NASA's Cold Atom Laboratory: Five Years of Quantum Science Operations in Space

Abstract

NASA's Cold Atom Laboratory (CAL) is a multi-user science facility for studying quantum gases in the microgravity environment of the International Space Station. The persistent microgravity environment of the ISS enables research with ultracold atoms in a temperature regime and force-free environment inaccessible to terrestrial laboratories, unlocking the potential to observe novel quantum phenomena. CAL launched to the ISS in May 2018, and has operated continuously since then as the worlds first multi-user quantum science facility in space. CAL is the first experimental facility to produce the fifth state of matter known as a Bose-Einstein condensate with ultracold rubidium atoms on orbit and, more recently, with mixtures of rubidium and potassium. We present an overview of CAL's design and operation, review the scientific contributions to date, and discuss recent on-orbit upgrades to extend its useful mission lifetime and provide enhanced science. We also consider opportunities for follow-on missions informed by lessons learned from over five years of operation on orbit.

Figures (7)

• Figure 1: Onset of Bose--Einstein condensation of rubidium atoms on the ISS Aveline2020. Each false-color image represents a separate experiment where atoms are released after evaporative cooling in a harmonic trap, then imaged following a short time of free expansion to reveal the velocity distribution of the atomic ensemble. The final image shows a macroscopic cloud of almost 50 000 atoms with over one quarter in a single quantum wave function determined by the initial conditions in the trap.
• Figure 2: Ultra-cold atoms in harmonic trap potentials aligned with gravity (a) on Earth and (b) in micro-gravity. The micro-gravity environment allows the use of much shallower potentials and optimal overlap in mixtures of different atomic species.
• Figure 3: Absorption images of non-condensed rubidium atoms after release from a shell potential in micro-gravity. The series of images illustrates the behavior as the bubble-shaped potential is "inflated" prior to release of the atoms. The near-uniform densities are only observable in the absence of gravity. The darker lobes at the upper and lower bounds of each cloud are artifacts of the column-averaged absorption imaging technique combined with the finite imaging resolution. Adapted from Ref. Carollo2022.
• Figure 4: Superposition of momentum states observed in ultra-cold rubidium atoms after applying a series of optical pulses to realize an atom interferometer. Each spatially-separated atom cloud is approximately 40 µm by 48 µm in size, and the clouds are separated in momentum space by two photon recoils. Prior to the observation, an individual atom's wave-function exists simultaneously in both locations.
• Figure 5: CAL Mission Operations Architecture.