# The Peres conjecture is false: One of the most famous problems in quantum information physics solved

Since 1999, the conjecture by Asher Peres, who invented quantum teleportation, has piqued the interest of many scientists in the field. According to his hypothesis, the weakest form of quantum entanglement can never result in the strongest manifestation of the phenomenon. Today, a team of researchers from the University of Geneva (UNIGE), Switzerland, and the Hungarian Academy of Sciences have proven this conjecture to be false, thus solving one of the most famous problems in quantum information physics. This news was published in *Nature Communications* review.

The physicist Asher Peres was very interested in the phenomenon of quantum entanglement and its different manifestations. When two objects (take photons, for example) are entangled, they remain correlated regardless of the distance that separates them physically: whether they are separated by a millimetre or by several kilometres, any action done to one of them will immediately affect the other. To check whether a system is entangled, scientists test for Bell's inequality. If the experimental measurements violate Bell's inequality, this means that the two objects are entangled, and that they correspond to two manifestations, in different locations, of the same single object. This is called nonlocality.

**A Problematic Conjecture**

In 1999, Asher Peres conjectured that the weakest form of an entanglement will never result in the strongest manifestation of the phenomenon. Explanations.

The violation of Bell's inequality represents the strongest form of entanglement. Two objects must indeed be strongly entangled in order for the system's experimental measurements to violate Bell's inequality. On the other hand, there also exist states with very weak entanglement. Asher Peres wondered if it would be possible to distil several wealky entangled states in order to make a strongly entangled one, as one would distil alcohol. The theory showed that this was possible, but not in every case. Certain states are in fact too weakly entangled to be distilled; this is the case of bound entanglement, which is considered the weakest form of the phenomenon. Peres therefore concluded that the weakest form of entanglement could never result in the strongest manifestation of the phenomenon, namely nonlocality.

Later, a number of scientists tried to prove his conjecture. Some succeeded in a few particular cases, but none were able to demonstrate the claim in general. Peres's conjecture was therefore considered to be one of the most famous unresolved problems in the field of quantum information physics... until now. In fact, Nicolas Brunner, a physics Professor at UNIGE's Faculty of science, and Tamas Vertesi, a researcher at the Hungarian Academy of Sciences, were able to disprove Peres's conjecture. "To do so, we just had to find a counter-example," explains Professor Brunner. "Using numerical algorithms, we showed that a bound entanglement can violate Bell's inequality, without needing to be distilled."

**Citation**: The Peres conjecture is false: One of the most famous problems in quantum information physics solved (2014, November 5) retrieved 15 June 2019 from https://phys.org/news/2014-11-peres-conjecture-false-famous-problems.html

## User comments

edseds727mikep608https://www.faceb...timeline

phaseshifterThis is completely wrong, and is exactly the spiel used to make homeopathy (and other pseudosciences) sound (to the uneducated) like it has a credible base in physics.

jdavis417AmritSorlihttp://www.degruy...14-5.xml

teenagewastelandshaveraA) there aren't hidden variables informing a particle how it "truly" is (quantum mechanics is truly random)

or

B) physics must allow for non-local, ie faster than light, processes.

The standard interpretation is to take A. Quantum particles are truly indeterminate. This means nothing at all is transmitted faster than light.

But it also means that an *entangled* system of particles has more information than either one of the particles carries alone. It's not that one particle changes the other particle by some voodoo magic. It's that you need to know BOTH particles' measurements to extract the system's information.

teenagewastelandantialias_physorgIn entanglement you do not have an encoded state (you can't 'set' the particle to any specific state beforehand, because this would be an interaction/measurement and break any entaglement).

So while entanglement may seem non-local the measurement of the entangled entites does not constitute information transmission (and hence particularly not FTL information transmission).

There's a reason why it's called "(spooky) action at a distance" and not "information transmission at a distance"

phaseshifterExactly. Entanglement relies on knowing a property of the system as a whole (i.e. total spin angular momentum).

Observing that property for one particle (by observing the spin, for instance) determines that property for the other particle. The only events exhibiting nonlocal effects are measurements of the correlated properties. Properties unrelated to the correlation will not exhibit nonlocal effects, and attempts to manipulate (rather than observe) the correlated property will break the correlation.

Da SchneibDa Schneibrussell_russellThe label "action" is used in this thread commentary.

Is this "action" kinematics (the study of motion) or dynamics (the study of forces) or neither?

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