High fidelity quantum state tomography of electron-$^{14}$N nuclear hybrid spin register in diamond using Rabi oscillations

TL;DR

This paper introduces Rabi-based Quantum State Tomography (RQST), a new method for high-fidelity quantum state characterization of electron and nuclear spins in diamond NV centers, validated through experiments showing near-perfect fidelities.

Contribution

The paper presents RQST, a novel quantum state tomography technique that improves fidelity and efficiency in characterizing single-qubit states in diamond NV centers.

Findings

Achieved average fidelity of 0.995 in electron spin control

Demonstrated maximum fidelity of 0.99992 for electron spin states

Validated RQST on nuclear spin states with similar high fidelities

Abstract

We report on a new quantum state characterisation method, which we call Rabi-based Quantum State Tomography (RQST), that we have validated on single-qubit quantum states, in particular on the electron and nuclear spins of a single nitrogen-vacancy (NV) centre in diamond, demonstrating high fidelities. The difference of RQST with conventional tomography methods is in the implementation of rotation operators and construction of density matrix from the measured data sets. We demonstrate efficient quantum state control of the electron spin at room temperature with an average fidelity of 0.995 over more than 40 measurements on different states on the Bloch sphere with a maximum fidelity of 0.99992. Also, we apply the methodology to the dark NV nuclear spin state. The state is read via the electron spin using the C-NOT two-qubit entanglement gate and demonstrate fidelities of the same order.