Independent Minds, Working Together

Cody Leary - Project 1

General Area of Research:

Quantum interference between the wave functions of two photons

Project Description:

In an often-quoted statement in his book The Principles of Quantum Mechanics, Paul Dirac wrote that in an interference experiment involving multiple particles of light, or photons, 'Each photon... interferes only with itself.' However, it was shown fairly recently that when two indistinguishable single photons are made to overlap at an optical beam splitter, they do in fact interfere with one another in the following sense: both photons 'stick together' upon exiting the beam splitter, proceeding together along one of two possible output paths. Remarkably, the outcome where one photon exits each beam splitter output never occurs, due to destructive quantum interference involving the indistinguishable probability amplitudes for this case. The observation of this phenomenon in 1987 by Hong, Ou, and Mandel clearly demonstrated this celebrated two-photon interference effect, which is a crucial component to quantum information processing schemes involving photons as the carriers of information.

In recently published research performed by Wooster students Thomas Gilliss and Deepika Sundarraman, a fundamental generalization was made to extend the present state of understanding of two-photon quantum interference. Building on the early work of Hong, Ou, and Mandel, which considered identical input photons with simple spatial wave functions and polarization states, we predicted the two-photon output state for input photons with distinct, nontrivial spatial and polarization properties. One of the interesting predictions that stemmed from this work is that if two photons are made to impinge on distinct input ports of an asymmetric Mach-Zehnder interferometer, two-photon interference can be made to occur in conjunction with the controlled conversion of the spatial wave functions of both photons. In other words, the photons always exit together out the same interferometer port, with a spatial intensity distribution controllable by the experimenter. This device, which has already been built and characterized in our lab, could allow for to new ways of storing and transferring quantum information between the spatial and polarization degrees of freedom of photons.

In this hands-on experimental project, we will continue efforts in our lab to build, characterize, and manipulate a two-photon quantum source of light, which will then be coupled with the aforementioned interferometer in order to verify the predictions of a rich class of two-photon quantum phenomena, including the two-photon interference with mode conversion described above. The project will provide ample opportunity to gain hands-on experience with experimental measurement and control of light in a quantum optics laboratory. In addition, the work may also involve symbolic matrix techniques in Mathematica for modeling of the various phenomena under study.

Related Majors: