Overcoming correlation fluctuations in two-photon interference experiments with differently bright and independently blinking remote quantum emitters

As a fundamental building block for quantum computation and communication protocols, the correct verification of the two-photon interference (TPI) contrast between two independent quantum light sources is of utmost importance. Here, we experimentally demonstrate how frequently present blinking dynamics and changes in emitter brightness critically affect the Hong–Ou–Mandel-type (HOM) correlation histograms of remote TPI experiments measured via the commonly utilized setup configuration. We further exploit this qualitative and quantitative explanation of the observed correlation dynamics to establish an alternative interferometer configuration, which is overcoming the discussed temporal fluctuations, giving rise to an error-free determination of the remote TPI visibility. We prove full knowledge of the obtained correlation by reproducing the measured correlation statistics via Monte Carlo simulations. As an exemplary system, we make use of two pairs of remote semiconductor quantum dots; however, the same conclusions apply for TPI experiments with flying qubits from any kind of remote solid-state quantum emitters.

Figure 1

(a) Setup sketch for remote TPI measurements: polarization control allows for indistinguishable (parallel) and distinguishable (orthogonal) configuration with photon overlap on a fiber-based BS. (b) High-resolution PL spectra of QDR and QDB at different operation temperatures. (c) Remote TPI experiment with clear signature of quantum interference for parallel polarization setting. (d) Blinking of QDR is quantified via long-term autocorrelation measurement, while not observable for QDB. Solid lines represent Monte Carlo simulations considering a nearby carrier trap.

Figure 2

(a) Exemplification of the two types of coincidences: “auto-coincidences” $A_{\text{auto}}$ (solid boxes) corresponding to events within the photon stream of an individual emitter, “cross-coincidences” $A_{\text{cross}}$ (dashed boxes) corresponding to events between the two emitters. (b) Resulting remote TPI measurement with QDR and QDB for orthogonal polarization setting with respective data from simulation. (c) Breaking of time synchronization of the two photon streams via a 1 m fiber (corresponding to ${\tau }_{\text{add}}\approx 5\mathrm{ns}$). (d) Resulting TPI measurement exhibiting separation of cross- from auto-coincidences.

Figure 3

(a) Unbalanced MZI setup enabling self-normalization on cross-coincidences, independently of blinking dynamics and brightness fluctuations. (b) Remote TPI measurement with QDR and QDB following the sketched approach: despite a count rate ratio $\eta =0.5$ and aforementioned blinking dynamics, a $g^{\left(2\right)}{\left(0\right)}_{\perp }\text{,expt}\approx 0.5$ is found in accordance to the expectation. (c) Prove of constant ratio of center peak triplet ($A^{(-)}$, $A^{\left(0\right)}$, $A^{(+)}$), in presence of blinking (top) or count rate mismatch (bottom), then enabling the mentioned self-normalization.