Demonstration of entanglement-by-measurement of solid state qubits

TL;DR

This paper demonstrates entanglement of solid-state nuclear spin qubits via projective measurement using an NV center, enabling Bell inequality violation and advancing quantum information processing techniques.

Contribution

It reports the first implementation of entanglement-by-measurement of nuclear spins in diamond using an NV center, overcoming previous experimental challenges.

Findings

Successfully performed two-qubit parity measurement on nuclear spins

Generated maximally entangled states from uncorrelated spins

Achieved violation of Bell's inequality with solid-state spins

Abstract

Projective measurements are a powerful tool for manipulating quantum states. In particular, a set of qubits can be entangled by measurement of a joint property such as qubit parity. These joint measurements do not require a direct interaction between qubits and therefore provide a unique resource for quantum information processing with well-isolated qubits. Numerous schemes for entanglement-by-measurement of solid-state qubits have been proposed, but the demanding experimental requirements have so far hindered implementations. Here we realize a two-qubit parity measurement on nuclear spins in diamond by exploiting the electron spin of a nitrogen-vacancy center as readout ancilla. The measurement enables us to project the initially uncorrelated nuclear spins into maximally entangled states. By combining this entanglement with high-fidelity single-shot readout we demonstrate the first violation of Bells inequality with solid-state spins. These results open the door to a new class of experiments in which projective measurements are used to create, protect and manipulate entanglement between solid-state qubits.