Monthly Archives: June 2023

Ever feel like you need more time? That its just flying by you?

And, then, do you ever wish you could reverse it?

A study published in Scientific Reports by an international team of researchers has demonstrated that a time-reversal program on a quantum computer is possible.

Researchers have pulled off a mind-boggling experiment using a quantum computer, and boy, does it mess with our understanding of time!

They wanted to see if they could make time reverse itself, just for a split second. You know, like rewinding a video, back in the olden days, but without the popcorn.

And guess what? They did it!

Well, sort of.

So, in the wacky world of quantum mechanics, where things can be particles and waves at the same time (talk about being indecisive!), these clever scientists created a thought experiment.

They imagined a bunch of billiard balls smashing into each other, going all haywire, and then magically rearranging themselves back into order. Like a cosmic cleanup crew, but with balls.

Now, reality check.

This time-reversal magic isnt happening spontaneously in nature. Nope, its as rare as finding a unicorn in a haystack. The chances are so slim that youd have to observe 10 billion freshly localized electrons every second for the entire lifetime of the universe to witness it once. And it would only send the electron back in time by a measly 10-billionth of a second.

But hold on, dont lose hope just yet. These mad scientists didnt stop there.

They went ahead and simulated the whole thing on a quantum computer, because why not? They managed to reverse time in 85 percent of the cases using a two-qubit setup. Its like playing with a time remote control, but with fancy quantum bits instead of buttons.

Now, I have to burst your bubble. This experiment doesnt mean well be hopping into time machines anytime soon.

Sorry, no Back to the Future adventures for us. But hey, its still a big deal!

It could help make quantum computers even more accurate in the future. And who knows, maybe one day well crack the code and unlock the secrets of time. Until then, keep dreaming and enjoy your non-reversible moments.

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A Quantum Computer Simulation Has Reversed Time And Physics May Never Be The Same - Twisted Sifter

May 30, 2023 Physics 16, 92

A new demonstration involving hundreds of entangled atoms tests Schrdingers interpretation of Einstein, Rosen, and Podolskys classic thought experiment.

In 1935, Einstein, Podolsky, and Rosen (EPR) presented an argument that they claimed implies that quantum mechanics provides an incomplete description of reality [1]. The argument rests on two assumptions. First, if the value of a physical property of a system can be predicted with certainty, without disturbance to the system, then there is an element of reality to that property, meaning it has a value even if it isnt measured. Second, physical processes have effects that act locally rather than instantaneously over a distance. John Bell subsequently proposed a way to experimentally test these local realism assumptions [2], and so-called Bell tests have since invalidated them for systems of a few small particles, such as electrons or photons [3]. Now Paolo Colciaghi and colleagues at the University of Basel, Switzerland, have tested EPRs argument for a larger system comprising clouds of hundreds of atoms [4]. Their results bring into question the validity of EPRs local realism for mesoscopic massive systems.

EPR considered a system of two spatially separated particles, A and B, that have pairs of noncommuting observables, such as their position and momentum. The systems are prepared so that the particles positions are correlated and their momenta are anticorrelated. This relationship between observables means that an experimentalist should be able to determine the position or momentum of particle A with certainty by making the appropriate measurement of B. Importantly, the system is set up so that the particles are space-like separated, meaning there can be no disturbance of A because of a measurement at B.

Assuming local realism, EPR concluded that the particles positions and momenta are both simultaneously well-defined. But quantum mechanics does not allow simultaneous, precisely defined values for both position and momentum. EPR proposed to resolve this paradox by suggesting that quantum mechanics is incomplete, implying that a full theory would include what physicists now term local hidden variablesa possibility that Bell tests have since ruled out [2, 3].

Whereas most Bell tests have been conducted on pairs of individual particles, Colciaghi and colleagues use clouds of several hundred rubidium-87 atoms. They start by preparing a single Bose-Einstein condensate in a trap and engineer an interaction to entangle the condensates atoms (Fig. 1). Once released from the trap, the condensate expands to form two entangled clouds separated by up to 100 m. In order to test the paradox, it is necessary to measure two noncommuting observables. Instead of using position and momentum as envisaged by EPR, Colciaghi and colleagues use pseudospinsa pair of quantum states that, like spin, constitute a two-level system. These spins are defined by two hyperfine levels, with the spin of each cloud determined by the number of atoms in one level minus the number of atoms in the other level. To measure the first of the noncommuting spin observables, the atoms in each level are counted directly. The second, complementary spin observable is measured using a pulse that interacts with the atoms prior to the count. EPR tests using atomic ensembles have been conducted before [57], but here there is an important difference: In this experiment, the choice of measurement settingsmeaning which of the two noncommuting spins is measuredis made independently for each cloud. This independence is essential for a genuine EPR paradox; without it we cannot rule out an influence between the systems [8].

Colciaghi and colleagues probe EPR correlations by determining the errors in inferring the spin of cloud A from measurements of the spin of cloud B, first when the pulses are absent, and then again when the pulses are applied for both A and B. While not zero, the product of these errors is small relative to the lower bound of the Heisenberg uncertainty product measured in the experiment. The paradox is therefore confirmed, since the noncommuting spins for A can be inferred with a precision not quantifiable by any local quantum state for A [9]. Yet, if these correlations are the result of a measurement made at B somehow affecting the outcome at A by nonclassical means, then the experiment, which involves a large number of atoms, is intriguingly macroscopic.

The researchers then make a very revealing modification to their experiment. In 1935, Schrdinger responded to EPRs argument with his famous example of the cat in a superposition state [10]. Less well known is his proposal of a situation in which the measurement settings are adjusted so that two complementary variables are measured simultaneously, one by direct, the other by indirect measurement. Schrdinger pondered whether the values for both variables would be precisely determined for this choice of measurement settings (when the settings are fixed but prior to the measurement being finalized), and he questioned whether this determination of values would be compatible with quantum mechanics. Colciaghi and colleagues create such a scenario by manipulating the pulses that determine which spin is measured: Keeping the setting of cloud B fixed, they change the setting of cloud A.

The researchers show that they can measure the value of one variable of cloud A directly, while inferring the value of the complementary variable indirectly from a measurement on cloud B. Furthermore, by adjusting the setting of A again, they show how the correlation with the measurement at B is regained. This illustrates that changing the setting of cloud A does not change the correctness of the prediction made for the complementary variable at A by measuring B. Does this finding imply that there is an element of reality for the outcome of the measurement at A once the setting at B is fixed? For the direct measurement of each variable, the system is prepared for the counting of atoms in the two levels after any interaction of the atoms with the pulses, when the measurement settings are determined. Are the atoms that would be counted already in those levels, whether or not the count takes place? The mesoscopic nature of the experiment would appear to strengthen Schrdingers argument: It seems that the values of the observables would be fixed once the measurement settings are determined but before the measurements are finalized by counting the atoms.

The implications of the results are not completely clear. To confirm the indirectly obtained value at A requires a further interaction to change the setting, which means the quantum state changes. Hence, the proposition that the values for both spins are determined prior to the measurement does not violate the uncertainty principle; nor are the values excluded by Bells theorem, which refers to variables defined prior to the interactions that fix the settings. Yet, as Schrdinger observed, it seems thataccording to quantum mechanicsafter the indirect measurement at B, the system A is described by a wave function for which the indirectly measured value is, as Schrdinger put it, fully sharp, but the directly measured value is fully indeterminate [10]. Schrdinger further questioned the legitimacy of the simultaneous values for position x and for momentum p by proving that the value of x2 + p2, when the two observables are measured simultaneously, must be an odd integer numberdespite x and p being continuous and therefore apparently not subject to this restriction [10]. Such questions remain open and may well be elucidated by a closer examination of the recent experiment.

Margaret D. Reid is professor and director of the Centre for Quantum Science and Technology at Swinburne University of Technology in Melbourne, Australia. She is a Fellow of the Australian Academy of Science, the American Physical Society, and the Optical Society of America and was previously an associate editor for Physical Review A. She completed her PhD at the University of Auckland in New Zealand and has held visiting research positions at ATT Bell Laboratories, Pierre and Marie Curie University, Institute for Theoretical Atomic Molecular and Optical Physics Harvard, and JILA. In 2019, she received the Moyal Medal for her work on how to demonstrate the Einstein-Podolsky-Rosen paradox using squeezing and parametric down conversion.

The gravitational fields of black holes and other compact objects are strong enough to wrest pairs of particles and antiparticles out of the vacuum and into existence, causing the objects to decay. Read More

Researchers move an individual Mg+ ion more than 100,000 times between different sites in a trapping array without dropping it or ruining its quantum coherence. Read More

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Realizing the Einstein-Podolsky-Rosen Paradox for Atomic Clouds - Physics

The United States and United Kingdom are sharing expertise and capabilities in the blossoming field of quantum information science across the pond. This new partnership between the countries will lead to new quantum devices, insights into their performance, ways to harness quantum information and discoveries in fundamental physics.

Research will be conducted under the Superconducting Quantum Materials and Systems Center, hosted by the U.S. Department of Energys Fermi National Accelerator Laboratory, with the United Kingdoms National Physical Laboratory and Royal Holloway, University of London. With the additional institutions, the SQMS Center collaboration now totals 28 partners.

From left to right: Marius Hegedus, Tobias Lindstrom and Alexander Tzalenchuk stand outside the door to Quantum Computing Lab-3 during their visit to SQMS Centers headquarters on Fermilabs campus. Photo: SQMS Center

These new additions to the SQMS Center are rooted in goals to increase cooperation in the field of quantum information science between the U.S. and U.K. governments. These goals were set in a November 2021 joint statement that emphasizes the importance of growing an ecosystem of international partners with shared values. The statement also highlights the impact of quantum technology on global health security, climate change and efficient resource use.

Our new U.K. partners bring unique characterization techniques that complement the SQMS Centers strengths, said Anna Grassellino, director of the SQMS Center. This partnership advances the centers mission of identifying and overcoming fundamental obstacles that interfere with quantum device performance, while also finding ways to use quantum devices to harness quantum information and perform physics and sensing experiments.

Quantum information science seeks to harness the behavior of quantum mechanics to process information in new ways, develop ultra-sensitive detectors and much more.

Under these new partnerships, researchers will investigate the following: losses of quantum information in quantum computing devices, new systems based on quantum technologies to search for new particles, new quantum algorithms, and the performance and fundamental limits of quantum computers.

The areas the SQMS Center focuses on are building high-quality superconducting qubits and looking at ways in which this will scale for both quantum computing and fundamental physics, said Sir Peter Knight, chair of the U.K. National Quantum Technologies Programme and SQMS Center advisory board member.

Scientists will use quantum computers to manipulate qubits the basic building block of information used by quantum computers to perform calculations that would be practically impossible for classical computers when the machines are fully realized.

Superconducting qubits can be used as a quantum computing engine, but equally in the other direction for dark matter detection, said Knight. Quantum has become a major part of the scientific adventure that everybody wants to participate in, and SQMS is going to be a beacon of getting stuff done. NPL and RHUL researchers are excited to become collaborative SQMS Center partners.

Quantum devices need to be cooled down to prevent information from being obscured or lost by noise produced by heat. Making devices ultra-cold might lead to better device performance and new insights on how quantum devices behave and operate.

RHUL performs cutting-edge research in quantum and hosts the London Low Temperature Laboratory. Researchers at RHUL have experience cooling quantum devices down to the microkelvin range, or millionths of degrees kelvin. This temperature regime is much colder than where researchers typically operate devices, which are the millikelvin range or thousandth degrees kelvin.

What my group brings to the table is expertise in low-temperature physics into the microkelvin regime, said John Saunders, a professor at RHUL and SQMS Center advisory board member. For approximately the last 10 years, weve been working on developing new low-temperature platforms and working on cooling down quantum circuits and quantum materials to the lowest possible temperatures. We are very interested in cooling them down to ultra-low temperatures to see how they behave, said Saunders.

This expertise in low temperatures complements the National Physical Laboratorys capabilities. The National Physical Laboratory serves a similar function as the United States National Institute of Standards and Technology, both of which perform precision measurements to maintain measurement standards for their respective countries. NIST is also a core partner within the SQMS Center.

Quantum has become a major part of the scientific adventure that everybody wants to participate in, and SQMS is going to be a beacon of getting stuff done. Sir Peter Knight, chair of the U.K. National Quantum Technologies Programme

As the NPL head of science for quantum technologies, I lead a team of about 100 scientists working on various aspects of computing, sensing, communications, metrology, and materials, said Alexander Tzalenchuk, the SQMS Center principal investigator for NPL. In particular, we strive to understand and mitigate noise in superconducting circuits, which affects their quantumness. We also work on algorithms and developing technologies that enable scalable quantum computing in the future. This formal collaboration is one of the first examples where the two countries can work together on closely aligned projects, which is enabled by the joint statement.

We want to make quantum technologies viable in order to provide new tools and capabilities that benefit our national initiative as well as, more broadly, the world, said Abid Patwa, program manager for SQMS in DOEs Office of High Energy Physics. We need to learn more about the fundamental aspects of QIS, such as cryogenics, and to understand the underlying mechanisms that currently limit quantum computing devices.

The United Kingdom continues to be an excellent partner to the United States and has theexpertise as well as theessential resources to test and build on the QIS fundamentals, said Patwa. These efforts will further advance our insights in quantum research to enable this emerging technology.

The Superconducting Quantum Materials and Systems Center at Fermilab is supported by the DOE Office of Science.

The Superconducting Quantum Materials and Systems Center is one of the five U.S. Department of Energy National Quantum Information Science Research Centers. Led by Fermi National Accelerator Laboratory, SQMS is a collaboration of 28 partner institutionsnational labs, academia and industryworking together to bring transformational advances in the field of quantum information science. The center leverages Fermilabs expertise in building complex particle accelerators to engineer multiqubit quantum processor platforms based on state-of-the-art qubits and superconducting technologies. Working hand in hand with embedded industry partners, SQMS will build a quantum computer and new quantum sensors at Fermilab, which will open unprecedented computational opportunities. For more information, please visit sqmscenter.fnal.gov.

Fermi National Accelerator Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science 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, please visit science.energy.gov.

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The US and UK team up to advance quantum information science - Fermi National Accelerator Laboratory

It is spring now in the Northern Hemisphere, and the world has greened around us. Outside my window, trees are filled with leaves that act as miniature factories, collecting sunlight and converting it into food. We know this basic transaction takes place, but how does photosynthesis really happen?

During photosynthesis, plants utilize quantum mechanical processes. In an attempt to understand how plants do this,scientists at the University of Chicagorecently modeled the workings of leaves at the molecular level. They were blown away by what they saw. It turns out that plants act like a strange, fifth state of matter known as a Bose-Einstein condensate. Even stranger is that these condensates are typically found at temperatures near absolute zero. The fact that they are all around us on a normal, temperate spring day is a real surprise.

The three most common states of matter are solid, liquid, and gas. When either pressure or heat is added or removed, a material can shift between these states. We often hear that plasma is the fourth state of matter. In a plasma, atoms break down into a soup of positively charged ions and negatively charged electrons. This typically occurs when a material is super-heated. The Sun, for example, is mostly a big ball of super-hot plasma.

If matter can be superheated, it can also be supercooled, causing particles to fall into very low energy states. Understanding what happens next requires some knowledge of particle physics.

There are two main types of particles, bosons, and fermions, and what differentiates them is a property called spin a weird, quantum-mechanical characteristic that relates to the particles angular momentum. Bosons are particles with integer spin (0, 1, 2, etc), while fermions have a half-integer spin (1/2, 3/2, etc). This property is described by thespin-statistics theorem, and it means that if you swap two bosons, you will retain the same wave function. You cannot do the same for fermions.

In aBose-Einstein condensate, the bosons within a material have such low energy that they all occupy the same state, acting as a single particle. This allows quantum properties to be seen on a macroscopic scale. ABose-Einstein condensatewas created in a lab for the first time in 1995, at a temperature of a mere 170 nanokelvin.

Now, lets look at what happens in a typical leaf during photosynthesis.

Plants need three basic ingredients to make their own food carbon dioxide, water, and light. A pigment called chlorophyllabsorbs energy from light at red and blue wavelengths.It reflects light at other wavelengths, which makes the plant look green.

At a molecular level, things get even more interesting. Absorbed light excites an electron within a chromophore, the part of a molecule that determines its reflection or absorption of light. This kicks off a series of chain reactions that end up producing sugars for the plant. Using computer modeling, the researchers at the University of Chicago examined what occurs in green sulfur bacteria, a photosynthetic microbe.

Light excites an electron. Now the electron and the empty space it left behind, called a hole, act together as a boson. This electron-hole pair is called an exciton. The exciton travels to deliver energy to another location, where sugars are created for the organism.

Chromophores can pass energy between them in the form of excitons to a reaction center where energy can be used, kind of like a group of people passing a ball to a goal, Anna Schouten, the studys lead author, explained to Big Think.

The scientists discovered that the paths of the excitons within localized areas resembled those seen within an exciton condensate a Bose-Einstein condensate made of excitons.The challenge with exciton condensates is that the electrons and ions tend to recombine quickly. Once this happens the exciton vanishes, often before a condensate can form.

These condensates are remarkably difficult to create in the lab, yet here they were, right in front of the scientists eyes, in a messy organism at room temperature. By forming a condensate, the excitons formed one single quantum state. In essence, they were acting like a single particle. This forms a superfluid a fluid with zero viscosity and zero friction allowing energy to flow freely between chromophores.

Their results were published inPRX Energy.

Excitons normally decay quickly, and when they do, they can no longer transfer energy. To give them a longer lifetime, they typically need to be very cold. In fact, exciton condensates have never been seen above temperatures of 100 Kelvin, which is a frosty negative-173 degrees Celsius. This is why it is so surprising to see this behavior in a messy, real-world system at normal temperatures.

So whats going on here? Just another way that nature is constantly surprising us.

Photosynthesis works at normal temperatures because nature has to work at normal temperatures in order to survive, so the process evolved to do that, says Schouten.

In the future, room-temperature Bose-Einstein condensates may have practical applications. Since they act as a single atom, Bose-Einstein condensates may give us insight into quantum properties that would be difficult to observe at the atomic level. They also have applications forgyroscopes,atom lasers,high-precision sensors of time, gravity, or magnetism, andhigher levels of energy efficiency and transfer.

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How plants can perform feats of quantum mechanics - Big Think

Many seemingly mundane materials, such as the stainless steel on refrigerators or the quartz in a countertop, harbor fascinating physics inside them. These materials are crystals, which in physics means they are made of highly ordered repeating patterns of regularly spaced atoms called atomic lattices. How electrons move through a lattice, hopping from atom to atom, determines many of a solid's properties, such as its color, transparency, and ability to conduct heat and electricity. For example, metals are shiny because they contain lots of free electrons that can absorb light and then reemit most of it, making their surfaces gleam.

In certain crystals the behavior of electrons can create properties that are much more exotic. The way electrons move inside graphenea crystal made of carbon atoms arranged in a hexagonal latticeproduces an extreme version of a quantum effect called tunneling, whereby particles can plow through energy barriers that classical physics says should block them. Graphene also exhibits a phenomenon called the quantum Hall effect: the amount of electricity it conducts increases in specific steps whose size depends on two fundamental constants of the universe. These kinds of properties make graphene intrinsically interesting as well as potentially useful in applications ranging from better electronics and energy storage to improved biomedical devices.

I and other physicists would like to understand what's going on inside graphene on an atomic level, but it's difficult to observe action at this scale with current technology. Electrons move too fast for us to capture the details we want to see. We've found a clever way to get around this limitation, however, by making matter out of light. In place of the atomic lattice, we use light waves to create what we call an optical lattice. Our optical lattice has the exact same geometry as the atomic lattice. In a recent experiment, for instance, my team and I made an optical version of graphene with the same honeycomb lattice structure as the standard carbon one. In our system, we make cold atoms hop around a lattice of bright and dim light just as electrons hop around the carbon atoms in graphene.

With cold atoms in an optical lattice, we can magnify the system and slow down the hopping process enough to actually see the particles jumping around and make measurements of the process. Our system is not a perfect emulation of graphene, but for understanding the phenomena we're interested in, it's just as good. We can even study lattice physics in ways that are impossible in solid-state crystals. Our experiments revealed special properties of our synthetic material that are directly related to the bizarre physics manifesting in graphene.

The crystal phenomena we investigate result from the way quantum mechanics limits the motion of wavelike particles. After all, although electrons in a crystal have mass, they are both particles and waves (the same is true for our ultracold atoms). In a solid crystal these limits restrict a single electron on a single atom to only one value of energy for each possible movement pattern (called a quantum state). All other amounts of energy are forbidden. Different states have separate and distinctdiscreteenergy values. But a chunk of solid crystal the size of a grape typically contains more atoms (around 1023) than there are grains of sand on Earth. The interactions between these atoms and electrons cause the allowed discrete energy values to spread out and smear into allowed ranges of energy called bands. Visualizing a material's energy band structure can immediately reveal something about that material's properties.

For instance, a plot of the band structure of silicon crystal, a common material used to make rooftop solar cells, shows a forbidden energy rangealso known as a band gapthat is 1.1 electron volts wide. If electrons can jump from states with energies below this gap to states with energies above the gap, they can flow through the crystal. Fortunately for humanity, the band gap of this abundant material overlaps well with the wavelengths present in sunlight. As silicon crystal absorbs sunlight, electrons begin to flow through itallowing solar panels to convert light into usable electricity.

The band structure of certain crystals defines a class of materials known as topological. In mathematics, topology describes how shapes can be transformed without being fundamentally altered. Transformation in this context means to deform a shapeto bend or stretch itwithout creating or destroying any kind of hole. Topology thus distinguishes baseballs, sesame bagels and shirt buttons based purely on the number of holes in each object.

Topological materials have topological properties hidden in their band structure that similarly allow some kind of transformation while preserving something essential. These topological properties can lead to measurable effects. For instance, some topological materials allow electrons to flow only around their edges and not through their interior. No matter how you deform the material, the current will still flow only along its surface.

I have become particularly interested in certain kinds of topological material: those that are two-dimensional. It may sound odd that 2-D materials exist in our 3-D world. Even a single sheet of standard printer paper, roughly 0.004 inch thick, isn't truly 2-Dits thinnest dimension is still nearly one million atoms thick. Now imagine shaving off most of those atoms until only a single layer of them remains; this layer is a 2-D material. In a 2-D crystal, the atoms and electrons are confined to this plane because moving off it would mean exiting the material entirely.

Graphene is an example of a 2-D topological material. To me, the most intriguing thing about graphene is that its band structure contains special spots known as Dirac points. These are positions where two energy bands take on the same value, meaning that at these points electrons can easily jump from one energy band to another. One way to understand Dirac points is to study a plot of the energy of different bands versus an electron's momentum a property associated with the particle's kinetic energy. Such plots show how an electron's energy changes with its movement, giving us a direct probe into the physics we're interested in. In these plots, a Dirac point looks like a place where two energy bands touch; at this point they're equal, but away from this point the gap between the bands grows linearly. Graphene's Dirac points and the associated topology are connected to this material's ability to display a form of the quantum Hall effect that's unique even among 2-D materialsthe half-integer quantum Hall effectand the special kind of tunneling possible within it.

To understand what's happening to electrons at Dirac points, we need to observe them up close. Our optical lattice experiments are the perfect way to do this. They offer a highly controllable replica of the material that we can uniquely manipulate in a laboratory. As substitutes for the electrons, we use ultracold rubidium atoms chilled to temperatures roughly 10 million times colder than outer space. And to simulate the graphene lattice, we turn to light.

Light is both a particle and a wave, which means light waves can interfere with one another, either amplifying or canceling other waves depending on how they are aligned. We use the interference of laser light to make patterns of bright and dark spots, which become the lattice. Just as electrons in real graphene are attracted to certain positively charged areas of a carbon hexagon, we can arrange our optical lattices so ultracold atoms are attracted to or repelled from analogous spots in them, depending on the wavelength of the laser light that we use. Light with just the right energy (resonant light) landing on an atom can change the state and energy of an electron within it, imparting forces on the atom. We typically use red-detuned optical lattices, which means the laser light in the lattice has a wavelength that's longer than the wavelength of the resonant light. The result is that the rubidium atoms feel an attraction to the bright spots arranged in a hexagonal pattern.

We now have the basic ingredients for an artificial crystal. Scientists first imagined these ultracold atoms in optical lattices in the late 1990s and constructed them in the early 2000s. The spacing between the lattice points of these artificial crystals is hundreds of nanometers rather than the fractions of a nanometer that separate atoms in a solid crystal. This larger distance means that artificial crystals are effectively magnified versions of real ones, and the hopping process of atoms within them is much slower, allowing us to directly image the movements of the ultracold atoms. In addition, we can manipulate these atoms in ways that aren't possible with electrons.

I was a postdoctoral researcher in the Ultracold Atomic Physics group at the University of California, Berkeley, from 2019 to 2022. The lab there has two special tables (roughly one meter wide by two and a half meters long by 0.3 meter high), each weighing roughly one metric ton and floating on pneumatic legs that dampen vibrations. Atop each table lie hundreds of optical components: mirrors, lenses, light detectors, and more. One table is responsible for producing laser light for trapping, cooling and imaging rubidium atoms. The other table holds an ultrahigh vacuum chamber made of steel with a vacuum pressure less than that of low-Earth orbit, along with hundreds more optical components.

The vacuum chamber has multiple, sequential compartments with different jobs. In the first compartment, we heat a five-gram chunk of rubidium metal to more than 100 degrees Celsius, which causes it to emit a vapor of rubidium atoms. The vapor gets blasted into the next compartment like water spraying from a hose. In the second compartment, we use magnetic fields and laser light to slow the vapor down. The sluggish vapor then flows into another compartment: a magneto-optical trap, where it is captured by an arrangement of magnetic fields and laser light. Infrared cameras monitor the trapped atoms, which appear on our viewing screen as a bright glowing ball. At this point the atoms are colder than liquid helium.

We then move the cold cloud of rubidium atoms into the final chamber, made entirely of quartz. There we shine both laser light and microwaves on the cloud, which makes the warmest atoms evaporate away. This step causes the rubidium to transition from a normal gas to an exotic phase of matter called a Bose-Einstein condensate (BEC). In a BEC, quantum mechanics allows atoms to delocalizeto spread out and overlap with one another so that all the atoms in the condensate act in unison. The temperature of the atoms in the BEC is less than 100 nanokelvins, one billion times colder than liquid nitrogen.

At this point we shine three laser beams separated by 120 degrees into the quartz cell (their shape roughly forms the letter Y). At the intersection of the three beams, the lasers interfere with one another and produce a 2-D optical lattice that looks like a honeycomb pattern of bright and dark spots. We then move the optical lattice so it overlaps with the BEC. The lattice has plenty of space for atoms to hop around, even though it extends over a region only as wide as a human hair. Finally, we collect and analyze pictures of the atoms after the BEC has spent some time in the optical lattice. As complex as it is, we go through this entire process once every 40 seconds or so. Even after years of working on this experiment, when I see it play out, I think to myself, Wow, this is incredible!

Like real graphene, our artificial crystal has Dirac points in its band structure. To understand why these points are significant topologically, let's go back to our graph of energy versus momentum, but this time let's view it from above so we see momentum plotted in two directionsright and left, and up and down. Imagine that the quantum state of the BEC in the optical lattice is represented by an upward arrow at position one (P1) and that a short, straight path separates P1 from a Dirac point at position two (P2).

To move our BEC on this graph toward the Dirac point, we need to change its momentumin other words, we must actually move it in physical space. To put the BEC at the Dirac point, we need to give it the precise momentum values corresponding to that point on the plot. It turns out that it's easier, experimentally, to shift the optical latticeto change its momentumand leave the BEC as is; this movement gives us the same end result. From an atom's point of view, a stationary BEC in a moving lattice is the same as a moving BEC in a stationary lattice. So we adjust the position of the lattice, effectively giving our BEC a new momentum and moving it over on our plot.

If we adjust the BEC's momentum so that the arrow representing it moves slowly on a straight path from P1 toward P2 but just misses P2 (meaning the BEC has slightly different momentum than it needs to reach P2), nothing happensits quantum state is unchanged. If we start over and move the arrow even more slowly from P1 toward P2 on a path whose end is even closer tobut still does not touchP2, the state again is unchanged.

Now imagine that we move the arrow from P1 directly through P2that is, we change the BEC's momentum so that it's exactly equal to the value at the Dirac point: we will see the arrow flip completely upside down. This change means the BEC's quantum state has jumped from its ground state to its first excited state.

What if instead we move the arrow from P1 to P2, but when it reaches P2, we force it to make a sharp left or right turnmeaning that when the BEC reaches the Dirac point, we stop giving it momentum in its initial direction and start giving it momentum in a direction perpendicular to the first one? In this case, something special happens. Instead of jumping to an excited state as if it had passed straight through the Dirac point and instead of going back down to the ground state as it would if we had turned it fully around, the BEC ends up in a superposition when it exits the Dirac point at a right angle. This is a purely quantum phenomenon in which the BEC enters a state that is both excited and not. To show the superposition, our arrow in the plot rotates 90 degrees.

Our experiment was the first to move a BEC through a Dirac point and then turn it at different angles. These fascinating outcomes show that these points, which had already seemed special based on graphene's band structure, are truly exceptional. And the fact that the outcome for the BEC depends not just on whether it passes through a Dirac point but on the direction of that movement shows that at the point itself, the BEC's quantum state can't be defined. This shows that the Dirac point is a singularitya place where physics is uncertain.

We also measured another interesting pattern. If we moved the BEC faster as it traveled near, but not through, the Dirac point, the point would cause a rotation of the BEC's quantum state that made the point seem larger. In other words, it encompassed a broader range of possible momentum values than just the one precise value at the point. The more slowly we moved the BEC, the smaller the Dirac point seemed. This behavior is uniquely quantum mechanical in nature. Quantum physics is a trip!

Although I just described our experiment in a few paragraphs, it took six months of work to get results. We spent lots of time developing new experimental capabilities that had never been used before. We were often unsure whether our experiment would work. We faced broken lasers, an accidental 10-degree-C temperature spike in the lab that misaligned all the optical components (there went three weeks), and disaster when the air in our building caused the lab's temperature to fluctuate, preventing us from creating a BEC. A great deal of persistent effort carried us through and eventually led to our measuring a phenomenon even more exciting than a Dirac point: another kind of singularity.

Before we embarked on our experiment, a related project with artificial crystals in Germany showed what happens when a BEC moves in a circular path around a Dirac point. This team manipulated the BEC's momentum so that it took on values that would plot a circle in the chart of left-momentum versus up-down momentum. While going through these transformations, the BEC never touched the Dirac point. Nevertheless, moving around the point in this pattern caused the BEC to acquire something called a geometric phasea term in the mathematical description of its quantum phase that determines how it evolves. Although there is no physical interpretation of a geometric phase, it's a very unusual property that appears in quantum mechanics. Not every quantum state has a geometric phase, so the fact that the BEC had one here is special. What's even more special is that the phase was exactly .

My team decided to try a different technique to confirm the German group's measurement. By measuring the rotation of the BEC's quantum state as we turned it away from the Dirac point at different angles, we reproduced the earlier findings. We discovered that the BEC's quantum state wraps around the Dirac point exactly once. Another way to say this is that as you move a BEC through momentum space all the way around a Dirac point, it goes from having all its particles in the ground state to having all its particles in the first excited state, and then they all return to the ground state. This measurement agreed with the German study's results.

This wrapping, independent of a particular path or the speed the path is traveled, is a topological property associated with a Dirac point and shows us directly that this point is a singularity with a so-called topological winding number of 1. In other words, the winding number tells us that after a BEC's momentum makes a full circle, it comes back to the state it started in. This winding number also reveals that every time it goes around the Dirac point, its geometric phase increases by .

Furthermore, we discovered that our artificial crystal has another kind of singularity called a quadratic band touching point (QBTP). This is another point where two energy bands touch, making it easy for electrons to jump from one to another, but in this case it's a connection between the second excited state and the third (rather than the ground state and the first excited state as in a Dirac point). And whereas the gap between energy bands near a Dirac point grows linearly, in a QBTP it grows quadratically.

In real graphene, the interactions between electrons make QBTPs difficult to study. In our system, however, QBTPs became accessible with just one weird trick.

Well, it's not really so weird, nor is it technically a trick, but we did figure out a specific technique to investigate a QBTP. It turns out that if we give the BEC a kick and get it moving before we load it into the optical lattice, we can access a QBTP and study it with the same method we used to investigate the Dirac point. Here, in the plot of momentum space, we can imagine new points P3 and P4, where P3 is an arbitrary starting point in the second excited band and a QBTP lies at P4. Our measurements showed that if we move the BEC from P3 directly through P4 and turn it at various angles, just as we did with the Dirac point, the BEC's quantum state wraps exactly twice around the QBTP. This result means the BEC's quantum state picked up a geometric phase of exactly 2. Correspondingly, instead of a topological winding number of 1, like a Dirac point has, we found that a QBTP has a topological winding number of 2, meaning that the state must rotate in momentum space around the point exactly twice before it returns to the quantum state it started in.

This measurement was hard-won. We tried nearly daily for an entire month before it eventually workedwe kept finding fluctuations in our experiment whose sources were hard to pinpoint. After much effort and clever thinking, we finally saw the first measurement in which a BEC's quantum state exhibited wrapping around a QBTP. At that moment I thought, Oh, my goodness, I might actually land a job as a professor. More seriously, I was excited that our measurement technique showed itself to be uniquely suited to reveal this property of a QBTP singularity.

These singularities, with their strange geometric phases and winding numbers, may sound esoteric. But they are directly related to the tangible properties of the materials we studyin this case the special abilities of graphene and its promising future applications. All these changes that occur in the material's quantum state when it moves through or around these points manifest in cool and unusual phenomena in the real world.

Scientists have predicted, for instance, that QBTPs in solid materials are associated with a type of exotic high-temperature superconductivity, as well as anomalous properties that alter the quantum Hall effect and even electric currents in materials whose flow is typically protected, via topology, from disruption. Before attempting to further investigate this exciting physics, we want to learn more about how interactions between atoms in our artificial crystal change what we observe in our lab measurements.

In real crystals, the electrons interact with one another, and this interaction is usually quite important for the most striking physical effects. Because our experiment was the first of its kind, we took care to ensure that our atoms interacted only minimally to keep things simple. An exciting question we can now pose is: Could interactions cause a QBTP singularity to break apart into multiple Dirac points? Theory suggests this outcome may be possible. We look forward to cranking up the interatomic interaction strength in the lab and seeing what happens.

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Physicists Make Matter out of Light to Find Quantum Singularities - Scientific American

New theoretical research by Michael Wondrak, Walter van Suijlekom and Heino Falcke of Radboud University has shown that Stephen Hawking was right about black holes, although not completely. Due to Hawking radiation, black holes will eventually evaporate, but the event horizon is not as crucial as had been believed. Gravity and the curvature of spacetime cause this radiation too. This means that all large objects in the universe, like the remnants of stars, will eventually evaporate.

Using a clever combination of quantum physics and Einstein's theory of gravity, Stephen Hawking argued that the spontaneous creation and annihilation of pairs of particles must occur near the event horizon (the point beyond which there is no escape from the gravitational force of a black hole). A particle and its anti-particle are created very briefly from the quantum field, after which they immediately annihilate. But sometimes a particle falls into the black hole, and then the other particle can escape: Hawking radiation. According to Hawking, this would eventually result in the evaporation of black holes.

Spiral

In this new study the researchers at Radboud University revisited this process and investigated whether or not the presence of an event horizon is indeed crucial. They combined techniques from physics, astronomy and mathematics to examine what happens if such pairs of particles are created in the surroundings of black holes. The study showed that new particles can also be created far beyond this horizon. Michael Wondrak: 'We demonstrate that, in addition to the well-known Hawking radiation, there is also a new form of radiation.'

Everything evaporates

Van Suijlekom: 'We show that far beyond a black hole the curvature of spacetime plays a big role in creating radiation. The particles are already separated there by the tidal forces of the gravitational field.' Whereas it was previously thought that no radiation was possible without the event horizon, this study shows that this horizon is not necessary.

Falcke: 'That means that objects without an event horizon, such as the remnants of dead stars and other large objects in the universe, also have this sort of radiation. And, after a very long period, that would lead to everything in the universe eventually evaporating, just like black holes. This changes not only our understanding of Hawking radiation but also our view of the universe and its future.'

The study was published on 2 June in the journal Physical Review Letters of the American Physical Society (APS). Michael Wondrak is excellence fellow at Radboud University and an expert in quantum field theory. Walter van Suijlekom is a Professor of Mathematics at Radboud University and works on the mathematical formulation of physics problems. Heino Falcke is an award-winning Professor of Radio Astronomy and Astroparticle Physics at Radboud University and known for his work on predicting and making the first picture of a black hole.

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Eventually everything will evaporate, not only black holes - Science Daily

June 2, 2023 Since the dawn of the Information Age in the middle of the 20th century, humanity has seen rapid developments in the realm of electronics and materials science. In the 1950s, the UNIVAC-I became the first commercially available, general-purpose computer, capable of just under 2,000 calculations per seconda far cry from a modern iPhone, capable of more than 10 trillion calculations per second.

Whether it is new medical devices, materials for advanced manufacturing applications, information technology innovations, or simply the vast array of consumer devices, our rapid technological advancements were born out of a better understanding of how atomic particles behave and interact with one another at a fundamental level.

Understanding these interactions is the work of researchers dedicated to fundamental science. The centers that comprise the Gauss Centre for Supercomputing (GCS)the High-Performance Computing Center Stuttgart (HLRS), the Jlich Supercomputing Centre (JSC), and the Leibniz Supercomputing Centre (LRZ)are dedicated to supporting fundamental research in the interest of laying the groundwork for tomorrows great technological advancements.

To that end, researchers at the Julius-Maximillians-Universitt Wrzburg (JMU) have been long-time users of high-performance computing (HPC) resources at LRZ to illuminate the complex, mysterious world of solid-state physicsa scientific domain focused on understanding how particles interact with one another and their environments at the atomic and subatomic levels. Recently, the team investigated a previously poorly studied quantum system dubbed Kondo heterostructures, which reveal a host of fascinating emergent collective properties that hold promise for further theoretical, numerical and experimental investigations.

The point of our research is to understand the quantum world and manipulate it, said Prof. Dr. Fakher Assaad, JMU professor and lead researcher on the project. In view of applications down the road, we have to bear in mind that the quantum effects that we consider take place at very low temperatures. A huge challenge is to realize these effects at room temperature. Before we can do that, though, we must be able to more fully understand and play with these systems.

Experiments and Simulations Work in Concert Toward New Insights

In 2016, a multi-institutional team of Dutch experimentalists published an article in Nature Physics studying cobalt adatomssmall numbers of magnetic atoms that are adsorbed, or stuck, to a material surface rather than being absorbed into a materialon a copper surface. The team used an experimental technique called scanning tunneling microscopy (STM), which uses an ultra-sharp tip as a microscope to both observe and manipulate individual atoms into specific patterns, or structures, in order to better understand their magnetic properties and quantum behavior under certain conditions.

Understanding atomic systems behavior is not as simple as just pointing a microscope at them, thoughexperimentally, it is impossible to know both an electrons speed and position at any given moment. This becomes even more daunting when looking at systems of many atoms and their many constituent electrons. In order to fully understand how nanosecond changes can impact these systems, researchers often turn to computational modelling to verify what they think they see experimentally.

In order to computationally model such a system, researchers rely on Monte Carlo simulations, which use statistical physics to sample all possible particle positions at a given moment. While the method is relatively straightforward, even a modest number of atoms has millions or billions of possible configurations, meaning researchers must have access to HPC resources to finish simulations in a reasonable amount of time. For quantum systems such as these, Assaad and his team do quantum Monte Carlo simulations. This translates quantum physics observed in the simulation into classical physics, but one dimension highera two-dimensional quantum system being translated into a three-dimensional classical system, for instance.

Using SuperMUC-NG at LRZ, Assaad and his collaborators applied their computational approach to the teams experimental system and were able to model it with one hundred percent accuracy. However, the team wanted to take the work further and grow the system size from a handful of atoms to a much larger volume in order to see whether the behavior would change. In the process, they uncovered a new type of system where particles quantum spins in a metallic environment behave differently than previously observed. These so-called Kondo heterostructures offer physicists a promising lead in their pursuit of novel quantum phases.

We have this simple model which reflects reality, but then you ask yourself, What happens if, instead of having 10 cobalt adatoms on a metallic surface, we have an infinite chain? said Assaad. This research started off motivated by a question that came from experiment. Since the model reproduced experimental data for a handful of cobalt adatoms, we know that it was correct.

Then the work evolved into something where we could help guide experimentalists in their search for interesting new physics. This work is close to experiment, motivated by experiment, and shows strong feedback between numerics and experiment.

Classical Computing Fuels the Quantum Revolution

As voracious HPC users, Assaad and his colleagues have been allocated time on both the CPU-centric SuperMUC-NG as well as the GPU-heavy JUWELS system at JSC, another GCS center. Assaad pointed out that in order to use different architectures, researchers must rework their applications to run efficiently on new machines. Luckily, they find good support for porting their applications at the centers. It works well when you have people who really know these machines, with whom you can work closely, discuss things, and ultimately get an understanding of how to quickly make your program run better, he said.

Having had long-term access to GCS resources, the researchers have developed a mature, stable computational workflow that remains flexible for studying a variety of quantum systems on diverse HPC architectures. This ultimately shines new light on the still-mysterious quantum world and brings research to life for a wider audience.

Moving forward, Assaad keeps dreaming: he indicated that he, like many other physicists, is always seeking out new and interesting problems that can be solved with todays technologies, while also keeping an eye toward what could be possible tomorrow. With its computational approach, the team is interested in seeking new classes of model systems that connect to materials, exhibit novel phases and phase transitions, and inspire new applications. The richness of physics is amazing. There is no limit to the variety of phenomena you can generate with materials, and we are pretty rudimentary in our understanding compared to what the quantum world offers. There is a huge potential for progress, but it takes time, Assaad said.

Source: Eric Gedenk, Gauss Centre for Supercomputing

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Julius-Maximillians-Universitt Wrzburg Researchers Use ... - HPCwire

It turns out that agroup calling themselvesthe Lazarus Project has been keeping humanity afloat by jumping the whole world back in time whenever natural events or human actions threaten a mass extinction event, to use their language. And while most people dont remember the alternate timelines, George has somehow woken up to them. Hes a mutant, and he joins the group of time-traveling world savers rather than be alone in the crazy-making do-overs.

As George goes deeper into the secret society of the Project, Essiedu works well as an everyman, both skeptical and excited. Its noteworthy to see a Black man in this part, a hero and a human, a flawed character we empathize with. The show doesnt remark on his race in the four episodes available for critics to screen, while it does note others, demonstrating that it knows what its doing. And The Lazarus Project keeps pushing, allowing Essiedu to flex his acting chops, sometimes comedic and at others heart-wrenching.

George is put through these paces by a set of arbitrary rules that the show doesnt explain, even though they determine everyones fate. George does ask how it works, but his guide and time-traveling mentor Archie (Anjli Mohindra) brushes aside his query (and that of the audience)by saying youd need to understand quantum physics for the answer to make sense. The basic gist is that they have a checkpoint of July 1st that they reset to if things go bad. Make it to the next July, and that year is locked.

And reset they do. The Lazarus Project offers up a pretty grim view of humanity in which we, as a group, regularly do ourselves in (thanks, nuclear weapons), and it takes the extraordinary actions of a few rogue heroes to keep that from happening again and again.

While all this sounds noble, it gets thorny for those who do remember the time resets. What if they get pregnant? Give birth? Lose a loved one? How do they balance their personal needs with humanitys? And if most dont remember, why cant they hit the reset button when needed?

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TNTs The Lazarus Project Uses Suspense Trapping to Ask Smart ... - Roger Ebert