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Can String Theory Be Explained with No Strings Attached?

Using a “bootstrap” approach, researchers show that a small set of assumptions may naturally lead to a string-theory description of certain high-energy processes.

String theory has been a remarkably influential conceptual framework for modern theoretical physics. While its description of nature in terms of tiny strings captures the imagination, the string framework has had profound impact in a broad range of subfields, going well beyond its lead role as a viable theory of quantum gravity. For instance, it has led to deeper understanding of black holes and their relation to entanglement and quantum information [1], and it has provided theoretical benchmarks for explaining quark–gluon plasma observations in quantum chromodynamics [2]. As a complement to direct calculations, theoretical physicists would like to understand string theory as emerging from a set of fundamental principles that any theory of nature must respect. Consistency with these bedrock conditions, so goes the idea, could perhaps make string theory inevitable.

Broken time-reversal symmetry phase in kagome metals may establish conditions for superconductivity

Physicists have long suspected that a peculiar quantum state lurks inside a class of materials known as kagome metals, but proving its existence has been elusive. Now, a team led by Yeongkwan Kim at the Korea Advanced Institute of Science and Technology has performed experiments on a kagome metal that provide the strongest evidence yet for this exotic state.

Published in Nature Physics, the team’s results could shed new light on how these materials transition into superconductivity.

Investigating quantum and molecular plumbing in nanofluidics research

Our body contains an intricate system of tiny vessels through which blood, water and other molecules flow. When the size of the pipes shrinks to the nanoscale, where only a few molecules can fit side by side, the classical laws of physics governing the behavior of water are influenced by the atomic structure of the walls. “It’s not that classical hydrodynamics breaks down, but rather that it gets mixed with the condensed matter physics of the solid walls,” says Nikita Kavokine, tenure-track assistant professor and leader of the EPFL Quantum Plumbing Lab.

How liquids, and water in particular, behave at scales of a few nanometers is one of the big gaps in modern physics. For example, in some experiments, it has been observed that water flows through carbon nanotubes orders of magnitude faster than expected. Scientists are trying to understand phenomena that biology has mastered after millions of years of evolution.

“At the nanometer scale, our body leverages specific properties of water to filter molecules with high energy efficiency,” explains Kavokine. Aquaporins, for example, are protein channels embedded in cell membranes that use these molecular-scale interactions to let water pass while blocking ions and other molecules.

Quantum gravity research links continuous parameters to local operators within the theory itself

A researcher at Kyushu University and his collaborators have shown that continuous parameters in quantum gravity may not be freely adjustable “dials” from outside the theory, but rather arise from operators within the theory itself, supporting the century-old claim by Albert Einstein about the fundamental laws of nature.

Einstein argued that the fundamental equations of physics contain no freely adjustable parameters. In other words, he believed that the laws of nature should not include arbitrary numbers chosen from outside a theory. Instead, such quantities should emerge naturally from physical processes.

This idea has become especially important in the search for quantum gravity, a theory that aims to combine gravity with quantum mechanics. Physicists expect that the equations governing quantum gravity should not contain freely adjustable quantities. Rather, all parameters should arise from physical fields.

Quantum mechanics theory may work without imaginary numbers, new analysis suggests

Physicists from Heinrich Heine University Düsseldorf (HHU) have examined a fundamental property of quantum mechanics in collaboration with the German Aerospace Center (DLR). In an article published in the journal Physical Review Letters, they show that this theory does not necessarily need to be formulated with imaginary numbers—real numbers can, in fact, also be used.

The physical theory of quantum mechanics describes the world of atomic and subatomic particles. Its development began in the 1900s with physicists such as Max Planck, Niels Bohr, Werner Heisenberg and Erwin Schrödinger.

Quantum mechanics can effectively describe phenomena at microscopic scales, including, for example, the diffraction of particles at a double slit —which shows that particles also exhibit wave-like behavior—and the quantum tunneling effect, in which a certain probability exists that particles can penetrate a barrier even if they have insufficient energy to do so. Particularly important phenomena today include entanglement and coherence, which are key for applications such as quantum computers and communication.

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How to create distinguishable states for quantum systems

Researchers around the world are racing to develop new quantum-based systems for sensing, communication, computing, and control that have the promise of outperforming traditional systems. Creating stable, measurable, distinguishable quantum states, which would be the heart of any such system, is a daunting task.

Quantum states possess unique properties that can be exploited for developing novel information processing systems. Two key properties, stability and distinguishability, are hard to achieve, however. Extracting information from a quantum system depends on the distinguishability of quantum states, an intrinsic property associated with a property known as orthogonality. Nevertheless, no two Gaussian states (a widely studied class of quantum states) are orthogonal, and this yields an unavoidable error when attempting to distinguish them.

In addition, present quantum devices tend to remain stable only for a fraction of a second, and require complex protocols to distinguish states. Now, researchers at MIT and the University of Ferrara have found a new approach for creating easily distinguishable states that could help to enable the development of these new quantum-based devices.

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