A Portable BEC Atom-Chip System—Towards Practical Atom Matter Wave Sensors

S. J. Kim, H. Yu, S. T. Gang +1 more

Matthew B. Squires, Evan A. Salim, William F. Holmgren +5 more

Shengwang Du

Shengwang Du, Matthew B. Squires, Leslie Czaia +6 more

Kai Hudek

The work in this thesis falls into two broad categories: creating Bose-Einstein condensates (BECs) in compact and portable systems, and manipulating neutral atoms in small systems to facilitate a continuously running neutral Rydberg atom quantum computer. The work with BECs focused on the miniaturization of ultracold matter systems. Ultracold matter has potential uses in many practical applications, such as atomic clocks, inertial sensors, and electric and magnetic field sensing. Much of the potential of atom chip based systems relies on the ability for the system to make its way out of the lab. The BEC system created occupies a volume of 0.4m^3 and operates at a repetition rate as high as 0.3Hz, creating Rubidium BECs of around 20k atoms. The system contains all of the components needed to produce and image BECs, including the UHV system, lasers, data acquisition hardware, electronics, and imaging equipment. The system can be easily reconfigured for different applications simply by changing the atom chip. As such, the hope is that it can serve as a standardized platform for a variety of portable experiments that utilize ultracold matter. The quantum computing work focuses on the ongoing work in atom manipulation for neutral Rydberg atom quantum computing. Neutral Rydberg atom quantum computing has great potential and, by harnessing the tool kit developed working with cold atoms, has the potential of scalability and continuous operation. An entirely new laser system and vacuum cell was built to work with Cesium. We have currently built a state of the art vacuum cell and developed far-detuned optical trapping and transport techniques to facilitate continuous quantum computing. Ongoing efforts include optical lattice generation and single-atom manipulation and imaging.

Hauke Müntinga

Inertial sensors based on matter-wave interferometry are currently approaching the precision and accuracy of state-of-the-art classical sensors. While these devices are often realised with ultracold but not Bose-condensed atoms as matter waves, employing Bose-Einstein Condensates (BEC) promises to overcome certain limitations, especially those related to the ensemble's expansion. The point-source like character of BECs also enables utilising spatial interference patterns to measure e.g. rotation rates in single-shot experiments. Matter wave-based inertial sensors are considered for experiments ranging from Gravitational Wave detection to tests of the Universality of Free Fall (UFF) to gain insight into the joint between Quantum Mechanics and General Relativity. In the scope of this thesis, matter-wave interferometry with BECs was demonstrated for the first time in a microgravity environment with the QUANTUS-1 apparatus. The same instrument was then employed as a quantum tiltmeter utilising a novel beam-splitting mechanism known as Bragg Double Diffraction. To this end, the QUANTUS-1 apparatus designed as a BEC instrument to be operated in the drop tower at ZARM at University of Bremen was equipped with optics and laser systems required for performing matter-wave interferometry based on Bragg Diffraction. The apparatus employs an atom chip to create BECs of around 10000 Rubidium 87 atoms within 15 s. With a Mach-Zehnder like interferometer scheme, spatial interference fringes were observed after a free evolution time in the interferometer of up to 677 ms. To achieve these long time scales, a method known as Delta-Kick Collimation (DKC) was adapted to slow the expansion of the BEC to a kinetic energy equivalent below 1 nK, and the atoms were transferred to a non-magnetic Zeeman state via an adiabatic rapid passage (ARP). A similar interferometer scheme with a newly developed beam-splitter mechanism known as Bragg Double Diffraction was used to measure the tilt of the instrument on ground with a precision of up to 4.4 AA rad. This thesis presents an overview of the apparatus including ground-based characterisations of all required experimental steps. Results from over 400 free fall experiments are evaluated for expansion studies of the BEC and matter-wave interferometry in microgravity. The time-evolution of first and second order Bragg Double Diffraction beam splitters is studied, and an interferometer sensitive to the tilt of the instrument is implemented. Based on this work, a gravimeter with a new launch mechanism comprising Bragg beam splitters and Bloch oscillations to enable atomic fountains in atom-chip based devices was developed. The microgravity experiments were adapted for the MAIUS-1 sounding-rocket instrument to create the first man-made BEC in outer space and study the feasibility of operating matter-wave interferometers on space-borne platforms. The results of this thesis lay the groundwork for future space-borne missions using matter-wave interferometry for precision measurements of inertial forces.