Going Down the Tube Two pillars of modern physics are quantum mechanics and general relativity. So far, both have remained apart with no quantum mechanical description of gravity available. Van Zoest et al. (p. 1540; see the Perspective by Nussenzveig and Barata) present work with a macroscopic quantum mechanical system—a Bose-Einstein condensate (BEC) of rubidium atoms in which the cloud of atoms is cooled into a collective quantum state—in microgravity. By dropping the BEC down a 146-meter-long drop chamber and monitoring the expansion of the quantum gas under these microgravity conditions, the authors provide a proof-of-principle demonstration of a technique that can probe the boundary of quantum mechanics and general relativity and perhaps offer the opportunity to reconcile the two experimentally. Studies of atomic quantum states in free-fall conditions may provide ways to test predictions of general relativity. Albert Einstein’s insight that it is impossible to distinguish a local experiment in a “freely falling elevator” from one in free space led to the development of the theory of general relativity. The wave nature of matter manifests itself in a striking way in Bose-Einstein condensates, where millions of atoms lose their identity and can be described by a single macroscopic wave function. We combine these two topics and report the preparation and observation of a Bose-Einstein condensate during free fall in a 146-meter-tall evacuated drop tower. During the expansion over 1 second, the atoms form a giant coherent matter wave that is delocalized on a millimeter scale, which represents a promising source for matter-wave interferometry to test the universality of free fall with quantum matter.

Bose-Einstein Condensation in Microgravity

In atomic sensors, continuous interrogation of laser-cooled atoms carries the benefits of improved sensitivity and high measurement bandwidth. However, cooling in proximity to coherent atomic state evolution can degrade performance in compact systems, due to decoherence. This study demonstrates an inertially sensitive matter-wave interferometer in a three-dimensionally-cooled atomic beam that mitigates decoherence while operating continuously. The technique could enable compact atom-interferometer sensors that measure continuously and with high sensitivity on dynamic platforms. 

/pdf/continuous-sub-doppler-cooled-atomic-beam-interferometer-for-2smayelp.pdf

Continuous Sub-Doppler-Cooled Atomic Beam Interferometer for Inertial Sensing

https://link.springer.com/content/pdf/10.1007/s00340-021-07717-3.pdf

Elimination of spatial Rabi frequency modulation by sideband suppression with a calcite crystal

Nowadays, atom-based quantum sensors are leaving the laboratory towards field applications requiring compact and robust laser systems. Here we describe the realization of a compact laser system for atomic gravimetry. Starting with a single diode laser operating at 780 nm and adding only one fiber electro-optical modulator, one acousto-optical modulator and one laser amplifier we produce laser beams at all the frequencies required for a Rb-87 atomic gravimeter. Furthermore, we demonstrate that an atomic fountain configuration can also be implemented with our laser system. The modulated system reported here represents a substantial advance in the simplification of the laser source for transportable atom-based quantum sensors that can be adapted to other sensors such as atomic clocks, accelerometers, gyroscopes or magnetometers with minor modifications.

Compact laser modulation system for a transportable atomic gravimeter.

The laser beam waist has an impact both in the sensitivity and systematic effects present in gravimetry and atom interferometry in general. In this paper we consider how different effects contribute to both aspects in order to make a better selection of the radius of the Raman beam given a particular laser power available. A large beam waist reduces systematic effects coming from wavefront curvature and Gouy phase contributions and improves the fringe contrast due to reduced intensity gradients. On the other hand, a large waist gives a smaller Rabi frequency, which lowers the sensitivity by reducing the fraction of atoms in the selected velocity range. Considering all contributions, we find that systematic effects usually have a dominant role in selecting a beam waist.

T. Roach

Papers

Selection of a Raman beam waist in atomic gravimetry