An international team of researchers has found a way to make quantum entanglement of particles reversible, which was previously thought to be impossible.
The new conceptual device, called the entanglement battery, allows the conversion and rotation of quantum states without losses. Scientists have discovered a rule in the quantum world that is very similar to the second law of thermodynamics, formulated by the French physicist Sadi Carnot 200 years ago.
The researchers called their discovery the second law manipulation of quantum entanglement. This law demonstrates, that quantum entanglement can be reversibly changed, similar to the way heat and other types of energy behave in thermodynamics.
Measuring one of the particles in a state of quantum entanglement can instantly provide information about the state of the one that is paired with it, even if they are at a great distance from each other. This property makes it possible to instantly transmit information, encrypt data using quantum cryptography, and quantum computing and much more.
Researchers have found similarities between quantum entanglement and thermodynamics. One example is the so-called «entanglement entropy» — is a property of ideal quantum systems that accurately reflects the principle of entropy in classical thermodynamics.
However, unlike thermodynamics, the reversibility of a quantum state does not depend on time symmetry, but on the ability of an external agent to transfer the system to another state and then return it to the original state without loss. Much of the research has focused on the scenario, where two remote people, notional Alice and Bob, want to exchange quantum information, but are locally confined to their own quantum systems and can only communicate using classical means — by phone or via the internet. This restriction to local operations and classical communication simplifies the situation, since no matter what Alice and Bob do, they cannot affect the inherently nonlocal entanglement properties between their quantum systems.
«It is known, that in this scenario, the confusion is irreversible when classical communication tools work. So the question is, can we somehow go beyond classical communication in a meaningful way and restore reversibility?», — says the lead author of the study Alexander Streltsov.
The researchers note, that the answer to the question: «Yes, we can», but provided that Alice and Bob share an additional quantum entanglement system — the entanglement battery. This battery works on a similar principle to conventional batteries that store and use the accumulated energy. Only in this case, the quantum entanglement battery stores information about the state of entanglement. The battery can be used in the state transformation process, and its state can be changed to perform operations. There is only one rule: whatever Alice and Bob do, they must not reduce the level of entanglement inside the battery.
Using their hypothetical confusion battery for standard operations using classical communication tools, the team demonstrated that any confusion transformation in the mixed state can be made reversible. The same principles apply to systems involving more than two entangled particles, opening the way to understanding and manipulating complex quantum networks and possibly developing future high-performance quantum technologies.
The results of the study are published in the journal Physical Review Letters
Source: SciTechDaily
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