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The layered chalcogenide Ta2NiSe5 has been proposed to host an excitonic condensate in its ground state, a phase that could offer a unique platform to study and manipulate many-body states at room temperature. However, identifying the dominant microscopic contribution to the observed spontaneous symmetry breaking remains challenging, perpetuating the debate over the ground state properties. Here, using broadband ultrafast spectroscopy we investigate the out-of-equilibrium dynamics of Ta2NiSe5 and demonstrate that the transient reflectivity in the near-infrared range is connected to the system's low-energy physics. We track the status of the ordered phase using this optical signature, establishing that high-fluence photoexcitations can suppress this order. From the sub-50 fs quenching timescale and the behaviour of the photoinduced coherent phonon modes, we conclude that electronic correlations provide a decisive contribution to the excitonic order formation. Our results pave the way towards the ultrafast control of an exciton condensate at room temperature. The dominant mechanism of the excitonic insulator transition in Ta2NiSe5 and the nature of its high-temperature phase are debated. The authors report transient reflectivity measurements indicating a significant electronic contribution to the transition and a gapped state of preformed excitons at high temperatures. [ABSTRACT FROM AUTHOR]

The elimination of defects from SiC has facilitated its move to the forefront of the optoelectronics and power-electronics industries. Nonetheless, because certain SiC defects have electronic states with sharp optical and spin transitions, they are increasingly recognized as a platform for quantum information and nanoscale sensing. Here, we show that individual electron spins in high-purity monocrystalline 4H-SiC can be isolated and coherently controlled. Bound to neutral divacancy defects, these states exhibit exceptionally long ensemble Hahn-echo spin coherence times, exceeding 1 ms. Coherent control of single spins in a material amenable to advanced growth and microfabrication techniques is an exciting route towards wafer-scale quantum technologies. [ABSTRACT FROM AUTHOR]

The negatively charged nitrogen vacancy center (NV) in diamond has generated significant interest as a platform for quantum information processing and sensing in the solid state. For most applications, high quality optical cavities are required to enhance the NV zero-phonon line (ZPL) emission. An outstanding challenge in maximizing the degree of NV-cavity coupling is the deterministic placement of NVs within the cavity. Here, we report photonic crystal nanobeam cavities coupled to NVs incorporated by a delta-doping technique that allows nanometer-scale vertical positioning of the emitters. We demonstrate cavities with Q up to ~24000 and mode volume V ~ 0.47(λ/n)³ as well as resonant enhancement of the ZPL of an NV ensemble with Purcell factor of ~20. Our fabrication technique provides a first step towards deterministic NV-cavity coupling using spatial control of the emitters. [ABSTRACT FROM AUTHOR]

The negatively charged nitrogen vacancy center (NV) in diamond has generated significant interest as a platform for quantum information processing and sensing in the solid state. For most applications, high quality optical cavities are required to enhance the NV zero-phonon line (ZPL) emission. An outstanding challenge in maximizing the degree of NV-cavity coupling is the deterministic placement of NVs within the cavity. Here, we report photonic crystal nanobeam cavities coupled to NVs incorporated by a delta-doping technique that allows nanometer-scale vertical positioning of the emitters. We demonstrate cavities with Q up to ~24000 and mode volume V ~ 0.47(λ/n)³ as well as resonant enhancement of the ZPL of an NV ensemble with Purcell factor of ~20. Our fabrication technique provides a first step towards deterministic NV-cavity coupling using spatial control of the emitters. [ABSTRACT FROM AUTHOR]

Hybrid architectures that combine nitrogen-vacancy centers in diamond with other materials and physical systems have been proposed to enhance the nitrogen-vacancy center's capabilities in many quantum sensing and information applications. In particular, spin waves in ferromagnetic materials are a promising candidate to implement these platforms due to their strong magnetic fields, which could be used to efficiently interact with the nitrogen-vacancy centers. Here, we develop an yttrium iron garnet-nanodiamond hybrid architecture constructed with the help of directed assembly and transfer printing techniques. Operating at ambient conditions, we demonstrate that surface confined spin waves excited in the ferromagnet can strongly amplify the interactions between a microwave source and the nitrogen-vacancy centers by enhancing the local microwave magnetic field by several orders of magnitude. Crucially, we show the existence of a regime in which coherent interactions between spin waves and nitrogen-vacancy centers dominate over incoherent mechanisms associated with the broadband magnetic field noise generated by the ferromagnet. These accomplishments enable the spin wave mediated coherent control of spin qubits over distances larger than 200 μm, and allow low power operations for future spintronic technologies. Quantum interactions going hybrid: ferromagnetically mediated coupling Hybrid architectures that combine materials and devices with widely different properties promise to be at the forefront of scalable quantum systems by unlocking access to more than the simple sum of their parts. A team led by David Awschalom at the University of Chicago has now revealed the possibility of using collective spin oscillations in a ferromagnet to mediate long-range, coherent interactions between a microwave source and spin qubits confined in diamond nanoparticles. The strong surface confinement of the ferromagnet excitations and their slow decay result in an effective amplification of the source field over hundreds of micrometers at ambient conditions. This effect can extend the capabilities of solid state qubits for quantum information and nanoscale quantum sensing applications. [ABSTRACT FROM AUTHOR]