Mechanical decoupling of quantum emitters in hexagonal boron nitride from low-energy phonon modes

Abstract

Quantum emitters in hexagonal boron nitride were recently reported to hold unusual narrow homogeneous linewidths of tens of megahertz within the Fourier transform limit at room temperature. This unique observation was traced back to decoupling from in-plane phonon modes. Here, we investigate the origins for the mechanical decoupling. New sample preparation improved spectral diffusion, which allowed us to reveal a gap in the electron-phonon spectral density for low phonon frequencies. This sign for mechanical decoupling persists up to room temperature and explains the observed narrow lines at 300 kelvin. We investigate the dipole emission directionality and reveal preferred photon emission through channels between the layers supporting the claim for out-of-plane distorted defect centers. Our work provides insights into the underlying physics for the persistence of Fourier transform limit lines up to room temperature and gives a guide to the community on how to identify the exotic emitters.

Spin defects in hBN as promising temperature, pressure and magnetic field quantum sensors

“…A remedy to these limitations may be provided by recently discovered defects in layered materials. One of the most prominent stackable 2D materials is hexagonal boron nitride (hBN) which hosts a large variety of atom-like defects including single-photon emitters 11 – 14 . Spin carrying defects have been theoretically predicted and experimentally confirmed in hBN 15 – 19 .…”

Review on coherent quantum emitters in hexagonal boron nitride

“…A detailed study shows that the observed PSB can be explained by coupling to bulk longitudinal optical (LO) phonons, and the asymmetric ZPL by additional longitudinal acoustic phonons (LA) as well as local modes [89]. The electronoptical-phonon sideband of the excited state can be investigated by PLE measurements, where resonant driving of the phonon resonances discloses the coupling of individual modes [19,88]. Investigations on the emitter's coupling efficiency to different phonon modes by means of PLE measurements demonstrates that the excitation mediated by the absorption of one in-plane optical phonon increases the emitter absorption probability by a factor of 10 as compared to that mediated by acoustic or out-of-plane optical phonons [88].…”

“…DOI: /10.1364/OPTICA.6.000542 a two-dimensional material could play a key role to overcome the requirements for sample cooling. The orbitals of hosted defect centers could be oriented in a mechanically isolated way such that optical transitions remain decoupled from phonon interactions of relevant phonon modes [19]. Although the exact orbital structure that enables the isolation is still unclear.…”

Grain Dependent Growth of Bright Quantum Emitters in Hexagonal Boron Nitride

“…[ 3 ] This class of materials is of a particular interest as their layered nature provides avenues for nanoscale manipulation and reliable integration with photonic devices. [ 4 ] hBN SPEs are especially promising due to the stability of the host, [ 5 ] room temperature operation, [ 6 ] outstanding optical properties, [ 7 ] and the presence of optically detected magnetic resonance signals. [ 8 ]…”

“…3,4 This class of materials is of a particular interest as their layered nature provides avenues for nanoscale manipulation and reliable integration with photonic devices. [5][6][7][8] hBN SPEs are especially promising due to the stability of the host, 9 room temperature operation, 10 outstanding optical properties, 11 and the presence of optically detected magnetic resonance signals. [12][13][14] SPEs in hBN can be engineered through chemical vapor deposition (CVD), [15][16][17] molecular beam epitaxy, 12,18 or metal organic vapor phase epitaxy.…”