High Fidelity Control of a Nitrogen-Vacancy Spin Qubit at Room Temperature using the SMART Protocol

TL;DR

This paper demonstrates a method to significantly enhance the fidelity and coherence time of nitrogen-vacancy center qubits at room temperature using the SMART protocol, enabling more reliable quantum operations.

Contribution

The work introduces the implementation of the SMART protocol for continuous protection of NV- qubits, achieving high-fidelity Clifford gates and extended coherence times without requiring nuclear spin initialization.

Findings

Clifford gate fidelity improved from 0.940 to 0.993

Qubit coherence times increased by over 30 times

Room temperature operation with fault-tolerant compatibility

Abstract

A practical implementation of a quantum computer requires robust qubits that are protected against their noisy environment. Dynamical decoupling techniques have been successfully used in the past to offer protected high-fidelity gate operations in negatively-charged Nitrogen-Vacancy (NV-) centers in diamond, albeit under specific conditions with the intrinsic nitrogen nuclear spin initialised. In this work, we show how the SMART protocol, an extension of the dressed-qubit concept, can be implemented for continuous protection to offer Clifford gate fidelities compatible with fault-tolerant schemes, whilst prolonging the coherence time of a single NV- qubit at room temperature. We show an improvement in the average Clifford gate fidelity from $0.940\pm0.005$ for the bare qubit to $0.993\pm0.002$ for the SMART qubit, with the nitrogen nuclear spin in a random orientation. We further show a $\gtrsim$ 30 times improvement in the qubit coherence times compared to the bare qubit.