Raman fingerprints on the Bloch sphere of a spinor Bose-Einstein condensate

We explore the geometric interpretation of a diabatic, two-photon Raman process as a rotation on the Bloch sphere for a pseudo-spin-1/2 system. The spin state of a spin-1/2 quantum system can be described by a point on the surface of the Bloch sphere, and its evolution during a Raman pulse is a trajectory on the sphere determined by properties of the optical beams: the pulse area, the relative intensities and phases, and the relative frequencies. We experimentally demonstrate key features of this model with a $^{87}$Rb spinor Bose-Einstein condensate, which allows us to examine spatially dependent signatures of the Raman beams. The two-photon detuning allows us to precisely control the spin density and imprinted relative phase profiles, as we show with a coreless vortex. With this comprehensive understanding and intuitive geometric interpretation, we use the Raman process to create and tailor as well as study and characterize exotic topological spin textures in spinor BECs.Comment: 13 pages, 13 figures, submitted to the Journal of Modern Optics "20 Years of Bose-Einstein condensates" Special Issu

Topological spin textures in Spinor Bose–Einstein condensates generated by stimulated Raman interactions

Thesis (Ph. D.)--University of Rochester. Department of Physics and Astronomy, 2016.Quantum fluids are characterized by integer-quantized vortices due to their phase coherence. Systems with additional internal degrees of freedom have far more complex behavior and can exhibit fractional vortices, superfluid spin flow, synthetic gauge potentials, and more. The interaction of spin and magnetism in an atomic spinor Bose–Einstein condensate (BEC) creates spinor order parameter manifolds with distinct symmetries that support a variety of these behaviors and topologically nontrivial excitations. Here we create and characterize a number of topological spinor structures that contain vortices in different spin states, including half-quantum vortices, non-Abelian vortices, skyrmions, monopoles, and full-Bloch BECs. Many of these are analogs of topological objects from across physics, ranging from liquid crystals and singular optics to cosmology and particle physics. BECs can be precisely controlled and measured, making them an ideal system to model such phenomena. We engineer the spinor wavefunction of a ⁸⁷Rb BEC with a coherent multiphoton stimulated Raman interaction and create vortices in specific spin states using optical beams with orbital (external) and spin (internal) angular momenta. The BEC cloud is analyzed using complementary techniques based in condensed matter physics (spin texture, vorticity, Majorana representation, etc.) and optics (atomic polarimetry), allowing us to completely reconstruct the spinor wavefunction up to a global phase. The evolution of the topological objects we have created will allow us to determine fundamental properties of ⁸⁷Rb, measure a proposed geometric phase in matter waves, and explore quantum information protocols

Simultaneous multi-axis inertial sensing with point source interferometry

International audienceIn point source atom interferometry (PSI), a cloud of laser-cooled atom expands within a pair of counterpropagatingRaman laser beams and, after a beamsplitter-mirror-beamsplitter Raman pulse sequence, asingle snapshot of the expanded cloud allows simultaneous measurements of one axis of acceleration and two axes of rotation. In PSI, the thermal expansion of the cold-atom cloud, which is undesirable in other atom interferometry methods, is used to establish a position-velocity correlation in the expanded atom cloud. This correlation is employed to map the velocity dependence of the interferometric phaseshift onto a two-dimensional spatial image plane. As a result, the thermal velocity spread of the cloud of laser-cooled atoms facilitates the parallel operation of many atom interferometers, which yields the simultaneous multi-axis sensitivity. PSI provides a new approach to applications of atom interferometers in navigation and space science. For example, the 2D rotation measurement with PSI can be used to find geographic north or to measure the precession of a rotation vector. We have developed a scheme using PSI that is amenable to portable applications and we have demonstrated the measurement of a rotation vector in a plane [1]. We will present our recent results on evaluating the performance and systematic errors in a compact setup and discuss our proposals to address the challenges toward implementing ahigh-precision and portable PSI system

Robust inertial sensing with point-source atom interferometry for interferograms spanning a partial period

International audiencePoint source atom interferometry (PSI) uses the velocity distribution in a cold atom cloud to simultaneously measure one axis of acceleration and two axes of rotation from the spatial distribution of interferometer phase in an expanded cloud of atoms. Previously, the interferometer phase has been found from the phase, orientation, and period of the resulting spatial atomic interference fringe images. For practical applications in inertial sensing and precision measurement, it is important to be able to measure a wide range of system rotation rates, corresponding to interferograms with far less than one full interference fringe to very many fringes. Interferogram analysis techniques based on image processing used previously for PSI are challenging to implement for low rotation rates that generate less than one full interference fringe across the cloud. We introduce a new experimental method that is closely related to optical phase-shifting interferometry that is effective in extracting rotation values from signals consisting of fractional fringes as well as many fringes without prior knowledge of the rotation rate. The method finds the interferometer phase for each pixel in the image from four interferograms, each with a controlled Raman laser phase shift, to reconstruct the underlying atomic interferometer phase map without image processing

Inertial sensing with point-source atom interferometry for interferograms with less than one fringe

International audiencePoint source atom interferometry (PSI) is an atom-optical method that measures one axis of acceleration and two axes of rotation from atom-interferometric fringe images. The number of fringes in an image can be less than or larger than one, depending on the system rotation rate and<br&gtthe atom interferometer's sensitivity setting. Previously used methods for analyzing the fringes, such as parametric fittings, are not suitable for a wide range of rotation rates. We introduce a new experimental method that is effective in either case. Our approach does not require prior knowledge of fringe contrast, orientation, frequency, and phase.<br&g

Enhanced observation time of magneto-optical traps using micro-machined non-evaporable getter pumps

International audienceWe show that micro-machined non-evaporable getter pumps (NEGs) can extend the time over which laser cooled atoms can be produced in a magneto-optical trap (MOT), in the absence of other vacuum pumping mechanisms. In a first study, we incorporate a silicon-glass microfabricated ultra-high vacuum (UHV) cell with silicon etched NEG cavities and alumino-silicate glass (ASG) windows and demonstrate the observation of a repeatedly-loading MOT over a 10 min period with a single laser-activated NEG. In a second study, the capacity of passive pumping with laser activated NEG materials is further investigated in a borosilicate glass-blown cuvette cell containing five NEG tablets. In this cell, the MOT remained visible for over 4 days without any external active pumping system. This MOT observation time exceeds the one obtained in the no-NEG scenario by almost five orders of magnitude. The cell scalability and potential vacuum longevity made possible with NEG materials may enable in the future the development of miniaturized cold-atom instruments

Two-dimensional rotation measurement with point source interferometry

International audienceIn analogy with a spinning rotor gyroscope, which precesses in response to a torque in the plane transverse to the axis of spin, point source atom interferometry (PSI) senses the components of rotation in the plane transverse to the direction of a pair of counter-propagating Raman laser beams. Based on the PSI technique, we demonstrate the two-dimensional measurement of a rotation vector projected into a plane. We characterize the sensitivity of the measurement, including the magnitude and the direction of the rotation vector component

Performance of a point source atom interferometer gyroscope

International audiencePoint source atom interferometry, employing optical Raman pulses and a cold atom source, enables measurements of rotation and acceleration in a compact experimental package. This system is uniquely sensitive to rotations in the plane perpendicular to the Raman beamline. Here we discuss our experiment’s sensitivity, stability, systematic errors, and other performance-limiting factors both fundamentaland technical. Our current measurements for the sensitivity to the magnitude and direction of the rotation vector are 0.6 mrad/s and 5 mrad, respectively

General methods for suppressing the light shift in atomic clocks using power modulation

International audienceWe show that the light shift in atomic clocks can be suppressed using time variation of the interrogation field intensity. By measuring the clock output at two intensity levels, error signals can be generated that simultaneously stabilize a local oscillator to an atomic transition and correct for the shift of this transition caused by the interrogating optical field. These methods are suitable for optical clocks using one- andtwo-photon transitions, as well as for microwave clocks based on coherent population trapping or direct interrogation. The proposed methods can be widely used both for high-precision scientific instruments and for a wide range of commercial clocks, including chip-scale atomic clocks