Exploring Dephasing of a Solid-State Quantum Emitter via Time- and Temperature-Dependent Hong-Ou-Mandel Experiments

We probe the indistinguishability of photons emitted by a semiconductor quantum dot (QD) via time- and temperature-dependent two-photon interference (TPI) experiments. An increase in temporal separation between consecutive photon emission events reveals a decrease in TPI visibility on a nanosecond time scale, theoretically described by a non-Markovian noise process in agreement with fluctuating charge traps in the QD’s vicinity. Phonon-induced pure dephasing results in a decrease in TPI visibility from $(96\pm 4)\%$ at 10 K to a vanishing visibility at 40 K. In contrast to Michelson-type measurements, our experiments provide direct access to the time-dependent coherence of a quantum emitter on a nanosecond time scale.

Figure 1

(a) Schematic view of the cross section of a monolithic microlens with a single deterministically integrated QD. Inset: Scanning electron microscopy image of a fully processed microlens. (b) Experimental setup: Hong-Ou-Mandel-type two-photon interference experiments are utilized to probe the indistinguishability of consecutively emitted photons with variable pulse separation $\delta t$ (MO: microscope objective, APD: avalanche photodiode).

Figure 2

$\mu \mathrm{PL}$ spectrum of a deterministic QD microlens under $p$-shell excitation ($T=7\mathrm{K}$). Inset: Second-order photon-autocorrelation measurement on the $X^0$ emission, demonstrating close to ideal single-photon emission.

Figure 3

(a)–(d) Two-photon interference histograms measured using a two-pulse excitation sequence with variable pulse separation $\delta t$ ($T=7\mathrm{K}$). Data corresponding to copolarized (crosspolarized) measurement configuration are displayed by solid blue (dashed grey) curves, together with a fit to the data (solid red lines) explained in the main text.

Figure 4

Two-photon interference visibilities of consecutively emitted single photons versus the time $\delta t$ elapsed between the emission processes. Experimental data for (a) the $X^0$ state and (b) the $X^{+}$ state are quantitatively described by a theoretical model assuming a non-Markovian noise correlation leading to spectral diffusion on a nanosecond time scale [see Eq. (3)]. A characteristic temperature-dependent correlation time ${\tau }_c$ is observed.

Figure 5

Impact of the temperature on the two-photon interference (TPI) visibility ($\delta t=2\mathrm{ns}$). (a)–(c) TPI histograms for copolarized configuration at 10, 25, and 35 K and corresponding fits (red solid curves). (d) Experimentally obtained TPI visibilities for various temperatures. We achieve qualitative agreement with a theoretical model assuming dephasing proportional to the phonon number (see Supplemental Material [22]).