Session S02: Fast Production and Control of Ultracold Systems

Live

We present a scheme for fast, efficient production of Bose-Einstein condensates (BECs) and degenerate Fermi gases (DFGs) of erbium in an optical dipole trap. This versatile scheme produces pure BECs of $10^5$ atoms in 900 ms, as well as DFGs of $10^5$ atoms with a $T/T_F$ = 0.1 in a few seconds. We start with very efficient loading into a two stage magneto-optical trap operating on two narrow transitions of erbium (190 kHz and 8 kHz), reaching sub-microKelvin temperatures. We then transfer the atoms into a dynamically tunable optical dipole trap, and apply a molasses cooling pulse to further increase the phase-space density of the cloud, which allows us to reach degeneracy with only a very short evaporation. Our result is promising for the field of degenerate quantum gases, as it significantly decreases the initial state preparation time. For quantum gas microscopy in particular, this is an order of magnitude improvement on state preparation time. This reduces the experiment's sensitivity to drifts and enables the study of questions that require a large number of statistics.   

Live

We have created a steady-state Bose-Einstein condensate (BEC), a BEC in which losses are continuously balanced by adding atoms to a thermal reservoir surrounding it. We create a steady-state BEC by streaming a beam of strontium atoms through a sequence of spatially separated laser cooling stages. Cooling the gas to 1$\mu$K while simultaneously increasing its density. After precooling on a MHz-wide transition, we capture atoms in a steady-state narrow-line (kHz) MOT [1]. A beam of atoms is then coupled into a dipole guide and transported to a laser cooled reservoir [2]. In the final stage, atoms accumulate in a "dimple" trap, in which they are protected from resonant light by a “transparency” beam that shifts the atomic energy levels out of resonance [3]. The dimple provides a density increase while temperature is maintained by elastic collisions with atoms from the reservoir. The result is a phase-space density enhancement reaching quantum degeneracy. Steady-state is reached within 8s after which we always destructively detect a BEC of 15000 atoms for randomly chosen times up to 300s. This research opens new possibilities in the fields of quantum sensors and open dissipative quantum systems.[1]PRL 119, 223202 (2017). [2]Phys.Rev.Applied 12,044014 (2019).[3]PRL 110, 263003 (2013).   

Live

BECCAL (Bose-Einstein Condensate and Cold Atom Laboratory) is a NASA – DLR mission dedicated to executing experiments with ultra-cold and condensed atoms on the International Space Station (ISS). BECCAL builds on the heritage of successful operation of atom optical experiments in microgravity, especially NASA’s CAL and the DLR funded QUANTUS program, covering experiments in the drop tower and on sounding rockets (MAIUS). CAL, installed on the ISS in 2018, offers experimental time to interested researchers for a variety of experimental campaigns. It is therefore an important milestone towards the realization of BECCAL. BECCALs main objective is to enable a broad range of experiments, covering atom interferometry, coherent atom optics, scalar Bose-Einstein gases, spinor Bose-Einstein gases and gas mixtures, strongly interacting gases, and quantum information. Thus, BECCAL is a unique multi-user facility for performing fundamental research in the microgravity environment of the ISS. In addition, it is a pathfinder for future quantum sensors on ground and in space. With this contribution we will present the capabilities of the facility and promote the involvement of the scientific community to develop and execute experiments with this unique instrument.   

Live

Despite recent progress in trapped-ion quantum computation, scaling to large numbers of qubits remains a challenge. For trapped-ion qubits, one proposal for extending beyond tens of ions in a single string is the `quantum CCD’ (QCCD) architecture. In this approach, ion qubits are transported between trapping zones dedicated to memory, readout and logical operations. To maximize the clock speed of QCCD processors, fast ion transport with low motional excitation is needed. In most prior QCCD experiments, low motional excitation was achieved by slow (adiabatic) ion transport between trap zones, and ion transit times were much longer than typical laser-driven gate interactions. Faster-than-adiabatic transport between neighboring trap zones has been previously demonstrated in relatively large three-dimensional traps, but low motional excitation was only achieved with particular choices of the transport duration. We report multi-zone faster-than-adiabatic transport in a surface electrode trap with reduced dependence of the final motional excitation on the duration of the transport.   

Live

We study the thermalization of polaritons in a semiconductor microcavity with a ring geometry above the condensation threshold. The lifetime of the polaritons is greater than the equilibration time for the system at cryogenic temperature (below 10 K), allowing the polariton condensate to come to thermal equilibrium. In the presence of a transverse electric and transverse magnetic splitting and a unidirectional cavity gradient (artificial gravity) in the ring, interesting polarization states emerge. We directly image the motion of the condensate in the ring using time-resolved optical microscopy techniques along with polarization resolution. The condensate is found to oscillate about the potential minimum, just like a rigid pendulum. The analogy to the rigid pendulum is verified by checking the dependence of the time period of the oscillations on the radius of the ring. Polarization dynamics provide an understanding of the interplay between the spin-orbit coupling, cavity tilt and energy dissipation which is behind the spatiotemporal polarization pattern formation in the ring.   

On Demand

Atom interferometers precision depends on the center-of-mass motion and the expansion rate of the atomic ensemble. By reducing the latter, systematic effects, e.g. through wavefront aberration, can be lowered. In our setup we utilize a dynamic time averaged optical dipole trap, generated by spatial modulation of the trapping beams in the horizontal plane. Via evaporation we produce Bose-Einstein condensates (BEC) of $2\times10^5$ condensed atoms with an effective temperature of about $30$nK after $3$s. Subsequently we carry out delta-kick collimation (DKC), performed in a trapped scheme. Contrary to pulsed DKC, we relax the trap confinement and release the atoms from the final trap at the minimum of their kinetic expansion. DKC can be performed at any stage of evaporative cooling, thus short-cutting the generation of ultra-cold radial expansion temperatures. In this talk we will show the results of fast BEC production and discuss the DKC results as well as limitations and the perspective of generating up to $10^6$ delta-kicked condensed atoms within $1$s.   

On Demand

The ability to prepare a sample of molecular ions in a known quantum state is useful for studies of state-dependent chemistry, precision measurements, blackbody thermometry among other applications. To take advantage of the long storage times of ion traps, there is a need to sustain control over the prepared states for a long duration. Using the technique of optical pumping with a spectrally pulse-shaped laser we have achieved a non-equilibrium rotational population distribution centered anywhere from N=0 to N=70 with $\delta$N $\sim$3 in the ground vibronic state of SiO$^+$. Furthermore, this technique allows us to sustain the control over an extended period. The fractional population in the target states and the timescale required to achieve state preparation quantify the success of the technique. In this talk, I will discuss our experiments and results to determine the timescale required for pumping into the ground rovibronic state in SiO$^+$ and to determine the fraction of population in the prepared distribution.   

Optimal Control Theory For Fast and Excitation-less transport of Bose-Einstein Condensation with an atom chip

Recent proposals for testing foundations of physics assume BECs as source of atom interferometry sensors.In this context, atom chip devices allow to build transportable BEC machines with high flux and high repetition rates,as demonstrated with MAIUS (rocket) micro-gravity experiment. In such experiments, the proximity of the atoms to the chip surface is however, limiting the optical access abd the available interferometry time necessary for high-precision measurements.This justifies the need of very well-designed BEC transport protocols in order to perform long base-line, and thus precise, atom interferometry measurements.We present optimal control theory protocols for the fast, excitation-less transport of BECs with atom chips,engineering transport ramps with duration not exceeding a 200 ms with realistic 3D anharmonic trap.This controlled transport is implemented over large distances, typically of the order of 1-2mm, i.e of about 1,000 times the size of the atomic cloud.The robustness of the transport protocol against experimental imperfections is evaluated, and the advantages over ' shorcut-to-adiabacity' schemes reported by our team will be discussed.Such robust control features are crucial for the success of novel implementation of atom interferometry experiments in space.   

Nanofiber testbed for guided atom interferometry (AI) in high dynamic environments

Laboratory based atomic inertial navigation sensors such as accelerometers and gyroscopes have demonstrated excellent performance and sensitivity that is comparable to conventional inertial measurement units. However, atom interferometry (AI) outside the laboratory necessitates operation in high dynamic environments. A promising avenue is guided AI which can increase the dynamic range of free space AI, fundamentally overcoming the potential problems of wavepacket mismatch, lateral atomic motion, and time-varying acceleration. In addition, the nanofiber testbed achieves strong atom-light interactions with low size, weight and power (SWaP) conditions due to its intrinsic small mode area. In this talk, we will present in-house capability of nanofiber fabrication, demonstration of one-dimensional optical dipole trap with two-color evanescent fields, atomic coherence verification of trapped atoms, and our progress toward guided atom interferometry.