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A new optical device measures photon indistinguishability—an important property for future light-based quantum computers.

Photons can be used to perform complex computations, but they must be identical or close to identical. A new device can determine the extent to which several photons emitted by a source are indistinguishable [1]. Previous methods only gave a rough estimate of the indistinguishability, but the new method offers a precise measurement. The device—which is essentially an arrangement of interconnected waveguides—could work as a diagnostic tool in a quantum optics laboratory.

In optical quantum computing, sequences of photons are made to interact with each other in complex optical circuits (see Synopsis: Quantum Computers Approach Milestone for Boson Sampling). For these computations to work, the photons must have the same frequency, the same polarization, and the same time of arrival in the device. Researchers can easily check if two photons are indistinguishable by sending them through a type of interferometer in which two waveguides—one for each photon—come close enough that one photon can hop into the neighboring waveguide. If the two photons are perfectly indistinguishable, then they always end up together in the same waveguide.

Laser experiments can track how the excitations of quantum states of a “buckyball” relax after the molecule collides with other particles.

A research team led by a physicist at the University of California, Riverside, has demonstrated a new magnetized state in a monolayer of tungsten ditelluride, or WTe₂, a new quantum material. Called a magnetized or ferromagnetic quantum spin Hall insulator, this material of one-atom thickness has an insulating interior but a conducting edge, which has important implications for controlling electron flow in nanodevices.

In a typical conductor, electrical current flows evenly everywhere. Insulators, on the other hand, do not readily conduct electricity. Ordinarily, monolayer WTe₂ is a special insulator with a conducting edge; magnetizing it bestows upon it more unusual properties.

“We stacked monolayer WTe₂ with an insulating ferromagnet of several atomic layer thickness—of Cr₂Ge₂Te₆, or simply CGT—and found that the WTe₂ had developed ferromagnetism with a conducting edge,” said Jing Shi, a distinguished professor of physics and astronomy at UCR, who led the study. “The edge flow of the electrons is unidirectional and can be made to switch directions with the use of an external magnetic field.”

Two-dimensional van der Waals materials have been the focus of work by numerous research groups for some time. Standing just a few atomic layers thick, these structures are produced in the laboratory by combining atom-thick layers of different materials (in a process referred to as “atomic Lego”). Interactions between the stacked layers allow the heterostructures to exhibit properties that the individual constituents lack.

Two-layered molybdenum disulfide is one such van der Waals material, in which electrons can be excited using a suitable experimental setup. These negatively charged particles then leave their position in the valence band, leaving behind a positively charged hole, and enter the conduction band. Given the different charges of electrons and holes, the two are attracted to one another and form what is known as a quasiparticle. The latter is also referred to as an electron-hole pair, or exciton, and can move freely within the material.

In two-layered molybdenum disulfide, excitation with light produces two different types of electron-hole pairs: intralayer pairs, in which the electron and hole are localized in the same layer of the material, and interlayer pairs, whose hole and electron are located in different layers and are therefore spatially separate from one another.

Researchers from Linköping University and the Royal Institute of Technology in Sweden have proposed a new device concept that can efficiently transfer the information carried by electron spin to light at room temperature—a stepping stone toward future information technology. They present their approach in an article in Nature Communications.

Light and electron charge are the main media for information processing and transfer. In the search for information technology that is even faster, smaller and more energy-efficient, scientists around the globe are exploring another property of electrons —their spin. Electronics that exploit both the spin and the charge of the electron are called “spintronics.”

Like the Earth, an electron spins around its own axis, either clockwise or counterclockwise. The handedness of the rotation is referred to as spin-up and spin-down states. In spintronics, the two states represent the binary bits and thus carry information. The information encoded by these spin states can be converted by a light-emitting device into light, which then carries the information over a long distance through fiber optics. The transfer of quantum information opens the possibility to exploit both electron spin and light, and the interaction between them, a technology known as “opto-spintronics.”

so-called qubits, to perform computations much faster than any classical computer ever could.

While multiple frontrunner startups have explored various technology platforms, from superconducting qubits and ion trap systems to diamond-based quantum accelerators, scaling the number of qubits from a few dozen to hundreds, thousands, and eventually millions of qubits has remained notoriously difficult. But this might change with photonic quantum computing.

The startup ORCA Computing builds photonic quantum computers that use photons, the fundamental particles of light, as qubits. Using quantum memories and established telecommunications technology, it can scale its devices more easily and integrate with existing computing infrastructure e.g. in data centers. Based on the core memory technology developed by Kris Kaczmarek, ORCA was officially co-founded by Ian Walmsley, Richard Murray, Josh Nunn, and Cristina Escoda in Oxford in the fall of 2019. This summer 2022, it has raised a $15M Series A led by Octopus Ventures and joined by Oxford Science Enterprises, Quantonation, and Verve Ventures, with additional, project-based funding provided by Innovate UK. Previous investors also include Atmos Ventures and Creative Destruction Lab.

The experiment seeks to answer fundamental questions about experimental physics.

Ten years ago, scientists announced the discovery of the Higgs boson, which helped explain why the smallest building blocks of nature have mass. For particle physicists around the world, it was a very important and long-awaited result that marked a new era of experimental physics. Physicists at the Large Hadron Collider — the world’s largest and most powerful particle accelerator — located at the European Organization for Nuclear Research (CERN) in Geneva discovered the Higgs boson largely due to results from the ATLAS experiment.

The largest general-purpose particle detector experiment at the Large Hadron Collider, ATLAS was one of the two LHC experiments involved in the discovery of the Higgs boson in July 2012.

Human space exploration has had its share of successes, with our probes going far into interstellar space. But humans themselves haven’t made it past the Moon yet. If we’re ever to find other Earth-like planets or alien civilizations we have to be able to traverse the immense span of space much quicker. One potential invention that could make this a reality is a theoretical space drive known as the “Bussard collector” or “Ramjet propulsion”. A recent physics paper published in the journal Acta Astronautica considers the feasibility of this technology.

The thrust from the jet would theoretically allow the ship to reach relativistic speeds, while carrying no onboard fuel. The concept is based on the presence of high-energy particles in space, with hydrogen especially existing in an ionized state that can be affected by magnetic fields.

A new technique makes it possible to capture videos of single atoms “swimming” at the interface between a solid and a liquid for the first time. The approach uses stacks of two-dimensional materials to trap the liquid, making it compatible with characterization techniques that usually require vacuum conditions. It could enable researchers to better understand how atoms behave at these interfaces, which play a crucial role in devices such as batteries, catalytic systems and separation membranes.

Several techniques exist to image single atoms, including scanning tunnelling microscopy (STM) and transmission electron microscopy (TEM). However, they involve exposing atoms on the surface of the sample to a high-vacuum environment, which can change the material’s structure. Techniques that do not require a vacuum, meanwhile, are either lower-resolution or only work for short time periods, meaning that the atoms’ motion cannot be captured on video.

Researchers led by materials scientists Sarah Haigh of the University of Manchester’s National Graphene Institute (NGI) have now developed a new approach that enables them to track the motion of single atoms on a surface when that surface is surrounded by liquid. They showed that the atoms behave very differently under these circumstances than they do in vacuum. “This is crucial,” explains Haigh, “since we want to understand atomic behaviour for realistic reaction/environmental conditions that the material will experience in use – for example, in a battery, supercapacitor and membrane reaction vessels.”