The controversy about interference of photons

L. Mandeļ

David Thomas Pegg

We extend and generalize previous work on the interference of light from independent cavities that began with the suggestion of Pfleegor and Mandel [Phys. Rev. 159, 1084 (1967)] that their observed interference of laser beams should not be associated too closely with particular states of the beams but more with the detection process itself. In particular we examine how the detection of interference induces a nonrandom-phase difference between internal cavity states with initial random phases for a much broader range of such states than has previously been considered. We find that a subsequent interference measurement should give results consistent with the induced phase difference. The inclusion of more cavities in the interference measurements enables the construction in principle of a laboratory in the sense used by Aharonov and Susskind, made up of cavity fields that can serve as frames of phase reference. We also show reasonably simply how intrinsic phase coherence of a beam of light leaking from a single cavity arises for any internal cavity state, even a photon number state. Although the work presented here may have some implications for the current controversy over whether or not a typical laboratory laser produces a coherent state, it is not the purpose of this paper to enter this controversy; rather it is to examine the interesting quantum physics that arises for cavities with more general internal states.

Varun S Bhatta

This thesis is a study about the insights and challenges provided by the concept of wave- particle duality for the understanding of physical entities. I specifically analyse the duality claim of photons and the related interference phenomena. To begin, I explore several notions of duality found in mathematics and various branches of science and present the similarities and differences amidst them. After this, with regard to wave-particle duality of radiation, I highlight the plurality associated with this concept based on a few important interpretations of duality. I then focus on the wave-particle duality claim about photons articulated in the context of two experiments: the anti-correlation experiment and photons’ behaviour in the Mach-Zehnder interferometer experiment. I argue that this claim can neither be substantiated through the complementarity principle nor by claiming that photons behave analogously to classical waves and particles. This detailed examination of the experiments brings to the forefront yet another confusion about photons that I subsequently evaluate. I discuss the controversy concerning the interpretation of the interference phenomenon of photons and identify the sources of this confusion. Through these arguments and conclusions drawn in this thesis, I demonstrate how philosophical analysis is crucial for the understanding of scientific entities.

F. Frémont

Harry J. Kimble

I thank Rodger Walser and his colleagues for organizing this conference to celebrate George \nSudarshan’s birthday and landmark achievements in science. It is an honor for me to be here and \nalso a great pleasure to be back in Austin to join the chorus of the FOGS. \nI would like begin with a brief historical introduction and then turn to topics that we \nhaven’t heard so much about thus far in the symposium, namely experiments in Quantum Optics. \nLet me remind you that blackbody radiation has had a profound impact on physics since the time \nof Planck. However, even in more modern times after the development of quantum mechanics \nand quantum electrodynamics, one really did not know how to describe the underlying field \nfluctuations as required for diverse interference phenomena. Emil Wolf laid critical foundations \nfor this enterprise with his theory of classical coherence developed in collaboration with Max \nBorn in their classic book Principles of Optics. \nA great challenge to the physics community was the experiment by R. H. Brown and R. \nQ. Twiss in 1956 [1], which led to a confusing and controversial time for photons and fields. In \n1958 Leonard Mandel helped to resolve the controversy by explaining how light fluctuations are \nconverted to photocurrents in the detection process, albeit in with a classical description of the \nfield [2]. The confusion arose from the effort to understand, on the one hand, interference \nphenomena that are expressed in terms of the complex amplitude of the electromagnetic field, for \nwhich only a classical description was available. On the other hand, quantum electrodynamics \nhad been developed based upon energy eigenstates (i.e., Fock states) with photons as quanta. It \nwas really difficult to understand how the electric and magnetic fields behave in terms of these \nquantum states. For example, the expectation value of any electromagnetic field is zero in a Fock \nstate. The confusion was compounded by the historic invention of the maser and laser and by the \npressing need for quantum theories of the dynamical processes of these and other laboratory \nadvances.

John Gordon King, Malcolm Correll