Charles E. Creffield

Quantum Control and Entanglement using Periodic Driving Fields

We propose a scheme for producing directed motion in a lattice system by applying a periodic driving potential. By controlling the dynamics by means of the effect known as coherent destruction of tunneling, we demonstrate a novel ratchetlike effect that enables particles to be coherently manipulated and steered without requiring local control. Entanglement between particles can also be controllably generated, which points to the attractive possibility of using this technique for quantum information processing.

Tuning the Mott transition in a Bose-Einstein condensate by multiple photon absorption.

We study the time-dependent dynamics of a Bose-Einstein condensate trapped in an optical lattice. Modeling the system as a Bose-Hubbard model, we show how applying a periodic driving field can induce coherent destruction of tunneling. In the low-frequency regime, we obtain the novel result that the destruction of tunneling displays extremely sharp peaks when the driving frequency is resonant with the depth of the trapping potential (multi-photon resonances), which allows the quantum phase transition between the Mott insulator and the superfluid state to be controlled with high precision. We further show how the waveform of the field can be chosen to maximize this effect.

Coherent control of self-trapping of cold bosonic atoms

We study the behavior of a Bose-Einstein condensate held in an optical lattice. We first show how a self-trapping transition can be induced in the system by either increasing the number of atoms occupying a lattice site, or by raising the interaction strength above a critical value. We then investigate how applying a periodic driving potential to the self-trapped state can be used to coherently control the emission of a precise number of correlated bosons from the trapping-site. This allows the formation and transport of entangled bosonic states, which are of great relevance to novel technologies such as quantum information processing.

Dynamical instability in kicked Bose-Einstein condensates

Bose-Einstein condensates subject to short pulses (kicks) from standing waves of light represent a nonlinear analog of the well-known chaos paradigm, the quantum kicked rotor. Previous studies of the onset of dynamical instability (i.e., exponential proliferation of noncondensate particles) suggested that the transition to instability might be associated with a transition to chaos. Here we conclude instead that instability is due to resonant driving of Bogoliubov modes. We investigate the Bogoliubov spectrum for both the quantum kicked rotor (QKR) and a variant, the double kicked rotor (QKR-2). We present an analytical model, valid in the limit of weak impulses which correctly gives the scaling properties of the resonances and yields good agreement with mean-field numerics.

Theory of 2 delta-kicked quantum rotors.

We examine the quantum dynamics of cold atoms subjected to pairs of closely spaced delta kicks from standing waves of light and find behavior quite unlike the well-studied quantum kicked rotor (QKR). We show that the quantum phase space has a periodic, cellular structure arising from a unitary matrix with oscillating bandwidth. The corresponding eigenstates are exponentially localized, but scale with a fractional power L is less similar to h(-0.75), in contrast to the QKR for which L is less similar to h(-1). The effect of intercell (and intracell) transport is investigated by studying the spectral fluctuations with both periodic as well as open boundary conditions.

Instability and control of a periodically driven Bose-Einstein condensate

We investigate the dynamics of a Bose-Einstein condensate held in an optical lattice under the influence of a strong periodic driving potential. Studying the mean-field version of the Bose- Hubbard model reveals that the condensate becomes dynamically unstable when the effective intersite tunneling becomes negative. We further show how controlling the sign of the tunneling can be used to manage the dispersion of an atomic wave packet.

Localization-Delocalization Transition in a System of Quantum Kicked Rotors

The quantum dynamics of atoms subjected to pairs of closely-spaced

Generation of uniform synthetic magnetic fields by split driving of an optical lattice

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Chaotic quantum ratchets and filters with cold atoms in optical lattices: Analysis using Floquet states

-kicks from optical potentials are shown to be quite different from the well-known paradigm of quantum chaos, the singly-

Finding zeros of the Riemann zeta function by periodic driving of cold atoms

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