Artificially intelligent Maxwell’s demon for optimal control of open…
A team of researchers used reinforcement learning (RL) to optimize feedback control strategies in quantum systems.
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Physicists are obsessed with black holes, but we still don’t know what’s going on inside of them. One idea is that black holes do not truly exist, but instead they are big quantum objects that have been called fuzzballs or frozen stars. This idea has a big problem. Let’s take a look.
Continue reading “These physicists say they know what’s inside a black hole” »
All physical observations are made relative to a reference frame, which is a system in its own right. If the system of interest admits a group symmetry, the reference frame observing it must transform commensurately under the group to ensure the covariance of the combined system. We point out that the crossed product is a way to realize quantum reference frames from the bottom-up; adjoining a quantum reference frame and imposing constraints generates a crossed product algebra. We provide a top-down specification of crossed product algebras and show that one cannot obtain inequivalent quantum reference frames using this approach. As a remedy, we define an abstract algebra associated to the system and symmetry group built out of relational crossed product algebras associated with different choices of quantum reference frames.
Recently Danielson, Satishchandran, and Wald (DSW) have shown that quantum superpositions held outside of Killing horizons will decohere at a steady rate. This occurs because of the inevitable radiation of soft photons (gravitons), which imprint a electromagnetic (gravitational) “which-path’’ memory onto the horizon. Rather than appealing to this global description, an experimenter ought to also have a local description for the cause of decoherence. One might intuitively guess that this is just the bombardment of Hawking/Unruh radiation on the system, however simple calculations challenge this idea—the same superposition held in a finite temperature inertial laboratory does not decohere at the DSW rate. In this work we provide a local description of the decoherence by mapping the DSW setup onto a worldline-localized model resembling an Unruh-DeWitt particle detector.
Quantum mechanics: it’s the realm of science where nothing is normal, and everything seems to undermine the fundaments of our common understanding of reality. Nonetheless, we simple humans tick on.
But quantum physicists, who pride themselves on staring into the abyss and gleaning its spooky secrets, have just discovered another baffling phenomenon to make your mind melt: “negative time.”
As detailed in a yet-to-be-peer-reviewed study covered by Scientific American, a team of researchers say they’ve observed photons exhibiting this bizarre temporal behavior as the result of what’s known as atomic excitation.
Physicists from the University of Basel have succeeded in coupling two Andreev qubits coherently over a macroscopic distance for the first time. They achieved this with the help of microwave photons generated in a narrow superconducting resonator. The results of the experiments and accompanying calculations were recently published in Nature Physics, laying the foundation for the use of coupled Andreev qubits in quantum communication and quantum computing.
The next generation of handheld devices requires a novel solution. Spintronics, or spin electronics, is a revolutionary new field in condensed-matter physics that can increase the memory and logic processing capability of nano-electronic devices while reducing power consumption and production costs. This is accomplished by using inexpensive materials and the magnetic properties of an electron’s spin to perform memory and logic functions instead of using the flow of electron charge used in typical electronics.
New work by Florida State University scientists is propelling spintronics research forward.
Professors Biwu Ma in the Department of Chemistry and Biochemistry and Peng Xiong in the Department of Physics work with low-dimensional organic metal halide hybrids, a new class of hybrid materials that can power optoelectronic devices like solar cells, light-emitting diodes, or LEDs and photodetectors.
Now, researchers at the U.S. Department of Energy’s (DOE) Argonne National Laboratory and the University of Chicago Pritzker School of Molecular Engineering (PME) have proposed a new type of memory, in which optical data is transferred from a rare earth element embedded within a solid material to a nearby quantum defect. Their analysis of how such a technology could work is published in Physical Review Research.
“We worked out the basic physics behind how the transfer of energy between defects could underlie an incredibly efficient optical storage method,” said Giulia Galli, an Argonne senior scientist and Liew Family Professor at PME. “This research illustrates the importance of exploring first-principles and quantum mechanical theories to illuminate new, emerging technologies.”
Most optical memory storage methods developed in the past, including CDs and DVDs, are limited by the diffraction limit of light. A single data point cannot be smaller than the wavelength of the laser writing and reading the data. In the new work, the researchers proposed boosting the bit density of optical storage by embedding many rare-earth emitters within the material. By using slightly different wavelengths of light—an approach known as wavelength multiplexing—they hypothesized that these emitters could hold more data within the same area.
Physicists showed that photons can seem to exit a material before entering it, revealing observational evidence of negative time.
By Manon Bischoff & Jeanna Bryner
Quantum physicists are familiar with wonky, seemingly nonsensical phenomena: atoms and molecules sometimes act as particles, sometimes as waves; particles can be connected to one another by a “spooky action at a distance,” even over great distances; and quantum objects can detach themselves from their properties like the Cheshire Cat from Alice’s Adventures in Wonderland detaches itself from its grin. Now researchers led by Daniela Angulo of the University of Toronto have revealed another oddball quantum outcome: photons, wave-particles of light, can spend a negative amount of time zipping through a cloud of chilled atoms. In other words, photons can seem to exit a material before entering it.
Adding extra dimensions to a theory known as “fuzzy gravity” may help bridge the gap between quantum mechanics and relativity.
A recent study has made strides toward solving one of physics’ biggest puzzles: including all known particles and interactions into the theory of quantum gravity.
The solution is to modify the quantum description of gravity dubbed “fuzzy gravity” by introducing extra dimensions to spacetime. In this theory, spacetime is treated not as a continuous entity but by a grid of discrete points, and adding extra dimensions to this grid results in the occurrence of other fields and particles.
