This thesis details the experimental investigation of a new type of atom interferometer using rubidium-85 atoms in the unexplored near-resonant domain. A cold cloud of atoms, all prepared in the same hyperfine ground state, are subjected to temporally periodic pulses of near-resonant standing waves of light. The standing wave pulses are made to act like an absorption grating where only atoms located around the low intensity region about the nodes remain in the initial ground state, the rest are pumped into a dark hyperfine ground state. The output of the atom interferometer is a measure of the fraction of atoms remaining in the initial ground state after N standing wave pulses for different times between the pulses. An increased survival rate is observed for certain times between pulses due to the occurrence of a coherence echo and the matter wave Talbot effect. This feature allows us to use our atom interferometer to make measurements of the Talbot time which is an important parameter in determinations of the fine structure constant alpha.\n\nWe provide a theoretical model to describe the relevant physics behind our atom interferometer that compares well with our empirical results. Design and implementation of the apparatus are discussed along with characterisation of parameters such as pulse duration, pulse number, and frequency. Finally we include a demonstration of how, in principle, our atom interferometer could be used to make precision measurements of the Talbot time along with some of the necessary steps to bring it in line with current leading measurements.
This thesis details the experimental investigation of a new type of atom interferometer using rubidium-85 atoms in the unexplored near-resonant domain. A cold cloud of atoms, all prepared in the same hyperfine ground state, are subjected to temporally periodic pulses of near-resonant standing waves of light. The standing wave pulses are made to act like an absorption grating where only atoms located around the low intensity region about the nodes remain in the initial ground state, the rest are pumped into a dark hyperfine ground state. The output of the atom interferometer is a measure of the fraction of atoms remaining in the initial ground state after N standing wave pulses for different times between the pulses. An increased survival rate is observed for certain times between pulses due to the occurrence of a coherence echo and the matter wave Talbot effect. This feature allows us to use our atom interferometer to make measurements of the Talbot time which is an important parameter in determinations of the fine structure constant alpha.\n\nWe provide a theoretical model to describe the relevant physics behind our atom interferometer that compares well with our empirical results. Design and implementation of the apparatus are discussed along with characterisation of parameters such as pulse duration, pulse number, and frequency. Finally we include a demonstration of how, in principle, our atom interferometer could be used to make precision measurements of the Talbot time along with some of the necessary steps to bring it in line with current leading measurements.
We have used an echo-type atom interferometer that manipulates laser-cooled atoms in a single ground state to investigate the effect of light scattering from pulsed and continuous-wave light. The interferometer uses two off-resonant standing-wave pulses applied at times t=0 and t=T to diffract and recombine momentum states separated by $2\ensuremath{\hbar}k$ at t=2T. Matter wave interference is associated with the formation of a density grating with period $\ensuremath{\lambda}/2$ in the vicinity of this echo time. The grating contrast is measured by recording the intensity of coherently backscattered light. The interferometer is perturbed by an additional pulse applied at $t=2T\ensuremath{-}\ensuremath{\delta}T$ or by continuous-wave background light. If the additional pulse is a standing wave, the momentum states interfering at t=2T are displaced and the grating contrast can be completely recovered due to constructive interference. In this case, the contrast shows a periodic modulation at the atomic recoil frequency as a function of $\ensuremath{\delta}T$. In a recent work, it was shown that the atomic recoil frequency can be measured easily and precisely when using coherence functions to model the signal shape. This paper provides an alternative description of the signal shape through an analytical calculation of echo formation in the presence of an additional standing-wave pulse. Using this treatment, it is possible to model the effects of spontaneous emission and spatial profile of the laser beam on the signal shape. Additionally, the theory predicts scaling laws as a function of the pulse area and the number of additional standing-wave pulses. These scaling laws are investigated experimentally and can be exploited to improve precision measurements of the atomic recoil frequency. We also show that coherence functions can be used to make a direct measurement of the populations of momentum states associated with the ground state under conditions where the Doppler-broadened velocity distribution of the sample is much larger than the recoil velocity. These measurements are consistent with Monte Carlo wave-function simulations. If the additional pulse is a traveling wave, we find that the grating contrast measured as a function of $\ensuremath{\delta}T$ can be modeled by a quasiperiodic coherence function as in previous experiments that utilized atomic beams. In this work, we investigate the dependence of the photon scattering rate on the intensity and detuning of the traveling wave. We also study the effects of perturbing the interferometer with continuous-wave light and find that the dependence of the photon scattering rate on the intensity and detuning of the perturbing field is consistent with expectations.
Matter - wave interferometry began with the development of electron interferometers and neutron interferometers in the 1950s and 1960s, but it wasn't until 1991 that the first atom matter - wave interferometer was realized. This was followed by a surge of activity sparked by the advent of sources of ultracold laser-cooled atoms. Some of the potential advantages of atom interferometry over neutron interferometry include: much higher particle fluxes, lower particle velocities, larger particle masses, particles with internal states, and laboratory-based sources. This volume is the first text on atom interferometry. It consists of ten comprehensive review articles by leading researchers in the field, many of whom pioneered the first atom interferometers in 1991. The articles describe the different types of atom interferometers developed to date, ranging from the three-grating Mach - Zehnder interferometer based on nanofabricated grating structures (MIT) or standing-wave light-field gratings (Innsbruck), to the Talbot - Lau atom interferometer (Berkeley and Michigan), to atom interferometers based on internal-state labelling such as separated light-field interferometers (PTB, Hannover and Paris-Nord) and light-pulse interferometers (Stanford). Some of the recent applications of atom interferometry described in the articles include high precision measurements of rotations, the gravitational acceleration, and the fine structure constant (Stanford); measurements of topological phases (PTB and Hannover); correlation experiments with atoms and photons (Konstanz) and with pairs of atoms (Tokyo); holographic manipulation of atoms (Tokyo); and experiments on the quantum theory of measurement (Garching, Harvard and Texas A&M). In summary, this volume provides an excellent up-to-date account of atom interferometry and is recommended as essential reading for all researchers and would-be researchers in the field. At the same time it contains sufficient background material and theory to serve as an excellent introduction for the non-specialist. The field is presently moving at such a rapid pace, however, that many of the latest results reported in this volume will already have been superseded by the time it reaches the library shelves.
The basic physical principles behind atom interferometers based on optical pulses of light are summarized. This method of atom interferometry is based on measurements in the time and frequency domain and is an inherently precise measurement technique. After a brief discussion of some of the important technical requirements for good fringe accuracy and visibility, we describe an interferometer that has measured the acceleration of an atom due to gravity with a resolution better than one part in 1010. We project that the absolute accuracy of our measurement will be of the order of a few parts in 109. We also describe an interferometer experiment that measures the recoil energy shift of an atom when it absorbs a photon. When combined with the value of the Rydberg constant and the mass ratios MCs/mp and mp/me, one can obtain a value for α, the fine structure constant. Currently, we have an experimental resolution Δα/α ∼ 10-8 after two hours of integration time and are studying the systematic effects that affect the measurement.
This thesis presents work performed to obtain an optical mask for conducting matter-wave interfer-ometry experiments with ultra-cold rubidium-85 atoms. The optical mask is essentially an absorptive diffraction grating made of light, and it can imprint a periodic density pattern on a cloud of atoms with a period of half the wavelength of the light used. The mask has an analogous effect to quickly passing a diffraction grating through the cloud, removing atoms located at the nodes of the grating (though the optical mask depumps atoms to a different hyperfine ground state rather than actually removes them). The mask should be useful in performing precision measurements of physical constants such as the fine-structure constant α, and acceleration due to gravity g. The thesis briefly expounds major historical developments in atom interferometry and laser cooling. Prerequisites for an optical mask include a functioning magneto-optical trap, and the ability to perform polarisation-gradient cooling on trapped atoms. The theory of these two techniques is reviewed and the principle of the the optical mask is explained. The experimental apparatus that was constructed to realise the optical mask is described, and technical developments made along the way are presented. Finally, aspects of the ex-periment relevant to the optical mask are characterised. The experiment can reliably produce samples of cold atoms at temperatures of around 10 µK, and can use the cold atoms as an optical frequency reference accurate to ∼ 1 MHz. Clear evidence that the cloud of atoms is being density-modulated by the optical mask is presented. Improvements required to make the experiment into a fully-functioning interferometer are also discussed. i ii
This thesis presents the experimental and theoretical studies of the survival resonances in a dissipative atom-optics system, and their applications. We demonstrate this resonant phenomenon by using an alternative approach to the standard atom-optics delta-kicked rotor (AODKR), where we add spatially periodic dissipation or loss to each pulse. The system evolution is therefore non-unitary.\n\nWe first investigate the emergence of the survival resonances by exposing a cloud of laser-cooled Rubidium-85 atoms to standing-wave light pulses. The frequency of the light is tuned close to an open atomic transition. Scattering of the light from the standing wave leads the atoms to decay into a dark state that is far-off-resonance to both the standing-wave light and the subsequent detection light. Once the atoms go to the dark state, they are considered to be lost. The atom number is thereby {\\it not} a conserved quantity. Consequently, a meaningful dynamic observable is the survival probability of the atoms. Varying the pulse interval reveals a series of resonant peaks at integer multiples of half the Talbot time. These peaks are deemed survival resonances and are a matter-wave interferometric phenomenon. The appearance of the peaks can be conceptually understood through the matter-wave Talbot-Lau effect. For a complete understanding, we build a model to simulate the system which captures the dynamics well.\n\nIn addition to acting as an optical mask that modulates the wave functions' amplitude, the still present optical dipole force of the standing wave imprints a phase pattern to the atomic wave functions. This gives rise to a micro-lensing effect that increases the peak survival dramatically. Using such an effect can help to enhance the incisiveness of the resonances, which might find applications in precision measurements.\n\nThe width of survival resonance peaks narrows faster than expected from the Fourier-limit when the pulse number is changed. The standard AODKR displays a similar sub-Fourier behavior.\n\nThis thesis also demonstrates two applications of using survival resonances. The temporally pulsed spatially periodic dissipation is used for preparing well-defined initial conditions. Feeding back lost atoms gives a non-thermal atomic state that enhances subsequent survival resonance measurements. This can find its application in the state preparation in atom interferometry.\n\nTo show the feasibility of using survival resonances in an atom interferometer, we construct a proof-of-concept atomic gravimeter. With a vertically arranged standing-wave light beam, we perform an interferometric measurement of the gravitational acceleration g utilizing the survival resonances. Gravity removes the survival resonances, but they re-emerge when the standing wave co-moves with the free-falling atomic cloud. To study the performance of this technique and find a good parameter combination, we carry out a series of simulations and experiments. We measure g with a precision of 5 ppm using a drop distance of less than 1 mm. The sensitivity improves with the square of the drop time, which indicates we can reach a precision of the mu-Gal regime with a drop distance of 10 cm. The simple implementation makes this technique an attractive candidate for a low cost and compact atomic gravimeter.
We have developed a technique for measuring the atomic recoil frequency using a single-state echo-type atom interferometer that manipulates laser-cooled atoms in the ground state. The interferometer relies on momentum-state interference due to two standing-wave pulses that produce density gratings. The interference is modified by applying a third standing-wave pulse during the interferometer pulse sequence. As a result, the grating contrast exhibits periodic revivals at the atomic recoil frequency r as a function of the time at which the third pulse is applied, allowing r to be measured easily and precisely. The contrast is accurately described by a coherence function, which is the Fourier transform of the momentum distribution, produced by the third pulse and by the theory of echo formation. If the third pulse is a traveling wave, loss of grating contrast is observed, an effect also described by a coherence function. The decay of the grating contrast as a function of continuous-wave light intensity is used to infer the cross section for photon absorption.