Universal logic with encoded spin qubits in silicon

TL;DR

This paper demonstrates a silicon quantum dot device capable of high-fidelity two-qubit gates and full control, advancing the development of fault-tolerant quantum computing with encoded spin qubits.

Contribution

It introduces a single-layer etch-defined gate architecture achieving high functional yield and coherence for encoded spin qubits in silicon quantum dots.

Findings

Achieved 97.1% average two-qubit Clifford fidelity

Demonstrated CNOT gate with 96.3% fidelity

Achieved SWAP gate with 99.3% fidelity

Abstract

Qubits encoded in a decoherence-free subsystem and realized in exchange-coupled silicon quantum dots are promising candidates for fault-tolerant quantum computing. Benefits of this approach include excellent coherence, low control crosstalk, and configurable insensitivity to certain error sources. Key difficulties are that encoded entangling gates require a large number of control pulses and high-yielding quantum dot arrays. Here we show a device made using the single-layer etch-defined gate electrode architecture that achieves both the required functional yield needed for full control and the coherence necessary for thousands of calibrated exchange pulses to be applied. We measure an average two-qubit Clifford fidelity of $97.1 \pm 0.2\%$ with randomized benchmarking. We also use interleaved randomized benchmarking to demonstrate the controlled-NOT gate with $96.3 \pm 0.7\%$ fidelity, SWAP with $99.3 \pm 0.5\%$ fidelity, and a specialized entangling gate that limits spreading of leakage with $93.8 \pm 0.7\%$ fidelity.