Protecting solid-state spins from a strongly coupled environment

Mo Chen,Jean-Christophe Jaskula,Paola Cappellaro,Kasturi Saha,Won Kyu Calvin Sun

doi:10.1088/1367-2630/aac542

Mo Chen, Jean-Christophe Jaskula + Show 3 more

Open Access

https://doi.org/10.1088/1367-2630/aac542

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Abstract

Quantum memories are critical for solid-state quantum computing devices and a good quantum memory requires both long storage time and fast read/write operations. A promising system is the nitrogen-vacancy (NV) center in diamond, where the NV electronic spin serves as the computing qubit and a nearby nuclear spin as the memory qubit. Previous works used remote, weakly coupled 13C nuclear spins, trading read/write speed for long storage time. Here we focus instead on the intrinsic strongly coupled 14N nuclear spin. We first quantitatively understand its decoherence mechanism, identifying as its source the electronic spin that acts as a quantum fluctuator. We then propose a scheme to protect the quantum memory from the fluctuating noise by applying dynamical decoupling on the environment itself. We demonstrate a factor of 3 enhancement of the storage time in a proof-of-principle experiment, showing the potential for a quantum memory that combines fast operation with long coherence time.

Highlights

Quantum technologies, especially those based on solid-state systems such as superconducting qubits [1], Nitrogen-Vacancy (NV) centers in diamond [2, 3], and dopant spins in silicon [4], have seen significant progress over the past few decades
We model the intrinsic 14N nuclear spin I of the NV center as a random walker, whose phase evolves subject to the state of its neighboring electronic spin S that acts as a strongly coupled fluctuator and generates random telegraph noise (RTN) (Fig. 1)
We apply these ideas to protect the nuclear spin from the NV RTN and extend its T2n beyond the limit of T1e

Summary

Introduction

Especially those based on solid-state systems such as superconducting qubits [1], Nitrogen-Vacancy (NV) centers in diamond [2, 3], and dopant spins in silicon [4], have seen significant progress over the past few decades. While further improvements can come from more carefully engineering the qubit systems to remove undesired noise sources and reduce the number of decoherence channels, achieving fault tolerance will still require some form of quantum error correction (QEC) Recent developments include both theoretical proposals for more powerful QEC protocols [6] and experimental attempts at correcting or detecting quantum errors [7, 8, 9, 10]. A simpler QEC strategy, avoiding measurement and recovery operations, is to decouple qubits from the environment using dynamical decoupling (DD) This technique, going back to NMR’s spin echo [12], enjoys great success thanks to its ease of implementation. DD has traditionally been applied to refocus slow-varying, weakly coupled environments that can often be modeled as classical bath [19], while its usefulness to decouple from strongly interacting quantum environments is less clear [20]

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