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Category: quantum physics – Page 138

How do we assess quantum advantage when exact classical solutions are not available?

A quantum advantage is a demonstration of a solution for a problem for which a quantum computer can provide a demonstrable improvement over any classical method and classical resources in terms of accuracy, runtime…

Today, algorithms designed to solve this problem mostly rely on what we call variational methods, which are algorithms guaranteed to output an energy for a target system which cannot be lower than the exact solution — or the deepest valley — up to statistical uncertainties. An ideal quality metric for the ground state problem would not only allow the user to benchmark different methods against the same problem, but also different target problems when tackled by the same method.

So, how can such an absolute metric be defined? And what would be the consequences of finding this absolute accuracy metric?

We construct our accuracy metric from an estimation of the energy and its variance for any specific algorithm used to solve the ground state problem, with additional parameters of the system such as the size and the nature of its interactions. We call this metric “variational-score,” or and show that it is an absolute metric for this benchmark.

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A research team led by National Tsing Hua University Department of Physics and Center for Quantum Science and Technology professor Chuu Chih-sung (褚志崧) has developed Taiwan’s first and the world’s smallest quantum computer, using a single photon, the university said yesterday.

Chuu said in the…

Bringing taiwan to the world and the world to taiwan.

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From subatomic particles to complex molecules, quantum systems hold the key to understanding how the universe works. But there’s a catch: when you try to model these systems, that complexity quickly spirals out of control—just imagine trying to predict the behavior of a massive crowd of people where everyone is constantly influencing everyone else. Turn those people into quantum particles, and you are now facing a “quantum many-body problem.”

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Twesh Upadhyaya, William F. Braasch, Jr., Gabriel T. Landi, and Nicole Yunger Halpern PRX Quantum 5, 030355 – Published 23 September 2024 https://journals.aps.org/prxquantum/abstract/10.1103/PRXQuantum.5.

As an ice cube melts in water, the heat exchange d by the two produces disorder. Imagine measuring the heat flow while the ice melts in each of many trials. From the measurement results, one can compute the disorder generated in each trial—the stochastic entropy production (SEP). The SEP is well understood in the case of two classical systems interacting; there is one widely accepted SEP definition that can be expressed equivalently via three formulas. But the situation is far murkier for quantum analogues, such as two atoms exchanging components of spin.

Generalizing the three SEP formulas to accommodate quantum systems, we prove that quantum effects render the three SEP formulas inequivalent. Each formula reasonably quantifies entropy production and highlights a different aspect of the underlying physics. The inequivalence of the formulas stems from the inability to simultaneously measure the exchange d quantities of the quantum systems, i.e., the uncertainty principle. This quantumness leads to negative and even nonreal entropy production. Though unusual, these entropy values herald notable physical phenomena. A negative entropy production signals superposition in the thermal initial states of the quantum systems. An imaginary entropy production witnesses contextuality, a precise notion of nonclassicality.

Our work reveals new facets of entropy production for quantum systems, with potential implications for the performance of future technologies. For example, negative entropy production could be harnessed to improve the efficiency of a quantum engine.

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Next Generation Biomanufacturing Technologies — Dr. Leonard Tender, Ph.D. — Biological Technologies Office, Defense Advanced Research Projects Agency — DARPA

Dr. Leonard Tender, Ph.D. is a Program Manager in the Biological Technologies Office at DARPA (https://www.darpa.mil/staff/dr-leonar…) where his research interests include developing new methods for user-defined control of biological processes, and climate and supply chain resilience.

Prior to coming to DARPA, Dr. Tender was a principal investigator and led the Laboratory for Molecular Interfaces in the Center for Bio/Molecular Science and Engineering at the U.S. Naval Research Laboratory. There, among other accomplishments, he facilitated numerous international collaborations with key external stakeholders in academia, industry, and government and his highly interdisciplinary research team, comprised of electrochemists, microbiologists, and engineers, is widely recognized for its many contributions to the field of microbial electrochemistry.

Dr. Tender earned a doctorate degree in analytical chemistry from the University of North Carolina, Chapel Hill; a bachelor’s degree in chemistry from the Massachusetts Institute of Technology; completed a post-doctoral fellowship in the Department of Chemistry from the University of California, Berkeley; and served as a visiting scientist in the Stanford University Department of Chemistry.

Dr. Tender co-founded the International Society for Microbial Electrochemistry and Technology and is a recipient of the Arthur S. Flemming Award, which honors outstanding federal employees, by the George Washington University’s Trachtenberg School of Public Policy and Public Administration.

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