Southwest Quantum Information and Technology

Experimental study of an optimized Kennedy receiver for multiple coherent states

Presenting Author: Matthew DiMario, Center for Quantum Information and Control (CQuIC), University of New Mexico
Contributing Author(s): F. E. Becerra

Non-Gaussian receivers for coherent states that have discrimination errors below the Quantum Noise Limit (QNL) are a valuable tool in communication. Discrimination of coherent states is fundamentally impossible to do with zero probability of error because of their intrinsic overlap. Therefore, the goal is to design and demonstrate discrimination strategies that minimize the error probability and outperform the perfect Heterodyne (QNL) measurements. We implement a strategy proposed by Sasaki et al. (PRA 86, 042328 (2012)) that is based on testing multiple hypotheses at once within a single-shot measurement to discriminate between quaternary phase-shift-keyed (QPSK) coherent states. The receiver is based on three displacement operations and single photon counting and in principle achieves errors below the QNL without the need for any feedback operations. The three displacement amplitudes are independently optimized to yield the absolute minimum overall probability of error given experimental imperfections. Our results align well with the theoretical predictions and allow us to identify how the critical parameters, such as visibility of the displacement operations and detection efficiency, influence the error probability. We are also able to identify what is required of these parameters for the strategy to out-perform a Heterodyne (QNL) measurement.

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