Silicon-Vacancy Spin Qubit in Diamond: A Quantum Memory Exceeding 10 ms with Single-Shot State Readout (1708.08852v2)

Abstract: The negatively-charged silicon-vacancy (SiV$^-$) color center in diamond has recently emerged as a promising system for quantum photonics. Its symmetry-protected optical transitions enable creation of indistinguishable emitter arrays and deterministic coupling to nanophotonic devices. Despite this, the longest coherence time associated with its electronic spin achieved to date ($\sim 250$ ns) has been limited by coupling to acoustic phonons. We demonstrate coherent control and suppression of phonon-induced dephasing of the SiV$^-$ electronic spin coherence by five orders of magnitude by operating at temperatures below 500 mK. By aligning the magnetic field along the SiV$^-$ symmetry axis, we demonstrate spin-conserving optical transitions and single-shot readout of the SiV$^-$ spin with 89% fidelity. Coherent control of the SiV$^-$ spin with microwave fields is used to demonstrate a spin coherence time $T_2$ of 13 ms and a spin relaxation time $T_1$ exceeding 1 s at 100 mK. These results establish the SiV$^-$ as a promising solid-state candidate for the realization of scalable quantum networks.

• The paper demonstrates that SiV– spin qubits achieve a 13 ms coherence time and 89% single-shot state readout fidelity, advancing quantum memory performance.
• It employs cryogenic cooling and CPMG sequences to suppress phonon-induced dephasing, significantly enhancing qubit stability.
• The experimental setup integrates a dilution refrigerator, confocal microscope, and optimized magnetic fields to enable precise spin control for quantum network applications.

Silicon-Vacancy Spin Qubit in Diamond: A Quantum Memory Exceeding 10 ms with Single-Shot State Readout

The research presented in the document focuses on the development and understanding of silicon-vacancy (SiV$^-$) color centers in diamond as a promising platform for quantum networks. The paper illustrates the extension of the electronic spin qubit coherence time by five orders of magnitude under cryogenic conditions, achieving a spin coherence time $T_2$ of 13 ms at 100 mK and a spin relaxation time $T_1$ exceeding 1 second.

Key Contributions and Findings

1. Quantum Information Storage: The SiV$^-$ center is shown to be suitable for quantum information storage due to its long coherence time, making it a candidate for use in solid-state quantum networks. The ability to store quantum information in long-lived memories and interface with optical photons is crucial for the development of quantum networks.
2. Suppression of Phonon-Induced Dephasing: The researchers addressed the challenge of phonon-induced dephasing by operating at temperatures below 500 mK. This approach led to a significant reduction in phonon interactions that previously limited the coherence time at higher temperatures, thus allowing for coherent manipulation and single-shot readout with high fidelity.
3. Experimental Setup and Results: A dilution refrigerator with a confocal microscope and vector magnet was used to conduct experiments on SiV$^-$ centers. The paper employed techniques such as microwave (MW) field control to achieve spin-coherent control, demonstrating a substantial extension in $T_2$ under dynamical decoupling with Carr-Purcell-Meiboom-Gill (CPMG) sequences.
4. Optical Spin Readout and Coherent Control: The single-shot readout of the SiV$^-$ spin was evidenced with 89% fidelity. Such precise control over spin states paves the path for reliable spin state initialization and readout, critical for quantum computation applications.
5. Role of Magnetic Fields: The optimization of the external magnetic field alignment along the SiV axis played a crucial role in extending the optical spin-pumping timescales and reducing decoherence rates.

Theoretical and Practical Implications

• Integration in Quantum Networks: The demonstrated capabilities suggest that SiV$^-$ centers can form the basis for scalable quantum network nodes. Their incorporation in integrated photonic devices can significantly enhance the efficiency and scalability of quantum information processing systems.
• Understanding of Noise Dynamics: The observed linear scaling of $T_2$ with the number of rephasing pulses under CPMG sequences suggests possible improvements in coherence time through further noise decoupling techniques. However, the exact nature of residual noise remains to be further studied, which holds potential for optimization.
• Future Prospects: The paper opens pathways for interfacing SiV$^-$ spins with other quantum systems such as superconducting qubits or mechanical resonators due to the center's demonstrated photonic properties and high coherence times. Such hybrid systems could lead to advanced quantum information processing platforms.

In conclusion, this paper rigorously outlines the procedures and potential of SiV$^-$ centers as robust platforms for developing quantum memory and interfacing technologies necessary to advance quantum network implementations. Further research into improving optical interfaces and understanding the limiting decoherence sources could enhance these findings, leading to practical quantum computing applications.