Quantum insulators create multilane highways for electrons

Nanowerk  December 16, 2020 In quantum anomalous Hall (QAH) insulators, electron flow is constrained to the edges, and electrons on one edge can only go in one direction and those on the other edge can only go the opposite direction. In prior studies, the QAH effect had been experimentally realized only in materials where the Chern number had a value of 1, essentially with a single two-lane highway for electrons. They observed some dissipation of current at connection points between QAH insulators and metallic electrodes, which occurs in the form of heat. However, by increasing the thickness of the QAH […]

Quantum algorithm breakthrough

Science Daily  November 16, 2020 A team of researchers in the US (Western Washington University, UC Santa Barbara, University of Michigan, NYCity University) has developed a quantum algorithm that uses quantum gates acting on neighboring qubits in a quasi-one-dimensional setting and its circuit depth is linear in the number of qubits. They identified correlation functions that serve as signatures of the Laughlin state and discussed how to obtain them on a quantum computer. Application of the algorithm provides tools to improve quantum computing devices. The algorithm opens a new venue to use the new quantum devices to study problems which […]

Researchers discover a uniquely quantum effect in erasing information

EurekAlert  October 16, 2020 Where computing protocols are concerned, finite-time processing in the quantum regime can dynamically generate coherence. An international team of researchers (UK, Ireland) has shown that this can have significant thermodynamic implications. They demonstrated that quantum coherence generated in the energy eigen basis of a system undergoing a finite-time information erasure protocol yields rare events with extreme dissipation. These fluctuations are of purely quantum origin. By studying the full statistics of the dissipated heat in the slow-driving limit, they proved that coherence provides a non-negative contribution to all statistical cumulants. Even a single bit erasure events yield […]

New quantum computing algorithm skips past time limits imposed by decoherence

Phys.org  October 5, 2020 An international team of researchers (USA – Los Alamos National Laboratory, industry, UK) has developed a hybrid quantum-classical algorithm, called variational fast forwarding (VFF) which is a hybrid combining aspects of classical and quantum computing. Although well-established theorems exclude the potential of general fast forwarding with absolute fidelity for arbitrary quantum simulations, the researchers get around the problem by tolerating small calculation errors for intermediate times to provide useful, if slightly imperfect, predictions. The errors that build up as simulation times increase limits potential calculations. Still, the algorithm allows simulations far beyond the time scales that […]

Collaboration yields promising material for quantum computing

Phys.org  September 16, 2020 A one-dimensional topological superconductor with Majorana states bound to its ends can be realized by coupling a semiconductor nanowire to a superconductor in the presence of a strong magnetic field. However, the applied magnetic fields are detrimental to superconductivity, and constrain device layout, components, materials, fabrication, and operation. Using a ferromagnetic insulator instead of an applied field was theoretically proposed. Researchers in Denmark report transport measurements in hybrid nanowires using epitaxial layers of superconducting Al and the ferromagnetic insulator EuS on semiconducting InAs nanowires. They infer a remanent effective Zeeman field exceeding 1 T and observe stable […]

First Photonic Quantum Computer on the Cloud

IEEE Spectrum  September 9, 2020 A Canadian company working with their US partners has made a quantum computing platform publicly available. Applicants can access 8, 12, and soon 24 qubit machines over the cloud. In the coming months, the company will release a blueprint for photonic quantum computing that is essentially a primer on how to scale to millions of qubits in a fault-tolerant manner. They use continuous variable quantum computing which relies on “squeezed states” consisting of superpositions of multiple photons. Squeezed states take advantage of Heisenberg’s uncertainty principle reducing the uncertainty in the measurements of a given variable […]

A molecular approach to quantum computing

Science Daily  September 2, 2020 Researchers in the US (Caltech) applied the concept of error correction to rotating molecules in superposition. If the orientation or angular momentum of the molecule shifts by a small amount, those shifts can be simultaneously corrected. They constructed quantum error-correcting codes that embed a finite-dimensional code space in the infinite-dimensional Hilbert space of rotational states of a rigid body. They protect against both drift in the body’s orientation and small changes in its angular momentum. Hence, they may be well suited for robust storage and coherent processing of quantum information. They have described codes and […]

Quantum researchers create an error-correcting cat

Science Daily  August 12, 2020 Until now, quantum researchers have tried to fix errors by adding greater redundancy. Instead of multiple physical qubits needed to maintain one effective qubit, an international team of researchers (Switzerland, USA – UT Austin) propose a single cat qubit that can prevent phase flips all by itself. It encodes an effective qubit into superpositions of two states within a single electronic circuit — in their case a superconducting microwave resonator whose oscillations corresponds to the two states of the cat qubit. They applied microwave frequency signals to a device that is not significantly more complicated […]

Scientists develop first quantum algorithm to characterize noise across large systems

EurekAlert  August 10, 2020 Ability to build large-scale quantum computers depends on the ability to characterize quantum noise reliably and efficiently with high precision. An international team of researchers (Australia, USA – Yale University, Canada) has developed a protocol and implemented it in a 14-qubit superconducting quantum architecture. They show how to construct a quantum noise correlation matrix allowing the easy visualization of correlations between all pairs of qubits, enabling the discovery of long-range two-qubit correlations in the 14-qubit device. Their results pave the way for noise metrology in next-generation quantum devices, calibration in the presence of crosstalk, and customized […]

Quantum leap: Photon discovery is a major step toward at-scale quantum technologies

EurekAlert  May 20, 2020 Architectures for photonic quantum computing place stringent demands on high quality information carriers. An international team of researchers (UK, Italy) has fabricated on-chip photon sources and demonstrated that they meet the computing requirements. The photon sources are fabricated in silicon using mature processes and exploit a dual-mode pump-delayed excitation scheme to engineer the emission of spectrally pure photon pairs through inter-modal spontaneous four-wave mixing in low-loss spiraled multi-mode waveguides. They measured a spectral purity of 0.9904 ± 0.0006, a mutual indistinguishability of 0.987 ± 0.002, and >90% intrinsic heralding efficiency and on-chip quantum interference with a visibility of 0.96 ± 0.02 between […]