Wednesday, August 31, 2016

Quantum Entanglement's Manifestations Finally Measured

As noted in an earlier (Aug. 29)  post to do with  the role of consciousness in physics, I pointed out that at least some connections vis-a-vis quantum entanglement needed to be made before a serious empirical discussion could even commence. This has now evidently occurred as physicists have finally measured connections between pairs of photons within a macroscopic beam of light. These connections have been said to qualify as quantum entanglement and represent a step toward understanding how the rules of QM scale up to phenomena such as superconductivity, involving large numbers of particles.

Physicist Henry Stapp has noted that the neural dynamics of the human brain in the vicinity of synapses involve large numbers of particles, namely Ca++ ions which - on account of synaptic cleft dimensions (200-300 nm)-   can be treated in wave form.  The brain then, like a full quantum computer, can be regarded as subject to effects of quantum entanglement and exploring such manifestations could lead to insights into consciousness.

But first things first.  The experiment - to be published in Physical Review Letters - describes a specially prepared light beam that enables the observation of individual photons in addition to charting the quantum links between them. Basically then, the team from the Institute of Photonic Sciences in Barcelona, under Morgan Mitchell, confirmed the theoretical prediction that all the photons involved would exhibit some degree of entanglement and that the most strongly "entangled" would be pairs of photons striking the detectors at the same time.

According to Mitchell, quoted in Science News, "entanglement should be present in pretty much any situation with a lot of particles interacting with each other."    Most physics' arguments, however, take the view that quantum level entanglement is a bad thing for quantum computing. After all, if the quantum particles that are the basis for one's Q-computer become "entangled" with quantum particles outside then it is possible for information leakage and lost security.

In the case of Mitchell's team, while the study of entangled particles in superconductivity would have been ideal, the problems involved would have been formidable. (SCs are so densely packed with electrons that measuring even a small subset would have been extremely difficult. Imagine then the tandem problem of measuring entanglement to do with brain neurons.)

So, as a result, the Barcelona team confined attention to the much simpler macroscopic system of a "squeezed" beam of light.  Not physically squeezed, obviously, but rather transmitted through a crystal enabling the measurement of a particular property, in this case polarization.

Polarization refers to that property whereby EM-radiation as it propagates can be confined say to one plane, or one rotation plane. If we say "circularly polarized" then the E-vector rotates through a full 360 degrees. If we say "linearly polarized" then it vibrates in one plane, e.g.




Thus, Mitchell's Barcelona team filtered the beam of light and probed it with polarization detectors.  A click at the detector location indicated the arrival of a photon with a particular polarization. Any pairs traveling in tandem (and arriving simultaneously) had corresponding polarizations. I.e. horizontally polarized such as indicated in the lower sketch above.

Clearly, much more work has to be done, especially by way of confirmation, as well as extending the conclusions to other systems for greater generality. A case in point would be to convince skeptics like Prof. Timothy Ralph of University of Queensland, who doesn't accept that the Mitchell team's results are applicable for any phenomena other than "squeezed" light.

We shall see!

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