Resonance Fluorescence from Waveguide-Coupled, Strain-Localized, Two-Dimensional Quantum Emitters

Abstract

Efficient on-chip integration of single-photon emitters imposes a major bottleneck for applications of photonic integrated circuits in quantum technologies. Resonantly excited solid-state emitters are emerging as near-optimal quantum light sources, if not for the lack of scalability of current devices. Current integration approaches rely on cost-inefficient individual emitter placement in photonic integrated circuits, rendering applications impossible. A promising scalable platform is based on two-dimensional (2D) semiconductors. However, resonant excitation and single-photon emission of waveguide-coupled 2D emitters have proven to be elusive. Here, we show a scalable approach using a silicon nitride photonic waveguide to simultaneously strain-localize single-photon emitters from a tungsten diselenide (WSe₂) monolayer and to couple them into a waveguide mode. We demonstrate the guiding of single photons in the photonic circuit by measuring second-order autocorrelation of g⁽²⁾(0) = 0.150 ± 0.093 and perform on-chip resonant excitation, yielding a g⁽²⁾(0) = 0.377 ± 0.081. Our results are an important step to enable coherent control of quantum states and multiplexing of high-quality single photons in a scalable photonic quantum circuit.

Figure 1

(a) Artistic illustration of the coupled WSe₂ monolayer (1L) single-photon emitter and the Si₃N₄ waveguide. (b) Finite element method eigenmode simulation of the fundamental quasi-TE and (c) quasi-TM waveguide modes at 770 nm wavelength. (d) Microscope image of the Si₃N₄ waveguide with (e) zoom-in of the WSe₂ flake. The monolayer is marked in red (1L). (f) Photoluminescence with defocused excitation shows strain-localized emitters along the waveguide edges. Emitter 1 is marked with a red circle.

Figure 2

(a) Modular setup consisting of a red laser excitation, a confocal detection path (detection top), and a second detection path from the waveguide facet through a lensed fiber (detection WG). In the fiber hub, the signals can be routed to the spectrometer or the Hanbury Brown and Twiss setup (HBT), which includes a free-space filtering by two tunable bandpass filters (TBP). DUT, device under test; BS, beam splitter; LP, long-pass filter; L, lens; BD, beam dump; SSPD, superconducting single-photon detector. (b) Spectra from emitter 1 at 770 nm taken from top and (c) through the waveguide from output 1 and (d) from output 2.

Figure 3

(a) Power series for emitter 1 with a repetition rate of 80 MHz. For all correlation measurements, the emitter was excited with 1.4 μW, that is, at the start of the saturation plateau. (b) Second-order autocorrelation measurement from the top, (c) with a lower repetition rate (10 MHz), and (d) through the waveguide output 1.

Figure 4

(a) Artistic illustration of the coupled WSe₂ monolayer single-photon emitter on the Si₃N₄ waveguide. The 2D emitter is excited with a continuous-wave (cw) laser coupled to the waveguide. The emitted signal is detected from the top through a microscope objective. (b) Resonance fluorescence (RF) spectrum of emitter 2 and residual laser in a semilogarithmic plot. (c) Second-order autocorrelation measurement under resonant excitation through the waveguide and detection from the top showing clear single-photon emission. Inset: Same measurement for a longer time window showing bunching originating from spectral diffusion.