Learn how Quantum Bayesianism challenges traditional quantum mechanics by focusing on the role of the observer in creating quantum reality.
Adam Shaw (Caltech)https://simons.berkeley.edu/talks/adam-shaw-caltech-2024-04-23Near-Term Quantum Computers: Fault Tolerance + Benchmarking + Quantum Advant…
The elegant equations of classical electromagnetism written by James Clark Maxwell in 1861 display a remarkable symmetry between electric and magnetic fields except for their sources. We know about electric charges but we have not found magnetic charges. Bar magnets are dipoles with two poles, north and south, for the magnetic field, resembling the configuration of an electric field sourced by a pair of positive and negative electric charges. However, we had never seen experimental evidence for a magnetic monopole, namely a magnetic charge with only one magnetic pole, a net north or south, from where magnetic field lines emanate, just like the electric field sourced by an electric charge. In a symmetric theory of electromagnetism, magnetic monopoles should exist.
The existence of monopoles with a net magnetic charge was proposed by Paul Dirac in 1931 to explain the quantized (discrete) values of electric charges. Dirac found that magnetic charges should be an integer multiple of a fundamental unit, g_D, equal to the electron charge, e, divided by twice the fine-structure constant, or about 68.5e.
In classical physics, the existence of magnetic monopoles restores symmetry to Maxwell’s equations. But in the broader context of quantum mechanics, Gerard ‘t Hooft and Alexander Polyakov showed in 1974 that magnetic monopoles are required in Grand Unified Theories of the strong, weak and electromagnetic interactions. Since the electric charge is quantized, magnetic charges are unavoidable in these theories. Magnetic charges with the lowest mass must be stable because magnetic charge is conserved and they cannot decay into lower-mass particles.
Recently I saw a post on twitter claiming that AI could be powered with quantum vacuum energy. The post was accompanied by a figure from a paper published in Nature. Unfortunately for the poster, but fortunately for science, the paper had nothing to do with extracting energy from the vacuum. Rather, it was a description of an experimental realization of a transistor that uses the Casimir effect to mediate and amplify energy transfer across a new kind of transistor.
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For this technique to work at very high fidelity, a very fast and very sensitive bolometer is needed to measure the quantum state before it decays. In 2020, the Finnish researchers unveiled a bolometer that used graphene as its absorber – a fast and sensitive design that was intended for use in quantum computing. Unfortunately, this bolometer degraded over time and the team instead used an older bolometer design involving interfaces between superconductors and normal metals.
Möttönen says that the researchers had initially not expected the older design to be effective for reading out the states of individual qubits. He also expects that the read-out fidelity could be boosted using improved graphene bolometers. “I’m hoping to get the new graphene bolometers out of the oven soon,” he says.
David Pahl at the Massachusetts Institute of Technology believes that the work is very preliminary, but potentially very important. He says that the two most important performance metrics for a scheme to read out quantum states are the fidelity and the speed: “The state of the art speed that we’ve seen in the past year is 0.1 μs and 99.5% fidelity…[Möttönen and colleagues] showed 14 μs and 61.7%,” he says.
Scientists have designed a physical qubit that behaves as an error-correcting “logical qubit,” and now they think they can scale it up to make a useful quantum computer using a few hundred.
The potential of quantum technology is huge but is today largely limited to the extremely cold environments of laboratories. Now, researchers at Stockholm University, at the Nordic Institute for Theoretical Physics and at the Ca’ Foscari University of Venice have succeeded in demonstrating for the very first time how laser light can induce quantum behavior at room temperature — and make non-magnetic materials magnetic. The breakthrough is expected to pave the way for faster and more energy-efficient computers, information transfer and data storage.
Within a few decades, the advancement of quantum technology is expected to revolutionize several of society’s most important areas and pave the way for completely new technological possibilities in communication and energy.
Of particular interest for researchers in the field are the peculiar and bizarre properties of quantum particles — which deviate completely from the laws of classical physics and can make materials magnetic or superconducting.
Researchers at EPFL have created the first detailed model explaining the quantum-mechanical effects that cause photoluminescence in thin gold films, a breakthrough that could advance the development of solar fuels and batteries.
Luminescence, the process where substances emit photons when exposed to light, has long been observed in semiconductor materials like silicon. This phenomenon involves electrons at the nanoscale absorbing light and subsequently re-emitting it. Such behavior provides researchers with valuable insights into the properties of semiconductors, making them useful tools for probing electronic processes, such as those in solar cells.
In 1969, scientists discovered that all metals luminesce to some degree, but the intervening years failed to yield a clear understanding of how this occurs. Renewed interest in this light emission, driven by nanoscale temperature mapping and photochemistry applications, has reignited the debate surrounding its origins. But the answer was still unclear – until now.
