@article{Patel2023,
title = {Dynamical Characterization and Room-Temperature Control of an Optically Addressable Single Spin in Hexagonal Boron Nitride},
author = {Raj N. Patel and Rebecca E. K. Fishman and Tzu-Yung Huang and Jordan A. Gusdorff and David A. Fehr and David A. Hopper and S. Alex Breitweiser and Benjamin Porat and Michael E. Flatté and Lee C. Bassett},
url = {https://arxiv.org/abs/2309.05604},
year = {2023},
date = {2023-09-14},
abstract = {Hexagonal boron nitride (h-BN), a wide bandgap, two-dimensional solid-state material, hosts pure single-photon emitters that have shown signatures of optically-addressable electronic spins. Here, we report on a single emitter in h-BN exhibiting optically detected magnetic resonance at room temperature, and we propose a model for its electronic structure and optical dynamics. Using photon emission correlation spectroscopy in conjunction with time-domain optical and microwave experiments, we establish key features of the emitter's electronic structure. Specifically, we propose a model that includes a spinless optical ground and excited state, a metastable spin-1/2 configuration, and an emission modulation mechanism. Using optical and spin dynamics simulations, we constrain and quantify transition rates in the model, and we design protocols that optimize the signal-to-noise ratio for spin readout. This constitutes a necessary step toward quantum control of spin states in h-BN.},
keywords = {2-dimensional systems, First-principles calculations, photon emission correlation spectroscopy, photon statistics, point defects},
pubstate = {forthcoming},
tppubtype = {article}
}

@article{Patel2022,
title = {Probing the Optical Dynamics of Quantum Emitters in Hexagonal Boron Nitride},
author = {Raj N. Patel and David A. Hopper and Jordan A. Gusdorff and Mark E. Turiansky and Tzu-Yung Huang and Rebecca E. K. Fishman and Benjamin Porat and Chris G. Van de Walle and Lee C. Bassett},
url = {https://journals.aps.org/prxquantum/abstract/10.1103/PRXQuantum.3.030331},
doi = {10.1103/PRXQuantum.3.030331},
year = {2022},
date = {2022-09-01},
journal = {PRX Quantum},
volume = {3},
number = {3},
pages = {030331},
abstract = {Hexagonal boron nitride is a van der Waals material that hosts visible-wavelength quantum emitters at room temperature. However, experimental identification of the quantum emitters’ electronic structure is lacking, and key details of their charge and spin properties remain unknown. Here, we probe the optical dynamics of quantum emitters in hexagonal boron nitride using photon emission correlation spectroscopy. Several quantum emitters exhibit ideal single-photon emission with noise-limited photon antibunching, g(2)(0)=0. The photoluminescence emission lineshapes are consistent with individual vibronic transitions. However, polarization-resolved excitation and emission suggests the role of multiple optical transitions, and photon emission correlation spectroscopy reveals complicated optical dynamics associated with excitation and relaxation through multiple electronic excited states. We compare the experimental results to quantitative optical dynamics simulations, develop electronic structure models that are consistent with the observations, and discuss the results in the context of ab initio theoretical calculations.},
keywords = {2-dimensional systems, color centers, photon emission correlation spectroscopy, photon statistics, point defects, quantum optics, single-photon sources},
pubstate = {published},
tppubtype = {article}
}

@article{Turiansky2019,
title = {Dangling bonds in hexagonal boron nitride as single-photon emitters},
author = {M E Turiansky and A Alkauskas and L C Bassett and Van C G de Walle},
url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.123.127401},
doi = {10.1103},
issn = {1079-7114},
year = {2019},
date = {2019-09-16},
journal = {Physical Review Letters},
volume = {123},
number = {12},
pages = {127401},
abstract = {Hexagonal boron nitride has been found to host color centers that exhibit single-photon emission, but the microscopic origin of these emitters is unknown. We propose boron dangling bonds as the likely source of the observed single-photon emission around 2 eV. An optical transition where an electron is excited from a doubly occupied boron dangling bond to a localized B pz state gives rise to a zero-phonon line of 2.06 eV and emission with a Huang-Rhys factor of 2.3. This transition is linearly polarized with the absorptive and emissive dipole aligned. Because of the energetic position of the states within the band gap, indirect excitation through the conduction band will occur for sufficiently large excitation energies, leading to the misalignment of the absorptive and emissive dipoles seen in experiment. Our calculations predict a singlet ground state and the existence of a metastable triplet state, in agreement with experiment.},
keywords = {2-dimensional systems, Condensed Matter, First-principles calculations, Optical absorption spectroscopy, Optical microcavities, optical sources, point defects, Quantum wells, Semiconductor compounds},
pubstate = {published},
tppubtype = {article}
}

@article{Exarhos2019,
title = {Magnetic-field-dependent quantum emission in hexagonal boron nitride at room temperature},
author = {A L Exarhos and D A Hopper and R N Patel and M W Doherty and L C Bassett},
url = {https://www.nature.com/articles/s41467-018-08185-8
https://www.nature.com/collections/rcdhyvxytb
https://spectrum.ieee.org/tech-talk/semiconductors/nanotechnology/qubits-and-nanosensors-in-a-2d-material
https://medium.com/penn-engineering/penn-engineers-develop-room-temperature-two-dimensional-platform-for-quantum-technology-cae3a5c0d8f9},
year = {2019},
date = {2019-01-15},
journal = {Nature Communications},
volume = {10},
number = {222},
abstract = {​Selected as Editor's Highlight (linked)
Press coverage in IEEE Spectrum and Penn Medium (linked)

Optically addressable spins associated with defects in wide-bandgap semiconductors are versatile platforms for quantum information processing and nanoscale sensing, where spin-dependent inter-system crossing transitions facilitate optical spin initialization and readout. Recently, the van der Waals material hexagonal boron nitride (h-BN) has emerged as a robust host for quantum emitters, promising efficient photon extraction and atom-scale engineering, but observations of spin-related effects have remained thus far elusive. Here, we report room-temperature observations of strongly anisotropic photoluminescence patterns as a function of applied magnetic field for select quantum emitters in h-BN. Field-dependent variations in the steady-state photoluminescence and photon emission statistics are consistent with an electronic model featuring a spin-dependent inter-system crossing between triplet and singlet manifolds, indicating that optically-addressable spin defects are present in h-BN.},
keywords = {2-dimensional systems, point defects},
pubstate = {published},
tppubtype = {article}
}

@article{Exarhos2017,
title = {Optical signatures of quantum emitters in suspended hexagonal boron nitride},
author = {A L Exarhos and D A Hopper and R R Grote and A Alkauskas and L C Bassett},
url = {https://pubs.acs.org/doi/abs/10.1021/acsnano.7b00665},
year = {2017},
date = {2017-03-07},
journal = {ACS Nano},
volume = {11},
pages = {3328-3336},
abstract = {Hexagonal boron nitride (h-BN) is rapidly emerging as an attractive material for solid-state quantum engineering. Analogously to three-dimensional wide-band-gap semiconductors such as diamond, h-BN hosts isolated defects exhibiting visible fluorescence at room temperature, and the ability to position such quantum emitters within a two-dimensional material promises breakthrough advances in quantum sensing, photonics, and other quantum technologies. Critical to such applications is an understanding of the physics underlying h-BN’s quantum emission. We report the creation and characterization of visible single-photon sources in suspended, single-crystal, h-BN films. With substrate interactions eliminated, we study the spectral, temporal, and spatial characteristics of the defects’ optical emission. Theoretical analysis of the defects’ spectra reveals similarities in vibronic coupling to h-BN phonon modes despite widely varying fluorescence wavelengths, and a statistical analysis of the polarized emission from many emitters throughout the same single-crystal flake uncovers a weak correlation between the optical dipole orientations of some defects and h-BN’s primitive crystallographic axes, despite a clear misalignment for other dipoles. These measurements constrain possible defect models and, moreover, suggest that several classes of emitters can exist simultaneously throughout free-standing h-BN, whether they be different defects, different charge states of the same defect, or the result of strong local perturbations.},
keywords = {2-dimensional systems, Condensed Matter, optical sources, point defects},
pubstate = {published},
tppubtype = {article}
}