Southwest Quantum Information and Technology

Unambiguous state discrimination as a limit of an optimal nonprojective measurement of two coherent states

Presenting Author: Spencer Dimitroff, University of New Mexico CQuIC
Contributing Author(s): Matt DiMario, F. Elohim Becerra

Recent advances in quantum measurement theory have shown that it is possible to realize an optimal inconclusive measurement (OIM) of two nonorthogonal coherent states based on linear optics, coherent displacement operations, continuous photon counting, and fast feedback [1]. The OIM is a nonprojective quantum measurement that generalizes the minimum error measurement and the optimal unambiguous measurement of two states, achieving the minimum error probability for a given probability of a conclusive result. We study this optimal nonprojective measurement to implement the zero-error optimal unambiguous state discrimination (USD) of two coherent states. While it is possible to implement optimal USD with a measurement based on displacement operations to the vacuum state without feedback [2], it is known that such an optimal measurement cannot be implemented in the presence of experimental imperfections due to the impossibility of perfectly realizing this displacement operation. We explore the use of the OIM in this zero-error regime, which does not fully rely on displacing to vacuum, with the aim of demonstrating a USD measurement that is more robust to imperfections. This robust quantum measurement can be critical in realistic implementations of quantum communication protocols based on USD of coherent states. [1] K. Nakahira and T. S. Usuda, Phys. Rev. A 86, 052323 (2012). [2] K. Banaszek, Phys. Lett. A 253, 12 (1999). Work supported by NSF Grant #PHY-1653670 and #2137233.

(Session 5 : Thursday from 12:00pm-2:00 pm)