High-fidelity entangling gate for double-quantum-dot spin qubits

Abstract

Electron spins in semiconductors are promising qubits because their long coherence times enable nearly 109 coherent quantum gate operations. However, developing a scalable high-fidelity two-qubit gate remains challenging. Here, we demonstrate an entangling gate between two double-quantum-dot spin qubits in GaAs by using a magnetic field gradient between the two dots in each qubit to suppress decoherence due to charge noise. When the magnetic gradient dominates the voltage-controlled exchange interaction between electrons, qubit coherence times increase by an order of magnitude. Using randomized benchmarking, we measure single-qubit gate fidelities of ~ 99%, and through self-consistent quantum measurement, state, and process tomography, we measure an entangling gate fidelity of 90%. In the future, operating double quantum dot spin qubits with large gradients in nuclear-spin-free materials, such as Si, should enable a two-qubit gate fidelity surpassing the threshold for fault-tolerant quantum information processing.Quantum computing: high-fidelity two-qubit entangling gateScientists have invented a new way to entangle electron spins. Entanglement, or “spooky action at a distance,” is one of the key requirements for a universal quantum computer, because it enables the transfer of information between quantum bits, or qubits. For qubits consisting of electron spins trapped in semiconductors, the Coulomb interaction between electrons can be harnessed to create entanglement. In this approach, however, the coherence of the individual spins is susceptible to spurious charge noise in the semiconductor. Amir Yacoby and colleagues at Harvard University and Purdue University overcame this challenge by using a large magnetic field gradient in a double-quantum-dot spin qubit to suppress the effects charge noise. By mitigating charge-noise-induced decoherence, the team demonstrated a two-qubit entangling gate fidelity of 90%. This high-fidelity entangling operation marks a significant milestone for spin qubits and points the way toward a scalable high-fidelity spin-based quantum computer.