Non-reciprocal quantum interactions without real or synthetic magnetic fields*

Non-reciprocal elements are a valuable resource in realizing scalable quantum circuits and networks. Conventional routes to non-reciprocity make crucial use of external magnetic fields or synthetic gauge fields (engineered, e.g., by dynamic modulation [1,2]). In the quantum case, the corresponding non-reciprocal interactions are ultimately described by a cascaded quantum-systems master equation [3,4]. Here, we discuss an alternate route to quantum non-reciprocity that does not necessarily require external magnetic fields (real or synthetic), and whose quantum dynamics is not described by a standard cascaded master equation. We show how an example of this dynamics can be realized in a regular circuit QED setup involving two cavities and a dispersively coupled qubit. We also show how this dynamics enables a number of new applications in quantum information processing, including a novel class of dissipative single- and two-qubit gates. Our ideas could be readily implemented in state-of-the-art superconducting qubit setups.

[1] K. M. Sliwa et al., Phys. Rev. X 5, 041020 (2015).

[2] K. Fang et al., Nat. Phys. 13, 465 (2017).

[3] C. W. Gardiner, Phys. Rev. Lett. 70, 2269 (1993).

[4] H. J. Carmichael, Phys. Rev. Lett. 70, 2273 (1993).