Enhancing Single Photon Emission (SPE) Purity via Design of Van der Waals Heterostructures

Single photon emitters (SPEs), or quantum emitters, are key components in a wide range of nascent quantum-based technologies. A solid-state host offers many advantages for realization of a functional system, but creation and placement of SPEs are difficult to control. We describe here a novel paradigm for encoding strain into 2D materials to create and deterministically place SPEs in arbitrary locations with nanometer-scale precision [1]. We demonstrate the direct writing of SPEs in monolayer WSe₂ using an atomic force microscope nano-indentation process. This quantum calligraphy allows deterministic placement and real time design of arbitrary patterns of SPEs for facile coupling with photonic waveguides, cavities and plasmonic structures. Because monolayer WSe₂ is a direct gap semiconductor, SPE emission at a given wavelength is often intermixed with classical light resulting from conventional excitonic recombination, reducing the purity of the quantum emission as quantified by the second order autocorrelation function g⁽²⁾(t=0). We show that this undesirable classical emission, arising primarily from defect bound excitonic processes, can be significantly suppressed by electrostatic gating [2] or incorporating the WSe₂ layer in a simple van der Waals heterostructure [3]. Suppression of this classical emission allows a more accurate assessment of the quantum emission character, and results in values of g⁽²⁾ as low as 0.07 at low temperature. In addition, the SPE intensity at a given wavelength can be strongly modulated by changing the polarity of the gate bias, a feature of technological importance for practical applications. Initial results for SPEs in hBN will also be summarized, time permitting.<br/><br/>[1] M.R. Rosenberger et al, ACS Nano <b>13</b>, 904 (2019). https://doi.org/10.1021/acsnano.8b08730<br/>[2] C.E Stevens et al, ACS Nano <b>16</b>, 20956 (2022). https://doi.org/10.1021/acsnano.2c08553<br/>[3] H.-J. Chuang et al, under review (2023).<br/>*Work done in collaboration with Matthew R. Rosenberger (Notre Dame), Hsun-Jen Chuang, Sungjoon Lee and Kathleen M. McCreary (Naval Research Laboratory), and Christopher Stevens and Joshua R. Hendrickson (Air Force Research Laboratory, Wright-Patterson AFB).<br/>† This work was supported by core programs at NRL.