a realist, used to say, we have to say not what the observables are, but what the viewables are. So Ive been developing this theory where we have events, and then have information or news that comes to them from the past, and thats whats real: those views. And the dynamics of the world doesnt depend on differential equations in space, or fields, it depends on the views, and the differences between those views. And the basic dynamical principle of the theory is that the Universe evolves to make the views as varied and as different from each other as possible.

ES: So you have a principle, then, of something thats either maximized or minimized.

LS: Of course.

ES: Is that something you could describe for us?

LS: Sure. Its called, the variety. It can be applied to many different kinds of systems, so lets take cities. Consider an old city: the center of Rome, which was preserved. Think of calling a friend and saying, Im lost, Im at some corner and heres what I see around me. Now, Rome is a city with a lot of variety, so your friend is gonna be able to say, Oh, youre there, near the [whatever] because every corner looks different. Rome is a city with high variety. On the other hand, there are some very suburban-dominated cities, in which you wouldnt know very much about where you are just from what you see when you look around, because many of the corners are similar to each other. So that can give you an example of what we mean when we say, we want to increase the variety.

ES: So when you say, we want to increase the variety, do you think that nature extremizes variety?

LS: Yes, and I can write that down as an equation within the framework I discussed, where there are these causal relations, and theres energy and momentum, but theres no space. We can construct a dynamical theory that extremizes, over time, the variety of the system. And we derive from that, quantum mechanics, and as a limit of that, classical mechanics.

Why do we get quantum mechanics out? Roughly speaking, there was an original realist interpretation of quantum mechanics called pilot wave theory, that Louis de Broglie invented in 1927, and it was reinvented by David Bohm in about 1952. And in that theory, theres potential energy and theres another new function of the wavefunction, and it sits where the potential energy usually sits. And they derive the Schrodinger equation from maximizing the influence of this function. Well, it turns out that this function that David Bohm invented is a certain limit of the quantity we call the variety, by the way with Julian Barbour, back in the 80s. And this was one of the great surprises of my working life.

ES: When you take this limit of the quantity you call the variety, and youre saying, were extremizing over that, this sounds to me like something that would be pretty analogous to some type of entropy, some type of thermodynamic quantity. So far, everyone I know whos tried to come up with a concept of gravity is emergent or space is emergent or some other quantity that we normally look at as fundamental is in fact emergent, takes something that in typical physics thought we view as emergent and makes that fundamental. I would say the typical view of physics is that entropy is an emergent property that you can calculate based on, say, the microscopic quantum state of all the particles aggregated together. Are you basically doing something similar to that, except with this thing you define as variety instead of entropy?

LS: Roughly speaking yes, but thats a long discussion. Because the role of entropy in cosmological theory is something we have to get our heads straight about. Theres a series of three very beautiful papers that Marina Corts, Andrew Liddle and Stu Kauffman have that weve been working on for a few years, and they contain some important new insights about very far-from-equilibrium systems and their relation to cosmology.

ES: Id like to ask about this idea that Heisenberg and a lot of other people had, which is that unless you have what we call an interaction in some sense one quantum interacting with another quantum thats the only thing that provides meaningful information about the Universe. If you dont make a measurement, then you dont have a quantifiable property of the Universe. So all of the information that we have has to come out of that act, which I look at, maybe naively, as fundamentally antagonistic to this idea of an objective reality. The fact that we cant make any measurements that discern between this Heisenberg-esque picture of reality and a objective reality exists picture of reality you have a certainty about your perspective that I dont share and that many physicists dont share. How do you make sense of this if you cant tell experimentally between these different interpretations?

LS: No, thats a fake. I dont know that, but its a good working fake. Let me tell you about how I look at quantum mechanics these days, because its new and its been very exciting to me. Our realization, actually following down some quotes of Heisenberg which were very mysterious at first, you know that Heisenberg said that the wavefunction description does not apply to the past. Somehow, the wavefunction was about the future, and the classical description is about the past. And a few people said this. Freeman Dyson said this at length; Schrodinger said something like that, and even deeper and more mysterious.

What we realized they were trying to say is that in the Copenhagen version of quantum mechanics, there is a quantum world and there is a classical world, and a boundary between them: when things become definite. When things that are indefinite in the quantum world become definite. And what theyre trying to say is that is the fundamental thing that happens in nature, when things that are indefinite become definite. And thats what now is. The moment now, the present moment, that all these people say is missing from science and missing from physics, that is the transition from indefinite to definite. And quantum mechanics, the wavefunction, is a description of the future which is indefinite and incomplete. And classical physics is how we describe the past.

Why? Because the past happened, what happened was definite, and it doesnt change, because its the past. So we have this different way of thinking about quantum mechanics, and it seems to be helpful, were having a good time.

ES: Its very hard to disagree with that. So when you look at, lets say, Wheelers delayed choice experiment. And Im thinking in particular of one where you send in a photon and you have a beam splitter, and the photon can take two paths around mirrors, and theyll meet up on the other side. And either youll have another beam splitter that will combine them and youll get your detector that will see an interference pattern of the recombined photons, or you wont put the splitter in there, and youll just get one of the photons that comes into your detector.

So, you can do this, and Wheelers idea is that you can send the photon through that first splitter, to have it go those two different ways. And then you can either put the second splitter there or not. And at the last second, you can either remove the splitter that was there (or not) or you can insert the splitter that wasnt there to try and, he called it, catch the photon deciding on what it was going to do before you made that measurement.

In hindsight, to no ones surprise, what did you measure at the detector? Well, if the splitter was there, you get the interference pattern back. And if the splitter wasnt there, youd just get the one photon back. Basically, nature doesnt know in advance what youre going to do. But once you do it, its like it knew all along what you were going to do. That, to me, and youre going to tell me thats not the only interpretation, has always meant the act of interacting, itself, is what gives you that meaningful information. If you didnt have any interactions taking place, you have not determined your reality yet. Your reality remains indeterminate until you make a measurement that would discern between the different possibilities.

LS: Yeah, but you see, I agree with that. Only, my line is now, is the boundary between the future and the past.

ES: Are you saying that right now, the in progress things, that have not yet been decided, that will be decided with an interaction at some point in the future, are you saying that everything in the past has already been determined, even those things where that measurement that will draw that line has not yet occurred?

LS: So that event has not yet occurred, so thats rather compatible. The notion of the now that gives rise to is not a thin instant, where it has to happen here; its what the philosophers call a thick now. So there can be events that turn something definite, that are late, or that are early, so our now can zigzag quite a bit. At least, thats the way we try to understand those cases. Theyre not in the original two papers, but were going through all these thought experiments in detail and show how to think about whats going on.

ES: This is stuff thats right on the cutting edge of trying to understand what the fundamental nature of reality is. Youve written very much, Id say, non-positively about many of the ideas in string theory, and how theyve become this dominant theoretical paradigm. One of the things Ive noticed about your work is that it seems to be relatively agnostic about other extensions to what might be out there: string theory, supersymmetry, grand unification, etc., you seem pretty agnostic about this all, which is maybe in contrast to what peoples public perception of you is.

LS: If people want to express an opinion about [my 2006 book, The Trouble With Physics], I would ask them the favor that they should read it. There was a lot of angst and conflict in that period, and I think people would be surprised here, but let me just tell you what I think. What I believe is that there are a number of interesting different approaches to quantum gravity, which so far are all incomplete. They all manage to explain something to us about what a quantum description of spacetime may be, but each of them also get stuck somewhere on some characteristic.

String theory is a beautiful set of ideas, which in my view has gotten stuck. And loop quantum gravity, which Im fortunate enough to have had the experience of working on while it was being invented, but its also clearly gotten stuck. Both of them express the same idea: that theres a duality between fields carrying forces, like the electromagnetic field, and quantum excitations of those fields can look like extended objects, like strings or loops, propagating. Both loop quantum gravity and string theory express in different contexts that fundamental conjecture.

What I tried to express in that book, and its always the authors fault when youre misunderstood, that book started as a case study of the role of conflict in science. Being a student of Paul Feyerabend, I think that conflict and disagreement are vital to the progress of science. And that book was meant to be an argument for that, using the case study that I knew best. As the book got shaped by me and by the editors, we flipped the book so that the case study came first and the analysis in terms of how the conflict plays a driving role in science came second, and most people only read the first half.

What I was against, and what I am against wherever I see it, is premature dogmatism: premature believing in something more than what the evidence supports. And this, unfortunately, is very common in science, because we all want to believe that weve done something good and discovered something. There was an atmosphere at the time, which I think is very dissipated now, of over-optimism in my view. I try to give a balanced view of what the strengths of string theory were and what the weaknesses were, and unfortunately some people reacted to that. But that was a long time ago.

ES: Can I ask you what you think of certain effective approaches to quantum gravity? Like asymptotically safe gravity, do you think that offers any promise? Ive always had an appreciation for that one because it seems to allow for predictions to be made in an otherwise inaccessible regime.

LS: Asymptotic safety has some very attractive points. Its basically an application by Steve Weinberg about some ideas about perturbatively non-renormalizable theories that Ken Wilson had, and he applied their ideas to gravity. Its a very attractive story, but theres a problem; as I said theres always a problem. The problem in asymptotic safety is unitarity. We know of an asymptotically safe theory which is present even in perturbation theory. Can we speak a little math here?

ES: Go ahead, Ill translate.

LS: The action principle to the theory is the Einstein action principle, plus the cosmological constant term, plus a term in the Ricci scalar squared plus a term in the Ricci tensor squared. And this last one invariably introduces instabilities and an impossibility to satisfy the principle of unitarity, which among other things means you cant guarantee that the probabilities for all the things that will happen will add up to one. And this has been a known problem since 1978 or 1982 or something, and I wrote the third paper in response to Steves paper that showed the violation of unitarity. So thats where it stands in my mind, but its always good to follow the kids, and theres a bunch of smart, young people working on this. Its not my bet, but its their bet, and theyre really good.

We dont have any senior faculty working on asymptotic safety at Perimeter, but we were so impressed by some of the young people who applied to us that, despite our own misgivings, we hired them for a few years. Because its interesting and exciting to have them around, and if you want your field to prosper, youve got to be able to listen to and promote young people who disagree with you, otherwise its not science.

ES: When Ive felt optimistic about it, Ive looked towards asymptotically safe gravity in the same way I now look back at the time-dependent Schrodinger equation. I say, okay, look, this has cases where it doesnt apply, and cases where it breaks down, because its not a relativistically invariant theory. But if you can find a formulation of it, like the Dirac equation, that is relativistically invariant, or if you could find a more general formulation, like quantum field theory that eliminates the need for that sort of thing. Maybe this idea can be salvaged, despite the fact that the way its formulated now, it doesnt guarantee unitarity.

LS: But if you turn it up so that it is giving you unitary answers to second or third order in perturbation theory, then the condition that there should be a non-trivial fixed point constrains the top quark mass by a measurable amount. They actually get a prediction that if this all works out, then heres the top quark mass.

ES: I remember reading a paper by Wetterich and Shaposhnikov years before they had measured the mass of the Higgs boson where they used the mass of all the particles except the Higgs to say, well, instead of getting the mass of the top were going to get the mass of the Higgs, and the value they got was ~126 1. But if I remember right, since then, the mass of the top has changed a little bit, and now if you put that same math back in, youd get something like 129 or 130, which doesnt agree with what theyve seen at the LHC.

LS: I didnt know that; thats interesting. Thats great. What else excites you?

ES: One thing Id like to press you on a little bit is this: if you have a dynamical spacetime, versus a static spacetime, how can you describe wavefunction collapse in a changing spacetime? If you have a wavefunction in a changing spacetime, what does wavefunction collapse look like, if your spacetime isnt static?

LS: Roger Penroses view of that is that the collapse of the wavefunction is a physical thing that happens when a certain measure of energy involved in that possible event is equal to the planck energy per planck time, or something like that. I dont remember the exact way he did it. So then, youre in a domain where neither the Einstein equation or the Schrodinger equation is quite right.

What Im really, really excited about is that there are some experiments under development where they actually test that. Theres a whole new generation of tabletop gravity or quantum gravity experiments that different people are working on.

ES: I like the tabletop experiments that are happening. One thing that I definitely wanted to ask you about is, youve talked, Ill say derisively about people who treat conclusions as if theyre foregone conclusions without having evidence to back that up. You want to remain open-minded to anything that may be possible before that critical evidence comes in. Do you worry that taking the stance of saying, I am a realist when it comes to quantum physics is violating that piece of advice. Do you worry about saying, Im a realist and I believe that reality is observer-independent is making that mistake?

LS: You know, I dont know whats wrong with me, but I love this stuff to death. I am having so much fun and theres nothing like it to be able to think about this stuff. Some people have this wire in them that says they have to be right, and I dont have that. I dont know why, maybe its a defect? So, sure, if you ask me, yeah, I could be wrong about that. I could be wrong about a lot of things.

Lets put us 1000 years in the future, well all look like fools for having missed the obvious things in neuroscience or planetary science or something that turned out to be important. There was a famous boxer who was asked how he felt about his career, and he said, you know, I did the best I could with what I was given. And Im happy with that. I dont gotta be right, but if I didnt follow what I believe in, I wouldnt be as happy a person now.

ES: I want to pull out a Niels Bohr quote and ask you your opinion of this, then. When we measure something, we are forcing an undetermined, undefined world to assume an experimental value. We are not measuring the world; we are creating it. This strikes me as a statement that I would expect you to fundamentally disagree with, but you might surprise me.

LS: No, it doesnt appeal to me, but wow, Im really sorry I never got to meet Bohr. He was an interesting guy; cant we just be on that level? In the end, Bohr was at a very weird place from our point of view in the development of western culture and society. He was influenced by Schopenhauer and people like that, and so he had what we would consider not just a non-realist viewpoint, but a radical non-realist viewpoint, and he did the best he could with that. But I dont believe that, that doesnt keep me up at night, but sure.

ES: Do you have any thoughts youd like to share that I havent asked you about that you think are too important to not share?

LS: Open up the scientific community to more people who are highly trained and really good. And maybe Im just getting this in because I like these ideas. For me, when people talk about diversity, that means not just women and blacks and aboriginals and who else, those are all very very important, but also very important are people who think differently. Now, to make a success in physics, you cant just be anyone off the streets, its like I couldnt compose a piece of music and send it to the New York Philharmonic and have them play it.

Youve gotta have your tools, youve got to be practiced, you gotta be good with your tools, youve gotta make a convincing case for the results that youve found in your work. Thats what a Ph.D. symbolizes But among the people who are excellent, technically, we want as wide a variety of ideas and viewpoints and types and personalities and gender and race its yes yes yes yes. I would hope that the next generation and the second-to-next generation live in a scientific world that is much more fun. Because if everyones like you, its not fun.

Lee Smolin will be appearing at the HowTheLightGetsIn London 2021 festival this September 18/19, with remaining tickets still available here.

Continued here:

Are we approaching quantum gravity all wrong? - Big Think

image:Co-doping diamond collaborators from left: Princeton Prof. Nathalie de Leon; David Graves, PPPL associate laboratory director for low temperature plasma surface interactions; Alastair Stacey of Australias Royal Melbourne Institute of Technology, with ultraviolet image showing emission from diamond color centers behind them. view more

Credit: From left: Sameer Khan/Fotobuddy; Elle Starkman/Office of Communications; photo courtesy of Alastair Stacey. Ultraviolet image courtesy of Science magazine; collage by Kiran Sudarsanan for Office of Communications.

The novel design for a next-generation diamond sensor with capabilities that range from producing magnetic resonance imaging (MRI) of single molecules to detecting slight anomalies in the Earths magnetic field to guide aircraft that lack access to global positioning systems (GPS) will be developed by a collaboration of scientists led by the U.S. Department of Energys (DOE) Princeton Plasma Physics Laboratory (PPPL).

Leading the collaboration to develop a new quantum sensor, under a highly competitive three-year, $5.2-million award from the DOE, is David Graves, PPPL associate laboratory director for low temperature plasma surface interactions, who will work closely with co-designers Nathalie de Leon of Princeton University, a renowned expert in quantum hardware, and physicist Alastair Stacey of Australias Royal Melbourne Institute of Technology (RMIT).

"Technologies of tomorrow"

The award was one of 10 critically reviewed DOE microelectronic grants for national laboratories. Microelectronics are the key to the technologies of tomorrow, said Secretary of Energy Jennifer M. Granholm, and with DOEs world-class scientists leading the charge, they can help bring our clean energy future to life and put America a step ahead of our economic competitors.

The award brings PPPL, traditionally a fusion-focused research lab, fully into the often-bizarre world of quantum physics. This is the start of a whole new activity for the laboratory that will make us leaders in the use ofplasma to make diamond to improve sensors, said Steve Cowley, PPPL director. It is also a marvelous example of how the laboratory, under David Gravess leadership, iscollaborating with Princeton University and Professor Nathalie de Leon and physicist Alastair Stacey in Melbourne.

Creation of diamond sensors calls for the synthesis of designer diamond material that begins with a diamond seed that is built up through the gradual deposition of plasma-enhanced vapor. The trick is to replace carbon atoms of the growing material with nitrogen atoms and vacant spaces a combination referred to as NV centers in diamonds. This combination creates the sensor and is commonly called a color center since it glows red when a light shines on it.

Tricky materials design

The tricky materials design requires the exquisitely careful doping, or implantation, of nitrogen atoms together with the creation of vacant spaces in the color center. The doping is done with microwave reactors that produce the plasma-enhanced vapors that enlarge the diamond. These reactors are in some ways similar to the microwave ovens used in homes but are modified to enable them to ignite plasmas. Such reactors are very touchy and peculiar, Graves said. You have to do the process just right to get the doping to work.=

The PPPL venture will follow the pathway suggested by Stacey of Australias RMIT, who explained thatincreasing the number of color centers addressed at a time will make the sensor more sensitive.However, he said, the traditional methodofdoing this byincreasing the densityof the centerscreates defects in the diamond that degrade the color center properties and thus limit the sensor improvement.To avoid that problem, he proposed adding the innovative step of co-doping the diamond with phosphorus plasma to increase the density without electrical interference.

The plasma must be carefully controlled to successfully incorporate both dopants and that requires significant advances in plasma physics and chemistry. Key plasma researchers include PPPL physicists Yevgeny Raitses and Igor Kaganovich, leaders of PPPLs Laboratory for Plasma Nanosynthesis, who will examine plasma used in the synthesis of diamond sensors. Plasma, the fourth state of matter that makes up 99 percent of the visible universe, consists of free electrons and atomic nuclei, or ions.

Room-temperature plasmas

Kaganovich and his team will model the room-temperature plasmas and perform quantum-chemistry calculations of diamond growth, while Raitses will use state-of-the-art diagnostics to measure the chemical species, or substances, in the plasma. The plasma studies will help guide the choice of synthesis conditions. The low-temperature, or cold, plasmas studied compare with the million-degree fusion plasmas that have been the hallmark of PPPL research.

The basic idea is to combine plasma science with modeling the surface chemistry of the plasma and doing experiments to grow the diamond, Graves said. We also want to understand the science behind how you build and operate a plasma reactor to give you this highly specialized and defect-free material for useful quantum sensors.

The plan calls for buying two commercial reactors to co-dope the diamond at PPPL: one for light phosphorous doping and one for heavy phosphorous doping. The combination will enable a range of doping concentrations, Graves said.

The development process will bring all collaborators together. The group headed by Princetons de Leon will lead measurements that include what are called the coherence properties of the diamonds color centers. Such properties refer to the length of time that electrons in the color center spin in quantum superposition, or simultaneously up and down, to activate the sensor.

"Tight collaboration"

Having a tight collaboration between diamond synthesis, plasma modeling, and quantum measurement will enable a new frontier in quantum sensors, de Leon said. These research areas are typically completely separate research communities, and I am excited about what we can achieve together.

Meanwhile, Stacey will lead measurements of the doping characteristics and growth of the diamond crystal, beginning with the seed. The seed is a piece of existing high-purity single= crystal diamond, Stacey said. We often only add a tiny bit of new diamond, just as a new layer on the surface, but this new layer has precisely engineered properties [such as doping agents and increased densities] which the original seed did not have.

Graves notes the significance of the project for PPPL. This is a big step, he said. Its our first competitive [quantum] proposal. Its a pretty big deal for PPPL to get a grant in an area like this that is so different from our traditional research, and I think symbolically its important.

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PPPL, on Princeton University's Forrestal Campus in Plainsboro, N.J., is devoted to creating new knowledge about the physics of plasmas ultra-hot, charged gases and to developing practical solutions for the creation of fusion energy. The Laboratory is managed by the University for the U.S. Department of Energys Office of Science, which is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visitenergy.gov/science(link is external).

Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.

Continued here:

A gem of a lab will bring the world of quantum physics into the light - EurekAlert

By Emily Dieckman, College of Engineering

Thursday

Zheshen Zhang, a University of Arizona assistant professor ofmaterials science and engineering, is leading a $5 million quantum technology project to advance navigation for autonomous vehicles and spacecraft, as well as measurement of otherworldly materials such as dark matter and gravitational waves.

The National Science Foundation'sConvergence Accelerator Program, which fast-tracks multidisciplinary efforts to solve real-world problems, is funding the Quantum Sensors project.

In September 2020, 29 U.S. teams received phase I funding to develop solutions in either quantum technology or artificial intelligence-driven data sharing and modeling. Ten prototypes have advanced to phase II, each receiving $5 million, including two projects led by UArizona researchers Zhang's project and another by hydrology and atmospheric sciences assistant professor Laura Condon.

"Quantum technology and AI innovation are a priority for the National Science Foundation," said Douglas Maughan, head of the NSF Convergence Accelerator program. "Today's scientific priorities and national-scale societal challenges cannot be solved by a single discipline. Instead, the merging of new ideas, techniques and approaches, plus the Convergence Accelerator's innovation curriculum, enables teams to speed their research into application. We are excited to welcome Quantum Sensors into phase II and to assist them in applying our program fundamentals to ensure their solution provides a positive impact on society at large."

Upgrading Gyroscopes and Accelerometers

The objects we interact with in our daily lives adhere to classic laws of physics, like gravity and thermodynamics. Quantum physics, however, has different rules, and objects in quantum states can exhibit strange but useful properties. For example, when two particles are linked by quantum entanglement, anything that happens to one particle affects the other, no matter how far apart they are. This means probes in two locations can share information, allowing for more precise measurements. Or, while "classical" light emits photons at random intervals, scientists can induce a quantum state called "squeezed" light to make photon emission more regular and reduce uncertainty or "noise" in measurements.

The Quantum Sensors project will take advantage of quantum states to create ultrasensitive gyroscopes, accelerometers and other sensors. Gyroscopes are used in navigation of aircraft and other vehicles to maintain balance as orientation shifts. In tandem, accelerometers measure vibration or acceleration of motion. These navigation-grade gyroscopes and accelerometers are light-based and can be extremely precise, but they are bulky and expensive.

Many electronics, including cellphones, are equipped with tiny gyroscopes and accelerometers that enable features like automatic screen rotation and directional pointers for GPS apps. At this scale, gyroscopes are made up of micromechanical parts, rather than lasers or other light sources, rendering them far less precise. Zhang and his team aim to develop chip-scale light-based gyroscopes and accelerometers to outperform current mechanical methods. However, the detection of light at this scale is limited by the laws of quantum physics, presenting a fundamental performance limit for such optical gyroscopes and accelerometers.

Rather than combat these quantum limitations with classical resources, Zhang and his team are fighting fire with fire, so to speak, by using quantum resources. For example, the stability of squeezed light can counterbalance the uncertainty of quantum fluctuations, which are temporary changes in variables such as position and momentum.

"The fundamental quantum limit is induced by quantum fluctuations, but this limit can be broken using a quantum state of light, like entangled photons or squeezed light, for the laser itself," said Zhang, director of the university's Quantum Information and Materials Group. "With this method, we can arrive at much better measurements."

Gaining an Edge on Earth and Beyond

The benefits of extremely precise measurements are numerous. If a self-driving car could determine its exact location and speed using only a compact, quantum-enhanced, onboard gyroscope and accelerometer, it wouldn't need to rely on GPS to navigate. A self-contained navigation system would protect the car from hackers and provide more stability. The same goes for navigation of spacecraft and terrestrial vehicles sent to other planets.

"In both space-based and terrestrial technologies, there are a lot of fluctuations. In an urban environment, you might lose GPS signal driving through a tunnel," Zhang said. "This method could capture information not provided by a GPS. GPS tells you where you are, but it doesnt tell you your altitude, the direction your vehicle is driving or the angle of the road. With all of this information, the safety of the passengers would be ensured."

Zhang is collaborating with partners at General Dynamics Mission Systems, Honeywell, the NASA Jet Propulsion Laboratory, the National institute of Standards and Technology, Purdue University, Texas A&M University, UCLA and Morgan State University.

"We are excited to work with the University of Arizona on this NSF Convergence Accelerator project," said Jianfeng Wu, Honeywell representative and project co-principal investigator. "The integrated entangled light sources can reduce the noise floor and enable the navigation-grade performance from chip-scale gyroscopes. The success of this program will significantly disrupt the current gyroscope landscape from many perspectives."

Because precise navigation would directly affect 700 million people worldwide, researchers estimate that quantum sensors could create a $2.5 billion market by 2035. They also expect that the precision and stability offered by the technology will give researchers a way to measure previously unmeasurable forces, such as gravitational waves and dark matter.

"As a leading international research university bringing the Fourth Industrial Revolution to life, we are deeply committed to advance amazing new information technologies like quantum networking to benefit humankind, said University of Arizona PresidentRobert C. Robbins. "The University of Arizona is an internationally recognized leader in this area, and I look forward to seeing how Dr. Zhang's Quantum Sensors project moves us forward in addressing real-world challenges with quantum technology."

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UArizona Engineer Awarded $5M to Build Quantum-Powered Navigation Tools - The University of Arizona Research

Vedika Khemani, assistant professor of physics at Stanford University, has been awarded a New Horizons in Physics Prize from the Breakthrough Prize Foundation. Khemani was recognized for pioneering theoretical work formulating novel phases ofnon-equilibrium quantum matter, including time crystals.

Vedika Khemani (Image credit: Rod Searcey)

Time crystals got their name for the fact that, like crystals, they are structurally arranged in a repeating pattern. But, while standard crystals like diamonds or salt have an arrangement that repeats in space, time crystals repeat across time forever. Importantly, they do so without any input of energy, like a clock that runs forever without batteries. Khemanis work offered a theoretical formulation for the first time crystals, as well as a blueprint for their experimental creation. But she emphasizes that time crystals are only one of the exciting potential outcomes of out-of-equilibrium quantum physics, which is still a nascent field.

None of the world is in equilibrium; just look out your window, right? Were starting to see into these vastly larger spaces of how quantum systems evolve through experiments, said Khemani, who is faculty in the School of Humanities and Sciencesand a member of Q-Farm, Stanfords broad interdisciplinary initiative in quantum science and engineering. Im very excited to see what kinds of new physics these new regimes will bring. Time crystals are one example of something new we could get, but I think its just the beginning.

The $100,000 New Horizons Prize in Physics is given each year to up to three promising junior researchers who have already produced important work, according to the prize website. New Horizons prizes are one of three groups of Breakthrough Prizes in physics the others are the $3 million Special Breakthrough Prize and the $3 million Breakthrough Prize. The Breakthrough Prizes also recognize researchers in mathematics and life sciences. Called the Oscars of Science, the prizes are celebrated at a gala award ceremony presented by superstars of movies, music, sports and tech entrepreneurship. Since the prizes began in 2012, 10 Stanford faculty and researchers have won Breakthrough Prizes.

The concept of time crystals was first proposed in 2012 by physicist and Nobel laureate Frank Wilczek, but the idea was met with significant skepticism and comparisons to the impossible perpetual motion machine. In 2014, shortly after Wilczeks proposal, it was shown by Masaki Oshikawa and Haruki Watanabe that fundamental laws of thermodynamics provably forbid the existence of time crystals. (Watanabe is a co-recipient of the New Horizons Prize.)

Thus, Khemani wasnt thinking of time crystals at all as she went about her graduate work at Princeton University on non-equilibrium quantum physics. But in 2016, a reviewer for a preprint paper co-authored by Khemani pointed out that she and her colleagues had, without intending to, outlined a working model for time crystals.

I think if we had set out to find the time crystal we would have run into the same kinds of objections as Wilczek, said Khemani. Instead, we were thinking about: How do we generalize the ideas of quantum phases of matter to systems that are out of equilibrium?

Khemani and her doctoral advisor, Shivaji Sondhi, a professor of physics at Princeton University, were working on the problem of many-body localization. In a many-body localized system, particles get stuck in the state in which they started and can never relax to an equilibrium state. As such, these systems lie strictly outside the framework of equilibrium thermodynamics, which underpins our conventional understanding of all phases of matter.

Sondhi and Khemani worked with Achilleas Lazarides and Roderich Moessner at the Max Planck Institute to figure out how to think about phases of matter in many-body localized systems that are periodically driven in time, for instance by a laser. They found that, while equilibrium thermodynamics goes out the window, the possibility of formulating phases of matter need not. In addition to abstract theoretical formulations, they studied a concrete model: a periodically driven system of Ising spins. (The Ising model is often described as the fruit fly of statistical physics and has been extensively studied in equilibrium to understand fundamental phenomena, such as magnetism.)

These researchers found a number of phases in the out-of-equilibrium Ising model, including a novel one in which the system displays a stable, repetitive flip between patterns that repeat in time forever, at a period twice that of the driving period of the laser. (As required by the definition of time crystals, the laser does not impart energy into the system.) The phase Khemani and co-workers had found was, in fact, a time crystal the out-of-equilibrium setting in which they were working allowed them to evade the constraints imposed by the laws of thermodynamics.

In the months that followed the preprint, important properties about the new phase were worked out by Khemani and her collaborators, notably Curt von Keyserlingk at the University of Birmingham, as well as a by Dominic Else, Bela Bauer and Chetan Nayak at Microsoft Station Q. (Else and collaborators also independently identified Khemanis model as a time crystal, and Else is a co-recipient of the New Horizons Prize.) It was found that the phase displays a remarkable amount of robustness and stability. Then, various early experiments in 2017 showed promising precursors of the phase although they were ultimately found to not realize a stable many-body time crystal.

Khemani describes work in the years that followed as creating a checklist of what actually makes a time crystal a time crystal, and the measurements needed to experimentally establish its existence, both under ideal and realistic conditions.

In 2020, Matteo Ippoliti, a postdoctoral scholar at Stanford working with Khemani, and others published a proposal for experimentally realizing a time crystal using the unique capabilities of Googles Sycamore quantum computer. Following this proposal, this summer, Ippoliti and Khemani, collaborating with the large Google Quantum AI team, published a preprint paper detailing the experimental creation of the first-ever time crystal on Googles device. That paper is now undergoing peer review.

Khemani sees great promise in these types of quantum experiments for many-body physics.

While many of these efforts are broadly motivated by the quest to build quantum computers which may only be achievable in the distant future, if at all these devices are also, and immediately, useful when viewed as experimental platforms for probing new nonequilibrium regimes in many-body physics, said Khemani.

As for the award recognizing all of this work, Khemani described how it reflects the bigger picture. This is called the New Horizons prize and I do think we are looking at new horizons in physics, she said. There are people at Stanford who think about black holes and big astronomical questions talking to people who are trying to build quantum computers, talking to many-body theorists, talking to quantum information scientists. Its really exciting when you start getting so many different perspectives and so many different new ways of looking at problems.

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Vedika Khemani wins Breakthrough New Horizons Prize | Stanford News - Stanford University News

After leaving the European Organization for Nuclear Research (CERN) physics laboratory years ago, I crossed the Swiss-German border by high-speed train. Looking out the window of the carriage, I was enthralled by the scenes flashing by: a young couple embracing on an otherwise deserted platform, an old man standing by a rusty wagon with a missing wheel, two girls wading into a reedy pond. Each was just a few flickering frames, gone in the blink of an eye, but enough for my imagination to fill in a story.

I had just finished writing up some theoretical work on muon particlesheavier cousins to electronsand it was out for the scrutiny of my particle physics colleagues during peer review. There was a symmetry between my thoughts as I looked out the train window that day and the research I had been working on. I had been analyzing the flickering effects of unseen virtual particles on muons, aiming to use the clues from these interactions to piece together a fuller picture of our quantum universe. As a young theorist just launching my career, I had heard about proposed experiments to measure the tiny wobbles of muons to gather such clues. I had just spent my last few months at CERN working on an idea that could relate these wobbling muons to the identity of the missing dark matter that dominates our universe and other mysteries. My mind fast-forwarding, I thought, Greatnow I just have to wait for the experiments to sort things out. Little did I suspect that I would end up waiting for a quarter of a century.

Finally, this past April, I tuned in to a Webcast from my home institution, Fermi National Accelerator Laboratory (Fermilab) near Chicago, where scientists were reporting findings from the Muon g-2 (g minus two) experiment. Thousands of people around the world watched to see if the laws of physics would soon need to be rewritten. The Fermilab project was following up on a 2001 experiment that found tantalizing hints of the muon wobble effect I had been hoping for. That trial didnt produce enough data to be definitive. But now Muon g-2 co-spokesperson Chris Polly was unveiling the long-awaited results from the experiments first run. I watched with excitement as he showed a collection of new evidence that agreed with the earlier trial, both suggesting that muons are not acting as current theory prescribes. With the evidence from these two experiments, we are now very near the rigorous statistical threshold physicists require to claim a discovery.

What is this wobble effect that has me and other scientists so intrigued? It has to do with the way a muon spins when it travels through a magnetic field. This variation in spin direction can be affected by virtual particles that appear and disappear in empty space according to the weird rules of quantum mechanics. If there are additional particles in the universe beyond the ones we know about, they, too, will show up as virtual particles and exert an influence on a muons spin in our experiments. And this seems to be what we are seeing. The Fermilab experiment and its precursor measured a stronger wobble in muons spins than what we expect based on just the known particles. If the current discrepancy holds up, this will be the biggest breakthrough in particle physics since the discovery of the Higgs bosonthe most recent novel particle discovered. We might be observing the effects of particles that could help unveil the identity of dark matter or even reveal a new force of nature.

My romance with physics began when I was a child, gazing in amazement at the Via Lactea (the Milky Way) in the deep dark sky of Argentinas Pampas where I grew up. The same wonder fills me now. It is my job as a particle physicist to investigate what the universe is made of, how it works and how it began.

Scientists believe there is a simple yet elegant mathematical structure, based on symmetries of nature, that describes the way microscopic elementary particles interact with one another through the electromagnetic, weak and strong forces; this is the miracle of particle physics that scientists prosaically call the Standard Model. The distant stars are made of the same three elementary matter particles as our bodies: the electron and the up and down quarks, the two latter of which form protons and neutrons. Starlight is the result of the electromagnetic force acting between the charged protons and electrons, liberating light energy at the hot surface of the star. The heat source of these stars, including our sun, is the strong force, which acts on the protons and neutrons to produce nuclear fusion. And the weak force, which operates on both the quarks and the electrons, turns protons into neutrons and positively charged electrons and controls the rate of the first step in the fusion process. (The fourth force of nature, gravity, is not part of the Standard Model, although integrating it with the other forces is a major goal.)

Physicists assembled the Standard Model piece by piece over the course of decades. At particle accelerators around the world, we have been able to create and observe all of the particles that the mathematical structure requires. The last to be found, the Higgs boson, was discovered almost a decade ago at CERNs Large Hadron Collider (LHC). Yet we know the Standard Model is not complete. It does not explain, for example, the 85 percent of the matter in the universedark matterthat holds the cosmos together, making galaxies such as our Milky Way possible. The Standard Model falls short of answering why, at some early time in our universes history, matter prevailed over antimatter, enabling our existence. And the Muon g-2 experiment at Fermilab may now be showing that the Standard Model, as splendid as it is, describes just a part of a richer subatomic world.

The subject of the experimentmuonsare produced in abundance by cosmic rays in Earths atmosphere; more than 10,000 of them pass through our bodies every minute. These particles have the same physical properties as the familiar electron, but they are 200 times heavier. The extra mass makes them better probes for new phenomena in high-precision laboratories because any deviations from their expected behavior will be more noticeable. At Fermilab, a 50-foot-diameter ring of powerful magnets stores muons created under controlled conditions by smashing a beam of protons from a particle accelerator into a target of mostly nickel. This process produces pions, unstable composite particles that then decay into neutrinos and muons through weak force effects. At this point, the muons enter a ring filled with the vacuum of empty space.

Like electrons, muons have electric charge and a property we call spin, which makes them behave as little magnets. Because of the way they were created, when negatively charged muons enter the ring their spins point in the same direction as their motion, whereas for positively charged muons (used in the Fermilab experiment) the spins point in the opposite direction of their motion. An external magnetic field makes the electrically charged muons orbit around the ring at almost the speed of light. At the same time, this magnetic field causes the spin of the muons to precess smoothly like a gyroscope, as the particles travel around the ring, but with a small wobble.

The rate of precession depends on the strength of the muons internal magnet and is proportional to a factor that we call g. The way the equations of the Standard Model are written, if the muon didnt wobble at all, the value of g would be 2. If that were the case, the muons direction of motion and direction of spin would always be the same with respect to each other, and g-2 would be zero. In that case, scientists would measure no wobble of the muon. This situation is exactly what we would expect without considering the properties of the vacuum.

But quantum physics tells us that the nothingness of empty space is the most mysterious substance in the universe. This is because empty space contains virtual particlesshort-lived objects whose physical effects are very real. All the Standard Model particles we know of can behave as virtual particles as a result of the uncertainty principle, an element of quantum theory that limits the precision with which we can perform measurements. As a result, it is possible that for a very short time the uncertainty in the energy of a particle can be so large that a particle can spring into existence from empty space. This mind-blowing feature of the quantum world plays a crucial role in particle physics experiments; indeed, the discovery of the Higgs boson was enabled by virtual particle effects at the LHC.

Virtual particles also interact with the muons in the Fermilab ring and change the value of g. You can imagine the virtual particles as ephemeral companions that a muon emits and immediately reabsorbsthey follow it around like a little cloud, changing its magnetic properties and thus its spin precession. Therefore, scientists always knew that g would not be exactly 2 and that there would be some wobble as muons spin around the ring. But if the Standard Model is not the whole story, then other particles that we have not yet discovered may also be found in that cloud, changing the value of g in ways that the Standard Model cannot predict.

Muons themselves are unstable particles, but they live long enough inside the Muon g-2 experiment for physicists to measure their spin direction. Physicists do this by monitoring one of the decay particles they create: electrons, from decays of negatively charged muons, or positronsthe antiparticle version of electronsfrom decays of positively charged muons. By determining the energy and arrival time of the electrons or positrons, scientists can deduce the spin direction of the parent muon. A team of about 200 physicists from 35 universities and labs in seven countries developed techniques for measuring the muon g-2 property with unprecedented accuracy.

The first experiments to measure the muon g-2 took place at CERN, and by the late 1970s they had produced results that, within their impressive but limited precision, agreed with standard theory. In the late 1990s the E821 Muon g-2 experiment at Brookhaven National Laboratory started taking data, with a similar setup to that at CERN. It ran until 2001 and got impressive results showing an intriguing discrepancy from the Standard Model calculations. It collected only enough data to establish a three-sigma deviation from the Standard Modelwell short of the five-sigma statistical significance physicists require for a discovery.

A decade later Fermilab acquired the original Brookhaven muon ring, shipped the 50-ton apparatus from Long Island to Chicago via highways, rivers and an ocean, and started the next generation of the Muon g-2 experiment. Nearly a decade after that, Fermilab announced a measurement of muon wobble with an uncertainty of less than half a part in a million. This impressive accuracy, achieved with just the first 6 percent of the expected data from the experiment, is comparable to the result from the full run of the Brookhaven trial. Most important, the new Fermilab results are in striking agreement with the E821 values, confirming that the Brookhaven findings were not a fluke.

To confirm this years results, we need not just more experimental data but also a better understanding of what exactly our theories predict. Over the past two decades we have been refining the Standard Model predictions. Most recently, more than 100 physicists working on the Muon g-2 Theory Initiative, started by Aida El-Khadra of the University of Illinois, have strived to improve the accuracy of the Standard Models value for the muon g-2 factor. Advances in mathematical methods and com putational power have enabled the most accurate theoretical calculation of g yet, taking into account the effects from all virtual Standard Model particles that interact with muons through the electromagnetic, weak and strong forces. Just months before Fermilab revealed its latest experimental measurements, the theory initiative unveiled their new calculation. The number disagrees with the experimental result by 4.2 sigma, which means that the chances that the discrepancy is purely a statistical fluctuation are about one in 40,000.

Still, the latest theoretical calculation is not iron-clad. The contributions to the g-2 factor governed by effects from the strong force are extremely difficult to compute. The Muon g-2 Theory Initiative used input from two decades of judiciously measured data in related experiments with electrons to evaluate these effects. Another technique, though, is to try to calculate the size of the effects directly from theoretical principles. This calculation is way too complex to solve exactly, but physicists can make approximations using a mathematical trick that discretizes our world into a gridlike lattice of space and time. These techniques have yielded highly accurate results for other computations where strong forces play a dominant role.

Teams around the world are tackling the lattice calculations for the muon g-2 factor. So far only one team has claimed to have a result of comparable accuracy to those based on experimental data from electron collisions. This result happens to dilute the discrepancy between the experimental and Standard Model expectationsif it is correct, there may not be evidence of additional particles tugging on the muon after all. Yet this lattice result, if confirmed by other groups, would itself conflict with experimental electron datathe puzzle then would be our understanding of electron collisions. And it would be hard to find theoretical effects that would explain such a result because electron collisions have been so thoroughly studied.

If the mismatch between Fermilabs measurements and theory persists, we may be glimpsing an uncharted world of unfamiliar forces, novel symmetries of nature and new particles. In the research I published 25 years ago searching for clues about the muons wobble, my collaborators and I considered a proposed property of nature called supersymmetry. This idea bridges two categories of particlesbosons, which can be packed together in large numbers, and fermions, which are antisocial and will share space only with particles of opposite spin. Supersymmetry postulates that each fermion matter particle of the Standard Model has a yet to be discovered boson particle superpartner, and each Standard Model boson particle also has an undiscovered fermion superpartner. Supersymmetry promises to unify the three Standard Model forces and offers natural explanations for dark matter and the victory of matter over antimatter. It may also explain the striking Muon g-2 results.

Just after the Fermilab collaboration announced its measurement, my colleagues Sebastian Baum, Nausheen Shah, Carlos Wagner and I posted a paper to a preprint server investigating this intriguing notion. Our calculations showed that virtual superparticles in the vacuum could make the muons wobble faster than the Standard Model predicts, just as the experiment saw. Even more exhilarating, one of those new particlescalled a neutralinois a candidate for dark matter. Supersymmetry can take numerous forms, many of them already ruled out by data from the LHC and other experimentsbut plenty of versions are still viable theories of nature.

The paper my team submitted was just one of more than 100 that have appeared proposing possible explanations for the Muon g-2 result since it was announced. Most of these papers suggest new particles that fall into one of two camps: either light and feeble or heavy and strong. The first category includes new particles that have masses comparable to or smaller than the muon and that interact with muons with a strength millions of times weaker than the electromagnetic force. The simplest theoretical models of this type involve new, lighter cousins of the Higgs boson or particles related to new forces of nature that act on muons. These new light particles and feeble forces could be hard to detect in terrestrial experiments other than Muon g-2, but they may have left clues in the cosmos. These light particles would have been produced in huge numbers after the big bang and might have had a measurable effect on cosmic expansion. The same ideathat light particles and feeble forces wrote a chapter missing from our current history of the universehas also been proposed to explain discrepancies in observations of the expansion rate of space, the so-called Hubble constant crisis.

The second category of explanations for the muon resultsheavy and stronginvolves particles with masses about as heavy as the Higgs boson (roughly 125 times the mass of a proton) to up to 100 times heavier. These particles could interact with muons with a strength comparable to the electromagnetic and weak interactions. Such heavy particles might be cousins of the Higgs boson, or exotic matter particles, or they might be carriers of a new force of nature that works over a short range. Supersymmetry offers some models of this type, so my youthful speculations at CERN are still in the running. Another possibility is a new type of particle called a leptoquarka strange kind of boson that shares properties with quarks as well as leptons such as the muon. Depending on how heavy the new particles are and the strength of their interactions with Standard Model particles, they might be detectable in upcoming runs of the LHC.

Some recent LHC data already point toward unusual behavior involving muons. Recently, for instance, LHCb (one of the experiments at the LHC) measured the decays of certain unstable composite particles similar to pions that produce either muons or electrons. If muons are just heavier cousins of the electron, as the Standard Model claims, then we can precisely predict what fraction of these decays should produce muons versus electrons. But LHCb data show a persistent three-sigma discrepancy from this prediction, perhaps indicating that muons are more different from electrons than the Standard Model allows. It is reasonable to wonder whether the results from LHCb and Muon g-2 are different, flickering frames of the same story.

The Muon g-2 experiment may be telling us something new, with implications far beyond the muons themselves. Theorists can engineer scenarios where new particles and forces explain both the muons funny wobbling and solve other outstanding mysteries, such as the nature of dark matter or, even more daring, why matter dominates over antimatter. The Fermilab experiment has given us a first glimpse of what is going on, but I expect it will take many more experiments, both ongoing and yet to be conceived, before we can confidently finish the story. If supersymmetry is part of the answer, we have a fair chance of observing some of the superparticles at the LHC. We hope to see evidence of dark matter particles there or in deep underground labs seeking them. We can also look at the behavior of muons in different kinds of experiments, such as LHCb.

All of these experiments will keep running. Muon g-2 should eventually produce results with nearly 20 times more data. I suspect, however, that the final measured value of the g-2 factor will not significantly change. There is still a shadow of doubt on the theory side that will be clarified in the next few years, as lattice computations using the worlds most powerful supercomputers achieve higher precision and as independent teams converge on a final verdict for the Standard Model prediction of the g-2 factor. If a big mismatch between the prediction and the measurement persists, it will shake the foundations of physics.

Muons have always been full of surprises. Their very existence prompted physicist I. I. Rabi to complain, Who ordered that? when they were first discovered in 1936. Nearly a century later they are still amazing us. Now it seems muons may be the messengers of a new order in the cosmos and, for me personally, a dream come true.

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Weird Muons May Point to New Particles and Forces of Nature - Scientific American

Thanu Padmanabhan had acquired outstanding mathematical abilities quite early in his life, thanks to the guidance of his father who was an extremely gifted mathematician but was forced to take up a job with the Forest Department in Kerala.

An academic career in pure mathematics was what Padmanabhan had decided to pursue. But that was before he had picked up Richard Feynmans classic Lectures in Physics, the book that has lured countless youngsters like him from several generations to physics. In a profile included in the book Gravity and the Quantum, a collection of Padmanabhans articles released on the occasion of his 60th birthday, his PhD students Jasjit Bagla and Sunu Engineer wrote that Feynmans book had a big influence on him even though he was not a big fan of the celebrated scientist as a person. It appeared to me that theoretical physics beautifully combines the best of objective science and the elegance of pure mathematics, Padmanabhan, who died in Pune on Friday, aged 64, is quoted in that profile as saying.

Padmanabhan, or Paddy as he was known to his colleagues and students, went on to achieve great heights in theoretical physics, making important contributions to the fields of gravity and quantum theory, structure and formation of universe.

His early work was done at Mumbais Tata Institute of Fundamental Research, where he did his PhD under Jayant Narlikar,starting an association that lasted a lifetime. Padmanabhan shifted to the Inter-University Centre for Astronomy and Astrophysics (IUCAA) in Pune in 1992 and remained there till his death, researching, teaching, and popularising science.

As a teacher, he could explain any topic or subject to a student with great ease. He taught me that discipline and hard work, when coupled, would ensure that one keeps growing, said Dr Tirthankar Roy Choudhury, Padmanabhans PhD student between 1999 and 2003 at IUCAA.

His demise came as a shock to the scientific community, especially those at IUCAA. A lot of them turned up to pay their lastrespects on Friday afternoon. He was later cremated at Aundh.

Padmanabhan could teach any course in Physics and Astronomy with equal ease, said Dr Yogesh Wadedekar, senior scientist at National Centre for Radio Astrophysics (NCRA),Pune.

Padmanabhan loved solving puzzles, playing chess and watching movies across genres.

There was a phase when he used to watch a lot of movies on TV. Some of us students used to pull his leg about his liking for the actress Tabu. He used to throw a party for us whenever he won an award or a recognition which were numerous.

Whenever we used to go out for dinners, he would order tiramisu for dessert and we used to again make fun of this habit, shared A N Ramaprakash, scientist and colleague at IUCAA.

He would often play games of chess on the computer. He was a sharp thinker and would be the problem spotter, recalled Sanjit Mitra, another colleague at IUCAA.

Many never get a chance to meet their idols in life but Tirthankar Roy Choudhury got to not only work closely but remain associated with his idol for nearly 20 years. When I was chosen under his guide-ship for PhD, it was like a dream cometrue. He would never stop or be tired and would often take up new and the most difficult problems, recalled Choudhury.

Padmanabhan was an outstanding scientist who could catch a scientific argument quickly while at the same time admit if he did not possess knowledge about the topic, said Prof Yashwant Gupta, centre director, NCRA.

Through his work over the past decade or so, Padmanabhan had discovered a deep connection between the underlying quantum nature of the structure of space-time and what we perceive as the macro properties of gravity, Ramaprakash stated. This is seminal and path-breaking. He was just warming up to understanding the consequences of this discovery, but had to go, he said.

Mitra particularly remnisences the extended conversations he had with Padmanabhan, when the two would cross paths during their respective evening walks.

We would get talking on any topic and would often end up having interesting discussions lasting even upto 45 minutes during the evening walks, he said.

While pursuing science was a daily affair, Padmanabhan also took to writing books both on advanced and popular science in the early 1990s, and soon realised the need of a personal computer at his home.

Roy Choudhury remembers Padmanabhans witty nature and said that some people would fail to understand the light humour. When assigned teaching responsibility many years ago, Padmanabhan guided Roy Choudhury from time-to-time.

Padmanabhans comic strip called The Story of Physics was both popular and loved by students, shared Dr Raka Dabhade, head, Department of Physics, Fergusson College. His humble nature always attracted students to interact with him. In spite of his busy schedule, he would find time to clear doubts of the students via emails, said Dabhade.

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The professor who loved puzzles, and had his own comic strip on physics - The Indian Express

Physicists have created the first-ever atomic vortex beam a swirling tornado ofatomsand molecules with mysterious properties that have yet to be understood.

By sending a straight beam of helium atoms through a grating with teeny slits, scientists were able to use the weird rules of quantum mechanics to transform the beam into a whirling vortex.

The extra gusto provided by the beam's rotation, called orbital angular momentum, gives it a new direction to move in, enabling it to act in ways that researchers have yet to predict.

For instance, they believe the atoms' rotation could add extra dimensions ofmagnetismto the beam, alongside other unpredictable effects, due to the electrons and the nuclei inside the spiraling vortex atoms spinning at different speeds.

Related:The 18 biggest unsolved mysteries in physics

"One possibility is that this could also change the magnetic moment of the atom," or the intrinsic magnetism of a particle that makes it act like a tiny bar magnet, study co-author Yair Segev, a physicist at the University of California, Berkeley, told Live Science.

In the simplified, classical picture of the atom, negatively-charged electrons orbit a positively-charged atomic nucleus. In this view, Segev said that as the atoms spin as a whole, the electrons inside the vortex would rotate at a faster speed than the nuclei, "creating different opposing [electrical] currents" as they twist.

This could, according to the famouslaw of magnetic inductionoutlined by Michael Faraday, produce all kinds of new magnetic effects, such as magnetic moments that point through the center of the beam and out of the atoms themselves, alongside more effects that they cannot predict.

The researchers created the beam by sendingheliumatoms through a grid of tiny slits each just 600 nanometers across.

In the realm ofquantum mechanics the set of rules which govern the world of the very small atoms can behave both like particles and tiny waves; as such, the beam of wave-like helium atoms diffracted through the grid, bending so much that they emerged as a vortex that corkscrewed its way through space.

The whirling atoms then arrived at a detector, which showed multiple beams diffracted to differing extents to have varying angular momentums as tiny little doughnut-like rings imprinted across it.

The scientists also spotted even smaller, brighter doughnut rings wedged inside the central three swirls. These are the telltale signs of helium excimers a molecule formed when one energetically excited helium atom sticks to another helium atom. (Normally, helium is a noble gas and doesn't bind with anything.)

The orbital angular momentum given to atoms inside the spiraling beam also changes the quantum mechanical "selection rules" that determine how the swirling atoms will interact with other particles, Segev said. Next, the researchers will smash their helium beams into photons, electrons, and atoms of elements besides helium to see how they might behave.

If their rotating beam does indeed act differently, it could become an ideal candidate for a new type of microscope that can peer into undiscovered details on the subatomic level. The beam could, according to Segev, give us more information on some surfaces by changing the image that is imprinted upon the beam atoms bounced off it.

"I think that as is often the case in science, it's not a leap of capability that leads to something new, but rather a change in perspective," Segev said.

The researchers published their findings September 3 in the journalScience.

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This article was originally published by Live Science. Read the original article here.

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Physicists Create Swirling Tornado of Helium With First-Ever Atomic Vortex Beam - ScienceAlert