Many-body quantum register for a spin qubit

TL;DR

This paper demonstrates a quantum register in a semiconductor quantum dot using nuclear spins, enabling controlled quantum state transfer and long storage times, advancing quantum network node capabilities.

Contribution

It introduces a functional quantum register in a quantum dot leveraging nuclear spins, with high-fidelity operations and long coherence times, a novel step in quantum node development.

Findings

Achieved 68.6% fidelity in quantum state transfer

Stored quantum information for 130 microseconds

Prepared 13,000 nuclear spins into a dark state

Abstract

Quantum networks require quantum nodes with coherent optical interfaces and multiple stationary qubits. In terms of optical properties, semiconductor quantum dots are highly compelling, but their adoption as quantum nodes has been impaired by the lack of auxiliary qubits. Here, we demonstrate a functional quantum register in a semiconductor quantum dot leveraging the dense, always-present nuclear spin ensemble. We prepare 13,000 host nuclear spins into a single many-body dark state to operate as the register logic state $|0\rangle$. The logic state $|1\rangle$ is defined as a single nuclear magnon excitation, enabling controlled quantum-state transfer between the electron spin qubit and the nuclear magnonic register. Using 130-ns SWAP gates, we implement a full write-store-retrieve-readout protocol with 68.6(4)% raw overall fidelity and a storage time of 130(16) $\mu$s in the absence of dynamical decoupling. Our work establishes how many-body physics can add step-change functionality to quantum devices, in this case transforming quantum dots into multi-qubit quantum nodes with deterministic registers.