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arXiv:2511.11428

Photon correlation Fourier spectroscopy of a B center in hBN

Aymeric Delteil, Stéphanie Buil, Jean-Pierre Hermier

quant-phcond-mat.otherSubmitted Nov 14, 2025• Announced Nov 17, 2025• Revised Mar 26, 2026 (v2)
v1 · Nov 14, 2025v2 · Mar 26, 2026
arXivHTMLPDF

Abstract

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.

Journal reference
Phys. Rev. B 113, 125308 (2026)
DOI
10.1103/ffp8-lgmp

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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.
We experimentally investigate a solid-state quantum emitter---a B center in hexagonal boron nitride (hBN)---that has lifetime-limited coherence at short times, and experiences inhomogeneous broadening due to spectral diffusion at longer times. By making use of power broadening in resonant laser excitation, we explore the crossover between the inhomogeneous and the homogeneous broadening regimes. With the support of numerical simulations, we show that the line shape, count rate, second-order correlations, and long-time photon statistics evolve from a regime where they are dictated by spectral diffusion to a regime where they are simply given by the homogeneous response of the emitter, yielding restored Lorentzian shape and Poissonian photon statistics. Saturation of the count rate and line broadening occur not at the onset of the Rabi oscillations, but when the power-broadened homogeneous response becomes comparable with the inhomogeneous linewidth. Moreover, we identify specific signatures in both the second-order correlations and long-time photon statistics that are well explained by a microscopic spectral diffusion model based on discrete jumps at timescales of micro- to milliseconds. Our work provides an extensive description of the photophysics of B centers under resonant excitation, and can be readily extended to a wide variety of solid-state quantum emitters.
Single-photon emitters in the solid state are subject to spectral broadening processes known as spectral diffusion and pure dephasing. Here, the authors show that a combination of quantum optics techniques, namely coherent laser drive and time-resolved photon correlations, can bring both processes to light in a single experimental protocol. This allows an extensive characterization of a large variety of solid-state quantum emitters. Their method is experimentally applied to a quantum emitter in the 2D material hexagonal boron nitride, further establishing this system as an appealing quantum photonics platform.
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.
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.
Hexagonal boron nitride (hBN) has emerged as a promising two-dimensional host for stable single-photon emission owing to its wide bandgap, high photostability, and compatibility with nanophotonic integration. We present a simulation-based study of temperature-dependent spectral dynamics and optical coherence in a mechanically decoupled quantum emitter in hBN. Employing a hybrid stochastic framework that combines Ornstein--Uhlenbeck detuning fluctuations with temperature-dependent, Gaussian-distributed discrete frequency jumps, motivated by experimentally observed spectral diffusion and blinking, we reproduce the measured evolution of inhomogeneous linewidth broadening and the progressive degradation of photon coherence across the relevant cryogenic range (5-30K). The model captures phonon-related spectral diffusion with a cubic temperature dependence and the onset of jump-like spectral instabilities at higher temperatures. By calibrating the hybrid diffusion, jump parameters to the experimentally measured full width at half maximum (FWHM) of the emission line and analyzing the second-order correlation function g(2)(τ)g^{(2)}(τ)g(2)(τ) under resonant driving, we establish a unified phenomenological description that links stochastic detuning dynamics to the decay of optical coherence in a resonantly driven emitter. Analysis of g(2)(τ)g^{(2)}(τ)g(2)(τ) under resonant driving reveals an additional dephasing rate γsd+jγ_{\mathrm{sd+j}}γsd+j​ that rises monotonically with temperature and drive strength, leading to a predicted critical crossover to overdamped dynamics at Tcrit≈25.91T_{\mathrm{crit}} \approx 25.91Tcrit​≈25.91~K. This hybrid framework provides a quantitative connection between accessible spectroscopic observables and the dominant noise mechanisms limiting coherent optical control in mechanically decoupled quantum emitters, exemplified in hBN and generalizable to similar emitters in other materials.
Mechanically isolated defect centers in hexagonal boron nitride are promising coherent quantum emitters, yet spectral instabilities persist, and their spin-related nature remains unclear. Here we investigate a single mechanically isolated quantum emitter in hBN integrated onto a coplanar waveguide. The emitter exhibits exceptionally bright resonant fluorescence with saturation count rates exceeding 10 Mc/s10\,\mathrm{Mc/s}10Mc/s. High-resolution spectroscopy reveals two closely spaced zero-phonon-line transitions originating from the same defect complex. Time-resolved spectroscopy shows that these transitions exhibit markedly different spectral diffusion dynamics, consistent with distinct donor-acceptor-pair-like recombination pathways with different sensitivities to local electrostatic fluctuations. Off-resonant blue illumination redistributes emission between the two transitions and increases the emission duty cycle without significantly modifying the dominant spectral diffusion rates at low temperature, indicating repumping from long-lived shelving states. Magnetic-field-dependent photoluminescence, optically detected magnetic resonance, and pump-probe measurements reveal millisecond-scale relaxation dynamics and magnetic-field-dependent fluorescence contrast, demonstrating spin-dependent population dynamics in the metastable shelving state. These results clarify how charge-driven spectral fluctuations and spin-dependent shelving jointly shape the optical cycling dynamics.