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Noise in an electronic circuit is a nuisance that can scramble information or reduce a detector’s sensitivity. But noise also offers a way to learn about the microscopic quantum mechanisms at play in a material or device. By measuring a circuit’s “shot noise,” a form of white noise, researchers have previously shed light on conduction in quantum Hall and spintronic systems, for instance. Now, a collaboration led by Oren Tal at the Weizmann Institute of Science, Israel, and by Dvira Segal at the University of Toronto, Canada, has shown that an easier-to-measure form of noise, called “flicker noise,” can also be a powerful probe of quantum effects [1].

Continue reading “Pink Noise as a Probe of Quantum Transport” »

Researchers have cooled indium atoms to a temperature close to 1 mK, making indium the first group-III atom to be made ultracold.

At temperatures near to absolute zero, atoms move slower than a three-toed sloth, allowing physicists to gain unprecedented experimental control over these systems. New phases of matter can form when atoms become ultracold and quirky quantum properties can emerge, yet much of the periodic table remains unexplored in the ultracold regime. Now, Travis Nicholson of the National University of Singapore and colleagues have successfully cooled indium to close to 1 mK [1]. Indium is the first “main group-III” atom—a specific group of transition metals on the periodic table—to be cooled to such a low temperature. The demonstration opens the door to studying systems with properties previously unexplored by ultracold physicists.

For their experiments, Nicholson and colleagues used a magneto-optical trap—a standard tool for trapping and cooling atoms. But because this was the first attempt at making indium atoms ultracold, the team had to make their own version of the apparatus rather than using one designed to cool other atoms. “The systems used for this research are highly customized to specific atoms,” Nicholson says. So every part of the setup from designing the laser systems to picking the screws had to be “hashed out by us.” With their custom setup, the group loaded 500,000,000 indium atoms into the trap using a laser beam and then cooled them.

Imagining our everyday life without lasers is difficult. We use lasers in printers, CD players, pointers, measuring devices, etc. What makes lasers so special is that they use coherent waves of light: all the light inside a laser vibrates completely in sync.

Meanwhile, quantum mechanics tells us that particles like atoms should also be considered waves. As a result, we can build ‘atom lasers’ containing coherent waves of matter. But can we make these matter waves last so they may be used in applications? In research that was published in Nature, a team of Amsterdam physicists shows that the answer to this question is affirmative.

Circa 2021 Evidence of string theory by black holes as fuzzballs.

Abstract: We examine an interesting set of recent proposals describing a ‘wormhole paradigm’ for black holes. These proposals require that in some effective variables, semiclassical low-energy dynamics emerges at the horizon. We prove the ‘effective small corrections theorem’ to show that such an effective horizon behavior is not compatible with the requirement that the black hole radiate like a piece of coal as seen from outside. This theorem thus concretizes the fact that the proposals within the wormhole paradigm require some nonlocality linking the hole and its distant radiation. We try to illustrate various proposals for nonlocality by making simple bit models to encode the nonlocal effects. In each case, we find either nonunitarity of evolution in the black hole interior or a nonlocal Hamiltonian interaction between the hole and infinity; such an interaction is not present for burning coal. We examine recent arguments about the Page curve and observe that the quantity that is argued to follow the Page curve of a normal body is not the entanglement entropy but a different quantity. It has been suggested that this replacement of the quantity to be computed arises from the possibility of topology change in gravity which can generate replica wormholes. We examine the role of topology change in quantum gravity but do not find any source of connections between different replica copies in the path integral for the Rényi entropy. We also contrast the wormhole paradigm with the fuzzball paradigm, where the fuzzball does radiate like a piece of coal. Just as in the case of a piece of coal, the fuzzball does not have low-energy semiclassical dynamics at its surface at energies $E\sim T$ (effective dynamics at energies $E\gg T$ is possible under the conjecture of fuzzball complementarity, but these $E\gg T$ modes have no relevance to the Page curve or the information paradox).

From: Marcel Hughes [view email]

Canadian quantum computer company, Xanadu, has used its photonic quantum computer chip, Borealis, to solve a problem in 36 microseconds versus classical supercomputers taking 9,000 years. This is 7,884 trillion times faster. This runtime advantage is more than 50 million times larger than that of earlier photonic demonstrations.

An earlier quantum photonic computer used a static chip. The Borealis optical elements can all be readily programmed.

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University of Queensland scientists have cracked a problem that’s frustrated chemists and physicists for years, potentially leading to a new age of powerful, efficient, and environmentally friendly technologies.

Using quantum mechanics, Professor Ben Powell from UQ’s School of Mathematics and Physics has discovered a “recipe” which allows molecular switches to work at room temperature.

“Switches are materials that can shift between two or more states, such as on and off or 0 and 1, and are the basis of all digital technologies,” Professor Powell said. “This discovery paves the way for smaller and more powerful and energy efficient technologies. You can expect batteries will last longer and computers to run faster.”

Researchers from the Institute of Laser Physics at Universität Hamburg have succeeded for the first time in realizing a time crystal that spontaneously breaks continuous time translation symmetry. They report their observation in a study published online by the journal Science on Thursday, 9 June, 2022.

The idea of a time crystal goes back to Nobel laureate Franck Wilczek, who first proposed the phenomenon. Similar to water spontaneously turning into ice around the freezing point, thereby breaking the translation symmetry of the system, the time translation symmetry in a dynamical many-body system spontaneously breaks when a time crystal is formed.

In recent years, researchers have already observed discrete or Floquet time crystals in periodically driven closed and open quantum systems. “In all previous experiments, however, the continuous-time translation symmetry is broken by a time-periodic drive,” says Dr. Hans Keßler from Prof. Andreas Hemmerich’s group at the Cluster of Excellence CUI: Advanced Imaging of Matter. “The challenge for us was to realize a system that spontaneously breaks the continuous time translation symmetry.”

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Not only do quantum computers have the edge over classical computers on some tasks, but they are also exponentially faster, according to a new mathematical proof.

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A collection of 16 qubits has been organized in such a way that they may be able to operate any computation without error. It is an important step toward constructing quantum computers that outperform standard ones.

When completing any task, a quantum computer consisting of charged atoms can detect its own faults. Because conventional computers constantly detect and rectify their own flaws, quantum computers will need to do the same in order to fully outperform them. Nevertheless, quantum effects can cause errors to propagate rapidly through the qubits, or quantum bits, that comprise these devices.

Continue reading “How Can a Quantum Computer Catch its Own Errors in Calculations?” »