Electrically switchable qubit can tune between storage and fast calculation modes

Science Daily  January 11, 2021 An international team of researchers (Switzerland, the Netherland) has created the qubits in the form of “hole spins” that can be switched from a stable idle mode to a fast calculation mode. The spins can be selectively coupled — via a photon, for example — to other spins by tuning their resonant frequencies. They can be coherently flipped from up to down in as little as a nanosecond allowing up to a billion switches per second. For their experiments, the researchers used a semiconductor nanowire made of silicon and germanium wire that has a diameter […]

New approach to circuit compression could deliver real-world quantum computers years ahead of schedule

EurekAlert  November 12, 2020 “Quantum advantage” has been achieved in Noisy Intermediate-Scale Quantum (NISQ) devices in early proof-of-principle experiments. But the NISQ devices are still prone to lots of errors that accumulate during their operation. To negate the need for millions of physical qubits for a fault-tolerant computer researchers in Japan proposed the use of the ZX-calculus as an intermediate language for braided circuit compression in large-scale fault-tolerant quantum computers. According to the researchers by compressing quantum circuits, they could reduce the size of the quantum computer and its runtime, which in turn lessens the requirement for error protection…read more. […]

Wiring the quantum computer of the future: A novel simple build with existing technology

Phys.org  April 23, 2020 A major hurdle for the scalability in quantum error-correction architecture using superconducting systems is the wiring problem, where qubits internal to a chipset become difficult to access by the external control/readout lines. An international team of researchers (Japan, Australia) carried out experiments to examine the feasibility of the new airbridge component whose measured quality factor of the airbridged resonator is below the simulated surface-code threshold required for a coupling resonator and not limit simulated gate fidelity. The measured crosstalk between crossed resonators is at most −49 dB in resonance. The spatial and frequency separation between the […]

Here’s a Blueprint for a Practical Quantum Computer

IEEE Spectrum  March 24, 2020 Researchers in the Netherlands have found that the functions needed for a quantum computer can naturally be divided into five such groups, conceptually represented by five layers of control. They are: Application layer, a key part of the overall system; Directly below the application layer is the classical-processing layer, which has three basic functions; Underneath the classical layer are the digital-, analog-, and quantum-processing layers, which together make up a quantum processing unit (QPU). To prepare for these developments, chip designers, chip-fabrication-process engineers, cryogenic-control specialists, experts in mass data handling, quantum-algorithm developers, and others will […]

Novel error-correction scheme developed for quantum computers

Science Daily  March 11, 2020 Bosonic rotation codes are based on phase-space rotation symmetry. Researchers in Australia present a universal quantum computing scheme applicable to a subset of this class which includes the well-known cat and binomial codes, among many others. The entangling gate in the scheme code can be used to interface different rotation-symmetric encodings. They propose a teleportation-based error-correction scheme that allows recoveries to be tracked entirely in software. Numerically have shown that the error-correction scheme is close to optimal for error-free ancillae and ideal measurements and present a scheme for fault-tolerant, universal quantum computing based on the […]

Quantum chemistry on quantum computers

Phys.org  January 2, 2019 Among many important and fundamental issues in science, solving the Schroedinger equation (SE) of atoms and molecules is one of the ultimate goals in chemistry, physics and their related fields. Researchers in Japan have found a novel quantum algorithm enabling us to perform full configuration interaction (Full-CI) calculations suitable for “chemical reactions” without exponential/combinatorial explosion. Full-CI gives the exact numerical solutions of SE, which are intractable problems even for supercomputers. Such a quantum algorithm contributes to the acceleration of implementing practical quantum computers…read more. Open Access TECHNICAL ARTICLE

Artificial intelligence controls quantum computers

Science Daily  October 25, 2018 Researchers in Germany show how a network-based “agent” can discover complete quantum-error-correction strategies, protecting a collection of qubits against noise. These strategies require feedback adapted to measurement outcomes. To find strategies without human intervention they developed two-stage learning with teacher and student networks and a reward quantifying the capability to recover the quantum information stored in a multiqubit system. Beyond its immediate impact on quantum computation, the work more generally demonstrates the promise of neural-network-based reinforcement learning in physics… read more. TECHNICAL ARTICLE

Shielded quantum bits

Phys.org  October 26, 2018 An international team of researchers (USA – Princeton University, Germany) proposes a quadrupolar exchange-only spin qubit that is highly robust against charge noise and nuclear spin dephasing, the dominant decoherence mechanisms in quantum dots. The qubit consists of four electrons trapped in three quantum dots and operates in a decoherence-free subspace to mitigate dephasing due to nuclear spins. Because of on-site exchange mediated by the Coulomb interaction, the qubit energy splitting is electrically controllable and can amount to several GHz even in the “off” configuration, making it compatible with conventional microwave cavities. The new method makes […]

Another step forward on universal quantum computer

Phys.org  August 13, 2018 Researchers in Japan have demonstrated non-adiabatic and non-abelian holonomic quantum gates over a geometric spin qubit on an electron or nitrogen nucleus, which paves the way to realizing a universal quantum computer. To avoid unwanted interference, they used a degenerate subspace of the triplet spin qutrit to form an ideal logical qubit in an NV center. This method facilitated fast and precise geometric gates at a temperature below 10 K, and the gate fidelity was limited by radiative relaxation. Based on this method, in combination with polarized microwaves, they succeeded in the manipulation of the geometric […]

Tuning into quantum: Scientists unlock signal frequency control of precision atom qubits

Phys.org  July 13, 2018 In their experiments, an international team of researchers (Australia, USA – Purdue University) has confirmed the ability to tune neighbouring qubits into resonance without impacting each other. Creating engineered phosphorus molecules with different separations between the atoms within the molecule allows for families of qubits with different control frequencies. Each molecule can be operated individually by selecting the frequency that controls its electron spin. It creates a built-in address which will provide significant benefits for building a silicon quantum computer. By engineering the atomic placement of the atoms within the qubits in the silicon chip, the […]