Phys.org February 14, 2023 Recent experiments in moiré transition metal dichalcogenide materials have reported the observation of a continuous bandwidth-tuned transition from a metal to a paramagnetic Mott insulator at a fixed filling of one electron per moiré unit cell. The electrical transport measurements reveal several puzzling features that are seemingly at odds with the theoretical expectations of an interaction-induced, but disorder-free, bandwidth-tuned metal-insulator transition. A team of researchers in the US (Cornell University, MIT) included the effects of long-wavelength inhomogeneities, building on the results for a continuous metal-insulator transition at fixed filling in the clean limit. They examined the […]
The ‘flip-flop’ qubit: Realization of a new quantum bit in silicon controlled by electric signals
Phys.org February 13, 2023 The spins of atoms and atom-like systems are among the most coherent objects in which to store quantum information. However, the need to address them using oscillating magnetic fields hinders their integration with quantum electronic devices. An international team of researchers (Australia, Japan) circumvented this hurdle by operating a single-atom “flip-flop” qubit in silicon, where quantum information is encoded in the electron-nuclear states of a phosphorus donor. The qubit was controlled using local electric fields at microwave frequencies, produced within a mos device. The electrical drive was mediated by the modulation of the electron-nuclear hyperfine coupling, […]
How to pull carbon dioxide out of seawater
MIT News February 16, 2023 In recent years, the ocean has come to be recognized as a global-scale reservoir for atmospheric CO2. Researchers at MIT have developed and demonstrated an effective asymmetric electrochemical system to capture oceanic CO2 using bismuth and silver electrodes that could capture and release chloride ions by Faradaic reactions upon application of appropriate cell voltages. The difference in reaction stoichiometry between the two electrodes enabled an electrochemical system architecture for a chloride-mediated electrochemical pH swing, which could be leveraged for effective removal of CO2 from oceanwater without costly bipolar membranes. With two silver-bismuth systems operating in […]
A liquid laser that is robust in air and tunable by wind
Phys.org February 10, 2023 Lasers made solely from liquids are promising toward flexible lasers, but they are intrinsically unstable and have been inapplicable to steady operation under ambient conditions unless they are enclosed in a tailored container or a matrix to prevent the evaporation of the liquid. To simulate the near-perfect water droplets that form on the lotus leaves and roll off, an international team of researchers (Japan, Germany) mixed 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4) with a dye that allowed it to become a laser. The droplets were highly robust and worked as efficient long-lasting laser oscillators. The lasing wavelength was sensitively […]
Mechanical engineering meets electromagnetics to enable future technology
Science Daily February 13, 2023 Reconfigurable electromagnetic devices, specifically reconfigurable antennas, have shown to be integral to the future of communication systems. However, mechanically robust designs that can survive real-world, harsh environment applications and high-power conditions remain rare. Researchers at Pennsylvania State University have developed the general framework for a field of both discrete and continuously mechanically reconfigurable devices by combining compliant mechanisms with electromagnetics. They demonstrated a reconfigurable compliant mechanism antenna which exhibited continuously tunable performance across a broad band of frequencies. Three additional examples were also introduced to showcase the versatility and advanced capabilities of compliant mechanism enabled […]
New photodiode with extremely low excess noise for optical communication and long-range LIDAR
Phys.org February 9, 2023 Avalanche photodiodes (APDs) have internal gain, which means that when compared to PIN-photodiodes they typically have a higher signal-to-noise ratio. Researchers in the UK designed and demonstrated photodiode that exhibits high multiplication factor with very little added noise. The new semiconductor alloy is based on a GaAsSb absorption region that has excellent detection efficiency at infrared wavelengths (up to 1,700 nanometers). The device incorporated an appropriate doping profile to suppress tunneling current from the absorption region, achieving a large avalanche gain, ∼130 at room temperature. It exhibits extremely low excess noise factors of 1.52 and 2.48 […]
Researchers find thermal limits of advanced nanomaterials
Phys.org February 15, 2023 Boron nitride nanotubes (BNNTs), structural analogues to carbon nanotubes, are a strong candidate for nanofillers in high-temperature composites due to their high thermal stability, oxidation resistance, excellent mechanical properties, and high thermal conductivity. A team of researchers in the US (FAMU-FSU College of Engineering, industry) tested samples of high-quality, high-purity BNNTs in an inert atmosphere for thermal failure up to 2500 °C. A significant fraction of the BNNTs survived temperatures as high as 2200°, and the BNNT samples were completely undamaged at temperatures as high as 1800 °C. Boron nitride (BN) nanopowders were tested identically to […]
Researchers realize complete family of logic gates using silicon-on-silica waveguides at 1.55 μm
Phys.org February 13, 2023 An international team of researchers (China, Greece) employed silicon-on-silica waveguides for the all-optical realization of a complete family of logic gates, including NOT, XOR, AND, OR, NOR, NAND and XNOR operated at 1.55 μm. The waveguide consists of three identical slots and six microring resonators, all made of silicon patterned on silica. The principle of operation of these logic gates was based on the constructive and destructive interference induced by the phase difference between the input signals. The gates’ performance is evaluated against the contrast ratio (CR) metric. According to the researchers, compared to existing waveguides, […]
Satellites may enable better quantum networks
Phys.org February 10, 2023 Satellite-based quantum links have been proposed to extend the network domain for quantum communication. An international team of researchers (USA – Oak Ridge National Laboratory, University of Illinois, Singapore) developed a quantum communication system, suitable for realistic satellite-to-ground communication and executed an entanglement-based quantum key distribution (QKD) protocol achieving quantum bit-error rates (QBERs) below 2% in all bases. They demonstrated low-QBER execution of a higher-dimensional hyperentanglement-based QKD protocol, using photons simultaneously entangled in polarization and time bin, leading to significantly higher secure key rates, at the cost of increased technical complexity and system size. They showed […]
Scientists boost quantum signals while reducing noise
MIT News February 9, 2023 Squeezing of the electromagnetic vacuum is an essential metrological technique used to reduce quantum noise in applications spanning gravitational wave detection, biological microscopy and quantum information science. In superconducting circuits, the resonator-based Josephson-junction parametric amplifiers conventionally used to generate squeezed microwaves are constrained by a narrow bandwidth and low dynamic range. An international team of researchers (USA – MIT, MIT Lincoln Laboratory, industry, Australia) developed a dual-pump, broadband Josephson travelling-wave parametric amplifier that combined a phase-sensitive extinction ratio of 56 dB with single-mode squeezing on par with the best resonator-based squeezers. They demonstrated two-mode squeezing at […]