Coherent control of quantum tunnelling is investigated analytically for two bosons held in a driven triple-well potential. In the high-frequency region within resonance, the non-Floquet states with slowly varying populations are constructed by the linear superposition of Floquet solutions. For the non-resonance case with appropriate reduced parameters, we obtain another set of analytical solutions and their numerical correspondences, which exhibits the selective tunnelling effect of atoms. Applying the presented analytical results, a scheme to transport two bosons from the first well to the third is suggested by adjusting the driving parameters.

We report on the first demonstration of chaos-assisted directed transport of a quantum particle held in an amplitude-modulated and tilted optical lattice, through a resonance-induced double-mean displacement relating to the true classically chaotic orbits. The transport velocity is controlled by the driving amplitude and the sign of tilt, and also depends on the phase of the initial state. The chaos-assisted transport feature can be verified experimentally by using a source of single atoms to detect the double-mean displacement one by one, and can be extended to different scientific fields.

We use three bosons held in a depth-tilt combined-modulated double-well to study coherent control of quantum transitions between quasi-degenerate stationary-like states (QDSLSs) with the same quasienergy. Within the high-frequency approximation and for multiple-resonance conditions, we analytically obtain the different QDSLSs including the maximal bipartite entangled states, which enable us to manipulate the transitions between QDSLSs without the observable multiphoton absorption and to simulate a two-qubit system with the considered bosons. The analytical results are confirmed numerically and good agreement is shown. The quantum transitions between QDSLSs can be observed and controlled by adjusting the initial and the final atomic distributions in the currently proposed experimental setup, and possess potential applications in qubit control based on the bipartite entangled states and in engineering quantum dynamics for quantum information processing.

We investigate the coherent manipulation of quantum tunnelling for a single atom held in a driven planar four-well potential with diagonal coupling. In the high-frequency regime, the non-Floquet states with slowly varying populations are constructed by the linear superposition of Floquet solutions. Based on the analytical results, the effect of the selective coherent destruction of tunnelling is exhibited and the two-pathway switching scheme is suggested by adjusting the driving parameters.

A classical analysis of two equal intensity coherent fields incident on a beamsplitter shows that the difference-phase noise of the output depends only on the noise in the difference of the amplitudes of the input fields and not on their phase noise. This suggests that in the quantum mechanical case squeezing in the amplitudes of the input beams can lead to squeezing in the phase difference of the output beams. We show that this is true. We also find the phase properties of the output when the input consists of two number states with an equal number of photons. The difference phase distribution consists of two narrow peaks, at θ = 0 and θ = π. States with small phase difference noise should be useful in the measurement of phase shifts.