Reservoir-engineering shortcuts to adiabaticity
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.