All-Optical Source of Ultra-Cold Atomic Ensembles for Microgravity Missions
Veröffentlichungsdatum
2026-04-16
Autoren
Woltmann, Marian
Betreuer
Herrmann, Sven
Gutachter
Krutzik, Markus
Zusammenfassung
Ultra-cold atoms have become indispensable in quantum sensing, quantum computing, and quantum
communication applications, as well as in fundamental sciences. In quantum sensing, they enable
precision measurements with outstanding sensitivities that can be of great benefit in navigation, geodesy,
and fundamental physics applications. The sensitivity of the atom interferometers used herefore typically
scales with the square of the interrogation time. Therefore, in atom interferometric measurements, one
seeks ensembles that feature a particularly low internal kinetic energy and can thus be detected after
a long time-of-flight. The lowest values are achieved using Bose-Einstein condensates in conjunction
with delta-kick collimation, a technique for the collimation of the atomic wave function. Bose-Einstein
condensation can be achieved using a multi-stage laser cooling scheme, followed by evaporative cooling,
which finally brings the temperature down to the critical temperature, typically in the nanokelvin regime.
In addition to the low thermal spread, microgravity enables particularly long observation times, as it
avoids limitations of the interrogation time due to vacuum chamber constraints, which are present when
falling freely under the influence of gravity. Additionally, microgravity enables measurements that are
not possible under normal gravity conditions, such as buoyancy-free miscibility studies, truly uniform
potentials, and advanced cold atom quantum memories, which are projected to feature unprecedented
time-bandwidth products.
For the preparation of a Bose-Einstein condensate, two techniques are widely used in science, namely
magnetic traps and optical dipole traps. For microgravity missions, magnetic traps on atom chips have
been used in nearly all setups so far due to their particularly low SWAP budget and high cold atom
flux. In contrast, ground-based experiments often prefer optical traps due to their higher versatility, full
optical access, and the absence of surfaces in proximity to the atoms, which is fundamental for precision
measurements. Additionally, optical traps enable the manipulation of intra- and inter-species scattering
lengths using Feshbach resonances. Compared to atom chip traps, they also feature an intrinsically better
symmetry of the trapping potential, in theory leading to fewer aberrations in matter-wave optics. The
latter could enable the generation of ensembles in the yet unreached femtokelvin regime using delta-kick
collimation with fewer perturbations.
This thesis is about the realization of a 1064nm optical dipole trap set up for the microgravity environment
of the Bremen Drop Tower. It aims to highlight the advantages of optical traps in conjunction with
microgravity and prepare optical trapping technology for use in future microgravity and space missions.
The thesis describes the experimental setup, the direct loading process, the characterization of the optical
potential, and the optimization and investigation of the evaporative cooling in the optical dipole trap.
For the evaporation process, the influence of gravity is comprehensively investigated through analytical
calculations and microgravity tests. Bose-Einstein condensation is demonstrated, proving the achievement
of condensation through absorption imaging of the spatial distribution, tests on the free evolution of the
ensemble, and investigation of the phase-space densities achieved. Up to (74 ± 4)% condensation of an
ensemble featuring (30 000 ± 13 000) atoms at a kinetic temperature of (37 ± 3) nK is demonstrated. The
evaporation shows high efficiency down to a 3 s evaporation time, while a critical phase-space density
can be achieved within (1.29 ± 0.07) s using an even faster evaporation ramp. This opens the door to
fundamental physics experiments on Bose-Einstein condensates in microgravity, as well as applications
pursuing atomic ensembles with exceptionally low expansion velocities.
communication applications, as well as in fundamental sciences. In quantum sensing, they enable
precision measurements with outstanding sensitivities that can be of great benefit in navigation, geodesy,
and fundamental physics applications. The sensitivity of the atom interferometers used herefore typically
scales with the square of the interrogation time. Therefore, in atom interferometric measurements, one
seeks ensembles that feature a particularly low internal kinetic energy and can thus be detected after
a long time-of-flight. The lowest values are achieved using Bose-Einstein condensates in conjunction
with delta-kick collimation, a technique for the collimation of the atomic wave function. Bose-Einstein
condensation can be achieved using a multi-stage laser cooling scheme, followed by evaporative cooling,
which finally brings the temperature down to the critical temperature, typically in the nanokelvin regime.
In addition to the low thermal spread, microgravity enables particularly long observation times, as it
avoids limitations of the interrogation time due to vacuum chamber constraints, which are present when
falling freely under the influence of gravity. Additionally, microgravity enables measurements that are
not possible under normal gravity conditions, such as buoyancy-free miscibility studies, truly uniform
potentials, and advanced cold atom quantum memories, which are projected to feature unprecedented
time-bandwidth products.
For the preparation of a Bose-Einstein condensate, two techniques are widely used in science, namely
magnetic traps and optical dipole traps. For microgravity missions, magnetic traps on atom chips have
been used in nearly all setups so far due to their particularly low SWAP budget and high cold atom
flux. In contrast, ground-based experiments often prefer optical traps due to their higher versatility, full
optical access, and the absence of surfaces in proximity to the atoms, which is fundamental for precision
measurements. Additionally, optical traps enable the manipulation of intra- and inter-species scattering
lengths using Feshbach resonances. Compared to atom chip traps, they also feature an intrinsically better
symmetry of the trapping potential, in theory leading to fewer aberrations in matter-wave optics. The
latter could enable the generation of ensembles in the yet unreached femtokelvin regime using delta-kick
collimation with fewer perturbations.
This thesis is about the realization of a 1064nm optical dipole trap set up for the microgravity environment
of the Bremen Drop Tower. It aims to highlight the advantages of optical traps in conjunction with
microgravity and prepare optical trapping technology for use in future microgravity and space missions.
The thesis describes the experimental setup, the direct loading process, the characterization of the optical
potential, and the optimization and investigation of the evaporative cooling in the optical dipole trap.
For the evaporation process, the influence of gravity is comprehensively investigated through analytical
calculations and microgravity tests. Bose-Einstein condensation is demonstrated, proving the achievement
of condensation through absorption imaging of the spatial distribution, tests on the free evolution of the
ensemble, and investigation of the phase-space densities achieved. Up to (74 ± 4)% condensation of an
ensemble featuring (30 000 ± 13 000) atoms at a kinetic temperature of (37 ± 3) nK is demonstrated. The
evaporation shows high efficiency down to a 3 s evaporation time, while a critical phase-space density
can be achieved within (1.29 ± 0.07) s using an even faster evaporation ramp. This opens the door to
fundamental physics experiments on Bose-Einstein condensates in microgravity, as well as applications
pursuing atomic ensembles with exceptionally low expansion velocities.
Schlagwörter
cold atoms
;
dipole trap
;
microgravity
;
weightlessness
;
evaporative cooling
;
BEC
;
Bose-Einstein-Condensation
;
ODT
Institution
Dokumenttyp
Dissertation
Sprache
Englisch
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