Entanglement Conditions Involving Intensity Correlations of Optical Fields: the Case of Multi-Port Interferometry |
| J. Ryua,b, M. Marciniak b, M. Wieśniakb,c, D. Kaszlikowskia,d, and M. Żukowskib,e
aCentre for Quantum Technologies, National University of Singapore, 3 Science Drive 2, 117543 Singapore, Singapore bInstitute of Theoretical Physics and Astrophysics, Faculty of Mathematics, Physics and Informatics, University of Gdańsk, 80-308 Gdańsk, Poland cInstitute of Informatics, Faculty of Mathematics, Physics and Informatics, University of Gdańsk, 80-308 Gdańsk, Poland dDepartment of Physics, National University of Singapore, 2 Science Drive 3, 117542 Singapore, Singapore eFaculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria |
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| Normalized quantum Stokes operators introduced in Phys. Rev. A 95, 042113 (2017) enable one to better observe non-classical correlations of entangled states of optical fields with undefined photon numbers. For a given run of an experiment the new quantum Stokes operators are defined by the differences of the measured intensities (or photon numbers) at the exits of a polarizer divided by their sum. It is this ratio that is to be averaged, and not the numerator and the denominator separately, as it is in the conventional approach. The new approach allows to construct more robust entanglement indicators against photon-loss noise, which can detect entangled optical states in situations in which witnesses using standard Stokes operators fail. Here we show an extension of this approach beyond phenomena linked with polarization. We discuss EPR-like experiments involving correlations produced by optical beams in a multi-mode bright squeezed vacuum state. EPR-inspired entanglement conditions for all prime numbers of modes are presented. The conditions are much more resistant to noise due to photon loss than similar ones which employ standard Glauber-like intensity, correlations. |
DOI: 10.12693/APhysPolA.132.1713 PACS numbers: 03.65.Ud, 42.50.-p, 03.67.Bg, 03.67.Mn |