# High-Fidelity Spin Measurement on the Nitrogen-Vacancy Center

## TL;DR

This paper investigates high-fidelity spin state measurement techniques for nitrogen-vacancy centers in diamond, proposing cavity QED methods to surpass traditional fluorescence limits for quantum computing and communication.

## Contribution

It introduces a cavity QED-based approach for NV center spin readout, achieving higher fidelity than conventional fluorescence methods, suitable for fault-tolerant quantum applications.

## Key findings

- Single-shot measurements can exceed fault-tolerance thresholds.
- High fidelity is achievable with weak optical pulses.
- Strong coupling regime enables efficient quantum state readout.

## Abstract

Nitrogen-vacancy (NV) centers in diamond are versatile candidates for many quantum information processing tasks, ranging from quantum imaging and sensing through to quantum communication and fault-tolerant quantum computers. Critical to almost every potential application is an efficient mechanism for the high fidelity readout of the state of the electronic and nuclear spins. Typically such readout has been achieved through an optically resonant fluorescence measurement, but the presence of decay through a meta-stable state will limit its efficiency to the order of 99%. While this is good enough for many applications, it is insufficient for large scale quantum networks and fault-tolerant computational tasks. Here we explore an alternative approach based on dipole induced transparency (state-dependent reflection) in an NV center cavity QED system, using the most recent knowledge of the NV center's parameters to determine its feasibility, including the decay channels through the meta-stable subspace and photon ionization. We find that single-shot measurements above fault-tolerant thresholds should be available in the strong coupling regime for a wide range of cavity-center cooperativities, using a majority voting approach utilizing single photon detection. Furthermore, extremely high fidelity measurements are possible using weak optical pulses.