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While taking snapshots with the high-speed “electron camera” at the Department of Energy’s SLAC National Acceleratory Laboratory, researchers discovered new behavior in an ultrathin material that offers a promising approach to manipulating light that will be useful for devices that detect, control or emit light, collectively known as optoelectronic devices, and investigating how light is polarized within a material. Optoelectronic devices are used in many technologies that touch our daily lives, including light-emitting diodes (LEDs), optical fibers and medical imaging.

As reported in Nano Letters (“Giant Terahertz Birefringence in an Ultrathin Anisotropic Semimetal”), the team, led by SLAC and Stanford professor Aaron Lindenberg, found that when oriented in a specific direction and subjected to linear terahertz radiation, an ultrathin film of tungsten ditelluride, which has desirable properties for polarizing light used in optical devices, circularly polarizes the incoming light.

Snapshot taken by SLAC’s high-speed electron camera, an instrument for ultrafast electron diffraction (MeV-UED), showing evidence of circular polarization of terahertz light by an ultrathin sample of tungsten ditelluride. (Sie et al., Nano Letters, 8 May 2024)

The idea of time travel has dazzled sci-fi enthusiasts for years. Science tells us that traveling to the future is technically feasible, at least if you’re willing to go near the speed of light, but going back in time is a no-go. But what if scientists could leverage the advantages of quantum physics to uncover data about complex systems that happened in the past?

New research indicates that this premise may not be that far-fetched. In a paper published June 27, 2024, in Physical Review Letters, Kater Murch, the Charles M. Hohenberg Professor of Physics and Director of the Center for Quantum Leaps at Washington University in St. Louis, and colleagues Nicole Yunger Halpern at NIST and David Arvidsson-Shukur at the University of Cambridge demonstrate a new type of quantum sensor that leverages quantum entanglement to make time-traveling detectors.

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Researchers have developed a new method to significantly enhance quantum technology performance by using the cross-correlation of two noise sources to extend coherence time, improve control fidelity, and increase sensitivity for high-frequency sensing. This innovative strategy addresses key challenges in quantum systems, offering a tenfold increase in stability and paving the way for more reliable and versatile quantum devices.

The work is published in the journal Physical Review Letters.

Researchers have made a significant breakthrough in quantum technology by developing a novel method that dramatically improves the stability and performance of quantum systems. This pioneering work addresses the longstanding challenges of decoherence and imperfect control, paving the way for more reliable and sensitive quantum devices.

Implementing a fault-tolerant quantum processor requires coupling qubits to generate entanglement. Superconducting qubits are a promising platform for quantum information processing, but scaling up to a full-scale quantum computer necessitates interconnecting many qubits with low error rates. Traditional methods often limit coupling to nearest neighbors, require large physical footprints, and involve numerous couplers, complicating fabrication.

For instance, coupling 100 qubits pairwise demands a vast number of couplers. Moreover, controlling individual circuit elements and couplers with separate cables for even 1,000 qubits would require an impractically large volume of cables, making it infeasible to fit such a system in a large lab, let alone manage millions of qubits. This highlights the need for more efficient and scalable coupling methods.

A team of theoretical physicists led by Mohd Ansari at FZJ, in collaboration with the experimental team of Britton Plourde at Syracuse University, introduced a novel approach using a multimode coupler that enables tunable coupling strength between any pair of qubits.

Electrons inherently carry both spin and orbital angular momentum (i.e., properties that help to understand the rotating motions and behavior of particles). While some physicists and engineers have been trying to leverage the spin angular momentum of electrons to develop new technologies known as spintronics, these particles’ orbital momentum has so far been rarely considered.

Currently, generating an orbital current (i.e., a flow of orbital angular momentum) remains far more challenging than generating a spin current. Nonetheless, approaches to successfully leverage the orbital angular momentum of electrons could open the possibility for the development of a new class of devices called orbitronics.

Researchers at Keio University and Johannes Gutenberg University report the successful generation of an orbital current from magnetization dynamics, a phenomenon called orbital pumping. Their paper, published in Nature Electronics, outlines a promising approach that could allow engineers to develop new technologies leveraging the orbital angular momentum of electrons.

Charge density waves are quantum phenomena occurring in some materials, which involve a static modulation of conduction electrons and the periodic distortion of the lattice. These waves have been observed in numerous condensed matter materials, including high-temperature superconductors and quantum Hall systems.

While many studies have investigated these states, so far experimental observations of the boundary states that emerge from charge density waves are still scarce. In a recent paper, published in Nature Physics, researchers at Princeton University and other institutes worldwide have visualized the bulk and boundary modes of the charge density wave in the topological material Ta₂Se₈I.

“Our research group focuses on discovering and investigating novel topological properties of quantum matter utilizing various state-of-the-art experimental techniques that probe electronic structure of the materials,” Maksim Litskevich, co-author of the paper, told Phys.org. “In recent years, the physics community has experienced excitement exploring the intriguing and rich properties of Kagome materials, which intricately intertwine geometry, topology, and electronic interactions.”

In a study published in Nature, a research team has, for the first time, observed the antiferromagnetic phase transition within a large-scale quantum simulator of the fermionic Hubbard model (FHM).

This study highlights the advantages of quantum simulation. It marks an important first step towards obtaining the low-temperature phase diagram of the FHM and understanding the role of quantum magnetism in the mechanism of high-temperature superconductivity. The team was led by Prof. Pan Jianwei, Prof. Chen Yuao, and Prof. Yao Xingcan from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences.

Strongly correlated quantum materials such as high-temperature superconductors are of scientific importance and have potential economic benefits. However, the physical mechanisms underlying these materials remain unclear, posing challenges to their large-scale preparation and application.

A team of experimental physicists led by the University of Cologne have shown that it is possible to create superconducting effects in special materials known for their unique edge-only electrical properties. This discovery provides a new way to explore advanced quantum states that could be crucial for developing stable and efficient quantum computers.

Their study, titled “Induced superconducting correlations in a quantum anomalous Hall insulator,” has been published in Nature Physics.

Superconductivity is a phenomenon where electricity flows without resistance in certain materials. The quantum anomalous Hall effect is another phenomenon that also causes zero resistance, but with a twist: It is confined to the edges rather than spreading throughout.

The Brewster reflectionless effect stands out as one of the simplest yet pivotal discoveries in manipulating waves. Initial investigations were limited to isotropic materials, but later, thanks to the advent of metamaterials, the phenomenon was found to expand into anisotropic materials.

An anomalous Brewster effect has recently been demonstrated in metamaterials, thus increasing the number of degrees of freedom. In materials without magnetic responses, the Brewster effect exclusively applies to transverse–magnetic (TM, or p–wave polarization) waves. Building on the equivalence between TM mode and 2D acoustics, the Brewster effect in acoustics with zero reflection has been demonstrated by utilizing acoustic metamaterials.

In their paper published in the journal Science Bulletin, the researchers first demonstrated this universal theory by matching the continuous boundary conditions and analyzing the relationship between the reflection coefficient and various parameters, proposing a precise method to confirm the near-zero reflection condition. Subsequently, they incorporated intrinsic losses into the permittivity tensors, illustrating a novel method to achieve asymmetric vortex transmission.