Two circuits were designed, built, and tested for the purpose of aiding in the transfer of 87Rb atoms from a MOT to dipole traps and for characterizing the final dipole traps. The first circuit was a current switch designed to quickly turn the magnetic fields of the MOT off. The magnetic coil switch was able to reduce the magnetic field intensity to 5 % of its initial value after 81 μs. The second circuit was an analog signal switch designed to turn the modulation signal of an AOM off. The analog switch was able to reduce the modulation signal intensity to 8.5 % of its initial magnitude in ~25μs. The performances of the two circuits discussed in this paper are sufficient for future atom transfer research based on predicted experimental requirements.
Two circuits were designed, built, and tested for the purpose of aiding in the transfer of 87Rb atoms from a MOT to dipole traps and for characterizing the final dipole traps. The first circuit was a current switch designed to quickly turn the magnetic fields of the MOT off. The magnetic coil switch was able to reduce the magnetic field intensity to 5 % of its initial value after 81 μs. The second circuit was an analog signal switch designed to turn the modulation signal of an AOM off. The analog switch was able to reduce the modulation signal intensity to 8.5 % of its initial magnitude in ~25μs. The performances of the two circuits discussed in this paper are sufficient for future atom transfer research based on predicted experimental requirements.
Cold atom experiments utilize magnetic fields, commonly generated by coils, as an essential tool to control and manipulate atomic samples. In these experiments, it is often necessary to rapidly switch the magnetic field between two values. However, typical power supplies have a limited switching time for the current flowing through the coil. We present a control scheme implemented as an electronic circuit that overcomes this limitation. A faster control is achieved by momentarily applying an on-demand high voltage when the control signal variation surpasses the limits that the conventional power supply can follow, allowing a faster current flow into the magnetic coil. In our specific application, a coil with an inductance of 491 μH and a resistance of 0.26 Ω, corresponding to a time constant of ∼1.9 ms, is driven so that its current faithfully follows the control signals from -1 to 1 A. It is capable of completing a full-scale transition in just ∼31 μs, with an effective bandwidth of 15.2 kHz. This corresponds to an improvement by a factor of more than 20 in both bandwidth and switching speed over a conventional power supply. By appropriately selecting the components of the circuit, both the bandwidth and switching time can be tuned to match specific needs within a wide range of inductive and power requirements.
We have constructed in our laboratory two rectangular shaped current carrying coils in accordance with the parameters used in our design so that they can be put in use in the Two Dimensional Magneto Optical Trap (2D-MOT)to obtain very high value of Optical Depth(OD). The dimensions of the coils are 8cm x 10cm. When put in anti-Helmholtz configuration as required in a 2D-MOT, these coils generate magnetic field such that it becomes zero along a line bisecting the space between the two coils. The magnetic field gradient near the zero magnetic field line is measured to be 3.33 Gauss/cm when the current passing through the coils is 3.5A. We have also made measurements at other values of current and found, as expected, this gradient increases with current. These results match nicely with the estimated values and hence a significant step forward towards the experimental realization of the design proposed by us.
The design and implementation of a current driver for the quadrupole coil of a magneto-optical trap are presented. The control and the power stages of the driver, both based on a push-pull configuration with high-speed transistors, are separated, allowing for a protection of the control electronics. Moreover, the coil current can be set by an analog voltage, a feature that makes possible both fast and adiabatic switching of the quadrupole magnetic field. In order to compensate magnetic field transients induced by eddy currents, the driver allows a quick reversal of the quadrupole coil current providing in such a way the required magnetic flux compensation. From a fit to the measured magnetic field transients, we have extracted the decay constants which confirm the efficiency of the compensation. Furthermore, we measured the influence of eddy currents on a sample of cold caesium atoms, testing at the same time the ultimate performance of the driver for our applications. The results show that the implemented electronic circuit is able to reduce substantially the transient effects with switching times of the magnetic field below 100 microseconds.
Abstract Atom chips provide flexible technologies for implementing modern concepts in quantum optics, quantum measurement, and quantum information processing. Atom chips are miniature devices that confine, control and manipulate cold atoms using electric, magnetic, and light fields. Due to the shrinkage of scale, arbitrary magnetic traps can be generated from current sources outside the chip’s vacuum compartment, in contrast to a traditional setup. This makes it easy to change trap configurations in an experiment that involves rapid prototyping of quantum states and quantum trajectory designs in free space. In this work, we show relevant parameters needed for transferring a cold atom cloud at the recoil limit from a magneto-optical trap (MOT) to an area close to the atom chip. To create a movable magnetic potential for this transfer, we used the MOT coils and an additional pair of coils in an anti-Helmholtz configuration. The properties of the movable potential were obtained by performing the Computer Simulation Tool (CST EM Studio suite®). Furthermore, an appropriate magnetic trap on a chip is developed, based on the simulation from COMSOL Multiphysics. We used a magnetic field gradient of around 20 G/cm to transport the cold atom with a distance over 20 mm with a temperature gain below 100 micro-Kelvin. The simulation results are based on an atom chip with a size of 2×2 cm2 and a copper wire thickness of 2 mm. The atom chip consists of Z, U and I-shaped wires that generate a quadrupole magnetic field. The resulting field minimum can be made at least 7 mm away from the chip surface.
The possibility to mould and control pure quantum systems has been offered by the experimental observation of Bose-Einstein condensation, a unique phase of matter when macroscopic quantities of a gas occupy the lowest quantum state. Techniques for creating these degenerate gases vary from laboratory to laboratory; each offers an unique test bed for studying quantum physics on a macroscopic scale. This thesis reports on the experimental design, construction and performance of an apparatus to create two-component 87Rb and 41K condensates for studies of non-equilibrium dynamics. This thesis is broken down as follows. In Chapter 1, a brief overview of the history and status of Bose Einstein condensates is presented, to affirm the motivation behind our work. Chapter 2 then presents the fundamental theory and background information to understand how and why our experiment was built. Chapter 3 describes the bulk of the work undertaken at the beginning of this thesis. In particular it describes the design choices, construction and performance of the vacuum, and laser and magnetic coil systems that are the key structural elements of the apparatus. In particular the vacuum system is a two-component differentially pumped system designed to optimise the number and lifetime of trapped atoms. Another integral element of the vacuum chamber is the science cell that enables high optical access, and close physical, access to an atomic cloud. As a result, high resolution imaging, ≃ 980 nm resolution at 780 nm is expected with a commercial microscope objective lens. The laser system is carefully de- signed to best combine and deliver the seven different optical frequencies required to simultaneously trap and manipulate 87Rb and 41K atoms. The magnetic coil system also represents an integral component of the apparatus, responsible for trapping and transferring atoms in a quadrupole field. One pair of coils is able to have their current direction reversed in order to generate bias fields. This allows access to Feshbach resonances between the two species, once they have been condensed. The second part of this thesis, Chapter 4, describes the performance of the apparatus when used to simultaneously trap 41K and 87Rb in the 3D magneto- optical trap (MOT) and produce a condensate of 87Rb atoms. In particular 1 × 109 rubidium atoms are routinely trapped in the 3D-MOT and transferred to the science chamber. In the hybrid trap the atoms are evaporatively cooled via microwave radiation, later to be used to sympathetically cool 41K, and loaded into a hybrid optical dipole and magnetic trap. At this stage ≃ 5 × 106 atoms are evaporatively cooled, by lowering the trap depth of the optical dipole beam, until a condensate of 87Rb is formed, containing 1.5 × 105 atoms. Additionally we are able to produce 3D MOTs of 41K simultaneously with the 87Rb 3D MOTs.
With a movable quadrupole magnetic trap (QMT) generated by two pairs of partly-overlapped magneto-optical trap (MOT) and transfer coils, a highly efficient transport of cold87Rb atoms to the atom chip surface is realized. By the QMT movable means of linearly increasing the current in the transfer coils but simultaneously keeping the current in the MOT coils constant, the velocity profile of the moving trap is Blackman-type-like. With this QMT movable scheme, the cold atoms are transferred to the atom chip surface from the MOT center. In the transfer process, the cold atom temperature is increased by about 30 μK, and the transfer efficiency is above 90%. This system provides an appropriate cold atoms source for the atom chip interferometer and also can be used to investigate the interaction between atom and chip surface. ? 2016, Chinese Lasers Press. All right reserved.