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Single photon measurements: Quantum State Discrimination

Summary

Using single-photon detection and an adaptive measurement strategy, we are able to determine the state of an optical pulse with errors below what is possible with even the best possible passive receiver, a limit often referred to as the "standard quantum limit".

Description

We tested schemes to optimally measure unknown quantum states for the purpose of surpassing what are typically considered to be the classical limits to such measurements.

experimental error probability chart
The experimental error probability (blue dots) for the discrimination of four nonorthogonal states in the QPSK format, together with the SQL (red line), an SQL adjusted for the 72% detection efficiency of our receiver (dashed line), the error probability limit for the optimized strategy with 10 adaptive measurements (blue line), and the Helstrom bound (black line). The experimental quantum receiver discriminates these states with lower error probabilities than the SQL for a range of mean photon numbers from 2 to 15.

Major Accomplishments

Experimental demonstration of a receiver beating the standard quantum limit for multiple nonorthogonal state discrimination, F. E. Becerra,J. Fan,G. Baumgartner, J. Goldhar,J. T. Kosloski & A. Migdall, Nature Photonics 7, 147–152 (2013)

Implementation of generalized quantum measurements for unambiguous discrimination of multiple non-orthogonal coherent states, F. E. Becerra, J. Fan & A. Migdall, Nature Communications 4, Article number: 2028 (2013)

Created September 30, 2015, Updated July 13, 2017