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

TL;DR

This paper demonstrates a high-fidelity entangling gate for double-quantum-dot spin qubits in GaAs, achieving 90% fidelity by using magnetic field gradients to suppress decoherence, advancing scalable quantum computing.

Contribution

The work introduces a novel entangling gate method leveraging magnetic field gradients to enhance coherence and fidelity in double quantum dot spin qubits.

Findings

Achieved approximately 99% single-qubit gate fidelity.

Demonstrated a 90% fidelity for the entangling two-qubit gate.

Magnetic field gradients significantly increase qubit coherence times.

Abstract

Electron spins in semiconductors are promising qubits because their long coherence times enable nearly 10^9 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 and self-consistent quantum measurement, state, and process tomography, we measure single-qubit gate fidelities of approximately 99% and 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.