Coherent control of interacting solid-state spins below the diffraction limit

TL;DR

This paper demonstrates coherent control and entangling operations of interacting solid-state spins in rare-earth ions, enabling scalable quantum network nodes with high-density spin registers.

Contribution

It introduces a method for coherent optical and spin control of interacting Er$^{3+}$ ions and a nuclear spin, advancing quantum information processing in solid-state systems.

Findings

Achieved two-qubit electron-electron gates between Er$^{3+}$ ions

Performed quantum non-demolition measurements on single ions

Demonstrated coherent storage and retrieval in nuclear spins

Abstract

Optically addressed atomic defects in the solid-state are widely used as single-photon sources and memories for quantum network applications. The solid-state environment allows for a high density of electron and nuclear spins with the potential to form registers for coherent information processing. However, it is challenging to reliably address individual spins at nanometer separations where interactions are large. Rare-earth ions offer a unique solution, as their narrow homogeneous optical linewidth allows frequency-domain resolution of a large number of emitters without regard to their spatial separation. In this work, we realize coherent optical and spin control of a pair of interacting Er$^{3+}$ ions, together with a nearby nuclear spin ancilla. We demonstrate two-qubit electron-electron gates and use them to perform repeated quantum non-demolition measurements on one of the Er$^{3+}$ ions. We also demonstrate electron-nuclear gates to allow coherent storage and retrieval of qubit information in a nuclear spin, and show that the nuclear spin coherence survives readout of the electron spin. These techniques can be readily scaled to larger numbers of electron and nuclear spins, paving the way for massively multiplexed quantum network nodes.