We developed a high sensitivity optical sensor for circular birefringence using a heralded photon source. The sensor can be employed for chirality measurements and, being based on single photons, can be exploited for fragile biological sample or in metrological applications where the light intensity must be kept as low as possible. We found the best operational condition; then, we calibrated the sensor and tested its performance up to a very long acquisition time, obtaining excellent stability and a sub-ppm birefringence detection limit (for a 100 μm sample), thus paving the way for fundamental physics test as well.
