Entanglement and Non-locality of Quantum Photonics

Thomas P. Pearsall

Jian-Wei Pan, Anton Zeilinger

Ralph Wiegner, Joachim von Zanthier, G. S. Agarwal

Christopher C. Gerry, Kimberley M. Bruno

This chapter focuses the concepts of entanglement and non-locality. Quantum mechanics has yet another mystery—one that occurs as a consequence of superposition states involving two or more particles or two or more beams of photons. This is referred to as entanglement, also known as non-separability. The existence of entangled states is allowed, and even mandated, by quantum mechanics, and this leads us into yet another mystery: non-locality. It demonstrates how subatomic particles can be put into entangled states which reveal strange correlation effects—the effects being the essence of entanglement. It discusses the EPR argument, from the 1935 paper by Einstein, Boris Podolsky, and Nathan Rosen; the polarization states of photons; Bell's theorem; and the Hardy–Jordan argument.

Rajarshi Pal, Sibasish Ghosh A

Entanglement breaking channels play a significant role in quantum information theory. In this work we investigate qubit channels through their property of 'non-locality breaking', which is defined in a natural way but within the purview of CHSH non-locality. This also provides a different perspective on the relationship between entanglement and non-locality through the dual picture of quantum channels instead of through states. For a channel to be entanglement breaking, it is sufficient to 'break' the entanglement of maximally entangled states. We provide examples to show that for CHSH nonlocality breaking such a property does not hold in general, although for certain channels and for a restricted class of states for all channels this holds. We also consider channels whose output remains local under SLOCC and call them 'strongly non-locality breaking'. We provide a closed-form necessary-sufficient condition for any two-qubit state to show hidden CHSH non-locality, which is likely to be useful for other purposes as well. This in turn allows us to characterize all strongly non-locality breaking qubit channels. It turns out that unital qubit channels breaking non-locality of maximally entangled states are strongly non-locality breaking while extremal qubit channels cannot be so unless they are entanglement breaking.

Andre Vatarescu

The interpretation of published experimental results intended to prove the existence of a quantum phenomenon of non-locality involving photonic entangled states did not take into consideration the existence of the quantum Rayleigh conversion of photons in dielectric media. This phenomenon leads to the existence of high levels of correlations between two independent photonic and linearly polarized quantum states generated after the entangled photons have been absorbed through the quantum Rayleigh conversion. Both pure and mixed individual states of polarization result in expressions normally associated with entangled photonic states, providing support for the view that the physical reality of quantum non-locality is highly questionable.