Lattice gauge theory and dynamical quantum phase transitions using noisy intermediate-scale quantum devices

Lattice gauge theories are a fascinating and rich class of theories relating to the most fundamental models of particle physics, and as experimental control on the quantum level increases there is a growing interest in nonequilibrium effects such as dynamical quantum phase transitions. To demonstrate how these physical theories can be accessed in near-term quantum devices, we study the dynamics of a (1 + 1)D U(1) quantum link model following quenches of its mass term. We find that the system undergoes dynamical quantum phase transitions for all system sizes considered, even the smallest where the dynamics can be solved analytically. We devise a gauge-invariant string order parameter whose zeros correlates with the structure of the Loschmidt amplitude, making the order parameter useful for experimental study in near-term devices. The zeros of the Loschmidt amplitude as well as the zeros of our order parameter are revealed by vortices in their phases, which can be counted by a topologically invariant winding number. With noisy intermediate-scale quantum devices in mind, we propose a class of superconducting circuits for the general implementation of U(1) quantum link models. The principles of these circuits can be generalized to implement other, more complicated gauge symmetries. Furthermore, the circuit can be modularly scaled to any lattice configuration. Simulating the circuit dynamics with realistic circuit parameters, we find that it implements the target dynamics with a steady average fidelity of 99.5% or higher. Finally, we consider readout of the circuit using a method that yields information about all the degrees of freedom with resonators coupled dispersively to only a subset of them. This constitutes a direct and relatively straightforward protocol to access both Loschmidt amplitudes and the order parameter.

Automated summary

Lattice gauge theories are fundamental in particle physics and there is increasing interest in studying nonequilibrium effects like dynamical quantum phase transitions. A U(1) quantum link model in (1 + 1)D was studied after quenches of its mass term, revealing dynamical quantum phase transitions for all system sizes. A gauge-invariant string order parameter was devised and implemented for experimental study in near-term devices, with vortices in phases indicating zeros of relevant amplitudes. Furthermore, a class of superconducting circuits for implementing U(1) quantum link models was proposed and shown to achieve target dynamics with high fidelity. Additionally, a method for readout of the circuit was suggested for accessing information about all degrees of freedom.