Solid-state single photon source with Fourier transform limited lines at room temperature

Rapid Communication

Solid-state single photon source with Fourier transform limited lines at room temperature

A. Dietrich, M. W. Doherty, I. Aharonovich, and A. Kubanek

Phys. Rev. B 101, 081401(R) – Published 5 February 2020

Abstract

Solid-state single photon sources with Fourier transform (FT) limited lines are among the most crucial constituents of photonic quantum technologies and have been accordingly the focus of intensive research over the last several decades. However, so far, solid-state systems have only exhibited FT limited lines at cryogenic temperatures due to strong interactions with the thermal bath of lattice phonons. In this Rapid Communication, we report a solid-state source that exhibits FT limited lines measured in photoluminescence excitation (sub-100-MHz linewidths) from 3 to 300 K. The studied source is a color center in the two-dimensional hexagonal boron nitride and we propose that the center's decoupling from phonons is a fundamental consequence of the material's low dimensionality. While the center's luminescence lines exhibit spectral diffusion, we identify the likely source of the diffusion and propose to mitigate it via dynamic spectral tuning. The discovery of FT limited lines at room temperature, which once the spectral diffusion is controlled, will also yield FT limited emission. Our work motivates a significant advance towards room-temperature photonic quantum technologies and a different research direction in the remarkable fundamental properties of two-dimensional materials.

Received 13 June 2019
Accepted 27 January 2020

DOI:https://doi.org/10.1103/PhysRevB.101.081401

Physics Subject Headings (PhySH)

Color centers Impurities Quantum optics Quantum optics with artificial atoms Single photon sources

Atomic, Molecular & Optical

Authors & Affiliations

A. Dietrich¹, M. W. Doherty², I. Aharonovich³, and A. Kubanek ^1,4,*

¹Institute for Quantum Optics, Ulm University, D-89081 Ulm, Germany
²Laser Physics Centre, Research School of Physics and Engineering, Australian National University, Australian Capital Territory 2601, Australia
³School of Mathematical and Physical Sciences, Faculty of Science, University of Technology Sydney, Ultimo, New South Wales 2007, Australia
⁴Center for Integrated Quantum Science and Technology (IQst), Ulm University, D-89081 Ulm, Germany

^*Corresponding author: alexander.kubanek@uni-ulm.de

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Issue

Vol. 101, Iss. 8 — 15 February 2020

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Images

Figure 1
(a) Atomic defect in hexagonal boron nitride that acts as a single photon emitter. The electronic wave function of the defect center embedded in the hexagonal structure of hexagonal boron nitride is illustrated as a ball-and-stick model. (b) The PL spectrum of the emitter. Inset: The PSB features that were used for the detection of the PLE signal via their selection using a 680-nm long-pass filter. (c) The polarization dependence of the dipole orientation shows an offset of $12^{\circ}$ when the polarizer is placed in the off-resonant excitation path or in the emission path (for details, see Ref. [21]). (d) The homogeneous linewidth in PLE over temperature. The linewidth stays close to the FT limit of $60.1 \pm 3.4$ MHz in a temperature range from 3 K up to room temperature. The recorded PLE spectra with the Lorentzian fits are depicted for 3, 100, 200, and 300 K.
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Figure 2
(a) Fluorescence time trace under resonant excitation (upper panel) and power dependency of the inhomogeneous linewidth (lower panel) at 3 K. (b) Fluorescence time trace under resonant excitation (upper panel) and power dependency of the inhomogeneous linewidth (lower panel) at 300 K. A threshold (depicted in the fluorescence traces) is defined to distinguish between the signal and noise and to estimate the amount of spectral diffusion that is the origin for inhomogeneous line broadening (see Supplemental Material [23] for details). The inhomogeneous linewidth shows a linear power dependency with a linewidth as broad as 773 GHz at 3 K and 300 nW excitation power and 1.4 THz at 300 K. (c) Temperature dependence of the PL ZPL energy. (d) Temperature dependence of the PL ZPL linewidth. Solid lines in (c) and (d) are fits of the function $a + b T^{3}$ , where $a = 471.6973 (3)$ THz and $b = 2.4 (1) \times 10^{- 9} THz / T^{3}$ for the shift and $a = 156 (6)$ GHz and $b = 9.4 (2) \times 10^{- 5} GHz / T^{3}$ for the width.
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Figure 3
(a) Configuration coordinate diagram depicting the double-well vibrational potential energy of the ground and excited electronic states as a function of the defect's out-of-plane displacement. (b) A similar diagram for the case where reflection symmetry has been lowered such that the defect statically distorts out of plane. Processes of optical ZPL emission and resonant and far off-resonance excitation are depicted, including indicative transition dipole moments. (c) and (d) Sketches of the spectral diffusion sources of defects within the hBN changing their polarization upon optical excitation and polar molecules hopping between adsorbate sites upon optical excitation.
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