Reservoir-engineering shortcuts to adiabaticity

TL;DR

This paper introduces a reservoir-engineering protocol that enables rapid adiabatic state transfer in a qubit system by coupling it to an ancilla and a thermal bath, improving fidelity through incoherent dynamics.

Contribution

It presents a novel reservoir-engineering approach for fast adiabatic transfer using an ancilla and thermal bath, with analysis of different dynamical regimes.

Findings

Fidelity improves with increased bath temperature in the high decay rate regime.

Low-temperature coupling with ancilla suppresses diabatic transitions via effective cooling.

Protocol is robust and implementable with pulsed, stroboscopic coupling.

Abstract

We propose a protocol that achieves fast adiabatic transfer between two orthogonal states of a qubit by coupling with an ancilla. The qubit undergoes Landau-Zener dynamics, whereas the coupling realizes a time-dependent Hamiltonian, which is diagonal in the spin's instantaneous Landau-Zener eigenstates. The ancilla (or meter), in turn, couples to a thermal bath, such that the overall dynamics is incoherent. We analyse the protocol's fidelity as a function of the strength of the coupling and of the relaxation rate of the meter. When the meter's decay rate is the largest frequency scale of the dynamics, the spin dynamics is encompassed by a master equation describing dephasing of the spin in the instantaneous eigenbasis. In this regime the fidelity of adiabatic transfer improves as the bath temperature is increased. Surprisingly, the adiabatic transfer is significantly more efficient in the opposite regime, where the time scale of the ancilla dynamics is comparable to the characteristic spin time scale. Here, for low temperatures the coupling with the ancilla tends to suppress diabatic transitions via effective cooling. The protocol can be efficiently implemented by means of a pulsed, stroboscopic coupling with the ancilla and is robust against moderate fluctuations of the experimental parameters.