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arXiv:2409.06313 · Physical Review Letters

Coherent Control of a Long-Lived Nuclear Memory Spin in a Germanium-Vacancy Multi-Qubit Node

Nick Grimm, Katharina Senkalla, Philipp J. Vetter, Jurek Frey, Prithvi Gundlapalli, Tommaso Calarco, Genko T. Genov, Matthias M. Müller, Fedor Jelezko

Published Jan 31, 2025• 11 citations
arXivHTMLPDF

Abstract

The ability to process and store information on surrounding nuclear spins is a major requirement for group-IV color center-based repeater nodes. We demonstrate coherent control of a ^{13}C nuclear spin strongly coupled to a negatively charged germanium-vacancy center in diamond with coherence times beyond 2.5 s at mK temperatures, which is the longest reported for group-IV defects. Detailed analysis allows us to model the system's dynamics, extract the coupling parameters, and characterize noise. We estimate an achievable memory time of 18.1 s with heating limitations considered, paving the way to successful applications as a quantum repeater node.

DOI
10.1103/physrevlett.134.043603

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The ability to process and store information on surrounding nuclear spins is a major requirement for group-IV color center-based repeater nodes. We demonstrate coherent control of a ^{13}C nuclear spin strongly coupled to a negatively charged germanium-vacancy center in diamond with coherence times beyond 2.5 s at mK temperatures, which is the longest reported for group-IV defects. Detailed analysis allows us to model the system's dynamics, extract the coupling parameters, and characterize noise. We estimate an achievable memory time of 18.1 s with heating limitations considered, paving the way to successful applications as a quantum repeater node.
Negatively charged group-IV defects in diamond show great potential as quantum network nodes due to their efficient spin-photon interface. However, reaching sufficiently long coherence times remains a challenge. In this work, we demonstrate coherent control of germanium vacancy center (GeV) at millikelvin temperatures and extend its coherence time by several orders of magnitude to more than 20 ms. We model the magnetic and amplitude noise as an Ornstein-Uhlenbeck process, reproducing the experimental results well. The utilized method paves the way to optimized coherence times of group-IV defects in various experimental conditions and their successful applications in quantum technologies.
Color centers associated with group-IV dopants in diamond with long-lived nuclear spins have emerged as major candidates for distributed quantum computing nodes and quantum repeaters. Several proof-of-principle experiments have already been demonstrated. A key operation for long-distance entanglement-distribution protocols are fast and robust gates between the electron spin and a nuclear spin. Here, we investigate numerically for an existing experimental platform of a Germanium-vacancy (GeV) center with a strongly-coupled 13{}^{13}13C spin, how such gates can be implemented via quantum optimal control. In the presence of realistic noise we investigate different parameter regimes and gate operations and obtain robust two-qubit gates with fidelities exceeding 99.9%99.9 \%99.9%. The framework provides a scalable strategy for group-IV quantum nodes and can be adapted to related architectures.
Quantum networks offer a way to overcome the size and complexity limitations of single quantum devices by linking multiple nodes into a scalable architecture. Group-IV color centers in diamond, paired with long-lived nuclear spins, have emerged as promising building blocks demonstrating proof-of-concept experiments such as blind quantum computing and quantum-enhanced sensing. However, realizing a large-scale electro-nuclear register remains a major challenge. Here we establish the germanium-vacancy (GeV) center as a viable platform for such network nodes. Using correlation spectroscopy, we identify single nuclear spins within a convoluted spin environment, overcoming limitations imposed by the color center's spin-1/21/21/2 nature and thereby enabling indirect control of these nuclear spins. We further demonstrate high-fidelity single-shot readout of both the GeV center (95.8 %95.8\,\%95.8%) and a neighboring 13C{}^{13}\text{C}13C nuclear spin (93.7 %93.7\,\%93.7%), a key tool for feed-forward error correction. These critical advances position the GeV center as a compelling candidate for next-generation quantum network nodes.
Nuclear spins near group-IV defects in diamond are promising candidates for quantum memories in quantum network applications. Here, we demonstrate high-fidelity control of a single C 13 nuclear spin coupled to a tin-vacancy center in diamond. We perform a combination of optical and microwave pumping to achieve initialization into a combined electronuclear spin state with a fidelity of 99.74(3)%. Harnessing a superconducting waveguide for radio-frequency driving, we demonstrate precise nuclear-spin control: Ramsey measurements reveal a coherence time of T 2 * = 1.5 ( 1 ) ms , and we use dynamical decoupling to extend it to 1.35(3) s. We perform randomized benchmarking, yielding a single-qubit gate fidelity of 99.92(1)%. This demonstrates a coherent spin-photon system with promising properties for quantum network nodes.
Abstract One ultimate goal of quantum information processing is to construct a quantum network for direct sharing of quantum information between distant parties based on stationary qubits for information storage and flying qubits for information transmission. This requires long‐lived quantum memories, efficient light–matter interface, and deterministic quantum gate operations. Among matter qubits, the electron spin of nitrogen vacancy center in diamond is an appealing option for its long coherence time at room temperature, deterministic microwave control, and optical preparation and readout of the qubit. However, its poor optical properties, including weak zero‐phonon‐line emission and large spectral diffusion, limit its potential for large‐scale deployment in quantum nodes. This has motivated the investigation for alternative quantum emitters that combine long‐time memory and coherent optical properties together. The emerging group‐IV split‐vacancy color centers in diamond, such as silicon‐vacancy, germanium‐vacancy, tin‐vacancy, and lead‐vacancy centers, are promising candidates of this ongoing exploration. These quantum emitters simultaneously possess microsecond spin coherence time and optically bright transitions with narrow linewidths. This review reports recent efforts on extending the spin coherence time of these color centers via temperature, strain, and charge control, which paves the road towards constructing solid‐based matter–photon interface for quantum network applications.
The germanium vacancy in diamond (GeV) is a promising candidate for color center based quantum networking. Yet, like for other group-IV vacancy defects in diamond, achieving fast, high-fidelity qubit operations using traditional magnetic resonance techniques is experimentally challenging due to a weak magnetic dipole and susceptibility to thermally induced decoherence. Here, we perform all-optical control of the GeV and realize Rabi frequencies exceeding ∼ 20 MHz. We do so by driving the two Λ -systems of the GeV simultaneously and apply this to probe the spin coherence ( T 2 * = 224 ± 14 ns, T 2 H = 11.9 ± 0.3 µ s ). Our control scheme is applicable to other color centers and particularly, other group-IV defects for which the scheme may be optimized to improve all-optical control in these systems.