Controlled Light-Matter Coupling for a Single Quantum Dot Embedded in a Pillar Microcavity Using Far-Field Optical Lithography

Using far-field optical lithography, a single quantum dot is positioned within a pillar microcavity with a 50 nm accuracy. The lithography is performed in situ at 10 K while measuring the quantum dot emission. Deterministic spectral and spatial matching of the cavity-dot system is achieved in a single step process and evidenced by the observation of strong Purcell effect. Deterministic coupling of two quantum dots to the same optical mode is achieved, a milestone for quantum computing.

Figure 1

(a) Schematic diagram of the experimental setup. (b) Schematic illustrating the method. (c) PL spectrum measured on the planar cavity during the photolithography process.

Figure 2

(a) QD PL intensity as a function of the sample position, along the dotted line on the inset image. Inset: Mapping of the QD exciton emission intensity as a function of the sample position. (b) QD PL spatial dependence width as a function of the excitation spot width on the sample. The insets show $6.4\mu \mathrm{m}\times 6\mu \mathrm{m}$ images of the excitation laser spot on the control camera. (c) QD PL intensity as a function of the sample position for various $E_{\mathrm{exc}}$. (d) red or gray square (respectively, black circle): Normalized PL intensity of the $X$ (respectively, $XX$). Red or gray line: square of the $X$ PL intensity.

Figure 3

(a) Energy of the pillar fundamental mode as a function of the pillar radius. (b) Pillar radius as a function of the resist exposure time for a 532 nm laser power of $500\mu \mathrm{W}$. Inset: Image of the Ni mask obtained after the lift-off of the resist. (c) Scanning electron microscope image of pillars with various radii designed to match QDs with various emission energies. (d) Actual mode energy as a function of target mode energy. (e) Quality factor and Purcell factor as a function of the pillar radius.

Figure 4

(a) [respectively, (d)]: Bottom: PL spectrum measured during the photolithography process at 10 K. Middle and top: PL spectra of pillar 1 (respectively, pillar 2) after etching at 10 and 32 K (respectively, 46 K) (a Lorentzian fit to the mode M is also shown). (b) [respectively, (e)] PL spectra between 18 and 32 K [respectively, 44 and 54 K] measured on pillar 1 (respectively, pillar 2). (c) Pillar 1: Circles: PL intensity of the $X$ line measured at saturation as a function of detuning with the optical mode: $\Delta =E_M-E_X$. Line: fit to the data with $F_P=9\pm 3$. (f) Pillar 2: Squares (circles): PL intensity measured at saturation of the QD1 (QD2) $X$ line as a function of detuning with the optical mode: ${\Delta }_{1(2)}=E_M-E_{\mathrm{QD}1(2)}$. Line: fit to the data with $F_P=6.5\pm 2.5$ for both QDs.