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Ref Arxiv: 1510.06565
DOI: 10.1016/j.crhy.2016.07.006
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DOI: 10.1103/PhysRevB.94.064413
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37 Citations
Résumé:

The Dzyaloshinskii-Moriya Interaction (DMI) has recently attracted considerable interest owing to its fundamental role in the stabilization of chiral spin textures in ultrathin ferromagnets, which are interesting candidates for future spintronic technologies. Here we employ a scanning nano-magnetometer based on a single nitrogen-vacancy (NV) defect in diamond to locally probe the strength of the interfacial DMI in CoFeB$|$MgO ultrathin films grown on different heavy metal underlayers X=Ta,TaN, and W. By measuring the stray field emanating from DWs in micron-long wires of such materials, we observe deviations from the Bloch profile for TaN and W underlayers that are consistent with a positive DMI value favoring right-handed chiral spin structures. Moreover, our measurements suggest that the DMI constant might vary locally within a single sample, illustrating the importance of local probes for the study of magnetic order at the nanoscale.

Ref HAL: hal-01383967_v1
DOI: 10.1103/PhysRevB.94.121405
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67 Citations
Résumé:

Among a variety of layered materials used as building blocks in van der Waals heterostructures, hexagonal boron nitride (hBN) appears as an ideal platform for hosting optically-active defects owing to its large bandgap ($\sim 6$~eV). Here we study the optical response of a high-purity hBN crystal under green laser illumination. By means of photon correlation measurements, we identify individual defects emitting a highly photostable fluorescence under ambient conditions. A detailed analysis of the photophysical properties reveals a high quantum efficiency of the radiative transition, leading to a single photon source with very high brightness ($\sim 4\times 10^6$ counts.s$^{-1}$). These results illustrate how the wide range of applications offered by hBN could be further extended to photonic-based quantum information science and metrology.

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Ref Arxiv: 1508.06914
DOI: 10.1103/PhysRevLett.116.043603
WoS: 000369337200009
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12 Citations
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Coherent control of quantum systems has far-reaching implications in quantum engineering. In this context, coherent population trapping (CPT) involving dark resonances 1,2 has played a prominent role, leading to a wealth of major applications including laser cooling of atoms 3 and molecules 4 , optical magnetometry 5 , light storage 6–8 and highly precise atomic clocks 9. Extending CPT methods to individual solid-state quantum systems has been only achieved in cryogenic environments for electron spin impurities 10–17 and superconducting circuits 18–21. Here, we demonstrate efficient CPT of a single nuclear spin in a room temperature solid. To this end, we make use of a three-level system with a Λ-configuration in the microwave domain, which consists of nuclear spin states addressed through their hyperfine coupling to the electron spin of a single nitrogen-vacancy defect in diamond. Dark state pumping requires a relaxation mechanism which, in atomic systems, is simply provided by spontaneous emission. In this work, the relaxation process is externally controlled through incoherent optical pumping and separated in time from consecutive coherent microwave excitations of the nuclear spin Λ-system. Such a pumping scheme with controlled relaxation allows us (i) to monitor the sequential accumulation of population into the dark state and (ii) to reach a new regime of CPT dynamics for which periodic arrays of dark resonances can be observed, owing to multiple constructive interferences. This work offers new prospects for quantum state preparation, information storage in hybrid quantum systems 22,23 and metrology. Nuclear spins in solids have attracted considerable interest over the last years owing to their high level of isolation from the environment, leading to very long coherence times 24–26. The detection and control of individual nuclear spins is usually achieved by exploiting their hy-perfine coupling to an ancillary electronic spin. This can be performed by using a nitrogen-vacancy (NV) defect in diamond 27,28 whose spin triplet ground state (S = 1) can be optically initialized, coherently manipulated with microwave fields and read-out by optical means through its spin-dependent photoluminescence (PL) intensity 29. Experiments making use of the hyperfine coupling between the NV defect and nearby long-lived nuclear spins are now reaching a level of control allowing to realize elaborate quantum information protocols 30–32. Here, we make use of electron spin transitions of a single NV defect to achieve coherent control of a single nuclear spin through CPT under ambient conditions. The spin system considered in this study is depicted in Fig. 1a. The electronic spin of a single NV defect is coupled by hyperfine interaction with a nearby 13 C nuclear spin (I = 1/2). In the m s = 0 (|0 e) electron spin mani-fold, the nuclear spin eigenstates are denoted |↑ and |↓ , corresponding to the nuclear spin projections along the NV defect quantization axis. In the m s = −1 (|−1 e) electron spin manifold, efficient nuclear spin mixing can be obtained by exploiting the anisotropic component of the hyperfine interaction in combination with a magnetic field applied along the NV defect axis 34. The nuclear spin

Ref HAL: hal-02493648_v1
DOI: 10.1140/epjd/e2015-60080-1
WoS: 000357045800001
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Ref HAL: hal-01116693_v1
Ref Arxiv: 1502.07071
DOI: 10.1038/ncomms9603
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31 Citations
Résumé:

Reminiscent of the bound character of a qubit's dynamics confined on the Bloch sphere, the observation of a Mollow triplet in the resonantly driven qubit fluorescence spectrum represents one of the founding signatures of Quantum Electrodynamics. Here we report on its observation in a hybrid spin-nanomechanical system, where a Nitro-gen Vacancy spin qubit is magnetically coupled to the vibrations of a Silicon Carbide nanowire. A resonant microwave field turns the originally parametric hybrid interac-tion into a resonant process, where acoustic phonons are now able to induce transitions between the dressed qubit states, leading to synchronized spin-oscillator dynamics. We further explore the vectorial character of the hybrid coupling to the bidimensional de-formations of the nanowire. The demonstrated microwave assisted synchronization of the spin-oscillator dynamics opens novel perspectives for the exploration of spin-dependent forces, the key-ingredient for quantum state transfer.

Ref HAL: hal-01271919_v1
Ref Arxiv: 1511.08175
DOI: 10.1103/PhysRevB.93.024305
WoS: 000369218500005
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48 Citations
Résumé:

We analyze the impact of electric field and magnetic field fluctuations in the decoherence of the electronic spin associated with a single nitrogen-vacancy (NV) defect in diamond by engineering spin eigenstates protected either against magnetic noise or against electric noise. The competition between these noise sources is analyzed quantitatively by changing their relative strength through modifications of the environment. This study provides significant insights into the decoherence of the NV electronic spin, which is valuable for quantum metrology and sensing applications.

Commentaires: 8 pages, 4 figures, including supplementary informations. Réf Journal: Phys. Rev. B 93, 024305 (2016)