A pair of theoretical physicists, from the University of Exeter (United
Kingdom) and the University of Zaragoza (Spain), have developed a quantum
theory explaining how to engineer non-reciprocal flows of quantum light and
matter. The research may be important for the creation of quantum
technologies which require the directional transfer of energy and
information at small scales.

Reciprocity, going the same way backward as forward, is a ubiquitous concept
in physics. A famous example may be found in Newton's Law: for every action
there is an equal and opposite reaction. The breakdown of such a powerful
notion as reciprocity in any area of physics, from mechanics to optics to
electromagnetism, is typically associated with surprises which can be
exploited for technological application. For example, a nonreciprocal
electric diode allows current to pass in forwards but not backwards and
forms a building block of the microelectronics industry.

In their latest research, Downing and Zueco provide a quantum theory of
non-reciprocal transport around a triangular cluster of strongly interacting
quantum objects. Inspired by the physics of quantum rings, they show that by
engineering an artificial magnetic field one may tune the direction of the
energy flow around the cluster. The theory accounts for strong particle
interactions, such that directionality appears at a swathe of energies, and
considers the pernicious effect of dissipation for the formation of
non-reciprocal quantum currents.

The research may be useful in the development of quantum devices requiring
efficient, directional transportation, as well for further studies of
strongly interacting quantum phases, synthetic magnetic fields and quantum
simulators.

Charles Downing from the University of Exeter explains: "Our calculations
provide insight into how one may instigate directional transport in closed
nanoscopic lattices of atoms and photons with strong interactions, which may
lead to the development of novel devices of a highly directional character".

"Non-reciprocal population dynamics in a quantum trimer" is published in
Proceedings of the Royal Society A, a historic journal which has been
publishing scientific research since 1905.

## Reference:

Nonreciprocal population dynamics in a quantum trimer, Proceedings of the
Royal Society A: Mathematical and Physical Sciences (2021).
DOI: 10.1098/rspa.2021.0507.

Tags:
Physics