In this blog post Vincenzo Tamma, founding director of the Quantum Science and Technology Hub at the University of Portsmouth, writes about a major breakthrough in quantum physics.

The record for the coldest temperature ever achieved was recently established in the cooling of matter waves to 38 picokelvins at the Bremen drop tower in Germany [1,2]. The work provides a new and exciting perspective in the development of quantum-enhanced sensors and tests of gravity at the quantum level.

The wave-particle duality is one of the most puzzling and at the same time exciting phenomena in quantum mechanics: “quantum objects” can be described as both particles and waves.  In particular, at ultralow temperatures, it is possible to generate matter waves in the form of Bose-Einstein condensates (BECs). 

BEC matter waves can interfere with each other in an interferometer analogously to optical waves but, differently from photonic waves, the presence of massive objects makes them ideal probes for gravitational effects at microscopic scales where quantum phenomena unravel themselves. Matter waves at colder and colder temperatures can reach longer and longer interferometer expansion times probing gravitational effects with higher and higher precision.

Ernst Rasel from Leibniz University Hannover in Germany and colleagues have reached for the first time the coldest temperature ever of 38pK for a BEC to interfere.

But how were they able to cool down matter waves at such a low temperature? It turns out that this can be done by focusing matter waves as one does with optical waves by using a lens to slow down their expansion in time. However, to maximise the effect of such a cooling process one needs to be able to slow down the BEC waves in all three directions.

Rasel and colleagues have achieved such a 3D collimation with  an innovative time-domain lens system enabling both a “ad hoc tuning” of the BEC atomic interactions for focusing the atoms along the BEC axial direction and a 2-D lens to focus them along the other two directions associated with the BEC waist.

“The ability to generate slowly expanding BECs (in all three directions) for tens of seconds can enable high-precision gravitational-wave detection, measurements of the gravitational constant, and the tidal force of gravity, as well as the search for ultralight dark matter and a stringent quantum verification of Einstein’s equivalence principle, both in drop towers and in space.

Furthermore, the 3D matter-wave lens system introduced by Rasel and his colleagues provides a new and exciting perspective on the quantum advantage hidden behind the presence of interatomic interactions, often viewed as a drawback in matter-wave optics with long expansion times. Indeed, such interactions can be exploited as a powerful metrological tool in the development of matter-wave quantum sensors, enabling not only high-coherence properties but also highly nonclassical correlations.

  1. C. Deppner et al., “Collective-mode enhanced matter-wave optics,” Phys. Rev. Lett. 127, 100401 (2021).
  1.  V. Tamma, “3D Collimation of Matter Waves“, Physics 14, 119 (2021)