Aberrations of atomic beam splitters

Antje Neumann

Matter-wave interferometry enables high-precision measurements of rotation and acceleration, applicable for inertial navigation and fundamental physics, like testing Einstein's weak equivalence principle.  We are part of the Opens external link in new windowQUANTUS (QUANTengase Unter Schwerelosigkeit) collaboration, where atom interferometry is the central method of their Opens external link in new windowfree-fall experiments, just like within the Opens external link in new windowMAIUS (Materie-Wellen-Interferometer Unter Schwerelosigkeit) mission, where the Opens external link in new windowfirst BEC in space was generated in 2017.
Like in optical systems all matter wave devices exhibit imperfections and the amount of these aberrations must be quantified. Therefore, we analytically and numerically study the performance of 3D atomic beam splitters and mirrors.  Describing these central components of a matter-wave interferometer as realistic as possible, we consider spatio-temporal laser beam envelopes and in the quasi Bragg regime we take into account the velocity dispersion as well as losses into unobserved momentum orders.

This work is supported by the German Aerospace Center (DLR) through grant 50 WM 1557, 1957.

Raman velocity filter

Three-level energy diagram for Calcium-40 ions. Laser 1 induces eg transitions and laser 2 couples the em transition.

Antje Neumann

The velocity distribution of a hot ionic beam can be filtered with a narrow stimulated Raman process to prepare a colder subensemble, as substantiated in this theoretical analysis. Using two counterpropagating far-detuned lasers, we can define a pi-pulse for the resonant velocity to transfer atoms within the linewidth of the Raman resonance between the ground states of a Lambda-system. Spontaneous emission from the two single-photon resonances, as well as the ground-state decoherence induced by laser noise, diminishes the efficiency of the filter. From a comprehensive master equation, we obtain conditions for the optimal frequency pair of lasers and evaluate the filter performance numerically as well as analytically. If we apply this analysis to current 40Ca+ ion experiments, we obtain a sensitivity for measuring high ion acceleration voltages on the ppm level or below.

This work is published as Editor's Suggestion in Physical Review A: Opens external link in new windowRaman velocity filter as a tool for collinear laser spectroscopy.

It is supported by the German Aerospace Center (DLR) through grant 50 WM 1557, 1957.

 

Aberration analysis in matter-wave optics with Bose-Einstein condensates

Trajectories and the corresponding wavefronts of a matter wave in a Mach-Zehnder interferometer.

Jan Teske

In 1934 Frits Zernike discovered the orthogonal `Kreisflächenpolynome' to describe the optical path difference between light waves and a spherical reference wavefront. Understanding the phase differences and minimizing the optical aberrations laid the base for the first phase-contrast microscope for which he was awarded the Nobel Prize in Physics 1953. Nowadays, the Zernike polynomials are widely used in optical system design as a standard description of imperfections in optical imaging. In contrast to visible light, massive particles have a much smaller de Broglie wavelength and therefore a possible higher resolving power. In particular matter-wave interferometry with ultracold atoms is paving the way to a new era of quantum technologies.

In this project, we develop a schematic aberration analysis for matter-wave optics with Bose-Einstein condensates. Following Zernike's idea, we introduce a set of orthogonal basis functions to quantify deviations from a chose reference state in terms of aberration coefficients. We study long expansion times that can be achieved in microgravity environments (Opens external link in new windowQUANTUS, Opens external link in new windowMAIUS, Opens external link in new windowISS) as well as the effect of Delta-kick collimation with real anharmonic magnetic chip trap potentials. Both are essential to understand the condensates' phase evolution which is necessary for a precise description of matter-wave interferometry. 

 

Stochastic approach to intensity noise suppression in superluminescent diodes

(Top) Distribution of a complex Gaussian field and (bottom) intensity noise suppression depending on the temperature, calculated with a stochastic model.

Kai Hansmann

We develop a novel approach to the investigation of quantum dot superluminescent diodes using stochastic methods. Under the assumption, that the emission of such diodes results as a superposition of independent, stochastically fluctuating emitters, we numerically simulate the complex electric field amplitude emitted by the diode. From this, key optical properties like first- and second-order temporal correlation functions and the spectral power density of the emission are calculated.

Suppression of intensity fluctuations in incoherent semiconductor light sources has been observed by Opens external link in new windowBlazek et al. in 2011. We use our stochastic approach to explain the noise suppression mechanisms in such diodes to match experimental facts. The results give an insight into general noise suppression processes in semiconductor diodes and open up the opportunity to customize noise-reduced broadband light sources.

 

  

 

Controlling multipole moments of a magnetic chip trap

Sketch of a Z-trap, including the resulting trap minimum. The sphere of radius R describes the region in which the multipole moments are evaluated.

Tobias Liebmann

Magnetic chip traps are standard devices to trap cold atoms via the Zeemann-potential. This work is part of the  Opens external link in new windowQUANTUS collaboration, using such trapping configurations for Bose-Einstein Condensates (BECs) in microgravity. With Opens external link in new windowMAIUS the first Opens external link in new windowspace-borne BEC was created in 2017. While magnetic chip traps exhibit pleasant confinement potentials, they are not necessarily harmonic. The Zeemann-potential exerted by a chip trap's magnetic induction field is only relevant in a limited space around the trap minimum. In this region, the magnetic induction field is described in terms of a magnetic potential, which satisfies Laplace's equation. The magnetic potential itself can be expressed as a series of regular solid harmonics, allowing for a complete description of the magnetic induction field by the multipole moments of the magnetic potential. Starting from a standard Z-trap configuration, the goal of this work is the description of its observed anharmonicities in terms of the corresponding multipole moments and reduce them by introducing a variation to the shape of the Z-trap's wires.

Kontakt

Prof. Dr. Reinhold Walser

Theoretische Quantendynamik
Institut für Angewandte Physik
Fachbereich 05 - Physik
Technische Universität Darmstadt
Hochschulstr. 4a
D-64289 Darmstadt

+49 6151 16-20320

+49 6151 16-20402

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