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Category: particle physics – Page 315

The defining feature of a Bose-Einstein condensate is that its atoms behave very differently from what we normally expect. Instead of acting as independent particles, they all have the same (very low) energy and are coordinated with each other.

This is similar to the difference between photons (light particles) coming from the Sun, which may have many different wavelengths (energies) and oscillate independently, and those in laser beams, which all have the same wavelength and oscillate together.

In this new state of matter, the atoms act much more like a single, wave-like structure than a group of individual particles. Researchers have demonstrated wave-like interference patterns between two different Bose-Einstein condensates and even produce moving “BEC droplets.” The latter can be considered the atomic equivalent of a laser beam.

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Scientists from the Faculty of Pure and Applied Sciences at The University of Tsukuba created scanning tunneling microscopy (STM) “snapshots” with a delay between frames much shorter than previously possible. By using ultrafast laser methods, they improved the time resolution from picoseconds to tens of femtoseconds, which may greatly enhance the ability of condensed matter scientists to study extremely rapid processes.

One picosecond, which is a mere trillionth of a second, is much shorter than the blink of an eye. For most applications, a movie camera that could record frames in a picosecond would be much faster than necessary. However, for scientists trying to understand the ultrafast dynamics of materials using STM, such as the rearrangement of atoms during a phase transition or the brief excitation of electrons, it can be painfully slow.

Now, a team of researchers at the University of Tsukuba designed an STM system based on a pump-probe method that can be used over a wide range of delay times as short as 30 femtoseconds (ACS Photonics, “Subcycle mid-infrared electric-field-driven scanning tunneling microscopy with a time resolution higher than 30 fs”).

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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.

The coupling of two different electron-hole pairs leads to a fusion of their properties. (Image: L. Sponfeldner, SNI and Department of Physics, University of Basel)

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Physicists from Japan and the U.S. used atoms about 3 billion times colder than interstellar space to open a portal to an unexplored realm of quantum magnetism.

“Unless an alien civilization is doing experiments like these right now, anytime this experiment is running at Kyoto University it is making the coldest fermions in the universe,” said Rice University’s Kaden Hazzard, corresponding theory author of a study published on September 1, 2022, in the journal Nature Physics.

As the name implies, Nature Physics is a peer-reviewed, scientific journal covering physics and is published by Nature Research. It was first published in October 2005 and its monthly coverage includes articles, letters, reviews, research highlights, news and views, commentaries, book reviews, and correspondence.

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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.

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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 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.”

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