Neutral Silicon-Vacancy Center in Diamond: Spin Polarization and Lifetimes

Abstract

We demonstrate optical spin polarization of the neutrally-charged silicon-vacancy defect in diamond (SiV 0 ), an S = 1 defect which emits with a zero-phonon line at 946 nm. The spin polarization is found to be most efficient under resonant excitation, but non-zero at below-resonant energies. We measure an ensemble spin coherence time T2>100 µs at low-temperature, and a spin relaxation limit of T1 > 25 s. Optical spin state initialization around 946 nm allows independent initialization of SiV 0 and NV − within the same optically-addressed volume, and SiV 0 emits within the telecoms downconversion band to 1550 nm: when combined with its high Debye-Waller factor, our initial results suggest that SiV 0 is a promising candidate for a long-range quantum communication technology.Point defects in diamond have attracted considerable interest owing to their application for quantum information processing, communication, and metrology. The most-studied defect, the negatively-charged nitrogenvacancy (NV − ) center, possesses efficient optical spin polarization and spin-state dependent fluorescence, enabling its exploitation as an ultra-sensitive nano-scale magnetic field sensor [1][2][3]. However, the zero phonon line (ZPL) of NV − accounts for only a few percent of its total emission [4], leading to low efficiency in coherent photonic applications. The negatively-charged siliconvacancy (SiV − ) center has also received significant interest as its high Debye-Waller factor (≈ 0.8 [5]) makes it an attractive candidate for long-range quantum computation and communication. However, the exceptional optical properties of SiV − are not matched by its spin properties, where a large spin-orbit coupling in the ground state enables phonon-assisted spin-state depopulation, resulting in spin-lattice relaxation-limited coherence lifetimes of 40 ns even at 5 K [6]: efforts are ongoing to overcome this limitation by strain engineering, but currently liquid helium temperatures and below are required to access and readout SiV − spin states [7].The neutrally-charged silicon-vacancy (SiV 0 ) has a ground state electron spin S = 1. Unlike the NV center, where the nitrogen remains covalently bonded to three carbon atoms and the nitrogen-vacancy axis forms a C 3v symmetry axis, the silicon atom in SiV adopts a bond-center location, with a D 3d axis formed by the 1 1 1 joining the split-vacancy [ Fig. 1(a)]. SiV 0 has been characterized both by electron paramagnetic resonance (EPR) [8,9] and optical absorption/photoluminescence (PL) [10]. Similarly to SiV − , the neutral charge state also has a high Debye-Waller factor, with the majority of its photons emitted at the primary zero-phonon line (ZPL) at 946 nm (1.31 eV) [ Fig. 1(b)]: this transition has been shown to occur between a 3 A 2g ground state (GS) We have studied SiV 0 in two samples grown by chemical vapor deposition (CVD); silicon was introduced by adding silane to the process gasses during growth. Sample A was grown on a {1 0 0}-oriented high pressure high temperature (HPHT) substrate, ir...

Spin Relaxation of the Neutral Germanium‐Vacancy Center in Diamond

“…Considering the similarity of the SiV 0 and GeV 0 centers, we decided to measure the spin relaxation times for GeV 0 center at 80, 90, 100, and 110 K to check if the spin‐lattice relaxation is determined by the Orbach relaxation mechanism. It is known that the Orbach process (but not the direct process or Raman process) determines the spin‐lattice relaxation for the SiV 0 center near the 80 K. The magnitude of activation energy could be estimated from our data. We reset the sample inside the EPR cavity to make the magnetic field B forms angle θ = 89.2° (90.8°) with defects axis.…”

“…The EPR signal corresponding to the GeV 0 paramagnetic center has very low intensity. We found some information about the spin polarization of the SiV 0 centers with laser light (for instance, at 532 nm) . Considering similarity of the GeV 0 and SiV 0 centers we tried to use this effect in our case.…”

“…Defects in diamond which electronic state can be affected by electromagnetic fields attract great attention nowadays. The nitrogen‐vacancy (NV 0/− ) and silicon‐vacancy (SiV 0/− ) centers are the most studied centers, they have narrow zero‐phonon lines and can be used in different applications in quantum optics . Also, the negatively charged germanium‐vacancy (GeV − ) and tin‐vacancy (SnV − ) centers have been detected recently by optical spectroscopy, these defects can be considered as the analogs of the silicon‐vacancy center .…”

“…Recently, a series of works devoted to the spin relaxation of the neutral silicon‐vacancy center has been published . It has been found that above 20 K spin‐lattice relaxation times decrease rapidly with a temperature dependence characteristic of an Orbach process (the obtained energy gap approximately equals to ≈20 meV).…”

The Many Facets of Diamond Crystals

“…Therefore, active research has also been undertaken to find out other optical centers in diamond with properties suitable for the novel applications [32]. Recently, silicon-vacancy [33,34], germanium-vacancy [35][36][37], and tin-vacancy [38,39] centers have been demonstrated to possess characteristics that are promising for single-photon applications. In addition, attempts at creating optical centers related to other impurities in diamond, such as Ni [40], Cr [41], and Eu [42] have been reported.…”