Quantum experiments with human eyes as detectors and micro-macro entanglement

It is interesting to think about ways of bringing quantum phenomena into the realm of everyday experience. One promising approach is via quantum optics. The human eye responds reliably to of order one hundred photons. It is possible to create entangled states of light of that order of magnitude by starting from a single entangled photon pair, and amplifying one of the two initial photons through a process known as quantum cloning by stimulated emission. This is an example of micro-macro entanglement, i.e. entanglement between a single microscopic quantum system and another system that is in some sense macroscopic (similar to Schroedinger's famous cat thought experiment). One can show that such micro-macro entanglement allows one in principle to violate Bell inequalities, thus allowing the demonstration of quantum non-locality using human eyes as detectors. This leads to the question whether the same kind of measurement also proves that the micro-macro state is entangled. A careful analysis shows that the Bell inequality violation only proves the original (micro-micro) entanglement. Unambiguously proving micro-macro entanglement seems to require measurements with single-photon resolution (which the human eye does not provide), raising the question whether quantum-level resolution is a general requirement for observing quantum effects in macroscopic systems. References: [1] P. Sekatski, N. Brunner, C. Branciard, N .Gisin, and C. Simon, Quantum Experiments with Human Eyes as Detectors based on Cloning via Stimulated Emission, Phys. Rev. Lett. 103, 113601 (2009). [2] P. Sekatski, B. Sanguinetti, E. Pomarico, N. Gisin, and C. Simon, Cloning Entangled Qubits to Scales One Can See, Phys. Rev. A 82, 053814 (2010). Popular description of some of this research: http://www.wired.com/wiredscience/2010/06/human-quantum-entanglement-detector/