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New Journal of Physics

Time-domain optics for atomic quantum matter

Simon Kanthak, Martina Gebbe, Matthias Gersemann, Sven Abend, Ernst Maria Rasel, Markus Krutzik

Published Jul 8, 2021• 7 citations
Publisher

Abstract

Abstract We investigate time-domain optics for atomic quantum matter. Within a matter-wave analog of the thin-lens formalism, we study optical lenses of different shapes and refractive powers to precisely control the dispersion of Bose–Einstein condensates. Anharmonicities of the lensing potential are incorporated in the formalism with a decomposition of the center-of-mass motion and expansion of the atoms, allowing to probe the lensing potential with micrometer resolution. By arranging two lenses in time formed by the potentials of an optical dipole trap and an atom-chip trap, we realize a magneto-optical matter-wave telescope. We employ this hybrid telescope to manipulate the expansion and aspect ratio of the ensembles. The experimental results are compared to numerical simulations that involve Gaussian shaped potentials to accommodate lens shapes beyond the harmonic approximation.

DOI
10.1088/1367-2630/ac1285

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Abstract We investigate time-domain optics for atomic quantum matter. Within a matter-wave analog of the thin-lens formalism, we study optical lenses of different shapes and refractive powers to precisely control the dispersion of Bose–Einstein condensates. Anharmonicities of the lensing potential are incorporated in the formalism with a decomposition of the center-of-mass motion and expansion of the atoms, allowing to probe the lensing potential with micrometer resolution. By arranging two lenses in time formed by the potentials of an optical dipole trap and an atom-chip trap, we realize a magneto-optical matter-wave telescope. We employ this hybrid telescope to manipulate the expansion and aspect ratio of the ensembles. The experimental results are compared to numerical simulations that involve Gaussian shaped potentials to accommodate lens shapes beyond the harmonic approximation.
In contrast to light, matter-wave optics of quantum gases deals with interactions even in free space and for ensembles comprising millions of atoms. We exploit these interactions in a quantum degenerate gas as an adjustable lens for coherent atom optics. By combining an interaction-driven quadrupole-mode excitation of a Bose-Einstein condensate (BEC) with a magnetic lens, we form a time-domain matter-wave lens system. The focus is tuned by the strength of the lensing potential and the oscillatory phase of the quadrupole mode. By placing the focus at infinity, we lower the total internal kinetic energy of a BEC comprising 101(37) thousand atoms in three dimensions to 3/2 k_{B}·38_{-7}^{+6} pK. Our method paves the way for free-fall experiments lasting ten or more seconds as envisioned for tests of fundamental physics and high-precision BEC interferometry, as well as opens up a new kinetic energy regime.
Abstract Motivated by the recent experimental realization of ultracold quantum gases in shell topology, we propose a straightforward implementation of matter-wave lensing techniques for shell-shaped Bose–Einstein condensates. This approach allows to significantly extend the free evolution time of the condensate shell after release from the trap and enables the study of novel quantum many-body effects on curved geometries. With both analytical and numerical methods we derive optimal parameters for realistic schemes to conserve the shell shape of the condensate for times up to hundreds of milliseconds.
Abstract Mixtures of ultracold quantum gases are at the heart of high-precision quantum tests of the weak equivalence principle, where extremely low expansion rates have to be reached with matter-wave lensing techniques. We propose to simplify this challenging atom-source preparation by employing magic laser wavelengths for the optical lensing potentials, which guarantee that all atomic species follow identical trajectories and experience common expansion dynamics. In this way, the relative shape of the mixture is conserved during the entire evolution while cutting in half the number of required lensing pulses compared to standard approaches.
The precision of atom interferometers, targeted for example in the Hannover Very Long Baseline Atom Interferometer (VLBAI) facility, imposes stringent requirements in several respects. They concern the control of center-of-mass motion and expansion of the wave packets by the matter-wave source as well as the number of atoms. By reducing the expansion, systematic errors, appearing e.g. through wavefront aberrations, can be lowered. These requirements can be matched by employing ultracold quantum gases or even quantum degenerate gases. A promising method to create those ensembles is evaporative cooling in a spatially modulated optical dipole trap. Here, the utilization of time-averaged potentials enables the fast creation of ultracold atomic ensembles with large number of atoms. Both, the higher number of atoms and the increased repetition rate, enhance the performance of the interferometer due to a lower quantum projection noise, which scales with 1/sqrt(N), and a larger bandwidth of the sensor due to faster sampling. The shaping of the matter-waves by techniques such as matter-wave lensing or Delta-Kick collimation is also feasible due to the dynamic control of the trapping potential. In this thesis the implementation and application of dynamic time-averaged optical potentials created via center position modulation of dipole trap beams is demonstrated. By evaporative cooling in these potentials, 1.9(0.4) x 10^5 condensed atoms with an expansion temperature of 29.2(1.3) nK were achieved after 3 s of evaporation. Up to 4.2(0.1) x 10^5 condensed atoms could be observed with slower evaporation of 5 s. Subsequent matter-wave lensing is carried out yielding expansion rates as low as 553(49) μms^-1 resulting in an effective temperature of 3.2(0.6) nK in two dimensions. This lens can be applied at any stage of evaporative cooling, thus short-cutting the generation of ultracold effective temperatures. In this thesis the limitations of optical matter-wave lensing in the current setup are revealed and ways to improve the performance are discussed. The fast generation of ultracold atomic ensembles will enhance the performance of the dual-species atom interferometer, which represents the experiment apparatus for this thesis and strives for a test of the Universality of Free Fall with an uncertainty on the order of 10^-9. The results of this thesis were used to test numerical simulations which were utilized to show the perspective of generating up to 10^6 collimated condensed atoms within 1 s of cycle time in the rubidium source system of Hannover’s VLBAI.
The experimental realization of Bose-Einstein condensates in dilute alkali gases has opened up the possibility to perform time and space domain interferometry with coherent matter waves. We have exploited different configurations realizing coherent matter wave interferometers: in a first set of exeperiments we create a twofold condensate sample investigating the interplay between internal and external degrees of freedom in the matter wave analogous of a Young diffraction experiment. In a second experimental arrangement we produce a one dimensional array of condensates in an optical lattice. Upon release from the optical lattice the condensates are made to interfere, the resulting interference pattern, this time analogous to an optical diffraction grating, is used to extract information about static and dynamical properties of the sample.
We present experiments investigating different aspects concerning the coherent manipulation of a Bose-Einstein condensate wavefunction with far blue detuned dipole potentials. In a first set of experiments we study a waveguide for matter waves as an important atom optical element allowing to hold and guide the atoms for long observation times. We present a flexible realization of this waveguide based on a tube shaped Laguerre Gaussian laser beam and investigate the dynamics of a Bose condensed ensemble transferred into this guide. In a second set of experiments we study the dynamics of dark solitons created by the manipulation of the phase of the condensate wave function by temporally applied dipole potentials. This method of phase imprinting represents a powerful tool for the design of matter waves and the controlled creation of various excitations. The dynamics of dark solitons in matter waves is investigated in detail by experimentally and numerically studying the temporal evolution of the condensate density as well as by mapping the velocity field of the excited condensate wavefunction. In these measurements we directly detect the flux of the wave function associated with the dark soliton using spatially resolved Bragg scattering. Experiments investigating the creation and interaction of several dark solitons conclude this chapter.