Quantum systems engineering

Abstract:

A method to change the interaction strength of a two-component condensate by π/2 pulses is introduced. It is shown that applying a specific series of pulses to the condensate leads to an effective time-averaged Hamiltonian, which is of the form of the original two-component Hamiltonian with an interaction strength depending on parameters of the external field. In addition, it is shown that it is possible to store a spin-squeezed state of a condensate for an arbitrarily long time.

Abstract:

We describe a technique for manipulating quantum information stored in collective states of mesoscopic ensembles. Quantum processing is accomplished by optical excitation into states with strong dipole-dipole interactions. The resulting "dipole blockade" can be used to inhibit transitions into all but singly excited collective states. This can be employed for a controlled generation of collective atomic spin states as well as nonclassical photonic states and for scalable quantum logic gates. An example involving a cold Rydberg gas is analyzed.

Abstract:

The relative phase of two initially independent Bose-Einstein condensates can be laser cooled to unite the two condensates by putting them into a ring cavity and coupling them with an internal Josephson junction. First, we show that this phase cooling process already appears within a semiclassical model. We calculate the stationary states, find regions of bistable behavior, and suggest a Ramsey-type experiment to measure the buildup of phase coherence between the condensates. We also study quantum effects and imperfections of the system.