Observation of an environmentally insensitive solid state spin defect in diamond (1706.01555v1)

Abstract: Engineering coherent systems is a central goal of quantum science. Color centers in diamond are a promising approach, with the potential to combine the coherence of atoms with the scalability of a solid state platform. However, the solid environment can adversely impact coherence. For example, phonon- mediated spin relaxation can induce spin decoherence, and electric field noise can change the optical transition frequency over time. We report a novel color center with insensitivity to both of these sources of environmental decoherence: the neutral charge state of silicon vacancy (SiV0). Through careful material engineering, we achieve over 80% conversion of implanted silicon to SiV0. SiV0 exhibits excellent spin properties, with spin-lattice relaxation times (T1) approaching one minute and coherence times (T2) approaching one second, as well as excellent optical properties, with approximately 90% of its emission into the zero-phonon line and near-transform limited optical linewidths. These combined properties make SiV0 a promising defect for quantum networks.

• The paper demonstrates the stabilization of a neutral SiV0 center in diamond via precise ion implantation, achieving up to 80% conversion efficiency.
• The paper reports spin relaxation times (T1) near one minute and coherence times (T2) approaching one second, indicating exceptional quantum performance.
• The paper highlights that the neutral SiV0 center emits nearly 90% of its light in the zero-phonon line with minimal spectral diffusion, promising scalable quantum networks.

Neutral Silicon Vacancy Center in Diamond: Properties and Prospects

The paper titled "Observation of an environmentally insensitive solid state spin defect in diamond" presents research on the stabilization and characterization of a novel color center in diamond—the neutral charge state of the silicon vacancy ($\text{SiV}^0$). This development has significant implications for quantum technologies due to the center's robust spin and optical properties, rendering it a robust candidate for advancing quantum networks.

Novel $\text{SiV}^0$ Center and Material Engineering

The stabilization of $\text{SiV}^0$ was achieved through meticulous material engineering, resulting in an 80% conversion efficiency from implanted silicon. This center exhibits characteristics largely insensitive to common sources of environmental decoherence, such as phonon-mediated spin relaxation and electric field noise, showcasing spin lattice relaxation times ($T_1$) nearing one minute and coherence times ($T_2$) of nearly one second. Furthermore, $\text{SiV}^0$ presents excellent optical properties, with approximately 90% of its emission concentrated in the zero-phonon line (ZPL) and minimal spectral diffusion.

Comparative Spin and Optical Features

The $\text{SiV}^0$ center mitigates several drawbacks associated with other diamond-based quantum defects, particularly the NV$^-$ center. The latter's limited spin-photon entanglement generation rate and static inhomogeneous linewidth restrict its potential in scalable quantum technologies. In contrast, $\text{SiV}^0$ combines favorable optical characteristics akin to negatively charged silicon vacancies but surpasses them in spin coherence properties. This dual advantage arises from the $\text{SiV}^0$'s molecular symmetry, eliminating permanent electric dipole moments that could perturb optical transitions.

Experimental Findings and Techniques

The researchers used a modulation-doped diamond to access various co-defect concentrations that facilitated cross-verifying the $\text{SiV}^0$ attributes. Ion implantation and subsequent annealing were pivotal in achieving uniform $\text{SiV}^0$ distributions without dipolar interactions. Time-resolved electron spin resonance (ESR) metrics in a homogeneous $\text{SiV}^0$ environment revealed single-exponential behavior, reaffirming the independence of $T_1$ from temperature, aligning with observations in NV$^-$.

Implications for Quantum Technologies

This paper indicates that $\text{SiV}^0$ holds considerable promise for integration into quantum applications, most notably in quantum memory and communication implementations, due to its long spin coherence and photon emission properties. Future research could explore the mechanisms governing the Orbach process at temperatures above 20 K and the dynamic stabilization of the charge state during optical excitation. Intrinsically, $\text{SiV}^0$ includes a more prolonged quantum memory via the $^2\text{Si}$ nuclear spin, with initial findings showing nuclear spin coherence times $T_{2n}$ of 0.45 ± 0.03 s, suggesting directions for further exploration.

Future Directions

The methodologies outlined for Fermi level stabilization provide a pathway for applying similar techniques to other color centers, such as germanium and tin vacancies, and for discovering potentially new quantum systems within diamond matrices. Such advancements could lead to enhanced scalability and functionality of quantum nanophotonic devices, particularly those requiring integrated diamond platforms. Conclusively, $\text{SiV}^0$ emerges as a prominent defect for enabling quantum information technologies by addressing both spin and optical constraints prevalent in existing systems.