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.