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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Coherent State Manipulation of Single Hexagonal Boron Nitride Quantum Emitters

Johann A. Preuß, Daniel Groll, Robert Schmidt, Thilo Hahn, Paweł Machnikowski, T. Kühn, Rudolf Bratschitsch, Daniel Wigger, Steffen Michaelis de Vasconcellos

Published Jun 26, 2023• 0 citations
Publisher

Abstract

Single-photon sources are crucial components for building quantum networks and communications, but their optical coherent control remains a significant challenge in the development of quantum technologies. Recently, single-photon sources in atomically thin 2D materials such as transition metal dichalcogenides and van der Waals materials have emerged as promising solid-state quantum light emitters [1]. Hexagonal boron nitride (hBN) is a 2D insulator, which hosts optically active states in its band gap that efficiently emit single photons even at room temperature. The wide range of emission wavelengths, narrow emission lines, and convenient tunability of these hBN emitters make them particularly interesting for quantum sensing and wavelength division multiplexed quantum communications. They can also be found in commercially available nanocrystals, making them ideal for creating large arrays of single-photon emitters [2] and efficient coupling to photonic structures, such as 3D-printed microlenses [3].

DOI
10.1109/cleo/europe-eqec57999.2023.10232085

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Single-photon sources are crucial components for building quantum networks and communications, but their optical coherent control remains a significant challenge in the development of quantum technologies. Recently, single-photon sources in atomically thin 2D materials such as transition metal dichalcogenides and van der Waals materials have emerged as promising solid-state quantum light emitters [1]. Hexagonal boron nitride (hBN) is a 2D insulator, which hosts optically active states in its band gap that efficiently emit single photons even at room temperature. The wide range of emission wavelengths, narrow emission lines, and convenient tunability of these hBN emitters make them particularly interesting for quantum sensing and wavelength division multiplexed quantum communications. They can also be found in commercially available nanocrystals, making them ideal for creating large arrays of single-photon emitters [2] and efficient coupling to photonic structures, such as 3D-printed microlenses [3].
Single-photon emitters in solid-state systems are important building blocks for scalable quantum technologies. Recently, quantum light emitters have been discovered in the wide-gap van der Waals insulator hexagonal boron nitride (hBN). These color centers have attracted considerable attention due to their quantum performance at elevated temperatures and wide range of transition energies. Here, we demonstrate coherent state manipulation of a single hBN color center with ultrafast laser pulses and investigate in our joint experiment–theory study the coupling between the electronic system and phonons. We demonstrate that coherent control can be performed not only resonantly on the optical transition giving access to the decoherence but also phonon-assisted, which reveals the internal phonon quantum dynamics. In the case of optical phonons, we measure their decoherence, stemming in part from their anharmonic decay. Dephasing induced by the creation of acoustic phonons manifests as a rapid decrease in the coherent control signal when traveling phonon wave packets are emitted. Furthermore, we demonstrate that the quantum superposition between a phonon-assisted process and resonant excitation causes ultrafast oscillations of the coherent control signal. Our results pave the way for ultrafast phonon quantum state control on the nanoscale and open up a new promising perspective for hybrid quantum technologies.
Sources of pure and indistinguishable single-photons are critical for near-future optical quantum technologies. Recently, color centers hosted by two-dimensional hexagonal boron nitride (hBN) have emerged as a promising platform for high luminosity room temperature single-photon sources. Despite the brightness of the emitters, the spectrum is rather broad and the single-photon purity is not sufficient for practical quantum information processing. Here, we report integration of such a quantum emitter hosted by hBN into a tunable optical microcavity. A small mode volume of the order of λ 3 allows us to Purcell enhance the fluorescence, with the observed excited state lifetime shortening. The cavity significantly narrows the spectrum and improves the single-photon purity by suppression of off-resonant noise. The complete device, including all optics, driving electronics, and control units, is compact and integrated in a small volume of 10 × 10 × 10 cm 3, allowing for portable usage in mobile applications.
Collective light emission from many-body quantum systems is a cornerstone of quantum optics, yet its implementation in solid-state platforms operating under ambient conditions remains highly challenging. Large-bandgap van der Waals materials such as hexagonal boron nitride (hBN) host stable room-temperature single-photon emitters with narrow linewidths across a broad spectral range. However, cooperative radiative effects in this system have not been previously explored. Here we demonstrate collective emission from quantum-emitter ensembles in hBN layers when the emitters are nearly indistinguishable and positioned within a sub-wavelength proximity. Using confocal microscopy and a Hanbury Brown-Twiss (HBT) configuration, we identify both isolated emitters and ensembles activated by localized electron-beam irradiation. Time-resolved photoluminescence measurements reveal a superlinear intensity enhancement and a pronounced acceleration of the radiative decay in tightly confined ensembles, with lifetimes approaching the temporal resolution of our experimental system (about 500 ps), compared to approximately 1.85 ns for single emitters or large, spatially extended ensembles. Complementary second-order photon-correlation measurements exhibit sub-Poissonian antidip consistent with emission from a few indistinguishable emitters. The simultaneous observation of lifetime shortening and enhanced emission provides direct evidence of cooperative emission at room temperature, achieved without optical cavities or cryogenic cooling. These results establish optically active defect ensembles in hBN as a scalable solid-state platform for engineered collective quantum optics in two-dimensional materials, opening avenues toward ultrabright superradiant light sources and nonclassical photonic states for quantum technologies.
Atom-like defects in hexagonal boron nitride (hBN) provide room-temperature single-photon emission and coherent spin states, making them attractive for quantum-computing and -sensing applications. However, their random spatial and spectral characteristics hamper deterministic coupling with nano-optical cavities, limiting their use as bright single-photon sources and sensitive quantum sensors. Here, we present tip-enhanced quantum-sensing spectroscopy of single-photon emitters in hBN. Through precise spatial positioning of individual emitters within tip-cavities with different plasmon resonances, we adaptively control the enhancement rates of both excitation and emission, as well as the single-photon purity. In this way, optimal selection of their relative contributions can effectively reconfigure solid-state single-photon sources, with simultaneous nano-spectroscopic space- and time-resolved analyses. Furthermore, we demonstrate tip-enhanced quantum-sensing with single spin defects through optically detected magnetic resonance (ODMR) experiments in tip-coupled hBN nanoflakes. Our approach provides a unique pathway toward highly-sensitive and deterministic quantum-sensing with room-temperature single-photon emitters.
Optically active defects in hexagonal boron nitride (hBN) have become amongst the most attractive single-photon emitters in the solid state, owing to their high-quality photophysical properties, combined with the unlimited possibilities of integration offered by the host van der Waals material. In particular, the B centres, with their narrow linewidth, low wavelength spread and controllable positioning, have raised a particular interest for integrated quantum photonics. However, to date, either their excitation or their detection has been performed non-resonantly due to the difficulty of rejecting the backreflected laser light at the same wavelength, thereby preventing to take full benefit from their high coherence in quantum protocols. Here, we make use of narrow-linewidth emitters integrated in a hybrid metal-dielectric structure to implement cross-polarisation laser rejection. This allows us to observe resonantly scattered photons, with associated experimental signatures of optical coherence in both continuous-wave (cw) and pulsed regimes, respectively the Mollow triplet and Hong-Ou-Mandel interference from zero-phonon-line emission. The two-photon interference visibilities of 0.93−0.21+0.070.9{3}_{-0.21}^{+0.07}0.93−0.21+0.07​ and 0.92−0.26+0.080.9{2}_{-0.26}^{+0.08}0.92−0.26+0.08​ we measured for two emitters demonstrate the potential of B centres in hBN for applications to integrated quantum information. Single-photon sources in van der Waals materials offer new perspectives of integration for quantum information applications. Here, the authors implement resonance fluorescence of a single colour centre in hBN, a quantum optics regime that simultaneously allows for emitter coherent control and generation of indistinguishable photons.
Defects in solid-state systems constitute a promising platform for the realization of deterministic quantum emitters. Among many candidate materials and emitters, point defects in hexagonal Boron Nitride (hBN) have recently emerged as particularly promising. In this work, we probe the coherence of an individual B center with a zero phonon line at 436 nm, under pulsed resonant excitation. We observe power-dependent Rabi oscillations up to 5π, demonstrating optical coherent control of the transition. We achieve an excellent single photon purity of 93% at π-pulse. Furthermore, we probe the coherence of the two-level system using Ramsey interferometry, revealing an inhomogeneous coherence time of T_2*=0.60 ns. These results establish B centers in hBN as viable candidates for triggered, coherent quantum emitters and represent an important step towards their integration into quantum photonic platforms.