The Quantum Information and Computing lab at the Raman Research Institute in Bangalore, India has been performing cutting edge research in quantum information processing towards quantum computation, quantum communication as well as fundamental tests of quantum mechanics itself using single and entangled photons.
In this talk, I will discuss one of our recent results which is a new insight to a widely used quantum optics phenomenon [1]. The famous Hong-Ou-Mandel two-photon coincidence- visibility dip (TPCVD), which accepts one photon into each port of a balanced beam splitter and yields an equal superposition of a bi-photon from one output port and vacuum from the other port, has numerous applications in photon-source characterization and to quantum metrology and quantum computing. Exceeding 50% two-photon-coincidence visibility is widely believed to signify quantumness. Here, we show theoretically that classical light can yield a 100% TPCVD for controlled randomly chosen relative phase between the two beam- splitter input beams and experimentally demonstrate a 99.635 +/- 0.002% TPCVD with classical microwave fields. We show quantumness emerges via complementarity for the biphoton by adding a second beam splitter to complete an interferometer thereby testing whether the biphoton interferes with itself: Our quantum case shows the proper complementarity trade-off whereas classical microwaves fail.
I will also give a general overview of some of our other ongoing experiments and end with our broad vision for the future with our mega project on Quantum Experiments using Satellite Technology (QuEST) in collaboration with the Indian Space Research Organization.
[1] Near-100 % two-photon-like coincidence-visibility dip with classical light and the role of complementarity, S. Sadana, D. Ghosh, K. Joarder, A. Nagalakshmi, B.C. Sanders, U.Sinha, arXiv:1810.01297