Spins in solids are cornerstone elements of quantum spintronics. Leading contenders such as defects in diamond or individual phosphorus dopants in silicon have shown spectacular progress, but either lack established nanotechnology or an efficient spin/photon interface. Silicon carbide (SiC) combines the strength of both systems: it has a large bandgap with deep defects and benefits from mature fabrication techniques. Here, we report the characterization of photoluminescence and optical spin polarization from single silicon vacancies in SiC, and demonstrate that single spins can be addressed at room temperature. We show coherent control of a single defect spin and find long spin coherence times under ambient conditions. Our study provides evidence that SiC is a promising system for atomic-scale spintronics and quantum technology.

Scalable quantum networking requires quantum systems with quantum processing capabilities. Solid state spin systems with reliable spin–optical interfaces are a leading hardware in this regard. However, available systems suffer from large electron–phonon interaction or fast spin dephasing. Here, we demonstrate that the negatively charged silicon-vacancy centre in silicon carbide is immune to both drawbacks. Thanks to its 4 A 2 symmetry in ground and excited states, optical resonances are stable with near-Fourier-transform-limited linewidths, allowing exploitation of the spin selectivity of the optical transitions. In combination with millisecond-long spin coherence times originating from the high-purity crystal, we demonstrate high-fidelity optical initialization and coherent spin control, which we exploit to show coherent coupling to single nuclear spins with ∼1 kHz resolution. The summary of our findings makes this defect a prime candidate for realising memory-assisted quantum network applications using semiconductor-based spin-to-photon interfaces and coherently coupled nuclear spins.

Although various defect centers have displayed promise as either quantum sensors, single photon emitters or light-matter interfaces, the search for an ideal defect with multi-functional ability remains open. In this spirit, we study the dichroic silicon vacancies in silicon carbide that feature two well-distinguishable zero-phonon lines and analyze the quantum properties in their optical emission and spin control. We demonstrate that this center combines 40% optical emission into the zero-phonon lines showing the contrasting difference in optical properties with varying temperature and polarization, and a 100% increase in the fluorescence intensity upon the spin resonance, and long spin coherence time of their spin-3/2 ground states up to 0.6 ms. These results single out this defect center as a promising system for spin-based quantum technologies.

Electron and nuclear spins associated with point defects in insulators are promising systems for solid state quantum technology [1][2][3] . While the electron spin usually is used for readout and addressing, nuclear spins are exquisite quantum bits 4,5 and memory systems 3,6 . With these systems single-shot readout of nearby nuclear spins 5 as well as entanglement 4,7,8 aided by the electron spin has been shown. While the electron spin in this example is essential for readout it usually limits nuclear spin coherence 9. This has set of the quest for defects with spin-free ground states 8,10 . Here, we isolate a hitherto unidentified defect in diamond and use it at room temperature to demonstrate optical spin polarization and readout with exceptionally high contrast (up to 45%), coherent manipulation of an individual excited triplet state spin, and coherent nuclear spin manipulation using the triplet electron spin as a meta-stable ancilla. By this we demonstrate nuclear magnetic resonance and Rabi oscillations of the uncoupled nuclear spin in the spin-free electronic ground state. Our study demonstrates that nuclei coupled to single metastable electron spins are useful quantum systems with long memory times despite electronic relaxation processes.Coupled electron and nuclear spins in solids are promising candidates for quantum memories and registers and present a particular class in the emerging field of hybrid quantum systems 7,[11][12][13][14] , in which different types of qubits perform distinct functions according to their advantageous properties. In this particular case, the nuclear spin, which is weakly coupled to the environment, serves as a long-lived arXiv:1302.4608v1 [quant-ph] 19 Feb 2013 quantum memory, whereas the electron spin, which has a short coherence time, but interacts strongly with external fields, serves as a readout gate 4,7,9 . In this architecture, the permanent presence of the electron spin is a source of decoherence to the nuclear spin 8 . To avoid such electron spin induced decoherence, the electron that carries the spin should be physically removed when it is not needed and returned to the nuclear spin only when the initialization or readout gate is applied. One approach to address this problem is to frequently remove the electron, e.g. by photo-ionization with a strong laser, resulting in a motional narrowing type of decoupling 9 . Another approach -that is followed in this workis to choose an electronic system with a spin-free ground state and a meta-stable excited spin state that can be optically pumped and activated prior to the application of the readout gate 8 . Such a system implemented with a single solid state defect would enable a universal nuclear spin gate. In the following we present a suitable defect in diamond and demonstrate coherent control of a single nuclear spin in the spin-free electronic ground state. Notably, besides the NV center, this is the second known single spin defect in the solid state, whose coherent spin motion is detectable at room temperature....

Silicon carbide is a promising platform for single photon sources, quantum bits (qubits), and nanoscale sensors based on individual color centers. Toward this goal, we develop a scalable array of nanopillars incorporating single silicon vacancy centers in 4H-SiC, readily available for efficient interfacing with free-space objective and lensed-fibers. A commercially obtained substrate is irradiated with 2 MeV electron beams to create vacancies. Subsequent lithographic process forms 800 nm tall nanopillars with 400-1400 nm diameters. We obtain high collection efficiency of up to 22 kcounts/s optical saturation rates from a single silicon vacancy center while preserving the single photon emission and the optically induced electron-spin polarization properties. Our study demonstrates silicon carbide as a readily available platform for scalable quantum photonics architecture relying on single photon sources and qubits.

In current long-distance communications, classical information carried by large numbers of particles is intrinsically robust to some transmission losses but can, therefore, be eavesdropped without notice. On the other hand, quantum communications can provide provable privacy and could make use of entanglement swapping via quantum repeaters to mitigate transmission losses. To this end, considerable effort has been spent over the last few decades toward developing quantum repeaters that combine long-lived quantum memories with a source of indistinguishable single photons. Multiple candidate optical spin qubits in the solid state, including quantum dots, rare-earth ions, and color centers in diamond and silicon carbide (SiC), have been developed. In this perspective, we give a brief overview on recent advances in developing optically active spin qubits in SiC and discuss challenges in applications for quantum repeaters and possible solutions. In view of the development of different material platforms, the perspective of SiC spin qubits in scalable quantum networks is discussed.

In this paper, we study the electron spin decoherence of single defects in silicon carbide (SiC) nuclear spin bath. We find that, although the natural abundance of 29 Si (p Si = 4.7%) is about 4 times larger than that of 13 C (p C = 1.1%), the electron spin coherence time of defect centers in SiC nuclear spin bath in strong magnetic field (B > 300 Gauss) is longer than that of nitrogen-vacancy (NV) centers in 13 C nuclear spin bath in diamond. The reason for this counter-intuitive result is the suppression of heteronuclear-spin flip-flop process in finite magnetic field. Our results show that electron spin of defect centers in SiC are excellent candidates for solid state spin qubit in quantum information processing.

Point defects in solids promise precise measurements of various quantities. Especially magnetic field sensing using the spin of point defects has been of great interest recently. When optical readout of spin states is used, point defects achieve optical magnetic imaging with high spatial resolution at ambient conditions. Here, we demonstrate that genuine optical vector magnetometry can be realized using the silicon vacancy in SiC, which has an uncommon S ¼ 3=2 spin. To this end, we develop and experimentally test sensing protocols based on a reference field approach combined with multifrequency spin excitation. Our work suggests that the silicon vacancy in an industry-friendly platform, SiC, has the potential for various magnetometry applications under ambient conditions.