One-second coherence for a single electron spin coupled to a multi-qubit nuclear-spin environment (1801.01196v1)

Abstract: Single electron spins coupled to multiple nuclear spins provide promising multi-qubit registers for quantum sensing and quantum networks. The obtainable level of control is determined by how well the electron spin can be selectively coupled to, and decoupled from, the surrounding nuclear spins. Here we realize a coherence time exceeding a second for a single electron spin through decoupling sequences tailored to its microscopic nuclear-spin environment. We first use the electron spin to probe the environment, which is accurately described by seven individual and six pairs of coupled carbon-13 spins. We develop initialization, control and readout of the carbon-13 pairs in order to directly reveal their atomic structure. We then exploit this knowledge to store quantum states for over a second by carefully avoiding unwanted interactions. These results provide a proof-of-principle for quantum sensing of complex multi-spin systems and an opportunity for multi-qubit quantum registers with long coherence times.

• The paper demonstrates an extension of electron spin coherence beyond one second using tailored dynamical decoupling sequences.
• It employs a cryogenic NV center system to probe interactions with isolated and coupled 13C nuclear spins, providing detailed characterization of spin coupling parameters.
• This achievement paves the way for advanced quantum registers by enhancing quantum sensing, error correction, and memory in solid-state systems.

One-Second Coherence for a Single Electron Spin

The paper "One-second coherence for a single electron spin coupled to a multi-qubit nuclear-spin environment" presents a novel paper in the field of quantum information processing using single nitrogen-vacancy (NV) centers in diamond, which has noteworthy implications for quantum sensing and quantum networks. The paper's primary achievement is the realization and demonstration of an electron spin coherence time exceeding one second, a significant extension compared to previous studies. The authors accomplish this by leveraging tailored decoupling sequences adapted to the microscopic nuclear-spin environment of a given NV center.

Key Experimental Approach

Utilizing a cryogenic setup with a single NV center in diamond, the research explores the coupling mechanisms between electron spins and $^{13}$C nuclear spins present in the environment. The experimental system minimizes external disturbances and enhances control over spin operations through the use of precision microwave techniques and magnetic fields aligned to the NV axis. The authors report an electron spin relaxation time ($T_1$) of $(3.6 \pm 0.3) \times 10^3$ s, which indicates the system's high-quality isolation from the surroundings.

Measurement and Control of Spin Environment

The notable feature of this work is its ability to probe and describe the complex spin environment surrounding the NV center. The NV electron is employed as a quantum sensor to investigate its local spin environment using dynamical decoupling techniques. The results indicate a complex structure with seven isolated $^{13}$C spins and six pairs of coupled $^{13}$C spins. The identification of these structures allows for a detailed characterization of interaction strengths and angles, vital parameters for developing sophisticated decoupling strategies.

Long Electron Spin Coherence

The most impactful result is the achievement of an electron spin coherence time that surpasses one second, verified through extensive dynamical decoupling sequences. The paper details the method of employing dynamically adjustable pulse sequences to maintain coherence, by systematically reducing unwanted interactions without compromising the control over relatively complex environments. This outstanding coherence is facilitated by effective manipulation of the $^{13}$C-$^{13}$C pairs, which serve as robust qubits in this setting.

Implications and Future Directions

This work marks a significant milestone in the development of quantum registers suitable for quantum network nodes. The combination of long electron spin coherence times and selective, controlled interactions with a multi-qubit system suggests enhanced capabilities for quantum error correction and quantum memory in a highly integrated form. The authors suggest that longer coherence times can be achieved by further optimizing decoupling sequences, highlighting the potential for future advancements.

In a broader context, this research indicates possibilities for translating these findings into scalable quantum technologies leveraging solid-state spin systems. Given the intricacies of coherent spin manipulation in dense environments, future work could explore applications in areas external to the host material or examine the interactions within even larger and more complex quantum systems.

Overall, this paper is a promising contribution to the field, providing both pivotal data for understanding spin interactions in noisier and denser environments and practical methodologies for extending the coherence lifetimes of qubits in quantum devices.