Fig. 2: Two-photon interference of a laser qubit.

a Autocorrelation of the QD fitted to a multi-level model (solid line). b Experimental schematic. A laser photon is interfered with a QD photon on a 99:1 unbalanced beamsplitter. Correlation measurements are performed on photons which exit via the same port of the beamsplitter using a standard Hanbury-Brown and Twiss (HBT) setup with a 50:50 beamsplitter and superconducting nanowire single-photon detectors (D1 & D2). The photon polarisation is controlled using a linear polariser (LP) and electronic polarisation controllers (EPCs). c Correlation measurements of TPI for indistinguishable (blue) and distinguishable (purple) photons. d Corresponding visibility of the TPI for the high and low-intensity regimes discussed in the text. e Calculated TPI visibility as a function of the relative QD/laser intensity ratio η∕α² for the ideal case where the degree of second-order coherence \({g}_{HBT}^{(2)}(0)=0\), and for the \({g}_{HBT}^{(2)}(0)=0.177\) and 0.095 corresponding to recorded values at P_sat and at P_sat∕20, respectively. Black points denote raw experimental values extracted from d. There is no correction for detection response.