Researchers find nondestructive method to study quantum wave systems

May 16, 2014
Figure 1: Quantum weak measurements allow the interference patterns created when a light wave passes through a double slit to be resolved in detail. Credit: RIKEN

The laws of classical physics that describe the world around us can be very different from those of the quantum world. At the quantum level, particles can behave more like waves that can pass through each other and display properties very different from those of classical objects. However, one of the complexities of quantum physics is that any experimental measurement disturbs, or even destroys, these wave-like quantum states, making it difficult to reach a better understanding of such states through experiments.

Justin Dressel and Franco Nori from the RIKEN Center for Emergent Matter Science and Konstantin Bliokh from the RIKEN Interdisciplinary Theoretical Science Research Group (iTHES) have now shown that it is possible to obtain a detailed view of the wave-like properties of a quantum system by averaging over many 'weak', nondestructive quantum measurements.

"Weak measurements allow us to gather information on a quantum system without strongly affecting its state," comments Nori. Unfortunately, although weak measurements provide a glimpse into the , the rules of permit this only if a single experiment does not provide too much information on the quantum state being probed. This means that these experiments are very 'noisy'—akin to measuring the properties of a ship on an ocean by studying the ripples of waves at a long distance.

The researchers have established a general theoretical framework for weak measurements of quantum systems, showing that such experiments provide useful information when many measurements are averaged. Even though it is not possible to measure a single quantum particle precisely by such experiments, information about a quantum state can still be extracted if a sufficient number of measurements are made. Related experiments have already mapped the streamlines of light particles passing through a double slit, revealing for the first time a detailed picture of how the resulting interference pattern is formed (Fig. 1).

The power of the mathematical theory proposed by Dressel, Bliokh and Nori is that it generalizes such concepts to any and any quantum system. Although these measurements are still not able to provide a full picture of the quantum world, they make it possible to relate the quantum world to the laws of . "Our results build a bridge between weak and classical theory," explains Dressel. "They show explicitly that the boundary between what is and what is classical becomes blurred when averaging over a large number of weak measurements."

Explore further: Good quantum states and bad quantum states

More information: Dressel, J., Bliokh, K. Y. & Nori, F. Classical field approach to quantum weak measurements. Physical Review Letters 112, 110407 (2014). On Arxiv:

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5 / 5 (2) May 16, 2014
Don't think this tells us anything new.
We already knew that as measurements get stronger the two slit experiment result mixes linearly between quantum and classical stripes on the screen.
We also know that if a measurement (disturbance) and its [nearly] opposite disturbance are applied the quantum stripes result is nearly preserved/restored.
We just need an Einstein/Dirac/Feynman to make sense of it all and give a useful interpretation besides "do the maths" on one interpretation or "consciousness and multiverses" on the wild and wacky interpretation.
May 17, 2014
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May 17, 2014
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Jun 03, 2014
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not rated yet Jun 03, 2014
have now shown that it is possible to obtain a detailed view of the wave-like properties of a quantum system by averaging over many 'weak', nondestructive quantum measurements
It's a nice show, but this approach is used at least twenty years already in most of QM related publications involving the weak measurement (compare the classical Elitzur–Vaidman bomb-testing problem from 1994). So it's rather difficult to estimate the originality of this work just from the above article.

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