Speedup of Adiabatic Multiqubit State-Transfer by Ultrastrong Coupling of Matter and Radiation

Abstract

Ultrastrongly coupled quantum hardware may increase the speed of quantum state processing in distributed architectures, allowing to approach fault-tolerant threshold. We show that circuit QED architectures in the ultrastrong coupling regime, which has been recently demonstrated with superconductors, may show substantial speedup for a class of adiabatic protocols resilient to the main source of errors, namely the interplay of dynamical Casimir effect and cavity losses.

Optimized state transfer in systems of ultrastrongly coupled matter and radiation

“…In order to improve on the results of [20] in what follows we investigate the optimal timedependence of g i (t) using the Quantum Optimal Control (QOC) [14,1] tools developed in [13].…”

“…To overcome this problem a communication channel implemented by an adiabatic protocol similar to STIRAP [21] has been proposed [20]. The system of two qubits (eigenstates |σ i ∈ {|g i , |e i } for i = 1, 2), coupled to a single resonator mode is described by the Rabi Hamiltonian [15]…”

“…We consider time-dependent couplings g i (t). In the regime where the RWA holds a STIRAPlike process implemented by turning on g 2 (t) is before g 1 (t): yields the state transfer [20]…”

Dynamical Casimir Effect and State Transfer in the Ultrastrong Coupling Regime

“…Novel schemes are required in order to counteract the DCE. Preliminary results [29] with a protocol inspired by stimulated Raman adiabatic passage (STIRAP) [30] show enhanced reliability of state transfer up to relatively large g ≈ 0.2, also in presence of cavity damping. Optimal control techniques [16,31] could also be applied to this problem, with foreseen further improvements for the reliability of quantum protocols in the USC regime.…”