Southwest Quantum Information and Technology

Towards full characterization of photonic gates with weak local oscillators

Presenting Author: Arik Avagyan, National Institute of Standards and Technology, Boulder

In the standard homodyne configuration, an unknown optical state is combined with a local oscillator (LO) on a beam splitter. Good quadrature measurements require a high-amplitude LO and two high-efficiency photodiodes whose signals are subtracted and normalized. By changing the LO phase, it is then possible to infer the optical state in the mode or modes matching the LO. For quantum information processing, the states of interest are in well-separated modes, corresponding to a pulsed configuration with one relevant LO mode per measurement. We determine what can be learned about the unknown optical state by counting photons in one or both outgoing paths after the beam splitter, keeping the local oscillator mode fixed but choosing its phase and amplitude. We prove that given the probabilities of photon counts of just one of the counters as a function of LO amplitude, it is possible to determine the content of the unknown optical state in the mode matching the LO conditional on each number of photons in orthogonal modes on the same path. If the unknown optical state has at most n photons, we determine finite sets of LO amplitudes sufficient for inferring the state.

(Session 5 : Sunday from 5:00pm - 7:00pm)