Phys.org June 16, 2023 Among the four fundamental forces, only gravity does not couple to particle spins according to the general theory of relativity. Researchers in China tested this principle by searching for an anomalous scalar coupling between the neutron spin and the Earth’s gravity on the ground. They developed an atomic gas comagnetometer to measure the ratio of nuclear spin-precession frequencies between 129Xe and 131Xe, and searched for a change of this ratio to the precision of 10−9 as the sensor is flipped in Earth’s gravitational field. The null results of this search set an upper limit on the […]
Tag Archives: Quantum science
Quantum random number generator operates securely and independently of source devices
Phys.org May 17, 2023 Quantum random number generators (QRNGs) can provide genuine randomness by exploiting the intrinsic probabilistic nature of quantum mechanics. However, the true randomness acquisition could be subjected to attacks from untrusted devices involved or their deviations from the theoretical modeling in real-life implementation. Researchers in China proposed and experimentally demonstrated a source-device-independent QRNG, which enabled accessing true random bits with an untrusted source device. The random bits were generated by measuring the arrival time of either photon of the time–energy entangled photon pairs produced from spontaneous parametric downconversion, where the entanglement was testified through the observation of […]
Laser light hybrids control giant currents at ultrafast times
Phys.org April 13, 2023 Spin and valley indices represent the key quantum labels of quasi-particles in a wide class of two-dimensional materials and form the foundational elements of the fields of spintronics and valleytronics. Researchers in Germany have discovered a route to induce and control the flow of spin and valley currents at ultrafast times with specially designed laser pulses, offering a new perspective on the ongoing search for the next generation of information technologies. They showed that femtosecond laser light combining optical frequency circularly polarized pulse and a terahertz (THz) frequency linearly polarized pulse can generate precisely tailored and […]
The quantum spin liquid that isn’t one
Phys.org April 18, 2023 For two decades, it was believed that a possible quantum spin liquid was discovered in a synthetically produced material. In this case, it would not follow the laws of classical physics even on a macroscopic level, but rather those of the quantum world. An international team of researchers (Austria, Spain) has shown that the promising material, κ-(BEDT-TTF)2Cu2(CN)3, is not the predicted quantum spin liquid, but a material that can be described using known concepts. They were able to precisely map the spin-gapped phase through the Mott transition by ultrahigh-resolution strain tuning. Through transport experiments they revealed […]
Absolute zero in the quantum computer: Formulation for the third law of thermodynamics
Phys.org April 4, 2023 Nernst’s unattainability principle states that infinite resources are required to cool a system to absolute zero temperature. An international team of researchers (Japan, Austria, Sweden, France, Denmark, Switzerland, Ireland, Brazil, Germany) provided a framework for identifying the resources that enable the creation of pure quantum states. They showed that perfect cooling is possible with Landauer energy cost given infinite time or control complexity. However, optimal protocols required complex unitaries generated by an external work source. Restricting to unitaries that can be run solely via a heat engine, they derived a novel Carnot-Landauer limit, along with protocols […]
Using quantum fluctuations to generate random numbers faster
Phys.org April 5, 2023 A popular approach to generating quantum random numbers is to use the quantum vacuum state. While convenient, this approach has been generally limited in speed compared to other schemes. Through custom codesign of optoelectronic integrated circuits and side-information reduction by digital filtering, an international team of researchers (Belgium, Denmark, Italy) experimentally demonstrated an ultrafast generation rate of 100 Gbit/s, setting a record for vacuum-based quantum random number generation by one order of magnitude. Their experimental demonstrations were well supported by an upgraded device-dependent framework that was secured against both classical and quantum side information and that […]
Researchers release roadmap for the development of quantum information technologies
Phys.org December 14, 2022 Q-NEXT, a U.S. Department of Energy (DOE) National Quantum Information Science Research Center, has created a roadmap for quantum interconnects research and its impact for quantum information science and technology. Q-NEXT members and participants are from academia, industry, and DOE national laboratories. The roadmap addresses the role of quantum interconnects in three emerging areas of quantum information: computing, communication, and sensing. The roadmap reviews the materials, components and systems used for these purposes; summarizes relevant scientific questions and issues; and addresses the most pressing research needs. It distills these considerations into recommendations for strategic science and […]
New measurements quantifying qudits provide glimpse of quantum future
Science Daily October 13, 2022 An international team of researchers (USA – Oak Ridge National Laboratory, Purdue University, industry, Switzerland) combined state-of-the-art frequency-bin production with state-of-the-art light sources to develop an effective technique to characterize high-dimensional qudit entanglement. They fully characterized an entangled pair of eight-level qudits, which formed a 64-dimensional quantum space — quadrupling the previous record for discrete frequency modes. The researchers began their experiments by shining a laser into a micro-ring resonator — a circular, on-chip device fabricated and designed to generate nonclassical light. This powerful photon source which took 1 square millimeter of space and allowed […]
Master equation to boost quantum technologies
Phys.org August 26, 2022 Measurement and feedback control are essential features of quantum science, with applications ranging from quantum technology protocols to information-to-work conversion in quantum thermodynamics. Theoretical descriptions of feedback control are typically given in terms of stochastic equations requiring numerical solutions or are limited to linear feedback protocols. An international team of researchers (Sweden, USA – University of Maryland, Switzerland) presented a formalism for continuous quantum measurement and feedback, both linear and nonlinear. The main result is a quantum Fokker-Planck master equation describing the joint dynamics of a quantum system and a detector with finite bandwidth. For fast […]
Researchers achieve record entanglement of quantum memories
Phys.org July 7, 2022 To fully use entanglement over long-distance quantum network links it is mandatory to know it is available at the nodes before the entangled state decays. An international team of researchers (Austria, Germany) demonstrated entanglement between two independently trapped single rubidium atoms generated over fibre links with a length up to 33 km. They generated atom–photon entanglement in two nodes located in buildings 400 m line-of-sight apart and to overcome high-attenuation losses in the fibres converted the photons to telecom wavelength using polarization-preserving quantum frequency conversion. The long fibres guided the photons to a Bell-state measurement setup in which […]