L. F. Wei

Quantum state engineering with flux-biased Josephson phase qubits by Stark-chirped rapid adiabatic passages

In this article, the scheme of quantum computing based on the Stark-chirped rapid adiabatic passage (SCRAP) technique [L. F. Wei, J. R. Johansson, L. X. Cen, S. Ashhab, and F. Nori, Phys. Rev. Lett. 100, 113601 (2008)] is extensively applied to implement quantum state manipulations in flux-biased Josephson phase qubits. The broken-parity symmetries of bound states in flux-biased Josephson junctions are utilized to conveniently generate the desirable Stark shifts. Then, assisted by various transition pulses, universal quantum logic gates as well as arbitrary quantum state preparations can be implemented. Compared with the usual {pi}-pulse operations widely used in experiments, the adiabatic population passages proposed here are insensitive to the details of the applied pulses and thus the desirable population transfers can be satisfyingly implemented. The experimental feasibility of the proposal is also discussed.

Algebraic structure and analytic solutions of generalized three-level Jaynes - Cummings models

A generalized three-level Jaynes - Cummings model (JCM) which includes various ordinary JCMs is shown explicitly to have an SU(3) structure: the Hamiltonian can be treated as a linear function of the generators of the SU(3) group. Based on this algebraic structure, the exact algebraic solutions of the Schrodinger equation, as well as eigenvalues and eigenstates of the Hamiltonian, are obtained by an algebraic method. Thus the three-level JCM is completely solved algebraically. The SU(N) structure of the N-level JCM is also constructed explicitly and can be solved by the same method.

Exact solutions of non-autonomous quantum systems with semisimple Lie algebraic structure

If a non-autonomous quantum system has an semisimple Lie algebraic structure and its Hamiltonian can be treated as a linear function of the generators of a semisimple Lie group, we show a method for finding a set of gauge transformations that transform the Hamiltonian to a linear function of Cartan operators. The exact solutions of the equations of motion, as well as a set of time-dependent invariant operators which commute with each other, are obtained by the inverse gauge transformations. An SU(3) model serves as an illustration.

Gains without inversion in quantum systems with broken parities

For a quantum system with broken parity symmetry, selection rules cannot hold and cyclic transition structures are generated. With these loop transitions we discuss how to achieve inversionless gain of the probe field by properly setting the control and auxiliary fields. Possible implementations of our generic proposal with specific physical objects with broken parities (e.g., superconducting circuits and chiral molecules) are also discussed.

Eigenstates of the higher powers of an annihilation operator for a time-dependent harmonic oscillator and their properties

In the framework of dynamical invariant theory, we introduce the annihilation operator and creation operator for a time-dependent harmonic oscillator. The orthonormalized eigenstates of the operator are constructed, and their mathematical and quantum statistical properties are discussed in detail. Specifically, a particle moving in a Paul trap with periodically varying frequency is treated as an example to demonstrate the dynamical squeezing effects for the eigenstates of the operator .

Excited states of coherent state and their nonclassical properties

QUANTIZED radiation fields exhibiting nonclassical properties have been of great theoretical andexperimental interest in the last two decades. It is shown that various nonclassical states suchas squeezed state and Schrodinger cat state can be generated out of coherent state in thenonlinear process of the interaction of atom and field although the radiation field in a coherent