Measuring photon correlation using laser feedback interferometry with time-correlated coherence measurements

In Paul Dirac's "The principles of quantum mechanics", he explains the basis for intensity fringes when a light beam is split into 2 beams and then made to interfere by stating: "Each photon then interferes only with itself. Interference between two different photons never occurs". Dirac's famous statement forms the basis for the presentation of optical interferometry in undergraduate modern physics courses. Regarding this quote, Roy J. Glauber said, during his Nobel Prize Lecture (awarded for contributions to the quantum theory of optical coherence in 2005), "Forgive me, this is quantum mechanical scripture, but it is also nonsense". Glauber then elaborates to explain the Hanbury Brown-Twiss photon correlation experiment and in his published Nobel Prize Lecture he writes: "It is not the photons that interfere physically, it is their probability amplitudes that interfere – and probability amplitudes can be defined equally well for arbitrary numbers of photons. "Of course, the contemporary importance of these ideas was highlighted with the 2022 Nobel Prize in Physics awarded to 3 scientists "... for experiments with entangled photons ...". We are exploring photon correlations using a unique setup based upon electro-optic, phase-modulated HeNe laser feedback interferometry. We have shown that the laser feedback interferometer is a dynamic instrument that responds to dc and oscillatory changes in the optical path that can be measured with nanometer precision. This approach enables photon interference as well as time-correlated coherence measurements.