Fisher zeros and persistent temporal oscillations in nonunitary quantum circuits

Abstract

We present a quantum circuit with measurements and postselection that exhibits a panoply of space- and/or time-ordered phases from ferromagnetic order to spin-density waves to time crystals. Unlike the time crystals that have been found in unitary models, those that occur here are incommensurate with the drive frequency. The period of the incommensurate time-crystal phase may be tuned by adjusting the circuit parameters. We demonstrate that the phases of our quantum circuit, including the inherently nonequilibrium dynamical ones, correspond to complex-temperature equilibrium phases of the exactly solvable square-lattice anisotropic Ising model.