Since their initial production in 1995, the study of Bose-Einstein Condensates (BECs) has offered exciting new insights into many fields including quantum mechanics and solid state physics. Atom chips, non-conducting surfaces with conducting lithographic traces printed on them, have proven successful in generating lower power magnetic traps for the formation of BECs. The combination of their lower power consumption, small form factor, and dense traps makes atom chips a promising way to face a ubiquitous challenge in the study of BECs: the effect of the earth’s gravitational field. To avoid these effects the NASA Cold Atom Laboratory aims to create BECs aboard the International Space Station (ISS) using an atom chip. This thesis presents the development of a similar atom chip based BEC experiment at Bates College, which will serve as a functional testbed for future research aboard the ISS. Both a theoretical background and a description of the experimental process by which a BEC is formed on an atom chip are provided. This process is primarily driven by laser cooling and magnetic trapping techniques. A 2D+ Magneto-Optical Trap (MOT), loaded from vapor pressure, is used as a slowed source of 87Rb in order to create a 3D MOT. We present measurements of the performance of both MOTs, and outline a path forward to condensation on the chip-based magnetic trap through use of radiofrequency evaporative cooling.
Since their initial production in 1995, the study of Bose-Einstein Condensates (BECs) has offered exciting new insights into many fields including quantum mechanics and solid state physics. Atom chips, non-conducting surfaces with conducting lithographic traces printed on them, have proven successful in generating lower power magnetic traps for the formation of BECs. The combination of their lower power consumption, small form factor, and dense traps makes atom chips a promising way to face a ubiquitous challenge in the study of BECs: the effect of the earth’s gravitational field. To avoid these effects the NASA Cold Atom Laboratory aims to create BECs aboard the International Space Station (ISS) using an atom chip. This thesis presents the development of a similar atom chip based BEC experiment at Bates College, which will serve as a functional testbed for future research aboard the ISS. Both a theoretical background and a description of the experimental process by which a BEC is formed on an atom chip are provided. This process is primarily driven by laser cooling and magnetic trapping techniques. A 2D+ Magneto-Optical Trap (MOT), loaded from vapor pressure, is used as a slowed source of 87Rb in order to create a 3D MOT. We present measurements of the performance of both MOTs, and outline a path forward to condensation on the chip-based magnetic trap through use of radiofrequency evaporative cooling.
A growing subfield of atomic physics is focused on the miniaturization of Bose-Einstein condensate (BEC)-producing apparatus. Perhaps the largest step forward in this area was the development of the so-called “atom chip.” These microfabricated devices can create tight traps for neutral atoms. In 2018, NASA’s Cold Atom Laboratory (CAL) was launched and installed aboard the International Space Station (ISS). It utilizes a modified miniature atom chip apparatus produced by ColdQuanta called the RuBECi. In this thesis, we present progress towards achieving BEC in a Bates-owned RuBECi, particularly focusing on the laser cooling and magneto-optical trapping stages of the BEC process.
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.
The construction of an apparatus capable of producing Bose-Einstein condensates marks a significant milestone in every experimental cold atom laboratory. In this thesis I describe the development of a system to create a Bose-Einstein condensate of 87Rb in a Time-Orbiting Potential trap.\n\nI review the optical and magnetic techniques required to trap and cool an atomic sample under vacuum, motivating our decision to build a double MOT system comprised of a high-pressure (10−9 torr) chamber to gather atoms and a low-pressure (10−11 torr) chamber to cool atoms to degeneracy.\n\nBy theoretically modeling the atom number and temperature inside the magnetic trap during evaporative cooling I demonstrate a simple approach to determining a cooling path that reaches the transition temperature. By making use of the condensates produced under these non-optimized conditions I determine the heating rate of the condensate in the TOP trap to be 300 nK/s. I further use the condensates to make a more precise measurement of the TOP trap bias field.\n\nI improve upon the conventional evaporation path used in TOP trap experiments by introducing and optimizing additional bias field compression stages in between RF evaporation ramps. I demonstrate how, by adding these additional stages, the system is capable of reaching the BEC phase transition with a final atom number of 2times105. In contrast, RF evaporation after only a single bias field ramp has yielded condensates with only 30times103 atoms.
In a Bose-Einstein Condensate (BEC), due to extremely low temperatures, wave functions of all particles in the system overlap and form a single macroscopic wavefunction. This brings quantum mechanical effects to the macroscopic scale and allows us to better understand known quantum mechanical laws and effects, as well as develop new ones. In addition to being of fundamental scientific interest, BEC can serve in practical applications, such as quantum metrology, atomic interferometry, and quantum information and communication. Here we describe our approach for producing BECs in 87Rb. To create atomic flux towards our science chamber, a 2-dimensional magneto-optical trap (2D-MOT) with push beam is used. The initial atomic cloud is formed in 15s by 3D-MOT and consists of 1e9 atoms at 500uK. After the MOT, atoms are cooled with optical molasses to 50uK and transferred to a quadrupole magnetic trap, where radio-frequency (RF) induced evaporation is performed, which lowers temperature to 10uK. After RF evaporation, the atomic cloud is transferred to a crossed beams optical dipole trap (ODT). During evaporation in the ODT, the temperature is reduced below the critical temperature Tc=286nK, where condensation starts, and eventually reaches 40nK. As a result, a quasi-pure BEC with 1e5 87Rb atoms is formed. The complete sequence from the MOT loading to the BEC formation takes about 30s. Observations of the inversion of the aspect ratio of the cloud during free expansion and a bimodal velocity distribution prove quantum degeneracy. Presented in this thesis are the necessary background for understanding the experimental steps, a description of the schemes and technical details of our setup, and a characterizations of all the experimental steps.
Bose-Einstein condensates (BECs) have been proposed for many applications in atom interferometry, as their coherence over long evolution times promises unprecedented sensitivity. To date, BECs can be efficiently created in devices using atom chips, but these are still complex and place high demands on size, weight and power. To further simplify these setups, we equipped an atom chip with a nano-structured diffraction-grating to derive all beams for the magneto-optical trap (MOT) from a single laser beam. Moreover, using a 2D+-MOT as an atomic source and a beam with uniform intensity for the grating illumination, we capture 1×109 atoms in one second, cool them to 14μK, and demonstrate magnetic trapping using the atom chip. This is a major step towards the simplification of portable BEC devices for quantum sensing on earth and in space.
We describe our high-performance experimental apparatus for producing large atom number 87Rb Bose-Einstein condensates by using a double magneto-optical trap (MOT) system that consists of a two-dimensional MOT (2D MOT) and a three-dimensional MOT (3D MOT). As an atomic beam source for loading the 3D MOT, we use a unique 2D MOT system with two-color pushing beams, which increase the loading rate and the total number of atoms in the 3D MOT, compared to a pure 2D MOT by a factor of 20. After MOT compression and polarization gradient cooling, atoms are optically pumped into a magnetically trappable hyperfine state |F = 1, m F = −1〉 to be loaded into a quadrupole-Ioffe-configuration (QUIC) trap. We enhance this optical pumping process by up to 300% by using two laser beams. After rf evaporative cooling, a Bose-Einstein condensate (BEC) with more than 2 × 107 atoms is achieved.