A recent paper entitled “Displacing entanglement back and forth between the micro and macro domains” discusses the experimental possibility of displacing quantum entanglement into the domain where it involves two macroscopically distinct states, i.e. two states characterized by a large enough number of photons. Specifically, the authors describe the process by which they start with two entangled spatially separated optical modes at the single photon level and subsequently displace one of these modes up to almost a thousand photons.
With so many photons, it would be possible, at least in principle, to see entangled photon pulses with our eyes. This would also make it possible to perform entanglement experiments with linear coarse-grain detectors (NOT single-photon detectors).
Mathieu Stephan, a high speed electronics engineer at the Swiss quantum information systems company id Quantique SA (and prolific hardware hacker) designed the very fast pulse amplifiers needed to acquire signals from avalanche photodiodes for this experiment. He has posted a thorough description of his design on his blog: http://www.limpkin.fr.
I. Rech, I. Labanca, M. Ghioni, and S. Cova of the Politecnico di Milano in Italy described an interesting modification to the Perkin Elmer SPCM-AQR Single-Photon Counting Module (SPCM) to improve its timing characteristics in:
