Thursday, April 28, 2011

Quantum Entanglement "Detected" By Human Eye

I'm not sure what to make of this.

This report describes a new and elegant experiment by the Gisin group. In this experiment, they have 2 entangled photons. One goes to a detector, the other gets amplified and generate a lot of photons with the same polarization state. In essence, the large number of photons are now a "macro" photon that is still entangled with the first photon. What they are doing is a micro-macro photon entanglement. This large number of photon is then detected by the human eye.

Using a similar set-up to that of Sciarrino, Gisin and his team entangled two photons. One was sent to a standard photon detector, while the other was amplified using a machine that generated a shower of photons with the same polarization, thereby, in theory, generating a micro–macro entangled state.

But Gisin replaced the photon detector Sciarrino used for the light field with a human. The beam of light produced by the amplifier could appear in one of two positions, and the location of the beam reflected the polarization state of the photons in the field. Gisin and his team sat in the dark for hours, marking the position of the light spot over repeated runs of the experiment, for the first time seeing the effects of quantum entanglement with the naked eye.

But then, they decided to check this by measuring the photon before it gets amplified, thereby destroying the entanglement with the first photon. Strangely enough, they get a false positive result!

But there was a hitch. What Gisin's team saw was not micro-macro entanglement. Gisin had a nagging suspicion that the Bell test may not be valid for macroscopic objects, so he deliberately set up the experiment so that the state of the second photon was measured before it was amplified. According to the rules of quantum mechanics, this act of measurement would break the entanglement, meaning that the first photon and the light field could not be in an entangled state. The system should not have passed the Bell test.

So essentially, they argued that the micro-macro entanglement isn't that convincing due to some issues. So I'm not sure how to spin this.


1 comment:

Jess said...

My understanding, after reading the paper, is that they showed their experiment does NOT show micro-macro entanglement. It did show micro-micro entanglement of the original two photons before one was amplified. However, the amplification was, quantum mechanically, a measurement, so while it retained information about the original entanglement, it destroyed the entanglement itself between the single photon and the amplified stream of photons.

The open question is if you can amplify a photon retaining all the information of the wave function. If you can, you can see micro-macro entanglement. Otherwise, by amplifying it, you measure it and collapse the wave function.