Post-Selected Indistinguishable Photons from the Resonance Fluorescence of a Single Quantum Dot in a Microcavity

Applying continuous-wave pure resonant $s$-shell optical excitation of individual quantum dots in a high-quality micropillar cavity, we demonstrate the generation of post-selected indistinguishable photons in resonance fluorescence. Close to ideal visibility contrast of 90% is verified by polarization-dependent Hong-Ou-Mandel two-photon interference measurements. Furthermore, a strictly resonant continuous-wave excitation together with controlling the spontaneous emission lifetime of the single quantum dots via tunable emitter-mode coupling (Purcell) is proven as a versatile scheme to generate close to Fourier transform-limited ($T_2/(2T_1)=0.91$) single photons even at 80% of the emission saturation level.

Figure 1

(a) Experimental setups for low temperature micro-photo-luminescence ($\mu$-PL), high-resolution PL (HRPL), and photon statistics (second-order correlation $g^{(2)}(\tau )$ and two-photon interference (HOM). [(P)BS: (polarizing) beamsplitter, FPI: Fabry-Pérot interferometer, PH: pinhole, SM: pol.-maintaining single-mode fiber, coll: collimator]. (b) Orthogonal excitation-detection geometry on individual micropillars; Inset: sideview of micropillars at the cleaved sample edge.

Figure 2

(a) Low-temperature ($T=10\mathrm{K}$) $\mu$-PL spectra from the $s$ shell of a single QD (excited via its $p$ shell), showing emission close to a fundamental micropillar mode (FM). (b) High-resolution spectra of the same QD. (c) Excitonic luminescence decay time as a function of QD-FM detuning $\Delta E(T)$. (d) Frequency scanning signal obtained from the narrow band cw-laser tuned over the $s$ shell of the single QD in (a).

Figure 3

(a) Power-dependent high-resolution PL (HRPL) spectra observed from a single QD under cw resonant $s$-shell excitation (log-scale). (b) Schematic of the evolution of a “dressed” state quadruplet with three nondegenerate transitions ${\omega }_0\pm \Omega$ (Mollow-triplet) under strong resonant excitation, derived from the bare transition ${\omega }_0$. (c) Excitation power-dependent Rabi splittings extracted from (a).

Figure 4

(a) 2nd-order correlation measurement under low-power resonant QD $s$-shell excitation (18 K): $g^{(2)}(0)=0.08$ (deconvoluted) reflects almost background-free single-photon emission. (b, c) Two-photon interference data under orthogonal and parallel polarizations of the interferometer arms, respectively. (d) Interference visibility obtained from traces (b) and (c). Solid lines (red) in all figures: Theoretical fits convolved with the system response ($\delta t=400\pm 10\mathrm{ps}$); dotted lines: deconvolved fits, i.e., corrected for $\delta t$.