Bipartite entanglement in a nuclear spin register mediated by a quasi-free electron spin

TL;DR

Researchers created a three-qubit nuclear spin register in diamond and demonstrated bipartite entanglement between two 13C nuclei using a silicon-vacancy electron spin.

Contribution

This work demonstrates nuclear spin entanglement in a diamond-based quantum register using a silicon-vacancy center as a mediator.

Findings

A three-qubit 13C nuclear spin register was entangled via a silicon-vacancy electron spin.

The electron spin’s long lifetime enabled sensing of nuclear-nuclear couplings at low frequencies.

A nuclear spin conditional phase-gate mediated bipartite entanglement without dynamic decoupling.

Abstract

Quantum networks will rely on photons entangled to robust, local quantum registers for computation and error correction. We demonstrate control of and entanglement in a fully connected three-qubit 13C nuclear spin register in diamond. The register is coupled to a quasi-free electron spin-1/2 of a silicon-vacancy center (SiV). High strain decouples the SiVs electron spin from spin-orbit interaction reducing the susceptibility to phonons at liquid helium temperature. As a result, the electron spin lifetime of hundreds of milli seconds enables sensing of nuclear-nuclear couplings down to few hertz. To detect and control the register we leverage continuous decoupling using shaped, low-power microwave and direct radio frequency driving. Furthermore, we implement a nuclear spin conditional phase-gate on the electron spin to mediate bipartite entanglement. This approach presents an alternative to dynamically decoupled nuclear spin entanglement, not limited by the electron spin-1/2’s nature, opening up new avenues to an optically-accessible, solid-state quantum register.

Group-IV color centers in diamond are promising for quantum networks, but despite progress on electron-nuclear spin registers in these systems, nuclear spin entanglement has remained unexplored. Here the authors demonstrate entanglement of two 13C nuclear spins in a three-qubit register coupled to a silicon-vacancy electron spin.

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