Parity-time Symmetry Goes Quantum

No physicist would tamper with the conservation of energy—the fundamental law that says energy cannot be created or destroyed. Researchers have, however, taken an interest in devices whose energy is conserved somewhat artificially. Known as PT-symmetric systems [1], these devices are engineered to have a balance of energy flowing in and out. And they feature many unusual properties, which have, for example, been harnessed to make optical components that only allow light to travel in one direction or that stop the flow of light altogether [2, 3]. Some of these properties might now be realized in the quantum domain. David Zueco of the University of Zaragoza in Spain and colleagues have proposed a realistic circuit in which microwaves interact with a quantum bit (qubit) and that would satisfy the requirements of PT symmetry [4].