Non-invasive zero-delay time calibration of Hanbury-Brown and Twiss interferometers

Measuring photon autocorrelations via a Hanbury-Brown and Twiss (HBT) setup is a widely used experimental technique in quantum optics and is the base for quantum characterizations via Hong-Ou-Mandel interferometry, Bell inequality tests or quantum state tomography. The most common use for HBT measurements is the demonstration of single-photon emission from a quantum emitter. In order to make a definite statement and analyze the coincidence histograms obtained in the experiment, the temporal position of the zero delay time (ZDT) must be accurately known. In many cases, determining the ZDT requires tedious calibration measurements using light sources with known non-trivial photon correlations. Here we report on a non-invasive technique for measuring the ZDT in HBT setups based on avalanche photodiodes (APDs). The technique relies on the deliberate enhancement of optical crosstalk between the APDs. It can be used with any conventional laser source and therefore means a significant improvement for the easy calibration of the ZDT in HBT setups.