Quantum pumping is a method of transporting particles through a circuit without an external applied voltage or chemical potential, but instead with localized time-varying potentials.Ballistic quantum pumping has been theorized in mesoscopic solid state sys tems, but experimental verifications have been challenging due to the capacitive coupling and rectification inherent to electronic systems.Using ultracold neutral atoms to test and verify the theoretical predictions of quantum pumping reduces these challenges while providing the advantages of easy confinement and manipulation, a high degree of coher ence, and bosons as well as fermions.In addition, ultracold atoms allow smooth tunability between classical thermal gases and quantum gases.Here, we design, build, characterize, and optimize a dual-species experimental apparatus capable of quantum pumping exper iments with Bose-Einstein condensates on an atom chip.We produce quasi-pure 87Rb Bose-Einstein condensates of ~ 104 atoms and successfully laser-cool 39K.We lay the experimental groundwork for quantum pumping experiments with ultracold atoms and characterize the classical dynamics of the system.These classical dynamics are supported with theoretical modeling that we have developed to compare the dramatic differences between the classical and quantum results of a double barrier turnstile pump as well as its single barrier building blocks.
Quantum pumping is a method of transporting particles through a circuit without an external applied voltage or chemical potential, but instead with localized time-varying potentials.Ballistic quantum pumping has been theorized in mesoscopic solid state sys tems, but experimental verifications have been challenging due to the capacitive coupling and rectification inherent to electronic systems.Using ultracold neutral atoms to test and verify the theoretical predictions of quantum pumping reduces these challenges while providing the advantages of easy confinement and manipulation, a high degree of coher ence, and bosons as well as fermions.In addition, ultracold atoms allow smooth tunability between classical thermal gases and quantum gases.Here, we design, build, characterize, and optimize a dual-species experimental apparatus capable of quantum pumping exper iments with Bose-Einstein condensates on an atom chip.We produce quasi-pure 87Rb Bose-Einstein condensates of ~ 104 atoms and successfully laser-cool 39K.We lay the experimental groundwork for quantum pumping experiments with ultracold atoms and characterize the classical dynamics of the system.These classical dynamics are supported with theoretical modeling that we have developed to compare the dramatic differences between the classical and quantum results of a double barrier turnstile pump as well as its single barrier building blocks.
A quantum pump is a device that transports particles through a circuit with localized time-varying potentials, and without the need for an external applied voltage or chemical potential. Quantum pumping was originally proposed in the context of electron transport in nanowires, but has proven difficult to implement. The ultracold atom approach represents a possible route around the current experimental bottleneck. We present an experiment to study 1D quantum mechanical scattering by an amplitude-modulated barrier. This experiment represents a first step toward implementing a quantum pump for ultracold atoms based on two such barriers modulated out of phase with one another. A single oscillating barrier imparts or subtracts kinetic energy in discrete amounts from the scattered atoms. In this manner, the energy spectrum of the scattered atoms resembles a comb with a tooth spacing proportional to the oscillation frequency of the barrier. This effect is analogous to the frequency modulation of a radio wave to add sidebands to a carrier frequency, where the carrier is the kinetic energy of ultracold atoms and the oscillating barrier provides the modulating signal. Numerical simulations of the scattering process confirm this basic scattering picture. We present dual chamber, dual-species a atom chip apparatus that produces quasi-pure Rubidium-87 Bose-Einstein condensates (BEC) of 10,000 atoms used to study the quantum scattering dynamics. The proposed experiment operates by releasing a BEC from a relaxed magnetic chip trap and directing it horizontally towards a tightly focused laser beam that serves as an oscillating barrier. A magnetic field gradient provided by is used to control the vertical motion of the BEC. Detection is carried out with a time of flight technique to resolve discrete atomic packet sidebands. This method can be used to study momentum sideband generation with a BEC in the presence of no or weak interactions. Dark-ground imaging can be used to detect small atom number BECs, which will have the benefit of weaker interactions.
We present a dual chamber atom chip apparatus for generating ultracold (87)Rb and (39)K atomic gases. The apparatus produces quasi-pure Bose-Einstein condensates of 10(4) (87)Rb atoms in an atom chip trap that features a dimple and good optical access. We have also demonstrated production of ultracold (39)K and subsequent loading into the chip trap. We describe the details of the dual chamber vacuum system, the cooling lasers, the magnetic trap, the multicoil magnetic transport system, the atom chip, and two optical dipole traps. Due in part to the use of light-induced atom desorption, the laser cooling chamber features a sufficiently good vacuum to also support optical dipole trap-based experiments. The apparatus is well suited for studies of atom-surface forces, quantum pumping and transport experiments, atom interferometry, novel chip-based traps, and studies of one-dimensional many-body systems.
Atom chips are an excellent tool for studying ultracold degenerate quantum gases, due to the high degree of controllability afforded by the precise potentials generated from the current-carrying microfabricated wires on the chip surface. The geometries of the trapping potentials are inherently capable of realising extreme aspect ratios, and therefore creating model systems with effectively reduced dimensionality, particularly the theoretically-tractable one-dimensional Bose gas. In addition, the temporal tunability makes it possible to impart non-adiabatic changes on the trapping potentials, allowing experimental investigation of samples which have been brought out of equilibrium - a situation which is not fully theoretically understood. This thesis describes the implementation, development and characterisation of an experimental system for producing the first Bose-Einstein condensates of atomic rubidium 87 gas trapped on the surface of an atom chip in Nottingham. Such an apparatus is very complex and requires careful characterisation in order to run in a stable and reliable way. Details of the experimental setup are thoroughly outlined, including the vacuum system, lasers, electronics, computer control and timing, and the optical imaging system. A newly installed compact two-dimensional magneto-optical trap provides an loading rate of 5e7 atoms per second for loading a three-dimensional mirror-magneto-optical trap with 1.5e8 atoms, at a temperature of 300uK within 10s. The cloud is then sub-Doppler cooled to 50uK, and spin-polarised with 96% purity into the |F=2,mF=+2> ground state within 5ms, in preparation for loading a purely magnetic trap. A millimeter sized copper Z-shaped conductor located beneath the atom chip surface creates a Ioffe-Pritchard magnetic trap, into which the laser cooled cloud is loaded with 70% efficiency, and can be held with a vacuum-limited lifetime of 40s. Evaporative cooling then pre-cools the sample to below 20uK within 10s, to allow the subsequent loading into potentials created by the atom chip with 100% efficiency. A final evaporation stage then cools the cloud below the phase transition temperature of 800nK, resulting finally in pure BECs with 105 atoms confined using the atom chip. Key measurements of various properties of the trapped condensates are presented, which are important in order to characterise the system fully, and to compare with theoretical expectations. In particular, included are the variation of condensate fraction with temperature, the BEC expansion dynamics, and the condensate lifetime in the trap, for example. Finally, it is demonstrated how BECs can be produced on the atom chip without the use of external macroscopic coils, achieved by using novel, integrated sheet structures located beneath the chip surface - unique to this experimental system - to create the necessary bias fields.
In modern quantum technology, different quantum systems have properties that make them effective for some tasks and less beneficial for others. Integrating these systems together into a single quantum hybrid system, exploiting the advantages of each systems strengths while suppressing their disadvantages, can advance the total performance. On-chip quantum hybrid systems coupled to an ensemble of ultracold atoms show a great potential for advancing quantum technology, because they combine the long coherence time of the atomic ensemble with access to conventional read-out techniques provided by the chip. This thesis presents an apparatus that we have built to carry out experiments with coupling ultracold 87Rb gases to various systems, including nanomechanics and optical cavities. The apparatus operates at ultra-high vacuum conditions, required for experiments with ultracold gases, and its design allows us to easily and quickly switch between different on-chip devices to perform and study quantum hybridization with ultracold gases. Such versatility is provided by separating the region where the ultracold gas is created from the location of the chip, and implementing a system which can optically transfer the atoms between these two regions. In this work we also describe atom cooling techniques used in this experiment, including magneto-optical trapping, sub-Doppler cooling in optical molasses and evaporative cooling. These methods have demonstrated cooling to temperatures below 100 uK. We also discuss a setup for optimal optical-dipole transport. Finally, we theoretically consider magnetic coupling between atoms and nanomechanical oscillators and propose using the Landau-Zener transitions as a method for reducing or measuring mechanical temperature of the resonators, and to create quantum entanglement between multiple devices.
This thesis is primarily a comprehensive discussion of the development of two experimental studies: the quantum transport and effects of heating of ultracold atoms. It specifically provides details of the manipulation and control of ultracold atoms in magnetic waveguides, optical lattices, and optical billiards. The design, construction, and implementation of experimental apparati are also outlined and additional experimental tests are summarized, including the realization of a macroscopic transport (> 20 cm) system for ultracold atoms and transmission of ultracold atoms through a random optical potential. The first experiment is a study of the quantum transport for atoms confined in a periodic potential. These results include a comparison made of thermal and BEC initial conditions. Here, observation of ballistic transport is made for all values of well depth and initial conditions, and the expansion rates for thermal atoms are shown to be in excellent agreement with a singleparticle model. For weak wells (V0/ER ≤ 6), the expansion of the BEC is also in excellent agreement with single-particle theory, using an effective temperature model based on single (non-interacting) particle theory. For deep wells (V0/ER ≥ 6), a crossover is observed to a new regime for the BEC case, indicating the importance of interactions on quantum transport. The second experiment is a study of the effect of different heating rates on a dilute Bose gas confined in a quasi-1D finite, leaky box. An optical kicked-rotor is used to transfer energy to the atoms while two repulsive optical beams are used to confine the atoms. The average energy of the atoms is localized after a large number of kicks and the system reaches a nonequilibrium steady state. A numerical simulation of the experimental data suggests that the localization is due to energetic atoms leaking over the barrier. Our data also indicates a correlation between collisions and the destruction of the BoseEinstein condensate fraction and an exponential decay in phase space density.
In this dissertation we study the development of microwave and RF near-field potentials for use with atom chip trapped atomic gases. These potentials are inherently spin-dependent, able to target individual spin states simultaneously. In contrast with traditional atom chip potentials, these RF traps can be operated at arbitrary bias magnetic field strengths and thus be combined with magnetic Feshbach resonances. Furthermore, these potentials can strongly suppress the potential roughness that plagues traditional atom chip potentials. We present a dual chamber atom chip apparatus for generating ultracold 87Rb and 39K atomic gases. The apparatus produces quasi-pure Bose-Einstein condensates of 104 87Rb atoms in an atom chip trap that features a dimple and good optical access. We have also demonstrated production of ultracold 39K and subsequent loading into the chip trap. We describe the details of the dual chamber vacuum system, the cooling lasers, the magnetic trap, the multi coil magnetic transport system, and the atom chip. The apparatus is well suited for studies of atom-surface forces, quantum pumping and transport experiments, atom interferometry, novel chip-based traps, and studies of one-dimensional many-body systems.