Controlling the arrow of time in circuit QED

The unitary time evolution of a quantum system implies that flipping the overall sign of a Hamiltonian is equivalent to reversing time. Time reversal operations have utility in, for example, measuring out-of-time-ordered correlators (OTOCs), which have been considered theoretically to quantify information scrambling and identify many-body localized phases. Following a proposal by Zhu, Hafezi, and Grover [Phys. Rev. A 94, 062329 (2016)], we present the design and preliminary measurements of a planar superconducting circuit where the sign of an effective Hamiltonian of bus-coupled qubits is controlled by the state of an ancilla qubit. We discuss some of the practical challenges of this approach and the implications for OTOC measurements.