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.
Mathieu’s colleagues intend to use these devices to amplify the measured light intensity difference between two photodiodes (both receiving less than nanosecond-long pulses). The amplifier spreads gain over four THS3202 op-amps to achieve a risetime of 950 ps. Mathieu encountered self-oscillation induced by heating of the op-amps, so he spent quite a bit of time optimizing the heatsink for the amplifier.
Check out Mathieu’s blog for more of his interesting high-level electronics projects!
Click here for the paper “Displacing entanglement back and forth between the micro and macro domains”
Click here for a pdf backup of the blog post and schematics: