New 'quantum distillation' method allows measuring coherence of quantum states

New “quantum distillation” method allows measuring coherence of quantum states
coherence

One of the main principles of quantum physics is the superposition of states. Systems exist simultaneously in different states until they are measured and the system opts for one of the possibilities. As long as the superposition lasts, the system is said to be in a coherent state. In real systems, sets of diverse elemental particles or atoms exist in a state of superposition, for example, in different positions simultaneously, with different levels of energy, or with two opposite spin orientations. These have weak coherence—the superposition is broken easily by the vibrations associated with temperature and the interactions with the environment.

In the scientific article, researchers from the Universitat Autònoma de Barcelona Department of Physics Andreas Winter and Dong Yang propose a groundbreaking method to measure the degree of coherence in any given quantum state. The researchers created simple formulas to calculate how much "pure coherence" is contained in a given quantum state by answering two fundamental questions: How efficiently can one transform the state into "pure coherence?" And how efficient is the reverse process?

"At first, the must be distilled. We must see how much coherence can be extracted from it," explains Andreas Winter. "Later, it once again forms a noisy state in which the coherence is diluted."

The distillation and dilution process allows measuring the strength of coherence of the initial state of with experiments tailored to each particular case. This is an outstanding contribution to the study of , given that "traditionally, to measure the degree of coherence of a superposition, it was necessary to measure the visibility of interference fringes, linked to standardised experiments," Winter says. "With our approach, the experiment can be adapted to every state in order to make the manifest itself better."


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More information: Andreas Winter et al. Operational Resource Theory of Coherence, Physical Review Letters (2016). DOI: 10.1103/PhysRevLett.116.120404
Journal information: Physical Review Letters

Citation: New 'quantum distillation' method allows measuring coherence of quantum states (2016, March 31) retrieved 15 September 2019 from https://phys.org/news/2016-03-quantum-distillation-method-coherence-states.html
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Mar 31, 2016
The property of superposition occurs in more conditions than is generally recognised. For instance electrons have no ordinality property and their position in space when they are not moving relative to an observer is indeterminate. This effectively means that their physical position in space is a superposition of many possible locations.

That is, effectively, two more forms of the superposition: ordinal and locational.

It is the implicit push to confine this weird property of nature that actually makes the whole quantum world more complicated. If, instead, superposition was seen as the default property then things would be simpler. As humans, however, we consider those properties that most resemble our human experience to be the natural and default properties of nature and those properties that are counter-intuitive to be the special case.

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