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arXiv:2602.18096

Pulsed coherent spectroscopy of a quantum emitter in hexagonal Boron Nitride

Jake Horder, Hugo Quard, Kenji Watanabe, Takashi Taniguchi, Nathan Coste, Igor Aharonovich

quant-phSubmitted Feb 20, 2026• Announced Feb 23, 2026• 0 citations
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Abstract

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.

Comments
12 pages, 3 figures

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cond-mat.mes-hallCross-listedarXiv:2602.05736•Feb 6, 2026
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.
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.
Abstract The coherent control of a two-level system is among the most essential challenges in modern quantum optics. Understanding its fundamental limitations is crucial, also for the realization of next generation quantum devices. The quantum coherence of a two-level system is fragile in particular, when the two levels are connected via an optical transition, which, at the same time, enables the manipulation of the system. When such quantum emitters are located in solids the coherence suffers from the interaction of the optical transition with the solid state environment, which requires the sample to be cooled to temperatures of a few Kelvin or below. Here, we use a mechanically isolated quantum emitter in hexagonal boron nitride to explore the individual mechanisms which affect the coherence of an optical transition under resonant drive. We operate the system at the threshold where the mechanical isolation collapses in order to study the onset and temperature-dependence of dephasing and independently of spectral diffusion. The insights on the underlying physical decoherence mechanisms reveal a limit in temperature until which coherent driving of the system is possible. This study enables to increase the operation temperature of hBN-based quantum devices, therefore reducing the need for cryogenic cooling.
The potential of solid-state quantum emitters for applications critically depends on several key figures of merit. One of the most important is the quantum coherence of the emitted single photons, which can be compromised by fast dephasing and spectral diffusion. In hexagonal boron nitride (hBN), blue-emitting color centers (or B centers) are seen as favorable in this regard, in the light of prior studies mainly based on resonant excitation. Yet, their coherence properties in the more accessible regime of non-resonant excitation (or photoluminescence) has not been extensively characterized. Here, we investigate the coherence and spectral diffusion of the photoluminescence from a B center in the continuous wave regime using photon correlation Fourier spectroscopy. We determine that the emission lineshape consists in a homogeneous contribution, whose linewidth increases with the laser power, and which is broadened by spectral diffusion at a timescale of 10 to 100 microseconds. At low power and short time, the emission line is only a factor ~2 above the Fourier limit, while at long times, the inhomogeneous linewidth increases up to more than a gigahertz. Our work deepens the understanding of decoherence processes of this preeminent family of quantum emitters in hBN.
Hexagonal boron nitride (hBN), a wide-bandgap 2D material, is rapidly emerging as a promising candidate for quantum optics experiments. In this work, we demonstrate, to the best of our knowledge, the first signature of Rabi oscillations, the time-domain analogue of the Mollow triplet, from a resonantly driven hBN quantum emitter. Resonant photoluminescence excitation measurements reveal that the emitter undergoes strong spectral diffusion with a time scale of 37±25  ms, resulting in a 0.6 GHz spectral diffusion broadened linewidth at the weak excitation limit. We further realize resonance fluorescence from the same emitter using a cross-polarized setup. The results shown here present an important step toward utilizing coherent optical control in 2D materials for the realization of scalable quantum information processing.
Color centers hosted in hexagonal boron nitride have emerged as a highly promising platform for single-photon emission and spin-photon technologies relevant to quantum communication and quantum networking. As a wide-bandgap van der Waals material, hBN can host optically active quantum defects across a broad spectral range. Here, we demonstrate a simple and scalable oxygen-plasma process that reproducibly creates single quantum emitters in hBN with blinking-free zero-phonon lines spanning the near-infrared from 700 up to 971 nm. These emitters combine MHz-level brightness, single-photon purity up to 99.9\%, and ultranarrow cryogenic linewidths down to 2.7~GHz under quasi-resonant excitation, placing them in a particularly attractive regime for quantum photonics. Photostability measurements further reveal resistance to photobleaching, sub-nm spectral stability over long timescales, and near-shot-noise-limited intensity fluctuations. Analysis of the phonon sidebands shows weak vibronic coupling and ZPL-dominated emission, with Debye--Waller factors approaching 50\%. Control experiments together with EDS elemental mapping support oxygen incorporation as a necessary ingredient in activating the NIR emitter population, while first-principles calculations identify ON_NN​VN_NN​ and ON_NN​VN_NN​H as the leading defect candidates. These results establish a high-performance NIR quantum-emitter platform in hBN for free-space quantum networking and future integrated quantum-photonic architectures.
Hyperbolic phonon polaritons (HPPs) in hexagonal boron nitride (hBN) confine mid-infrared light to deep-subwavelength scales and may offer a powerful route to strong light-matter interactions. Generation and control of HPPs are typically accessed using classical near-field probes, which limits experiments at the quantum level.A complementary frontier in hBN research focuses on color centers: bright, stable, atomically localized emitters that have rapidly emerged as a promising platform for solid-state quantum optics. Here we establish a key connection between these two directions by developing a cavity-QED framework in which a single hBN color center serves as a quantum source of HPPs. We quantify the emitter-HPP interaction and analyze two generation schemes. The first is spontaneous emission into the phonon sideband, which can produce single-HPP events and, in ultrathin slabs, becomes single-mode with an enhanced decay rate. The second is a stimulated Raman process that provides frequency selectivity, tunable conversion rate, and narrowband excitation. This drive launches spatially confined, ray-like HPPs that propagate over micrometer distances. We also outline a two-emitter correlation measurement that can directly test the single-polariton character of these emissions. By connecting color-center quantum optics with hyperbolic polaritonics, our approach enables quantum emitters to act as on-chip quantum sources and controls for HPPs, while HPPs provide long-range channels that couple spatially separated emitters. Together, these capabilities point to a new direction for mid-infrared photonic experiments that unite strong coupling, spectral selectivity, and spatial reach within a single material system.