Optical signatures of silicon-vacancy spins in diamond (1312.2997v1)

Abstract: Colour centres in diamond have emerged as versatile tools for solid-state quantum technologies ranging from quantum information to metrology, where the nitrogen-vacancy centre is the most studied to-date. Recently, this toolbox has expanded to include different materials for their nanofabrication opportunities, and novel colour centres to realize more efficient spin-photon quantum interfaces. Of these, the silicon-vacancy centre stands out with ultrabright single photon emission predominantly into the desirable zero-phonon line. The challenge for utilizing this centre is to realise the hitherto elusive optical access to its electronic spin. Here, we report spin-tagged resonance fluorescence from the negatively charged silicon-vacancy centre. In low-strain bulk diamond spin-selective excitation under finite magnetic field reveals a spin-state purity approaching unity in the excited state. We also investigate the effect of strain on the centres in nanodiamonds and discuss how spin selectivity in the excited state remains accessible in this regime.

Optical Signatures of Silicon-Vacancy Spins in Diamond

The paper of color centers in diamond, particularly the negatively charged silicon-vacancy ($SiV^-$) center, provides valuable insights into solid-state quantum technologies. This paper explores the optical signatures of $SiV^-$ spins in diamond, showcasing the impurity centers' potential for applications ranging from quantum information to metrology. Primarily, the authors focus on achieving optical access to the electronic spin of the $SiV^-$ center, previously a challenging pursuit due to the limitations in spin-state purity.

Spin-Tagged Resonance Fluorescence

One of the major contributions of this research is the demonstration of spin-tagged resonance fluorescence from $SiV^-$ centers in low-strain bulk diamond. The authors successfully utilize spin-selective excitation under a finite magnetic field which reveals a spin-state purity in the excited state nearing unity. This level of purity is unprecedented in the field and has significant implications for effectively utilizing these centers in quantum technology. The paper also analyzes the impact of strain on nanodiamonds, concluding that access to spin selectivity in strained environments remains feasible.

Electronic Structure and Magnetic Field Influence

Delineating the electronic structure of $SiV^-$ centers, the authors provide a detailed theoretical and empirical basis supported by DFT and group theoretic analysis. The paper elaborates on the spin-orbit coupling and Jahn-Teller effect within $SiV^-$ centers, hinting at an intrinsic quantization axis along the crystal's <111> direction. Spin-resolved measurements reveal that magnetic field orientation significantly influences spin purity—the alignment of a magnetic field parallel to the symmetry axis can enhance spin purity in the ground state to over 90% and retain near unity in the excited state.

Resonance Fluorescence Measurements and Spin Selectivity

Using resonance fluorescence measurements at cryogenic temperatures, the paper captures the $SiV^-$ centers' optical spectrum exhibiting a fine structure composed of four transitions around 737 nm. These are attributed to doubly split ground and excited states, further discriminated under magnetic fields revealing quadruplet splitting indicative of spin-1/2 states. The paper expands on the spin selectivity achieved under resonant conditions, demonstrating starkly different spectral manifestations when driving particular transitions.

Implications and Future Directions

The paper lays a promising groundwork for future experiments, hinting at approaches for enhanced spin selectivity through crystal orientation or ultrafast optical techniques. The proprietary optical access to well-defined spin states positions $SiV^-$ centers as prime candidates for spin-photon quantum interfaces. The paper suggests exploring spin-coherence and optical readout mechanisms, potentially propelling advancements in quantum computing and spintronics.

In conclusion, this research provides comprehensive evidence for the viability of $SiV^-$ color centers in diamond as robust quantum tools. By systematically dissecting the center's optical and spin properties, the authors open avenues for cutting-edge quantum technology applications and invite further inquiry into overcoming existing spin manipulation limitations.