Quasiparticle cooling via engineered dissipation in Floquet quantum circuits

We introduce an approach to realise non-trivial steady states in systems of many superconducting qubits out of equilibrium. The approach combines periodic application of unitary gates, which implements Floquet evolution of the system, and ancilla qubits that are periodically reset. The coupling of ancillas to the system realises a dissipative channel engineered to extract quasiparticle excitations from the system. The quasiparticles are defined in a general case by the Floquet circuit, with Hamiltonian evolution being a particular example. This drives the system to a steady state where quasiparticle occupation numbers are low, despite the uncontrollable weak noise inevitably present in the device. We demonstrate applications ranging from many-body states with low energy density to quantum transport in correlated systems. Effect of external weak noise on the steady state properties, including quasiparticle occupation numbers and entanglement, is analyzed. This work provides a scalable experimental path to realising long-lived entangled states in noisy intermediate-scale quantum devices.