An accelerator mode based technique for studying quantum chaos

We experimentally demonstrate a method for selecting small regions of phase space for kicked rotor quantum chaos experiments with cold atoms. Our technique uses quantum accelerator modes to selectively accelerate atomic wavepackets with localized spatial and momentum distributions. The potential used to create the accelerator mode and subsequently realize the kicked rotor system is formed by a set of off-resonant standing wave light pulses. We also propose a method for testing whether a selected region of phase space exhibits chaotic or regular behavior using a Ramsey type separated field experiment.Comment: 5 pages, 3 figures, some modest revisions to previous version (esp. to the figures) to aid clarity; accepted for publication in Physical Review A (due out on January 1st 2003

Beam splitting mechanisms for a caesium atom interferometer

This thesis presents a detailed investigation of a caesium atom interferometer which uses a combination of microwaves and momentum-changing adiabatic transfer pulses to implement a beam splitter. This combination allows the arms of the interferometer to be spatially separated in a Mach-Zehnder configuration. An examination of the efficiency of the adiabatic transfer process is made through both numerical modelling and experimental testing. Further investigations are made into the limiting factors of the interferometer as a whole, with the experimentally achieved fringe contrast being well accounted for by the theory. The process of Raman transfer, a beam splitting mechanism popular with other groups working in atom interferometry, is also analyzed theoretically to establish if it would be advantageous in our interferometer. It is found that, although it would result in a small improvement if implemented in the current apparatus, to exploit its advantages fully would require large modifications to our setup. Finally, a third possible beam splitting mechanism, accelerator modes, is investigated both experimentally and theoretically. This is a new technique, using a pulsed standing wave of off-resonant light, capable of transferring momenta greater than 100(h/2#pi#)k with high efficiency. We investigate how the efficiency and amount of momentum transfer depend on the parameters of the light field and consider the potential of this technique as an atom optical beam splitter. (author)Available from British Library Document Supply Centre-DSC:D210731 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Signatures of Quantum Stability in a Classically Chaotic System.

We experimentally and numerically investigate the quantum accelerator mode dynamics of an atom optical realization of the quantum delta-kicked accelerator, whose classical dynamics are chaotic. Using a Ramsey-type experiment, we observe interference, demonstrating that quantum accelerator modes are formed coherently. We construct a link between the behavior of the evolution's fidelity and the phase space structure of a recently proposed pseudoclassical map, and thus account for the observed interference visibilities

Approaching classicality in quantum accelerator modes through decoherence.

We describe measurements of the mean energy of an ensemble of laser-cooled atoms in an atom optical system in which the cold atoms, falling freely under gravity, receive approximate δ-kicks from a pulsed standing wave of laser light. We call this system a “δ-kicked accelerator.” Additionally, we can counteract the effect of gravity by appropriate shifting of the position of the standing wave, which restores the dynamics of the standard δ-kicked rotor. The presence of gravity (δ-kicked accelerator) yields quantum phenomena, quantum accelerator modes, which are markedly different from those in the case for which gravity is absent (δ-kicked rotor). Quantum accelerator modes result in a much higher rate of increase in the mean energy of the system than is found in its classical analog. When gravity is counteracted, the system exhibits the suppression of the momentum diffusion characteristic of dynamical localization. The effect of noise is examined and a comparison is made with simulations of both quantum-mechanical and classical versions of the system. We find that the introduction of noise results in the restoration of several signatures of classical behavior, although significant quantum features remain

International Timescales with Optical Clocks (ITOC)

A new collaborative European project “International timescales with optical clocks” (ITOC) aims to tackle the key challenges that must be addressed prior to a redefinition of the SI second. A coordinated programme of comparisons will be carried out between European optical clocks developed in five different laboratories, enabling their performance levels to be validated at an unprecedented level of accuracy. Supporting work will be carried out to evaluate relativistic effects that influence the comparisons, including the gravitational redshift of the clock transition frequencies. A proof-of-principle experiment will also be performed to demonstrate that optical clocks could be used to make direct measurements of the Earth’s gravity potential with high temporal resolution