Topological photonic chips can be controlled globally, across the lattice, and locally, at the level of individual sites. This Review discusses these programmable and reconfigurable technologies for topological, quantum and non-Hermitian physics.
Category: quantum physics
Tim Maudlin | Bell’s Theorem and Beyond: Nobody Understands Quantum Mechanics | The Cartesian Cafe
Tim Maudlin is a philosopher of science specializing in the foundations of physics, metaphysics, and logic. He is a professor at New York University, a member of the Foundational Questions Institute, and the founder and director of the John Bell Institute for the Foundations of Physics.
#quantum #physics #philosophy #determinism.
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In this very in-depth discussion, Tim and I probe the foundations of science through the avenues of locality and determinism as arising from the Einstein-Poldosky-Rosen (EPR) paradox and Bell’s Theorem. These issues are so intricate that even the Nobel Prize committee incorrectly described the significance of Bell’s work in their press release for the 2022 prize in physics. Viewers motivated enough to think deeply about these ideas will be rewarded with a conceptually proper understanding of the nonlocal nature of physics and its manifestation in quantum theory.
I. Introduction.
00:25 : Biography.
05:26 : Interdisciplinary work.
11:45 : Physicists working on the wrong things.
16:47 : Bell’s Theorem soft overview.
24:14: Common misunderstanding of \.
Alternating atomic layers enable rare electron pairing mechanism in new unconventional superconductor
Superconductors, materials that can conduct electricity with a resistance of zero, have proved to be highly promising for the development of quantum technologies, medical imaging devices, particle accelerators and other advanced technologies. These materials can be divided into two broad categories: conventional and unconventional superconductors.
In conventional superconductors, the formation of electron pairs (i.e., Cooper pairs) that underpin superconductivity occurs at low temperatures, prompted by interactions between electrons and lattice vibrations. Unconventional superconductors, on the other hand, typically enter the superconducting phase at higher temperatures.
In unconventional superconductors, the formation of cooper pairs is prompted by other physical phenomena beyond electron-phonon interactions, such as magnetic fluctuations, interactions between electrons or other unknown mechanisms. Electrons in most superconductors form so-called spin-singlet pairs, pairs of electrons with an opposite intrinsic angular momentum (i.e., spin), which have a total spin of zero.
Put a nanodiamond under intense pressure and it becomes flexible
Diamond is among the hardest naturally occurring substances on Earth, but if you shrink it down to the nanoscale, it is surprisingly elastic. And that could be useful for a host of applications such as quantum computing. In a paper published in the journal Physical Review X, Chongxin Shan at Zhengzhou University in China and colleagues studied diamonds as small as four nanometers across to see how they respond to pressure.
Scientists already know that nanodiamonds, which are thousands of times smaller than a grain of sand, can survive being stretched or squeezed in ways that destroy a regular diamond. But nobody knew how.
So the team placed individual nanodiamonds (ranging from 4 to 13 nanometers across) inside a transmission electron microscope between two diamond indenters and compressed them. These were connected to a sensor that measured how strongly each nanodiamond resisted being squeezed while a high-resolution camera imaged diamond atoms as they moved. The researchers backed up their observations with computer simulations.
Pressure-tuned quantum spin liquid-like behavior observed in material Y-kapellasite
A quantum spin liquid is a phase of matter in which the magnetic moments in a material do not align or freeze, even at temperatures close to absolute zero (i.e., at 0 K). The experimental realization of this highly dynamic state could have important implications for the development of quantum computers and other technologies that operate leveraging quantum mechanical effects.
Previous studies have collected evidence that a quantum spin liquid phase emerges in various materials, including herbertsmithite, α-RuCl3, and EtMe3Sb[Pd(dmit)2]2. However, so far none of these materials have been conclusively confirmed to host this state.
Researchers at University Paris-Saclay-CNRS, University of Stuttgart and other institutes in Europe gathered evidence of quantum spin liquid-like behavior in a recently discovered material called Y-kapellasite. Their paper, published in Physical Review Letters, shows that this material is a promising experimental platform for studying exotic states of matter, particularly those driven by quantum magnetism.
Spacetime does not exist
Einstein’s picture of spacetime, a four-dimensional fabric uniting space and time, breaks down at the smallest scales, where quantum mechanics takes over. For decades, physicists have searched for an account of how spacetime “emerges” from this deeper quantum reality. But philosopher Sam Baron argues that the whole idea of spacetime “emerging” from something else makes no sense. All our accounts of how things “emerge” from something more fundamental presuppose spacetime, so the idea that spacetime itself emerges is circular. His radical conclusion is that we must abandon the project of reconciling spacetime and quantum mechanics, and accept that spacetime, at least as Einstein described it, does not exist.
Universal Quantum Computing as a Markov Chain
Let’s say you have a probabilistic computer with a single bit of memory. Some algorithms on the computer will stochastically flip the single bit of memory such that its new value will be uniformly distributed with a 50% chance of being 0 and a 50% chance of being 1. Other programs will place it into a degenerate distribution, meaning it either has 100% chance of being 0 every time you run the program, or other programs will produce 1 100% of the time.
A magician tells you to run one of the programs in one of the two categories of your choosing and then copy the computer’s memory state onto a thumb drive and hand it to him. You pick one, run the program, copy the bit of the memory to your thumb drive, then hand it to the magician. The magician then does something with the thumb drive you cannot see, then looks up at you and tell you exactly what category the program you ran to produce that bit came from.
Curious, you repeat this many times over: you run a program from one of the two categories (degenerate or uniform), copy the bit value produced from the algorithm, and then hand the thumb drive to the magician. Each and every time he always correctly guesses which category of program was ran to produce it.
How Elasticity Shapes Nematic Criticality
A 19th-century theory of elasticity inspires a new way to analyze a quantum phase transition that has become central to modern quantum materials research.
When a crystalline metal enters a so-called nematic state, the onset of strong fluctuations among interacting electrons spontaneously breaks the crystal’s rotational symmetry and distorts both the physical lattice and the notional Fermi surface. This transition, known as nematic criticality, has been observed near the onset of superconductivity in cuprates, pnictides, and twisted bilayer graphene and could hold the key to explaining these poorly understood forms of superconductivity. Now Joe Meese and Rafael Fernandes of the University of Illinois-Champaign have proposed that nematic criticality is more selective in how it breaks rotational symmetry than previously assumed [1, 2]. The selectivity arises not from a novel microscopic mechanism but from a geometric constraint.
Nematic order typically develops spontaneously upon cooling; hydrostatic pressure can shift the transition, while uniaxial stress can tune the transition or induce nematicity by linearly coupling to lattice strain. Because of this connection, nematic order obeys the same mechanical laws as other continuous lattice deformations do. Consequently, as Meese and Fernandes showed, nematic order splits into two classes. One class is compatible with the lattice and can turn critical; the other is incompatible with the lattice and is therefore suppressed (Fig. 1). In the conventional picture, the energy cost of completing a nematic transition is “softened”—that is, reduced by the emergence of fluctuations as the transition is approached. That condition remains true in Meese and Fernandes’ picture, but the softening is not spread over all the possible distortions allowed by symmetry. Rather, elasticity itself selects the modes that participate in nematic criticality.
Bringing quantum time into the lab—a single clock can run young and old at once
Few concepts in physics are as familiar, yet as enigmatic, as time. In Einstein’s theory of relativity, time is not absolute: its passage depends on motion and gravity. But when combined with quantum physics, this relativistic form of time becomes even more counterintuitive.
According to quantum theory, the flow of time itself may exist in a genuine quantum superposition, ticking faster and slower at the same time. Now, a new paper titled “Quantum signatures of proper time in optical ion clocks”, published in Physical Review Letters, shows that this striking possibility may soon be tested in the laboratory.
In this work, a team led by Assistant Professor of theoretical physics Igor Pikovski at Stevens Institute of Technology, in collaboration with experimental groups of Christian Sanner at Colorado State University and Dietrich Leibfried at the National Institute of Standards and Technology (NIST), explores quantum aspects of the flow of time and how they can be accessed with atomic clocks.
A long-sought quantum computing milestone arrives as fermionic atom gates top 99% accuracy
Two independent research teams have each demonstrated collisional quantum gates using fermionic atoms: a long-sought milestone in quantum computing where logic operations are performed through the direct physical overlap of atoms, rather than forcing them into fragile, highly excited states.
The studies have been published simultaneously in Nature: the first led by Petar Bojović at the Max Planck Institute for Quantum Optics in Garching, Germany, and the second by Yann Kiefer and colleagues at ETH Zurich, Switzerland.