Cavity-enhanced optical readout and control of nuclear spin qubits

TL;DR

This paper demonstrates all-optical initialization, control, and high-fidelity readout of nuclear spin qubits in erbium-doped yttrium orthosilicate using a cryogenic cavity, advancing quantum network technology.

Contribution

It introduces a novel cavity-enhanced method for optical manipulation of nuclear spin qubits with high fidelity and long coherence times in a solid-state platform.

Findings

Single-shot readout fidelity of 91(2)% achieved.

Coherence times exceed 0.2 seconds under magnetic field.

Frequency-multiplexed optical addressing demonstrated.

Abstract

Their exceptional coherence makes nuclear spins in solids a prime candidate for quantum memories in quantum networks and repeaters. Still, the direct all-optical initialization, coherent control, and readout of individual nuclear spin qubits have been an outstanding challenge. Here, this is achieved by embedding 167-Er dopants in yttrium orthosilicate in a cryogenic Fabry-Perot cavity, whose linewidth of 65 MHz is much smaller than the 0.9 GHz separation of neighboring hyperfine levels. Frequency-selective emission enhancement thus enables a single-shot readout fidelity of 91(2)%. Furthermore, a large magnetic field freezes paramagnetic impurities, leading to coherence times exceeding 0.2 s. The combination of nuclear-spin qubits with frequency-multiplexed addressing and lifetime-limited photon emission in the minimal-loss telecommunications C-band establishes 167-Er as a leading platform for long-range, fiber-based quantum networks.