Lifeboat Foundation

Circa 2016 face_with_colon_three

The Deutsche Physikalische Gesellschaft (DPG) with a tradition extending back to 1,845 is the largest physical society in the world with more than 61,000 members. The DPG sees itself as the forum and mouthpiece for physics and is a non-profit organisation that does not pursue financial interests. It supports the sharing of ideas and thoughts within the scientific community, fosters physics teaching and would also like to open a window to physics for all those with a healthy curiosity.

Circa 2018 face_with_colon_three Quantum storage.

A broadband-light storage technique using the Autler–Townes effect is demonstrated in a system of cold Rb atoms. It overcomes both inherent and technical limitations of the established schemes for high-speed and long-lived optical quantum memories.

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.

Quantum entanglement and spacetime wormholes helped to solve a long-standing quandary.

By George Musser

By:George Musser

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.”

Squeaky, cloudy or spherical—electron orbitals show where and how electrons move around atomic nuclei and molecules. In modern chemistry and physics, they have proven to be a useful model for quantum mechanical description and prediction of chemical reactions. Only if the orbitals match in space and energy can they be combined—this is what happens when two substances react with each other chemically. In addition, there is another condition that must be met, as researchers at Forschungszentrum Jülich and the University of Graz have now discovered: The course of chemical reactions also appears to be dependent on the orbital distribution in momentum space. The results were published in the journal Nature Communications.

Chemical reactions are ultimately nothing more than the formation and breakdown of electron bonds, which can also be described as orbitals. The so-called molecular orbital theory thus makes it possible to predict the path of chemical reactions. Chemists Kenichi Fukui and Roald Hoffmann received the Nobel Prize in 1981 for greatly simplifying the method, which led to its widespread use and application.

“Usually, the energy and location of electrons are analyzed. However, using the photoemission tomography method, we looked at the momentum distribution of the orbitals,” explains Dr. Serguei Soubatch. Together with his colleagues at the Peter Grünberg Institute (PGI-3) in Jülich and the University of Graz in Austria, he adsorbed various types of molecules on metal surfaces in a series of experiments and mapped the measured momentum in the so-called momentum space.

The introduction of topology in photonic systems has attracted considerable attention not only for the elaborate molding of light but also for its practical applications in novel photonic devices. Originally, the quantum Hall effect of light was realized in photonic crystals (PCs) by introducing external electric or magnetic fields to break the time-reversal symmetry (TRS).

Instead of breaking the TRS, the quantum spin-Hall effect of light has been achieved in TRS-preserved systems where photonic pseudospins can be constructed. Recently, the valley Hall effect of light has been realized by introducing the binary valley degree of freedom (DoF) into photonic systems. One of the vital features of the valley Hall effect is the nontrivial photonic band gap, which is characterized by the nonzero valley Chern number.

Furthermore, valley-dependent edge modes are supported at the domain wall which consists of two PCs with opposite-valley Chern numbers. The valley Hall effect of light is commonly realized in a triangular-lattice PC with broken mirror symmetry or in a honeycomb-lattice PC with broken spatial inversion symmetry, and it is compatible with existing nanophotonic fabrication technique.

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.”