Postselected indistinguishable single-photon emission from the Mollow triplet sidebands of a resonantly excited quantum dot

Applying high-power continuous-wave resonant $s$-shell excitation to a single self-assembled InGaAs quantum dot, we demonstrate the generation of postselected single-indistinguishable photons from the Mollow triplet sidebands. A sophisticated spatial filtering technique based on a double Michelson interferometer enabled us to separate the spectrally close lying individual Mollow components and perform almost background-free two-photon interference measurements. Showing high consistency with the results of an independent determination of the emission coherence of $\sim$$250\pm 30$ ps, our analysis reveals a close to ideal visibility contrast of up to $97\%$. Due to their easy spectral tunability and their distinct advantage of cascaded-photon emission between the individual Mollow sidebands, they resemble a versatile tool for quantum information applications.

Figure 1

Double Michelson filtering technique: High-resolution spectrum of (a) the full Mollow triplet without Michelson filtering, (b) the Mollow triplet sidebands (suppressed Rayleigh line after first filtering step), and (c) only the red Mollow sideband (after second filtering step). (d) Illustration of the double Michelson interferometer setup used to spatially separate one Mollow component from the other two.

Figure 2

Coherence time extraction: Power-dependent Mollow triplet spectra. The belonging sidebands are marked with black arrows, and the additional peaks reflect the different orders of interference of the scanning Fabry-Pérot interferometer. Inset: FWHM of the Mollow sidebands, extracted from Lorentzian fits to the HRPL data and the herefrom calculated coherence time $T_2$ vs ${\Omega }^2$.

Figure 3a

central Mollow peak revealing long-term bunching with a time scale of ${\tau }_{\text{bunch}}=9.51\text{ns}$. (b)–(d) Autocorrelation, and perpendicular and parallel Hong-Ou-Mandel measurements on the photon emission of the red Mollow sideband. The fits reveal a modified emission time of ${\tau }_r=540\text{ps}$ and $T_2=300\text{ps}$ close to the independently derived coherence time of $264\text{ps}$ from the HRPL spectra. The deconvoluted values show a high degree of two-photon visibility $V_{\text{HOM}}=0.93\pm 0.01$ (convoluted $V_{\text{HOM}}=0.47\pm 0.08$). (II) Similar data set as in (I) but at for $\Omega =53.8\mu \text{eV}$. The values for fitting all correlation measurements are found to be ${\tau }_{\text{bunch}}=14.3\text{ns}$, $T_2=237\text{ps}$, ${\tau }_r=570\text{ps}$, exhibiting a visibility of $V_{\text{HOM}}=0.97\pm 0.02$ (convoluted $V_{\text{HOM}}=0.43\pm 0.07$). (III) Auto- and HOM correlations for the blue Mollow sideband at $\Omega =53.8\mu \text{eV}$. The fitting values ${\tau }_r=570\text{ps}$ and $T_2=237\text{ps}$ are in accordance with all correlation measurements. Here the evaluations reveal $V_{\text{HOM}}=0.92\pm 0.02$ (convoluted $V_{\text{HOM}}=0.39\pm 0.08$).

Figure 3

Correlation measurements: Blue dashed (red straight) line convoluted (deconvoluted) fits to the $g^{\left(2\right)}\left(\tau \right)$ data. (I) Data set for the two-photon interference measurements of the red Mollow sideband for $\Omega =45.5\mu \text{eV}$. (a) Autocorrelation of the