Short answer: A Bose-Einstein condensate (BEC) is a cloud of ultracold atoms that share one wave function, which makes it a coherent source for matter-wave interferometry. Three experiments cover a condensate gravimeter in 2011, an atom-chip interferometer that generated a non-classical state in 2013, and condensate interference in free fall on a sounding rocket in 2021. These are laboratory and flight experiments, not deployed sensors.
Why use a condensate in an interferometer?
The 2021 Nature Communications abstract says BECs in free fall are a promising source for space-borne interferometry. The authors give three reasons: BECs have a slowly expanding wave function, display large spatial coherence, and can be engineered and probed with optical techniques.
What did the 2011 gravimeter show?
The 2011 Physical Review A paper presents a cold-atom gravimeter that uses a sample of Bose-condensed rubidium-87 atoms. In a Mach-Zehnder configuration with the two arms separated by a two-photon Bragg transition, the authors observe interference fringes with a visibility of 83 plus or minus 6 percent at an interrogation time of 3 ms. They use large momentum transfer beam splitting, with higher-order Bragg transitions and Bloch oscillations, to increase the enclosed space-time area. Comparing condensed and thermal sources, they observe a reduced visibility of 58 plus or minus 4 percent for the thermal source, and suspect the loss is partly caused by wave-front aberrations, to which a thermal source is more susceptible because of its larger transverse momentum spread. They also present a simple mean-field model and conclude that, with currently available parameters, interaction-induced dephasing will not limit the sensitivity of inertial measurements with freely falling coherent sources. That is a model result.
What did the atom-chip interferometer show?
The 2013 Nature Communications paper demonstrates a full Mach-Zehnder sequence with trapped Bose-Einstein condensates confined on an atom chip. The authors note that particle interactions in the condensate create a nonlinearity absent in photon optics, and use it to generate a non-classical state with reduced number fluctuations inside the interferometer. With spatially separated wave packets, they apply a controlled phase shift and read it out with a non-adiabatic matter-wave recombiner. They report coherence times a factor of three beyond what is expected for coherent states, which they say highlights the potential of entanglement as a resource for metrology, and that the results pave the way for integrated quantum-enhanced matter-wave sensors. That second statement is an outlook.
What did the rocket experiment show?
The 2021 paper explores matter-wave fringes of multiple spinor components of a BEC released in free fall, using light pulses to drive Bragg processes and induce phase imprinting on a sounding rocket. The authors say the prevailing microgravity played a crucial role in observing the interference, which reveals the spatial coherence of the condensates and allows them to measure differential forces. They say their work marks the beginning of matter-wave interferometry in space, with future applications in fundamental physics, navigation and earth observation. Those applications are stated as future possibilities.
How to read this
The three experiments use different geometries, interrogation times and goals, so their results cannot be ranked. Visibility is a measure of fringe contrast and not a sensitivity. This post is based on abstracts and visible introductions, and full texts were not checked. It makes no claim about products or instruments in use. For related work, see our posts on atom-interferometer gravimetry and gyroscopes.
FAQ
Why do condensates help?
They offer a coherent, slowly expanding source, according to the 2021 abstract.
How much did a condensate beat a thermal source?
Fringe visibility was 83 percent against 58 percent in the 2011 gravimeter.
What did interactions do in the 2013 experiment?
They produced a non-classical state with reduced number fluctuations.
Was an interferometer flown in space?
A condensate interferometry experiment was run on a sounding rocket in the 2021 paper.
All field notes