High-fidelity quantum driving

The ability to accurately control a quantum system is a fundamental requirement in many areas of modern science such as quantum information processing and the coherent manipulation of molecular systems. It is usually necessary to realize these quantum manipulations in the shortest possible time in order to minimize decoherence, and with a large stability against fluctuations of the control parameters. While optimizing a protocol for speed leads to a natural lower bound in the form of the quantum speed limit rooted in the Heisenberg uncertainty principle, stability against parameter variations typically requires adiabatic following of the system. The ultimate goal in quantum control is to prepare a desired state with 100% fidelity. Here we experimentally implement optimal control schemes that achieve nearly perfect fidelity for a two-level quantum system realized with Bose-Einstein condensates in optical lattices. By suitably tailoring the time-dependence of the system's parameters, we transform an initial quantum state into a desired final state through a short-cut protocol reaching the maximum speed compatible with the laws of quantum mechanics. In the opposite limit we implement the recently proposed transitionless superadiabatic protocols, in which the system perfectly follows the instantaneous adiabatic ground state. We demonstrate that superadiabatic protocols are extremely robust against parameter variations, making them useful for practical applications.Comment: 17 pages, 4 figure

High-fidelity superadiabatic population transfer of a two-level system with a linearly chirped Gaussian pulse

We investigate high-fidelity superadiabatic quantum driving in a chirped Gaussian two-level model with a Gaussian temporal envelope and a linear detuning. We show that the nonadiabatic losses can be canceled to any desired order by constructing and adjusting an auxiliary Hamiltonian (counter-diabatic field) and a symmetry in the fidelity arises on the counter-diabatic field ratio. A high-fidelity, robust, and accelerated (in a shorter time) transitionless superadiabatic population transfer is achieved that ensures a perfect following of the instantaneous adiabatic ground state even in the nonadiabatic regime. The features make the superadiabatic protocol a potentially important tool for quantum information. Copyright (C) EPLA, 2016National Basic Research Program of China (973 Program) [2013CBA01502, 2013CB834100]; National Natural Science Foundation of China [11665020, 11547046, 11374040, 11475027, 11575027, 11274051]; China Postdoctoral Science Foundation [2015M580068]; Natural Science Foundation of Gansu Province, China [1606RJZA081]SCI(E)ARTICLE611