Matter-waves exposed to the external world: From decoherence to gravity, and back

Ron Folman and the Atom Chip group / Ben-Gurion University of the Negev

Spatial clock interferometry [4].

Ultra-cold atoms, at a billionth of one degree Kelvin away from absolute zero - the coldest system known to science in the lab or in nature, are called matter-waves as they behave as waves. This has extra-ordinary consequences; for example, a single atom can go through two slits simultaneously (in a so-called quantum spatial superposition) and form an interference pattern on a screen. Such an interference experiment may be used as an extremely sensitive probe of numerous fundamental forces and interactions in our universe.

In this talk we present several such interferometry experiments realized with a Bose-Einstein condensate on an atom chip [1] and in which different effects of the environment on the atom have been investigated. First, we bring such a cold-atom interferometer very close (5μm) to a room temperature surface [2,3], to study the ways in which the classical environment attempts to destroy delicate quantum states. The details of this decoherence process are crucial for our understanding of the border between the classical and quantum worlds, as well as for the implementation of quantum technology such as the quantum computer. Next, we present an experiment in which a single clock is put in two places simultaneously, and show how it could probe the interplay of quantum mechanics and general relativity [4,5], the unification of which has been a long standing goal of science. Finally, we discuss Stern-Gerlach interferometry [6,7] and present a unique realization almost a century after the effect was discovered. Here atoms are split according to their spin, a fundamental quantum property, allowing us to test the limits of quantum operations originating in classical devices such as macroscopic magnets.

[1] Mark Keil, Omer Amit, Shuyu Zhou, David Groswasser, Yonathan Japha, Ron Folman, Fifteen years of cold matter on the atom chip: Promise, realizations and prospects, Journal of Modern Optics 63, 1840 (2016).
[2] Shuyu Zhou, David Groswasser, Mark Keil, Yonathan Japha, Ron Folman, Robust spatial coherence  from a room temperature atom-chip, Phys. Rev. A 93, 063615 (2016).

[3] Yonathan Japha, Shuyu Zhou, Mark Keil and Ron Folman, Carsten Henkel, Amichay Vardi, Suppression and enhancement of decoherence in an atomic Josephson junction, New J. Phys. 18, 055008 (2016).
[4] Yair Margalit, Zhifan Zhou, Shimon Machluf, Daniel Rohrlich, Yonathan Japha, Ron Folman, A self-interfering clock as a which path witness, Science 349, 1205 (2015).

[5] Zhifan Zhou, Yair Margalit, Daniel Rohrlich, Yonathan Japha, and Ron Folman, Clock complementarity in the context of general relativity, submitted.
[6] Shimon Machluf, Yonathan Japha and Ron Folman, Coherent Stern-Gerlach momentum splitting on an atom chip, Nature Communications 4, 2424 (2013).

[7] Atom Chip group, Probing time irreversibility with a high visibility Stern-Gerlach interferometer, in preparation.