Resonant and phonon-assisted ultrafast coherent control of a single hBN color center

Abstract

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 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 not only be performed 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 of the coherent control signal when traveling phonon wave packets are emitted. Furthermore, we demonstrate that the quantum superposition between a phonon-assisted process and the 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.

How to Read Out the Phonon Number Statistics via Resonance Fluorescence Spectroscopy of a Single‐Photon Emitter

“…This in principle allows for the absorption of a photon of frequency ω 0 ZPL + κω, when going from the state |i⟩ G to |j 2 ⟩ X , even for κ ̸ = j 2 − i, since there is the possibility that ω 0 ZPL + κω = ω ZPL + j 2 ω − iω due to the fluctuation of ω ZPL . The variance of the fluctuations is directly connected to the pure dephasing rate γ pd [48,74] and these inelastic processes become more relevant for increasing γ pd [compare Eq. ( 21) in the limit of vanishing phonon coupling γ → 0 with Ref.…”

“…Our model consists of a two-level system (TLS), coupled to a single phonon mode, where the transition energy of the TLS is significantly larger than the phonon energy. As potential realizations of this model, one could consider a quantum dot [31,42,43,44,45,46] or a color center [32,36,47,48] (TLS) inside an acoustic or mechanical resonator [34] or coupled to a dispersion-less, e.g., optical, phonon mode [35,49,50]. The full Hamiltonian of our system, including optical driving, is given by [31,45,51,52,53]…”

“…2 [68]. Note, that the derivation of the final RF signal is independent of the particular choice of the detector model and one could in principle also choose other detector response functions than the one used here [48]. A derivation of the timeintegrated spectrum, starting from the time-dependent spectrum [68], is given in Sec.…”

Exploring the phonon-assisted excitation mechanism of luminescent centres in hexagonal boron nitride by photoluminescence excitation spectroscopy

“…We note that low temperatures are necessary to reveal differences between C 2 C N , C 2 C B , and V N C B -in particular in their emission line shape. Further methods like pump-probe schemes [33,34] and nuclear magnetic resonance (NMR) [35] are needed to identify the nature of 2 eV luminescent centres in hBN. To exclude the possibility of multiple defects responsible for luminescent centres, auto-correlation (g (2) function) and cross-correlation measurements [36] are required.…”

Combining experiments on luminescent centres in hexagonal boron nitride with the polaron model and ab initio methods towards the identification of their microscopic origin

“…[8][9][10][11][12][13][14] Whilst this method can calculate the linear absorption and emission spectra with atomistic precision, it cannot resolve coherent dynamics between electronic states of the defect transition, and is limited to unstructured electromagnetic environments. As the field strives towards coherent control of hBN luminescent centres, 15 and interfacing emitters with plasmonic 16 and photonic structures, 17 new theoretical methods are required to describe the behaviour of defect complexes.…”