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arXiv:1904.05010 · New Journal of Physics

Discrete time symmetry breaking in quantum circuits: exact solutions and tunneling

Feng-Xiao Sun, Qiongyi He, Qihuang Gong, Run Yan Teh, M. D. Reid, P. D. Drummond

Published Aug 30, 2019• 14 citations
arXivHTMLPDF

Abstract

Abstract We discuss general properties of discrete time quantum symmetry breaking in degenerate parametric oscillators. Recent experiments in superconducting quantum circuit with Josephson junction nonlinearities give rise to new properties of strong parametric coupling and nonlinearities. Exact analytic solutions are obtained for the steady-state of this single-mode case of subharmonic generation. We also obtain analytic solutions for the tunneling time over which the time symmetry-breaking is lost above threshold. We find that additional anharmonic terms found in the superconducting case increase the tunneling rate, and can also lead to new regimes of tristability as well as bistability. Our analytic results are confirmed by number state calculations.

DOI
10.1088/1367-2630/ab3f5e

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Abstract We discuss general properties of discrete time quantum symmetry breaking in degenerate parametric oscillators. Recent experiments in superconducting quantum circuit with Josephson junction nonlinearities give rise to new properties of strong parametric coupling and nonlinearities. Exact analytic solutions are obtained for the steady-state of this single-mode case of subharmonic generation. We also obtain analytic solutions for the tunneling time over which the time symmetry-breaking is lost above threshold. We find that additional anharmonic terms found in the superconducting case increase the tunneling rate, and can also lead to new regimes of tristability as well as bistability. Our analytic results are confirmed by number state calculations.
We consider quantum dynamics of a parametrically driven anharmonic oscillator (PDAO) at a few-photon level. In this scheme the oscillatory mode is excited through the degenerate down-conversion process. This scheme could be experimentally realized in superconducting solid-state devices based on the nonlinearity of the Josephson junction or in cooled nano-mechanical oscillators. We investigate PDAO in the strong quantum regime that means strong Kerr-nonlinearity of the mode with respect to the mode’s dissipation for two cases of excitations: by a monochromatic driving field or by a train of Gaussian pulses. We demonstrate production of the nonclassical oscillatory states with two-fold symmetry in phase-space which are approximately close to the lower pure Fock states. Production of the superposition of the Fock states for time-intervals exceeding the characteristic time of decoherence and dissipation is also shown.
The reduction of spatial symmetry can have qualitative effects for a given quantum system, such as splitting of energy levels that are degenerate in the unperturbed case. Can the breaking of temporal symmetry have a similar effect? Using a nonlinear quantum mechanical model to describe the effective interaction of simple, exactly solvable quantum systems with some dissipative environment, the time-symmetry-breaking effect of this interaction on the ground-state energy of these systems can be studied analytically. Also, in the case of dynamical properties such as tunnelling currents, the breaking of time-reversal symmetry can have quite unexpected effects. In general, a dissipative environment is assumed to inhibit the motion of a dynamical system, e.g., by reducing the frequency and amplitude of a harmonic oscillator. Our study shows, however, that under certain resonance-like conditions, the interaction with the environment can also create currents that are not present in the unperturbed system. These results follow directly from the analytical solutions of our model.
Discrete time crystals are novel phases of matter that break the discrete time translational symmetry of a periodically driven system. In this Letter, we propose a classical system of weakly nonlinear parametrically driven coupled oscillators as a test bed to understand these phases. Such a system of parametric oscillators can be used to model period-doubling instabilities of Josephson junction arrays as well as semiconductor lasers. To show that this instability leads to a discrete time crystal we first show that a certain limit of the system is close to Langevin dynamics in a symmetry breaking potential. We numerically show that this phase exists even in the presence of Ising symmetry breaking using a Glauber dynamics approximation. We then use a field theoretic argument to show that these results are robust to other approximations including the semiclassical limit when applied to dissipative quantum systems.
We review recent advances in the research on quantum parametric phenomena in superconducting circuits with Josephson junctions. We discuss physical processes in parametrically driven tunable cavity and outline theoretical foundations for their description. Amplification and frequency conversion are discussed in detail for degenerate and non-degenerate parametric resonance, including quantum noise squeezing and photon entanglement. Experimental advances in this area played decisive role in successful development of quantum limited parametric amplifiers for superconducting quantum information technology. We also discuss nonlinear down-conversion processes and experiments on self-sustained parametric and subharmonic oscillations.
We discuss general properties of the equilibrium state in superconducting quantum circuits with anharmonic nonlinearities and detunings, in the nonlinear regime. By comparing moments of the steady state and those of a Schroinger cat, we show that true Schroinger cats cannot survive in the steady state if there is a single-photon loss. A delta-function `cat-like' steady-state distribution can be formed, but this only exists in the limit of extremely large nonlinearity. In general, the steady state is a mixed state whose purity is reduced by driving.
We review recent advances in the research on quantum parametric phenomena in superconducting circuits with Josephson junctions. We discuss physical processes in parametrically driven tunable cavity and outline theoretical foundations for their description. Amplification and frequency conversion are discussed in detail for degenerate and nondegenerate parametric resonance, including quantum noise squeezing and photon entanglement. Experimental advances in this area played decisive role in successful development of quantum limited parametric amplifiers for superconducting quantum information technology. We also discuss nonlinear down-conversion processes and experiments on self-sustained parametric and subharmonic oscillations.