STAGE TIME-ASYMMETRIC ARTIFICIAL ATOM

Superconducting circuits are solid state devices whose macroscopic variables, such as voltages and currents, manifest quantum coherence. They represent one of the most promising quantum technologies, both for the implementation of novel fundamental quantum

phenomena and for applications to quantum computing tasks. Indeed, the number of laboratories and of large tech firms (IBM, Google, Intel) doing active research in this field has been steadily growing in the last few years. In superconducting circuits, quantum-electrical signals can propagate in one-dimensional media called transmission line resonators, which are the microwave counterpart of optical

waveguides. Transmission line resonators can be coupled to artificial atoms, that is, strongly non-linear systems used as effective two-level quantum systems (qubits). The high degree of scalability and tunability of superconducting circuits make this quantum platform very

versatile and interesting to study from the theoretical point of view. We will design a superconducting artificial atom that breaks the time-reversal symmetry, namely, that couples in different ways to signals travelling in opposite directions. In other words, this implies that the artificial atom is transparent when seen from one side, while it is able to backscatter photons on the other. Time-reversal-symmetry breaking can be induced by means of a magnetic flux threading a non-linear superconducting ring, thus inducing a preferential propagation direction