Effect of broadband noise on adiabatic passage in superconducting nanocircuits

With the rapid technological progress in quantum-state engineering in superconducting devices there is an increasing demand for techniques of quantum control. Stimulated Raman adiabatic passage (STIRAP) is a powerful method in quantum optics which has remained largely unknown to solid-state physicists. It is used to achieve highly efficient and controlled population transfer in (discrete) multilevel quantum systems[1]. Apart from other potential applications in solid-state physics, adiabatic passage offers interesting possibilities to manipulate qubit circuits, in particular for the generation of nonclassical states in nanomechanical or electromagnetic resonators[2]. In this contribution, we study in detail a possible implementation of the STIRAP protocol in the Quantronium, a superconducting nanocircuit based on Josephson junctions in the so called charge-phase regime. Il has been proposed[2] that this devices is a good candidate for observing coherent adiabatic population transfer for its characteristics of low decoherence and efficient addressability by external AC electromagnetic fields. In particular we present a detailed analysis of the efect of broadband charge noise, which is the main source of decoherence for this device, extending to a three level system the theory proposed in Ref.[3]. It is shown that the effect of high-frequency noise is similar to the quantum optical case. The main problem in solid state devices comes from low-frequency noise, which has the 1/f form. In this case it may produce stray two-photon detunings which prevent the device to evolve adiabaticaly towards the correct target state. However inducing Zener tunneling between Autler-Townes states it is shown to increase the population transfer efficiency, minimizing the effect of low-frequency noise.