Ultracold atoms magnetically trapped inside an optical resonator on a microfabricated chip

Igor Teper

James Garvie-Cook

This thesis describes atomic physics experiments performed using a microfabricated photonic waveguide chip: a device that enables the interaction of cold atoms with an array of 12 microscopic light beams emitted by optical waveguides, inside a microscopic trench that has been cut into the chip, across all of the waveguides. The chip uses standard cold-atom control techniques along with readily available photonics technologies to provide an integrated atomic physics device that is not ‘scalable’ so much as already scaled. We describe experiments where atoms are driven into the trench using magneto-optical traps and magnetic traps. In the latter case, the large, homogeneous magnetic field that is present during the atom-light interaction allows us to observe polarization-dependent effects in absorption signals from the trench. Vacuum difficulties have limited the efficiency of rf-driven evaporative cooling in our magnetic trap to 0.4 (with a final phase-space density of 2×10^-5). To circumvent this issue, we have developed a novel evaporative cooling process, in which a dimple potential, comprised of an optical trap and a magnetic trap, is used to perform cycles of isentropic trap deformation and selective atom removal. Using this cooling process increases our evaporative cooling efficiency to 1.2. Various other cooling strategies that involve the dimple are also investigated. Using the dimple, we achieve a phase-space density of 0.04. Having cooled the cloud using the dimple, we move it into the trench and measure absorption signals of 50%, much larger than those achieved previously. We investigate the possibility of producing microscopic optical dipole traps in the trench by sending red-detuned light through the waveguides, and show results of preliminary experiments looking at light shifts.

Andrew A. Geraci, Ying-Ju Wang, Matthew Eardley +2 more

Andrew A. Geraci, John E. Kitching

We propose an experiment utilizing an array of cooled microcantilevers coupled to a sample of ultracold atoms trapped near a microfabricated surface. The cantilevers allow individual lattice site addressing for atomic state control and readout, and potentially may be useful in optical lattice quantum computation schemes. Assuming resonators can be cooled to their vibrational ground state, the implementation of a two-qubit controlled-NOT gate with atomic internal states and the motional states of the resonator is described. We also consider a protocol for entangling two or more cantilevers on the atom chip with different resonance frequencies, using the trapped atoms as an intermediary. Although similar experiments could be carried out with magnetic microchip traps, the optical confinement scheme we consider may exhibit reduced near-field magnetic noise and decoherence. Prospects for using this system for tests of quantum mechanics at macroscopic scales or quantum information processing are discussed.

József Fortágh, Sebastian Kraft, Andreas Günther +3 more

G. Lewis, Z. Moktadir, C. Gollasch +7 more

Ultracold atoms can be manipulated using microfabricated devices known as atom chips. These have significant potential for applications in sensing, metrology, and quantum information processing. To date, the chips are loaded by transfer of atoms from an external macroscopic magnetooptical trap (MOT) into microscopic traps on the chip. This transfer involves a series of steps, which complicate the experimental procedure and lead to atom losses. In this paper, we present a design for integrating a MOT into a silicon wafer by combining a concave pyramidal mirror with a square wire loop. We describe how an array of such traps has been fabricated, and we present magnetic, thermal, and optical properties of the chip.