Purcell enhancement and polarization control of single-photon emitters in monolayer WSe2 using dielectric nanoantennas

Abstract

Two-dimensional (2D) materials have shown great promise as hosts for high-purity deterministic single-photon sources. In the last few years, the underlying physics of single photon emission in 2D materials have been uncovered, and their optical properties have been improved to meet criteria for a variety of quantum technologies and applications. In this work, we take advantage of the unique characteristics of dielectric nanoantennas in manipulating the electromagnetic response on a sub-wavelength scale to localize and control defect-based single-photon emitters (SPEs) in 2D layered materials. We show that dielectric nanoantennas are capable of inducing high Purcell enhancement >20 and therefore brighter single-photon emission, which is characterized by a reduction of the emitters' radiative lifetimes and enhancement of their brightness by more than an order of magnitude. We demonstrate that the sub-wavelength-scale dielectric nanoantennas can be designed to also impose a predetermined strain profile that determines the confinement potential of the SPE, leading to robust control over the optical polarization with up to 94% extinction ratio. The combination of large Purcell enhancement, polarization orientation, and site control through strain engineering demonstrates the advantages and unique capabilities of dielectric nanoantennas for enhancing the quantum optical properties of 2D SPEs for quantum information technologies.

Keywords: Purcell enhancement; dielectric nanoantennas; photonic integrated circuits; quantum emitters; single photon sources; two-dimensional materials.

Figure 1:

Engineering single-photon emission using dielectric nanoantennas. A schematic of a 2D flake on top of a (a) dimer and (b) monomer nanoantenna. The scattered electric field normalized to the incident wave’s amplitude ${\left(|E_{\text{s}}|/|E_0|\right)}^2$ shows the field enhancement of (c) a square-shaped dimer with a side length of 475 nm and a gap width of 40 nm at a wavelength 700 nm, (d) similarly for a wavelength 800 nm, and (e) of a single square-shaped nanoantenna with a side length of 475 nm at 800 nm wavelength. (f) Simulated scattering cross-section of the square dimer with varying side length. The scattering cross-section is normalized to the physical area of the dimer. (g) A scanning electron microscope image of the square-shaped dimer with a side length of 475 nm and a gap width of 40 nm. The scale bar is 5 μm. Inset is a zoomed-in scanning electron microscope image of the cross-section of a single dimer to show the gap. The scale bar is 500 nm. (h) Photoluminescence spectrum of a representative SPE in monolayer WSe₂ on top of a dimer measured at 5 K. The inset shows the second-order auto-correlation measurement demonstrating $g^{\left(2\right)}\left(0\right)=0.11$ . The data are raw with no correction for the background or detector dark counts.

Figure 2:

Purcell enhancement of single photon emitters on a dimer nanoantenna. (a) The lifetime of a single photon emitter on a dimer (green dots), a random emitter off-dimer (blue dots), and the instrument response function (IRF, red). The solid lines are the exponential fits resulting in 0.49 ns (corrected for the instrument response) and 7.3 ns for emitters on and off dimers, respectively. (b) A scatter plot of the lifetimes of SPEs from the dimer sample as a function of their wavelength. (c) Simulated Purcell factor of an emitter positioned 5 nm on top of the center of a square dimer perpendicular to the dimer’s gap with a 40 nm gap as a function of the dimer side length. The black dashed line represents the fabricated sample with a side length of 475 nm with which the measurements are performed. (d) A scatter plot of the lifetimes of a group of random emitters.

Figure 3:

Polarization control of single photon emitters using dielectric nanoantennas. (a) A scanning electron microscope image of a dimer sample with varying the axis of the dimer by step of 30° and a side length of 475 nm and a 40 nm gap. The scale bar is 5 μm. (b) Photoluminescence spectrum of SPEs on a dimer showing three single-photon emitters at a dimer oriented at 30° angle as highlighted by the yellow circle in the schematic inside the inset. The inset shows a schematic of the dimer sample fabricated and measured with a monolayer WSe₂ transferred onto the sample. (c)–(e) Polarization measurements of the three emitters shown in (b) showing an angle of $\sim 30°$ matching that of the dimer orientation.