Daily Archives: August 27, 2022

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Credit: Image credit: Bjrn Annby-Andersson

As the size of modern technology shrinks down to the nanoscale, weird quantum effectssuch as quantum tunneling, superposition, and entanglementbecome prominent. This opens the door to a new era of quantum technologies, where quantum effects can be exploited. Many everyday technologies make use of feedback control routinely; an important example is the pacemaker, which must monitor the users heartbeat and apply electrical signals to control it, only when needed. But physicists do not yet have an equivalent understanding of feedback control at the quantum level. Now, FQXi-funded physicists have developed a master equation that will help engineers understand feedback at the quantum scale. Their results are published in the journal Physical Review Letters.

It is vital to investigate how feedback control can be used in quantum technologies in order to develop efficient and fast methods for controlling quantum systems, so that they can be steered in real time and with high precision, says co-author Bjrn Annby-Andersson, a quantum physicist at Lund University, in Sweden.

An example of a crucial feedback-control process in quantum computing is quantum error correction. A quantum computer encodes information on physical qubits, which could be photons of light, or atoms, for instance. But the quantum properties of the qubits are fragile, so it is likely that the encoded information will be lost if the qubits are disturbed by vibrations or fluctuating electromagnetic fields. That means that physicists need to be able to detect and correct such errors, for instance by using feedback control. This error correction can be implemented by measuring the state of the qubits and, if a deviation from what is expected is detected, applying feedback to correct it.

It is vital to investigate how feedback control can be used in quantum technologies in order to develop efficient and fast methods for controlling quantum systems, so that they can be steered in real time and with high precision, says co-author Bjrn Annby-Andersson, a quantum physicist at Lund University, in Sweden.

But feedback control at the quantum level presents unique challenges, precisely because of the fragility physicists are trying to mitigate against. That delicate nature means that even the feedback process itself could destroy the system. It is necessary to only interact weakly with the measured system, preserving the properties we want to exploit, says Annby-Andersson.

It is thus important to develop a full theoretical understanding of quantum feedback control, to establish its fundamental limits. But most existing theoretical models of quantum feedback control require computer simulations, which typically only provide quantitative results for specific systems. It is difficult to draw general, qualitative conclusions, Annby-Andersson says. The few models that can provide qualitative understanding are only applicable on a narrow class of feedback controlled systemsthis type of feedback is typically referred to as linear feedback.

Pen and Paper

Annby-Andersson and his colleagues have now developed a master equation, called a Quantum Fokker-Planck equation, that enables physicists to track the evolution of any quantum system with feedback control over time. The equation can describe scenarios that go beyond linear feedback, says Annby-Andersson. In particular, the equation can be solved with pen and paper, rather than having to rely on computer simulations.

The team tested their equation by applying it to a simple feedback model. This confirmed that the equation provides physically sensible results and also demonstrated how energy can be harvested in microscopic systems, using feedback control. The equation is a promising starting point for future studies of how energy may be manipulated with the help of information on a microscopic level, says Annby-Andersson.

The analysis and related experiments are partially funded by a grant from the Foundational Questions Institute, FQXi. It is a great example of a successful collaboration between two different teams based at the University of Maryland, College Park, and at Lund University, says co-author and FQXi member Peter Samuelsson, a quantum physicist at Lund University.

The equation is a promising starting point for future studies of how energy may be manipulated with the help of information on a microscopic level, says Annby-Andersson.

The team is now investigating a system that makes use of feedback to manipulate energy in quantum dotstiny semiconducting crystals just billionths of a meter across. An important future direction is to use the equation as a tool for inventing novel feedback protocols that can be used for quantum technologies, says Annby-Andersson.

This work was partially supported through FQXi's Information as Fuel program.You can read more about the teams grant in the Foundational Questions Institute, FQXi article: Connect the Quantum Dots for a New Kind of Fuel,by Colin Stuart.

Journal reference: Quantum Fokker-Planck Master Equation for Continuous Feedback Control

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The Foundational Questions Institute, FQXi, catalyzes, supports, and disseminates research on questions at the foundations of science, particularly new frontiers in physics and innovative ideas integral to a deep understanding of reality but unlikely to be supported by conventional funding sources. Visit fqxi.orgfor more information.

Physical Review Letters

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Quantum Fokker-Planck Master Equation for Continuous Feedback Control

25-Jul-2022

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Todays stories include Quantum Theory of Consciousness Challenged to Is Life on Earth the Standard Model for the Universe to The 50 Million-Year-Old Treasures of Fossil Lake, and much more.

What makes the human brain different? Yale study reveals clues What makes the human brain distinct from that of all other animals including even our closest primate relatives? In an analysis of cell types in the prefrontal cortex of four primate species, Yale researchers identified species-specific particularly human-specific features, they report Aug. 25 in the journal Science.

Seven Million Years Ago, the Oldest Known Early Human Was Already Walking, reports The Smithsonian. Analysis of a femur fossil indicates that a key species could already move somewhat like us.

Extraterrestrial Life Is Earth the Standard Model for the Universe? asks The Daily Galaxy. By the end of this century, says astrophysicist Martin Rees, we should be able to ask whether or not we live in a multiverse, and how much variety of the laws of physics its constituent universes display. The answer to this question, says Rees, will determine how we should interpret the biofriendly universe in which we live (sharing it with any aliens with whom we might one day make contact).

Unfathomable Abodes of Life? Water Worlds of the Milky WayBefore life appeared on land some 400 million years ago, all life on Earth including the mind evolved in the sea. Astronomers have recently conjectured that blue exoplanets with endless oceans may be orbiting many of the Milky Ways one trillion stars, reports The Daily Galaxy.

What Drives Galaxies? The Milky Ways Black Hole May Be the Key--What Drives Galaxies? The Milky Ways Black Hole May Be the Key. Supermassive black holes have come to the fore as engines of galactic evolution, but new observations of the Milky Way and its central hole dont yet hang together, reports Quanta.

Quantum theory of consciousness put in doubt by underground experiment, reports Physics World. A controversial theory put forward by physicist Roger Penrose and anesthesiologist Stuart Hameroff that posits consciousness to be a fundamentally quantum-mechanical phenomenon has been challenged by research looking at the role of gravity in the collapse of quantum wavefunctions.

How quantum physicists are looking for life on exoplanets, reports Northeastern University. News@Northeastern spoke to Gregory Fiete, a physics professor at Northeastern, about some of the broad applications of quantum research, from developing renewable energy sources and building more powerful computers, to advancing humanitys quest to discover life beyond the solar system.

The Plan to Look for Life on VenusWithout NASA--A private group of scientists and rocket engineers might be the first to find signs of extraterrestrial life on the second planet from the sun, reports The Daily Beast.

After Millennia of Agricultural Expansion, the World Has Passed Peak Agricultural Land, reports Dr. Hannah Ritchie for Singularity HubHumans have been reshaping the planets land for millennia by clearing wildlands to grow crops and raise livestock. As a result, humans have cleared one-third of the worlds forests and two-thirds of wild grasslands since the end of the last ice age.

The 50 Million-Year-Old Treasures of Fossil Lake In a forbidding Wyoming desert, scientists and fortune hunters search for the surprisingly intact remains of horses and other creatures that lived long ago, reports The Smithsonian..

Drought Exposes Dinosaur Tracks in Texas--The 113-million-year-old footprints were largely made by the carnivorous Acrocanthosaurus, reports The Smithsonian. A severe drought in Texas has revealed 113-million-year-old dinosaur tracks in Dinosaur Valley State Park. The prints are usually covered by the Paluxy Riverthe last time they were visible was in the year 2000, according to BBC News.

Doppelgngers Dont Just Look AlikeThey Also Share DNANew research finds genetic and lifestyle similarities between unrelated pairs of virtual twins, reports the Smithsonian. People with very similar faces also share many of the same genes and lifestyle traits, according to a new paper published Tuesday in the journal Cell Reports.

Shape of human brain has barely changed in past 160,000 years An analysis of fossils suggests changes in the shape of the braincase during human evolution were linked to alterations in the face, rather than changes in the brain itself, reports New Scientist.

Humanity Is Woefully Unprepared for a Major Volcanic Eruption, reports Gizmodo. When the Hunga Tonga-Hunga Haapai volcano erupted in Tonga on January 15, the result was devastation. The eruption literally blew up an island, caused mass flooding in the surrounding areas, coated whole communities in a thick layer of ash, and took out telecommunications for weeks. Yet in that eruption, we got lucky, according to a new commentary article .

Scientists discovered a 5 million-year-old time capsule buried in Antarctica--Its an ice core with bubbles containing remains of ancient Earth atmosphere, reports ZME Science.

When will Chinas population peak? It depends who you ask--Data show the country is facing a demographic crisis, with an aging population and young couples having fewer children, reports Nature.

MIT professor wrongfully accused of spying for China helps make a major discovery Gang Chen, who was cleared after a lengthy DOJ investigation, said he is stepping away from federally funded research because of anxieties around being racially profiled, reports NBC.

Reconstructing ice age diets reveals an unraveling web of lifeWhile about 6% of land mammals have gone extinct in that time, we estimate that more than 50% of mammal food web links have disappeared, said ecologist Evan Fricke, lead author of the study. And the mammals most likely to decline, both in the past and now, are key for mammal food web complexity, reports Rice University.

Why Thinking Hard Wears You OutConcentrating for long periods builds up chemicals that disrupt brain functioning, reports Scientific American.

Tiny Caribbean crustaceans and their bioluminescent mating displays are shining new light on evolution, reports Science. No bigger than a grain of sand, ostracods abound in fresh and saltwater. They are very cute but also sort of bizarrelike a cross between a crab and a tiny spaceship, says Timothy Fallon, an evolutionary biochemist at the University of California (UC), San Diego.

The Biggest Offshore Wind Farm in the World Will Be Fully Online This Month, reports Singularity Hub. A massive offshore wind project has been underway off the coast of England for over four years. Construction of Hornsea One started in January 2018, and generated its first power a year and a half later. Meanwhile, construction of neighboring Hornsea Two got underway, with that site first coming online last December.

Eye movements in REM sleep mimic gazes in the dream world, reports the University of California, San Francisco. When our eyes move during REM sleep, were gazing at things in the dream world our brains have created, according to a new study by researchers at UC San Francisco. The findings shed light not only into how we dream, but also into how our imaginations work.

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In some pockets of space, far beyond the limits of our observations, wrote cosmologist Dan Hooper at the University of Chicago in an email to The Daily Galaxy, referring to the theory of eternal inflation and the inflationary multiverse: the laws of physics could be very different from those we find in our local universe. Different forms of matter could exist, which experience different kinds of forces. In this sense, what we call the laws of physics, instead of being a universal fact of nature, could be an environmental fact, which varies from place to place, or from time to time.

I think I know how the universe was born, said Andrei Linde, Russian-American theoretical physicist and the Harald Trap Friis Professor of Physics at Stanford University. Linde is one of the main authors of the inflationary universe theory, as well as the theory of eternal inflation and inflationary multiverse.

According to quantum models, galaxies like the Milky Way grew from faint wrinkles in the fabric of spacetime. The density of matter in these wrinkles was slightly greater compared to surrounding areas and this difference was magnified during inflation, allowing them to attract even more matter. From these dense primordial seeds grew the cosmic structures we see today. Galaxies are children of random quantum fluctuations produced during the first 10-35 seconds after the birth of the universe, said Linde.

As a result, the universe becomes a multiverse, an eternally growing fractal consisting of exponentially many exponentially large parts, Linde wrote. These parts are so large that for all practical purposes they look like separate universes.

Late one summer night in 1981, while still a junior research fellow at Lebedev Physical Institute in Moscow, Andrei Linde was struck by a revelation. Unable to contain his excitement, he shook awake his wife, Renata Kallosh, and whispered to her in their native Russian, I think I know how the universe was born.

Kallosh, a theoretical physicist herself, muttered some encouraging words and fell back asleep. It wasnt until the next morning that I realized the full impact of what Andrei had told me, recalled Kallosh, now a professor of physics at the Stanford Institute for Theoretical Physics.

Lindes nocturnal eureka moment had to do with a problem in cosmology that he and other theorists, including Stephen Hawking, had struggled with.

A year earlier, a 32-year-old postdoc at SLAC National Accelerator Laboratory named Alan Guth shocked the physics community by proposing a bold modification to the Big Bang theory. According to Guths idea, which he called inflation, our universe erupted from a vacuum-like state and underwent a brief period of faster-than-light expansion. In less than a billionth of a trillionth of a trillionth of a second, space-time doubled more than 60 times from a subatomic speck to a volume many times larger than the observable universe.

Guth envisioned the powerful repulsive force fueling the universes exponential growth as a field of energy flooding space. As the universe unfurled, this inflation field decayed, and its shed energy was transfigured into a fiery bloom of matter and radiation. This pivot, from nothing to something and timelessness to time, marked the beginning of the Big Bang. It also prompted Guth to famously quip that the inflationary universe was the ultimate free lunch.

As theories go, inflation was a beauty. It explained in one fell swoop why the universe is so large, why it was born hot, and why its structure appears to be so flat and uniform over vast distances. There was just one problem it didnt work.

To conclude the unpacking of space-time, Guth borrowed a trick from quantum mechanics called tunneling to allow his inflation field to randomly and instantly skip from a higher, less stable energy state to a lower one, thus bypassing a barrier that could not be scaled by classical physics.

But closer inspection revealed that quantum tunneling caused the inflation field to decay quickly and unevenly, resulting in a universe that was neither flat nor uniform. Aware of the fatal flaw in his theory, Guth wrote at the end of his paper on inflation: I am publishing this paper in the hope that it will encourage others to find some way to avoid the undesirable features of the inflationary scenario.

Linde Answers Guth

Guths plea was answered by Linde, who on that fateful summer night realized that inflation didnt require quantum tunneling to work. Instead, the inflation field could be modeled as a ball rolling down a hill of potential energy that had a very shallow, nearly flat slope. While the ball rolls lazily downhill, the universe is inflating, and as it nears the bottom, inflation slows further and eventually ends. This provided a graceful exit to the inflationary state that was lacking in Guths model and produced a cosmos like the one we observe. To distinguish it from Guths original model while still paying homage to it, Linde dubbed his model new inflation.

Models of Inflation Theory

By the time Linde and Kallosh moved to Stanford in 1990, experiments had begun to catch up with the theory. Space missions were finding temperature variations in the energetic afterglow of the Big Bang called the cosmic microwave background radiation that confirmed a startling prediction made by the latest inflationary models. These updated models went by various names chaotic inflation, eternal inflation, eternal chaotic inflation and many more but they all shared in common the graceful exit that Linde pioneered.

Quantum Fluctuation Fingerprints

Inflation predicted that these quantum fluctuations would leave imprints on the universes background radiation in the form of hotter and colder regions, and this is precisely what two experiments dubbed COBE and WMAP found. After the COBE and WMAP experiments, inflation started to become part of the standard model of cosmology, Shamit Kachru said.

Pocket Universes New Inflating Regions in the Universe

Linde and others later realized that the same quantum fluctuations that produced galaxies can give rise to new inflating regions in the universe. Even though inflation ended in our local cosmic neighborhood 13.8 billion years ago it can still continue in disconnected regions of space beyond the limits of our observable universe The consequence is an ever-expanding sea of inflating space-time dotted with pocket universes like our own where inflation has ceased.

As a result, the universe becomes a multiverse, an eternally growing fractal consisting of exponentially many exponentially large parts, Linde wrote. These parts are so large that for all practical purposes they look like separate universes.

Linde took the multiverse idea even further by proposing that each pocket universe could have differing properties, a conclusion that some string theorists were also reaching independently.

Its not that the laws of physics are different in each universe, but their realizations, Linde said. An analogy is the relationship between liquid water and ice. Theyre both H2O but realized differently.

Lindes multiverse is like a cosmic funhouse filled with reality-distorting mirrors. Some pocket universes are resplendent with life, while others were stillborn because they were cursed with too few (or too many) dimensions, or with physics incompatible with the formation of stars and galaxies. An infinite number are exact replicas of ours, but infinitely more are only near-replicas. Right now, there could be countless versions of you inhabiting worlds with histories divergent from ours in ways large and small. In an infinitely expanding multiverse, anything that can happen will happen.

The inflationary universe is not just the ultimate free lunch, its the only lunch where all possible dishes are served, Linde said.

While disturbing to some, this eternal aspect of inflation was just what a small group of string theorists were looking for to help explain a surprise discovery that was upending the physics world dark energy.

The Last Word -Brian Keating and Avi Loeb

When asked, will Lindes pocket universes be subject to the same laws of physics as our Universe, Brian Keating, Distinguished Professor of Physics at the Center for Astrophysics & Space Sciences at University of California, San Diego, told The Daily Galaxy: No, not necessarily. Its not mandatory that the properties of space-time be consistent from universe to universe. Nor is it impossible that the laws of logic and mathematics be consistent throughout the universe. This has led some physicists such as Paul Steinhart claiming that the multiverse concept is not a self-consistent or proper subject with the traditions of the scientific method.

Not so certain of the existence of Lindes free lunch, Harvard astrophysicist Avi Loeb told The Daily Galaxy: Advances in scientific knowledge are enabled by experimental tests of theoretical ideas. Physics is a dialogue with nature, not a monologue. I am eagerly waiting for a proposed experimental test of the multiverse idea.

Avi Shporer, Research Scientist, with the MIT Kavli Institute for Astrophysics and Space Research via Dan Hooper, Brian Keating, Avi Loeb and Stanford University

The Galaxy Report newsletter brings you twice-weekly news of space and science that has the capacity to provide clues to the mystery of our existence and add a much needed cosmic perspective in our current Anthropocene Epoch.

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Avi Shporer,Research Scientist, MIT Kavli Institute for Astrophysics and Space Research. AGoogle Scholar, Avi was formerly aNASA Sagan Fellowat the Jet Propulsion Laboratory (JPL). His motto, not surprisingly, is a quote from Carl Sagan: Somewhere, something incredible is waiting to be known.

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Quantum Birth of the Universe (Weekend Feature) - The Daily Galaxy --Great Discoveries Channel