Atom interferometers serve as high-precision sensors for quantities like acceleration, rotation, or magnetic fields. The sensitivity of atom interferometers is greatly enhanced by long interrogation times, as they are available in spaceborne applications. Second-long interrogation times favor the employment of atomic Bose-Einstein condensates (BECs) with their well-controlled spatial mode and their slow expansion rates. The sensitivity can be increased even further by employing squeezed atomic ensembles that enable measurements beyond the standards quantum limit. The INTENTAS project develops a source of entangled atoms that can be tested under microgravity conditions. Microgravity is provided by Hannover’s Einstein Elevator, which offers up to 4s of free fall. A key feature is the fast all-optical BEC generation which is performed in a crossed-beam optical dipole trap. In this poster, the status of the project will be presented, which includes operation in microgravity.
Atom interferometers serve as high-precision sensors for quantities like acceleration, rotation, or magnetic fields. The sensitivity of atom interferometers is greatly enhanced by long interrogation times, as they are available in spaceborne applications. Second-long interrogation times favor the employment of atomic Bose-Einstein condensates (BECs) with their well-controlled spatial mode and their slow expansion rates. The sensitivity can be increased even further by employing squeezed atomic ensembles that enable measurements beyond the standards quantum limit. The INTENTAS project develops a source of entangled atoms that can be tested under microgravity conditions. Microgravity is provided by Hannover’s Einstein Elevator, which offers up to 4s of free fall. A key feature is the fast all-optical BEC generation which is performed in a crossed-beam optical dipole trap. In this poster, the status of the project will be presented, which includes operation in microgravity.
Abstract The INTENTAS project aims to develop an atomic sensor utilizing entangled Bose-Einstein condensates (BECs) in a microgravity environment. This key achievement is necessary to advance the capability for measurements that benefit from both entanglement-enhanced sensitivities and extended interrogation times. The project addresses significant challenges related to size, weight, and power management (SWaP) specific to the experimental platform at the Einstein-Elevator in Hannover. The design ensures a low-noise environment essential for the creation and detection of entanglement. Additionally, the apparatus features an innovative approach to the all-optical creation of BECs, providing a flexible system for various configurations and meeting the requirements for rapid turnaround times. Successful demonstration of this technology in the Einstein-Elevator will pave the way for a future deployment in space, where its potential applications will unlock high-precision quantum sensing.
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.
Recent advances in atom interferometry have led to the development of quantum inertial sensors with outstanding performance in terms of sensitivity, accuracy, and long-term stability. For ground-based implementations, these sensors are ultimately limited by the free-fall height of atomic fountains required to interrogate the atoms over extended timescales. This limitation can be overcome in Space and in unique “microgravity” facilities such as drop towers or free-falling aircraft. These facilities require large investments, long development times, and place stringent constraints on instruments that further limit their widespread use. In this work, we present a new approach in which atom interferometry is performed in a laboratory-scale Einstein Elevator. We demonstrate an acceleration sensitivity of 6 × 10−7 m/s2 per shot, with a total interrogation time of 2T = 200 ms. We further demonstrate the capability to perform long-term statistical studies by operating the Einstein Elevator over several days with high reproducibility. We present atom interferometry performed in a laboratory-scale Einstein Elevator over several days with high reproducibility. This table-top experiment enables long-term metrological assessments of quantum inertial sensors in microgravity.
Quantum sensors based on the interference of cold atoms have advanced to the forefront of precision measurements in geodesy, metrology and tests of fundamental physics. The ultimate potential of these devices is realized using quantum degenerate atoms in extended free fall. This can be achieved on microgravity platforms such as drop towers, parabolic flights, ballistic rockets, satellites and space stations. The transition to mobile and robust devices that can withstand the demands of these environments comes with many challenges. Quantum sensors need to be scaled down and integrated without compromising their performance. In fact, they need to significantly outpace conventional instruments, since microgravity time is an expensive resource and limited to a few seconds at a time on the most accessible platforms. This thesis describes the construction, qualification and operation of a miniaturized ultracold atom experiment that meets these challenges. The QUANTUS-2 apparatus features a payload weight of 147 kg and a payload volume of 0.3 m^3. It generates Bose-Einstein condensates of 4×10^5 ^87Rb atoms every 1.6 seconds, a flux of ultra-cold atoms that is on par with the best lab-sized devices. Ensembles of 1×10^5 atoms can be created at a 1 Hz rate. It is currently the fastest machine of its kind and achieves the highest atom number of any atom chip setup. The apparatus continuously withstands peak accelerations of up to 45 g during microgravity campaigns at the drop tower facility in Bremen, Germany. Here, the payload has accrued 208 drops and 9 catapult launches over 24 month. The setup is the first atom optics experiment to stand up to the technical demands of catapult operation. Four condensates can be created and observed consecutively during nine seconds of free fall in a single catapult launch. In total, the experiment has been suspended in microgravity for over 17 minutes. With the record source performance, the repetition rate for microgravity experiments with ultra-cold atoms was increased by a factor of four compared to previous devices. The total atom number was increased by a factor of 40, vastly improving the signal to noise ratio for absorption images of spatially extended clouds. The ensembles can be prepared consistently over many weeks of drop tower operation. The variance of the mean center of mass velocity in two observable directions is 7.3 μm/s and 6.9 μm/s. Magnetic lensing techniques were employed to manipulate the expansion of the ensembles. First results yield a residual expansion rate in three dimensions of σ_v = 116.9 ± 13.9 μm/s, which implies a three-dimensional effective temperature of T = 47.6 ± 11.3 pK at an average condensate atom number of N = 93000. These values constitute the best collimation of any atomic ensemble and the most promising source for atom interferometry reported to date. Optimizing the current lensing sequence will reduce the expansion rate further to effective temperatures in the femtokelvin regime. The level of control demonstrated over the condensates is highly relevant for the advancement of matter-wave optics and quantum sensors. Controlling the motion and size of atomic clouds is intrinsically tied to many systematic effects in high precision measurements. QUANTUS-2 will provide a platform to explore and mitigate these limitations on unprecedented time scales of up to seven seconds of free evolution.
Inertial sensors based on matter-wave interferometry are currently approaching the precision and accuracy of state-of-the-art classical sensors. While these devices are often realised with ultracold but not Bose-condensed atoms as matter waves, employing Bose-Einstein Condensates (BEC) promises to overcome certain limitations, especially those related to the ensemble's expansion. The point-source like character of BECs also enables utilising spatial interference patterns to measure e.g. rotation rates in single-shot experiments. Matter wave-based inertial sensors are considered for experiments ranging from Gravitational Wave detection to tests of the Universality of Free Fall (UFF) to gain insight into the joint between Quantum Mechanics and General Relativity. In the scope of this thesis, matter-wave interferometry with BECs was demonstrated for the first time in a microgravity environment with the QUANTUS-1 apparatus. The same instrument was then employed as a quantum tiltmeter utilising a novel beam-splitting mechanism known as Bragg Double Diffraction. To this end, the QUANTUS-1 apparatus designed as a BEC instrument to be operated in the drop tower at ZARM at University of Bremen was equipped with optics and laser systems required for performing matter-wave interferometry based on Bragg Diffraction. The apparatus employs an atom chip to create BECs of around 10000 Rubidium 87 atoms within 15 s. With a Mach-Zehnder like interferometer scheme, spatial interference fringes were observed after a free evolution time in the interferometer of up to 677 ms. To achieve these long time scales, a method known as Delta-Kick Collimation (DKC) was adapted to slow the expansion of the BEC to a kinetic energy equivalent below 1 nK, and the atoms were transferred to a non-magnetic Zeeman state via an adiabatic rapid passage (ARP). A similar interferometer scheme with a newly developed beam-splitter mechanism known as Bragg Double Diffraction was used to measure the tilt of the instrument on ground with a precision of up to 4.4 AA rad. This thesis presents an overview of the apparatus including ground-based characterisations of all required experimental steps. Results from over 400 free fall experiments are evaluated for expansion studies of the BEC and matter-wave interferometry in microgravity. The time-evolution of first and second order Bragg Double Diffraction beam splitters is studied, and an interferometer sensitive to the tilt of the instrument is implemented. Based on this work, a gravimeter with a new launch mechanism comprising Bragg beam splitters and Bloch oscillations to enable atomic fountains in atom-chip based devices was developed. The microgravity experiments were adapted for the MAIUS-1 sounding-rocket instrument to create the first man-made BEC in outer space and study the feasibility of operating matter-wave interferometers on space-borne platforms. The results of this thesis lay the groundwork for future space-borne missions using matter-wave interferometry for precision measurements of inertial forces.
Atom interferometers belong among today's most precise sensors and offer a broad range of possible metrological applications. Given their ability to measure accelerations and rotations precisely, they are suitable for inertial sensing, navigation and geodesy. Beyond this, they proved indispensible for time-keeping as well as fundamental research. This explains why the improvement of achievable sensitivities of atom interferometers is of particular interest. However the sensitivity of atom interferometers is fundamentally restricted by the standard quantum limit. The standard quantum limit can only be surpassed by employing entangled many-partice states. Entangled states, such as the twin-Fock state, allow atom interferometers to improve the phase sensitivity beyond the standard quantum limit, but they are reliant on an accurate detection of the interferometric out come. In this work, an experimental apparatus is designed and set up that will allow for routine generation of highly entangled twin-Fock states in a Rubidium-87 spinor Bose-Einstein condensate. As the main feature of this apparatus, an accurate atom counting fluorescence detection has been implemented. This detection achieves single-particle resolving fluorescence measurements for 1 up to 30 atoms. According to the noise analysis the single-atom resolution extends to a limiting atom number of 390(20) atoms. The implemented quadrupole coils with their strong gradient of up to 300 G/cm offer a tight confinement that in combination with the 55 W optical dipole trap laser will enable a fast repetition rate of the creation of highly entangled quantum states.