Using a small quantum system consisting of three superconducting qubits, researchers at UC Santa Barbara and Google have uncovered a link between aspects of classical and quantum physics thought to be unrelated: classical chaos and quantum entanglement. Their findings suggest that it would be possible to use controllable quantum systems to investigate certain fundamental aspects of nature.

"It's kind of surprising because chaos is this totally classical concept -- there's no idea of chaos in a quantum system," Charles Neill, a researcher in the UCSB Department of Physics and lead author of a paper that appears in Nature Physics. "Similarly, there's no concept of entanglement within classical systems. And yet it turns out that chaos and entanglement are really very strongly and clearly related."

Initiated in the 15th century, classical physics generally examines and describes systems larger than atoms and molecules. It consists of hundreds of years' worth of study including Newton's laws of motion, electrodynamics, relativity, thermodynamics as well as chaos theory -- the field that studies the behavior of highly sensitive and unpredictable systems. One classic example of chaos theory is the weather, in which a relatively small change in one part of the system is enough to foil predictions -- and vacation plans -- anywhere on the globe.

At smaller size and length scales in nature, however, such as those involving atoms and photons and their behaviors, classical physics falls short. In the early 20th century quantum physics emerged, with its seemingly counterintuitive and sometimes controversial science, including the notions of superposition (the theory that a particle can be located in several places at once) and entanglement (particles that are deeply linked behave as such despite physical distance from one another).

And so began the continuing search for connections between the two fields.

All systems are fundamentally quantum systems, according Neill, but the means of describing in a quantum sense the chaotic behavior of, say, air molecules in an evacuated room, remains limited.

Imagine taking a balloon full of air molecules, somehow tagging them so you could see them and then releasing them into a room with no air molecules, noted co-author and UCSB/Google researcher Pedram Roushan. One possible outcome is that the air molecules remain clumped together in a little cloud following the same trajectory around the room. And yet, he continued, as we can probably intuit, the molecules will more likely take off in a variety of velocities and directions, bouncing off walls and interacting with each other, resting after the room is sufficiently saturated with them.

"The underlying physics is chaos, essentially," he said. The molecules coming to rest -- at least on the macroscopic level -- is the result of thermalization, or of reaching equilibrium after they have achieved uniform saturation within the system. But in the infinitesimal world of quantum physics, there is still little to describe that behavior. The mathematics of quantum mechanics, Roushan said, do not allow for the chaos described by Newtonian laws of motion.

To investigate, the researchers devised an experiment using three quantum bits, the basic computational units of the quantum supercomputer. Unlike classical computer bits, which utilize a binary system of two possible states (e.g., zero/one), a qubit can also use a superposition of both states (zero and one) as a single state. Additionally, multiple qubits can entangle, or link so closely that their measurements will automatically correlate. By manipulating these qubits with electronic pulses, Neill caused them to interact, rotate and evolve in the quantum analog of a highly sensitive classical system.

The result is a map of entanglement entropy of a qubit that, over time, comes to strongly resemble that of classical dynamics -- the regions of entanglement in the quantum map resemble the regions of chaos on the classical map. The islands of low entanglement in the quantum map are located in the places of low chaos on the classical map.

"There's a very clear connection between entanglement and chaos in these two pictures," said Neill. "And, it turns out that thermalization is the thing that connects chaos and entanglement. It turns out that they are actually the driving forces behind thermalization.

"What we realize is that in almost any quantum system, including on quantum supercomputers, if you just let it evolve and you start to study what happens as a function of time, it's going to thermalize," added Neill, referring to the quantum-level equilibration. "And this really ties together the intuition between classical thermalization and chaos and how it occurs in quantum systems that entangle."

The study's findings have fundamental implications for quantum supercomputing. At the level of three qubits, the computation is relatively simple, said Roushan, but as researchers push to build increasingly sophisticated and powerful quantum supercomputers that incorporate more qubits to study highly complex problems that are beyond the ability of classical supercomputing -- such as those in the realms of machine learning, artificial intelligence, fluid dynamics or chemistry -- a quantum processor optimized for such calculations will be a very powerful tool.

"It means we can study things that are completely impossible to study right now, once we get to bigger systems," said Neill.

Freezing water is a central issue for climate, geology and life. On earth, ice and snow cover 10 percent of the land and up to half of the northern hemisphere in winter. Polar ice caps reflect up to 90 percent of the sun's incoming radiation. But how water droplets freeze, whether from within or from the surface, has been a topic of much controversy over past decade among chemists and physicists.

A team of researchers at Beijing Institute of Technology and Zhejiang University in China propose another question, "Where in the droplet does the crystallization of water or liquid silicon begin?" The team explains their findings this week in The Journal of Chemical Physics, from AIP Publishing. This is an interesting problem and one that is crucial to understanding the crystallization mechanism of nanoscale tetrahedral liquid drops like water and silicon. 

In their work, they used supercomputer simulation, to find that the ripple-like density waves are markedly excited before crystallization of liquid silicon drops and films due to the volume expansion in a confined environment. The ripple-like density fluctuations create waves capable of promoting nucleation, eventually resulting in a ripple-like distribution of nucleation probability in drops and films. These results suggest that the freezing of nanoscale water or silicon liquid drops is initiated at a number of different distances from the center of the droplet, providing new insights on a long-standing dispute in the field of material and chemical physics. 

The research team employed a molecular dynamics simulation to investigate the freezing of nanoscale silicon drops and films, a method widely used for the investigations of microscopic thermodynamic and dynamic process. In supercomputer simulations of crystallization events, the short simulation time makes it difficult to observe. To address this issue some special simulation methods, namely, the rare event sampling algorithms, were proposed. But these methods inevitably drop some high probability regions of nucleation in the trajectory sampling starting from a single configuration, so the team employed brute-force simulation and sampled massive and independent crystallization processes. "Although the method is 'brute,' it can faithfully represent the distribution of nuclei," explained Yongjun Lü, a physicist at Beijing Institute of Technology and Zhejiang University. "This is why we were able to observe the ripple-like distribution of nucleation probability while it is absent in other studies."

A challenge for the team was the great calculation costs. To achieve the credible probability distributions of nucleation in drops and films requires massive statistical sampling, requiring more than 6 months of CPU time.

The implications of this research are far-reaching. "We can extend the present results to all the tetrahedral liquids including water due to their similarity in molecular structure," Lü said. "It suggests that the surface environment does not play a decisive role in the formation of ice and snow as expected. The density fluctuations inside drops result in that the possible freezing regions cover the middle and the surface regions, depending on the drop size. The freezing from the surface or from within may be random."

The next steps for the research team are to simulate the crystallization of water in geometric constrained space and under high-pressure conditions to study the freezing mechanism of water in microcracks and micropores of rock. By deepening the understanding of the freezing of water drops will significantly enhance the understanding of its effects on the planet and its climate.

CAPTION Artist's rendering of a rare B-meson "penguin" (decay process) showing the quark-level process. CREDIT Daping Du, Syracuse University

A team of theoretical high-energy physicists in the Fermilab Lattice and MILC Collaborations has published a new high-precision calculation that could significantly advance the indirect search for physics beyond the Standard Model (SM). The calculation applies to a particularly rare decay of the B meson (a subatomic particle), which is sometimes also called a "penguin decay" process.

After being produced in a collision, subatomic particles spontaneously decay into other particles, following one of many possible decay paths. Out of one billion B mesons detected in a collider, only about twenty decay through this particular process.

With the discovery of the Higgs boson, the last missing piece, the SM of particle physics now accounts for all known subatomic particles and correctly describes their interactions. It's a highly successful theory, in that its predictions have been verified consistently by experimental measurements. But scientists know that the SM doesn't tell the whole story, and researchers around the globe are eagerly searching for evidence of physics beyond the SM.

"We have reason to believe that there are yet undiscovered subatomic particles that are not part of the SM," explains Fermilab scientist Ruth Van De Water. "Generally, we expect them to be heavier than any subatomic particles we have found so far. The new particles would be part of a new theory that would look like the SM at low energies. Additionally, the new theory should account for the astrophysical observations of dark matter and dark energy. The particle nature of dark matter is a complete mystery."

University of Illinois physicist Aida El-Khadra adds, "Scientists are attacking this problem from several directions. Indirect searches focus on virtual effects that the conjectured new heavy particles may have on low-energy processes. Direct searches look for the production of new heavy particles in high-energy collisions. The interplay of both indirect and direct searches may ultimately provide us with enough pieces of the puzzle to make out the new underlying theory that would explain all of these phenomena."

Syracuse University physicist John "Jack" Laiho describes why "penguin decays" provide powerful probes of new physics: "In the observation of a rare decay, because contributions from the SM are relatively small, there is a good possibility that contributions from new virtual heavy particles may be significant. These would be observed as deviations from SM predictions. However, in order to know that such a deviation (if observed) is not just a statistical fluctuation, the difference must be conclusive--it must be at least five times larger than the experimental and theoretical uncertainties. So rare decays require high precision in both the experimental measurements and the theoretical calculations."

B mesons belong to class of subatomic particles that are bound states of quarks and they feel the so-called strong interactions, also known by the colorful name Quantum Chromodynamics (QCD). Quarks are found inside protons and neutrons--which make up the atomic nucleus--as well as within other sub-atomic particles, such as pions and the aforementioned B mesons.

The new high-precision calculation employs lattice QCD to calculate the effects of the strong interaction on the process in question.

"Decay processes that involve bound states of quarks receive contributions from the strong interactions, which are very difficult to quantify, especially at low energies," explains Fermilab scientist Andreas Kronfeld. The only first-principles method for calculating with controlled errors the properties of subatomic particles containing quarks is lattice QCD, where the unwieldy integrals of QCD are cast into a form that makes it possible to calculate them numerically."

The project was started when Syracuse University researcher Daping Du was a postdoctoral fellow at Illinois with El-Khadra.

"Our calculation is clean," asserts Du. "We focused on a process for which lattice QCD methods yield small and completely quantified uncertainties."

"We have witnessed amazing progress in lattice QCD calculations in recent years," observes Enrico Lunghi, a non-lattice theorist at Indiana University, who joined the team for his expertise in rare decay phenomenology. "Lattice calculations have advanced to the point where they provide ab initio predictions of strong interaction effects with small and reliable uncertainties. This is how we are able to obtain a SM prediction of this process with better precision than previously possible."

The team's high precision lattice QCD calculation required large-scale computational resources.

"Fortunately, we were able to leverage supercomputing resources across the U.S. for this project," comments Indiana University physicist Steven Gottlieb. "In fact, this project is part of a larger effort by the Fermilab Lattice and MILC Collaborations to produce precise theoretical calculations of the strong interaction effects for a range of important processes relevant to precision frontier experiments. We used allocations at Fermilab (provided by the USQCD Collaboration), at the Argonne Leadership Computing Facility, the National Energy Research Scientific Computing Center, the Los Alamos National Laboratory, the National Institute for Computational Science, the Pittsburgh Supercomputer Center, the San Diego Supercomputer Center, and the Texas Advanced Computing Center. "

After completing the new calculation and prior to its publication in Physical Review Letters [115, 152002 (2015)] in the article entitled, " B?π?? Form Factors for New Physics Searches from Lattice QCD", the LHCb experiment at CERN in Switzerland announced a new experimental measurement of the differential decay rate for this decay process.

Fermilab scientist Ran Zhou concludes, "The recent measurements are compatible with our SM predictions, with commensurate uncertainties from theory and experiment. This puts interesting constraints on possible new physics contributions which are very useful for building models of beyond the SM physics."

The team also recently completed another paper, "Phenomenology of semileptonic B meson decays with form factors from lattice QCD", in which they make additional predictions for related rare decays that have not yet been experimentally observed. Once observed, these decay processes likewise may play an important role in the quest to find the new fundamental theory that lies beyond the SM.

Tags:
The image shows a quartz surface above the electrodes used to trap atoms. The color map on the surface shows the electric field amplitude.

A University of Oklahoma-led team of physicists believes chip-based atomic physics holds promise to make the second quantum revolution—the engineering of quantum matter with arbitrary precision—a reality.  With recent technological advances in fabrication and trapping, hybrid quantum systems are emerging as ideal platforms for a diverse range of studies in quantum control, quantum simulation and supercomputing.

James P. Shaffer, professor in the Homer L. Dodge Department of Physics and Astronomy, OU College of Arts and Sciences; Jon Sedlacek, OU graduate student; and a team from the University of Nevada, Western Washington University, The United States Naval Academy, Sandia National Laboratories and Harvard-Smithsonian Center for Astrophysics, have published research important for integrating Rydberg atoms into hybrid quantum systems and the fundamental study of atom-surface interactions, as well as applications for electrons bound to a 2D surface.

“A convenient surface for application in hybrid quantum systems is quartz because of its extensive use in the semiconductor and optics industries,” Sedlacek said. “The surface has been the subject of recent interest as a result of it stability and low surface energy.  Mitigating electric fields near ‘trapping’ surfaces is the holy grail for realizing hybrid quantum systems,” added Hossein Sadeghpour, director of the Institute for Theoretical Atomic Molecular and Optical Physics, Harvard-Smithsonian Center for Astrophysics.

In this work, Shaffer finds ionized electrons from Rydberg atoms excited near the quartz surface form a 2D layer of electrons above the surface, canceling the electric field produced by rubidium surface adsorbates.  The system is similar to electron trapping in a 2D gas on superfluid liquid helium.  The binding of electrons to the surface substantially reduces the electric field above the surface.

“Our results show that binding is due to the image potential of the electron inside the quartz,” said Shaffer.  “The electron can’t diffuse into the quartz because the rubidium adsorbates make the surface have a negative electron affinity.  The approach is a promising pathway for coupling Rydberg atoms to surfaces as well as for using surfaces close to atomic and ionic samples.”

A paper on this research was published in the American Physics Society’s Physical Review Letters.  The OU part of this work was supported by the Defense Advanced Research Projects Agency Quasar program by a grant through the Army Research Office, the Air Force Office of Scientific Research and the National Science Foundation. 

Tags: ,

Successful Sales Executive Joins the Industry Leader in FCoE to Accelerate Market Share Gains, Spearhead Revenue Growth: QLogic today announced the appointment of Jim Rothstein to vice president of North America Sales. With an established rack record of growing profitable storage companies, Rothstein, who multiplied sales at Brocade (Nasdaq:BRCD) and Hitachi, Ltd.'s Data Systems unit, will spearhead the company's sales in North America across all channels-including OEM Sales and the QLogic Partner Program-while advancing its go-to-market capabilities. He will report to Scott Genereux, senior vice president of Worldwide Sales and Marketing at QLogic.

"Jim Rothstein will synergistically unify our North America channel and OEM sales organizations under a single leader, thereby strengthening our competitive positioning and enabling our partners to win more business in high growth markets such as Fibre Channel over Ethernet," said Genereux. "Jim brings a history of proven sales management skills and consistent execution balanced with an aggressive, dynamic approach that will be a welcome addition to the QLogic management team."

Commenting on his appointment, Rothstein said, "QLogic has been taking extensive market share from competitors for the past year in the Fibre Channel adapter market. The emergence of FCoE in next-generation data centers presents a significant growth opportunity for companies with tangible products today. With QLogic now at the forefront of network convergence, I look forward to helping the company expand its share in this rapidly emerging market and leading the North America sales organization to its next stage of growth."

Rothstein's career spans a multitude of sales and sales management roles over a period of 18 years in the storage industry. Rothstein spent seven years at Brocade in strategic sales roles with increasing levels of responsibility, including vice president of Worldwide Tapestry Sales and vice president of North America Sales. At Brocade, Rothstein established a scalable sales growth model and was responsible for managing a $400 million enterprise sales organization. He is credited with significantly expanding the company's addressable market by implementing go-to-market models that increased the company's sales coverage in both established and emerging markets.

Page 1 of 17