Monday, 27 August 2007

Quantum Mechanics again

QM seems to have a practically unfathomable reservoir of surprises. A recent work on Progressive field-state collapse and quantum non-demolition photon counting by Christine Guerlin, Julien Bernu, Samuel Deléglise, Clément Sayrin, Sébastien Gleyzes, Stefan Kuhr, Michel Brune, Jean-Michel Raimond & Serge Haroche, published in Nature 448, 889-893 (23 August 2007) has caught my attention.

The experiment is designed to observe, with as little disturbence as possible, the quantum state of a cavity containing an initially unknown number of photons. The authors describe it as follows:

The irreversible evolution of a microscopic system under measurement is a central feature of quantum theory. From an initial state generally exhibiting quantum uncertainty in the measured observable, the system is projected into a state in which this observable becomes precisely known. Its value is random, with a probability determined by the initial system's state. The evolution induced by measurement (known as 'state collapse') can be progressive, accumulating the effects of elementary state changes. Here we report the observation of such a step-by-step collapse by measuring non-destructively the photon number of a field stored in a cavity. Atoms behaving as microscopic clocks cross the cavity successively. By measuring the light-induced alterations of the clock rate, information is progressively extracted, until the initially uncertain photon number converges to an integer. The suppression of the photon number spread is demonstrated by correlations between repeated measurements. The procedure illustrates all the postulates of quantum measurement (state collapse, statistical results and repeatability) and should facilitate studies of non-classical fields trapped in cavities.

I must admit that my understanding of QM gets more and more inadequate with every such report. For example I do not understand how the `non-destructive' measurements, proposed by the authors really influence the state of the photons. Perhaps they do not change their number.

In this experiment, light is an object of investigation repeatedly interrogated by atoms. Its evolution under continuous non-destructive monitoring is directly accessible to measurement, making real the stochastic trajectories of quantum field Monte Carlo simulations

What is observed is the collapse of the state into one with a defined number of photons. Then the observed number remains constant - until the cavity absorbs one of the photons (on a much larger timescale) and then the measurements show this smaller number.

When I find the words `repeated interrogation' my mind jumps to `continuous measurement' and thus to the Quantum Zeno Effect. Is there any connection?

And one more remark: the short article on the discovery on has attracted a few comments. By far the most extensive is one by Andrei P. Kirilyuk, who is a champion of "Universal Concept of Complexity by the Dynamic Redundance Paradigm: Causal Randomness, Complete Wave Mechanics, and the Ultimate Unification of Knowledge"

OK, OK - I admit I do not iunderstand him neither. But there are some tell-tale signs of going beyond normal science. Such as mentioning by Kirilyuk that ALL famous science creators, from Descartes and Newton to Einstein and de Broglie were notorious mavericks understood by almost nobody at the time of their discoveries. Which supposedly builds up his credentials. This reminds me of a famous quote:
They laughed at Copernicus.
They laughed at the Wright Brothers.
Yes, well, they also laughed at the Marx Brothers.
Being laughed at does not mean you are right.

Another signal is that Citebase lists 18 articles quoting the Kirilyuk work ... all of them by ... Kirilyuk himself.

Concluding: it is difficult to follow the new developments in physics. A lot depends on the peer review. But - should we have some sort of mechanism for the strange approaches that are out of the mainstream science? Would the famous EPR paper be published today? Especially if the author list did not include Einstein?

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