Divacancy defects in silicon carbide have long-lived electronic spin states and sharp optical transitions. Because of the various polytypes of SiC, hundreds of unique divacancies exist, many with spin properties comparable to the nitrogen-vacancy center in diamond. If ensembles of such spins can be all-optically manipulated, they make compelling candidate systems for quantum-enhanced memory, communication, and sensing applications. We report here direct all-optical addressing of basal plane-oriented divacancy spins in 4H-SiC. By means of magneto-spectroscopy, we fully identify the spin triplet structure of both the ground and the excited state, and use this for tuning of transition dipole moments between particular spin levels. We also identify a role for relaxation via intersystem crossing. Building on these results, we demonstrate coherent population trapping -a key effect for quantum state transfer between spins and photons- for divacancy sub-ensembles along particular crystal axes. These results, combined with the flexibility of SiC polytypes and device processing, put SiC at the forefront of quantum information science in the solid state.

Electromagnetically induced transparency with an ensemble of donor-bound electron spins in a semiconductor Sladkov, Maksym; Chaubal, A. U.; Bakker, M. P.; Onur, A. R.; Reuter, D.; Wieck, A. D.; van der Wal, C. H.

We present how optical coherent population trapping (CPT) of the spin of localized semiconductor electrons stabilizes the surrounding nuclear spin bath via the hyperfine interaction, resulting in a state which is more ordered than the thermal equilibrium state. We find distinct control regimes for different signs of laser detuning and examine the transition from an unpolarized, narrowed state to a polarized state possessing a bistability. The narrowing of the state yields slower electron spin dephasing and self-improving CPT. Our analysis is relevant for a variety of solid state systems where hyperfine-induced dephasing is a limitation for using electron spin coherence. arXiv:1409.7576v2 [cond-mat.mes-hall]

We experimentally demonstrate how coherent population trapping (CPT) for donor-bound electron spins in GaAs results in autonomous feedback that prepares stabilized states for the spin polarization of nuclei around the electrons. CPT was realized by excitation with two lasers to a bound-exciton state. Transmission studies of the spectral CPT feature on an ensemble of electrons directly reveal the statistical distribution of prepared nuclear spin states. Tuning the laser driving from blue to red detuned drives a transition from one to two stable states. Our results have importance for ongoing research on schemes for dynamic nuclear spin polarization, the central spin problem and control of spin coherence.PACS numbers: 03.65. Yz, 42.50.Ex, 76.30.Mi, 76.70.Hb, 78.47.jh Following the emergence of electron spins in quantum dots and solid state defects as candidates for spin qubits it has become a major goal to realize control over the nuclear spins in such nanostructures. In many experimental settings, interaction with disordered nuclear spins in the crystal environment is detrimental to the coherent evolution of carefully prepared electron spin states [1][2][3]. Preparation of nuclear spins in a state that has reduced spin fluctuations with respect to the thermal equilibrium state will help to overcome this problem [4]. Proposals to achieve this goal have been put forward for electron spin resonance (ESR) on one-or two-electron quantum dots [5,6], and for optical preparation techniques that either rely on a quantum measurement technique [7,8] or a stochastic approach [9][10][11]. Experimental advances have been made with ESR and optical techniques on single quantum dots [12][13][14][15][16][17][18] and nitrogen-vacancy centers [19], and on quantum dot ensembles [20,21].Several of these works [8-11, 15, 18, 19] make use of the optical response of the electronic system near the coherent-population-trapping resonance (CPT, explained below) because it is highly sensitive to perturbations from nuclear spins. Notably, these experiments so far have focussed on quantum dots where, due to the particular anisotropic confinement, hyperfine coupling with a hole-spin in the excited state is reported to dominate [15]. In recent work [22] we discussed how the interplay between electron-nuclear spin interaction and CPT influences the stochastics of the nuclear spin bath for a class of systems where hyperfine interaction with the groundstate electron spin dominates.Here we report experiments on this latter class of systems. We demonstrate an all-optical technique that stabilizes the nuclear spin bath around localized donor electrons in GaAs into a non-thermal state under conditions of two-laser optical pumping. We show that the nuclear spin system is directed either towards a single stable state or (probabilistically) towards one of two stable states, depending on laser detuning from the excited state. Our results show how feedback control arises from the interplay between CPT and dynamic nuclear spin polarization (DNP), and confi...

Electromagnetically induced transparency (EIT) is a phenomenon that can provide strong and robust interfacing between optical signals and quantum coherence of electronic spins. In its archetypical form, mainly explored with atomic media, it uses a (near-)homogeneous ensemble of three-level systems, in which two low-energy spin-1/2 levels are coupled to a common optically excited state. We investigate the implementation of EIT with c-axis divacancy color centers in silicon carbide. While this material has attractive properties for quantum device technologies with near-IR optics, implementing EIT is complicated by the inhomogeneous broadening of the optical transitions throughout the ensemble and the presence of multiple ground-state levels. These may lead to darkening of the ensemble upon resonant optical excitation. Here, we show that EIT can be established with high visibility also in this material platform upon careful design of the measurement geometry. Comparison of our experimental results with a model based on the Lindblad equations indicates that we can create coherences between different sets of two levels all-optically in these systems, with potential impact for RF-free quantum sensing applications. Our work provides an understanding of EIT in multi-level systems with significant inhomogeneities, and our considerations are valid for a wide array of defects in semiconductors.

We report the observation of electromagnetically induced transparency (EIT) with an ensemble of donor-bound electrons in low-doped n-GaAs. We used pure GaAs layers with Si doping at very low concentration in a strong magnetic field. EIT was implemented with the two optical transitions that exist for the three-level system that is formed by the two electron spin states and a donor-bound trion state. Our results show that EIT with n-GaAs can serve as a platform for studies of nonlocal quantum entanglement with spins in semiconductors, as well as for controlling and probing dynamical nuclear polarization with coherent electron spins.