Connecting identical models via PT-symmetric disorder

- Researchers ponder the possibility of quantum communication in systems with many degrees of freedom -

In the last few years, major efforts have been put in finding quantum mechanical systems composed of two identical parts that, although classically disconnected, can communicate among themselves by means of quantum mechanical effects. Motivated initially by prominent questions arising from quantum gravity and string theory, explicit examples of such models could be of relevance in several other domains of science. For instance, models of this kind could be considered as explicit realizations of quantum teleportation and other kinds of communication controlled by quantum effects, without a classical analog.

It was soon realized that a practical way to make possible such a scenario was to consider disordered quantum systems, which means quantum systems where impurities are modeled via the presence of randomness in the coupling constants defining the model itself. By additionally requiring that the two parts were having exactly identical disorder, it was possible to show that some form of quantum communication was possible. However, in all the results at disposal in the literature, quantum communication was a sub-leading phenomenon, i.e. it was a phenomenon that was not visible when considering systems composed by many degrees of freedom.

In recent research published by the Center for Theoretical Physics of Complex Systems (PCS) within the Institute for Basic Science (IBS), the researchers have shown analytically the first explicit example in which these communication effects are dominant when considering systems composed by many degrees of freedom. The crucial ingredient, which made possible this result and which was missing in all the previous attempts, is to make the model non-Hermitian (as in usual quantum mechanics) but PT-symmetric only. The latter property can be thought of as a particular example of dissipation, i.e. the physical scenario in which the system dissipates energy through its dynamics. The group explicitly showed that by allowing dissipation, the two systems are able to communicate via quantum mechanical effects in a way that is still dominant when the two systems are made of many degrees of freedom.

These findings of the PCS researchers have potential implications in several different domains. First of all, this result represents a critical step towards solving the so-called “information paradox” in quantum gravity, which is the problem of reconciling the process of black hole evaporation with the requirement of unitarity required by quantum mechanics. On a more concrete ground, this paves the way for finding the first examples of isolated states in quantum many-body systems which are able to evade thermalization (the so-called many-body scars) even in presence of dissipation. Also, the result shares striking similarities with the phenomenon of quantum synchronization and it could lead to the first examples of quantum synchronization in a many-body setup.