title: A self-interfering clock as a "which path" witness.
abstract: In Einstein's general theory of relativity, time depends locally on gravity; in standard quantum theory, time is global-all clocks "tick" uniformly. We demonstrate a new tool for investigating time in the overlap of these two theories: a self-interfering clock, comprising two atomic spin states. We prepare the clock in a spatial superposition of quantum wave packets, which evolve coherently along two paths into a stable interference pattern. If we make the clock wave packets "tick" at different rates, to simulate a gravitational time lag, the clock time along each path yields "which path" information, degrading the pattern's visibility. In contrast, in standard interferometry, time cannot yield "which path" information. This proof-of-principle experiment may have implications for the study of time and general relativity and their impact on fundamental effects such as decoherence and the emergence of a classical world.
authors.affiliation: Department of Physics, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel.
authors.forename: Yair
authors.initials: Y
authors.lastname: Margalit
authors.affiliation: Department of Physics, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel.
authors.forename: Zhifan
authors.initials: Z
authors.lastname: Zhou
authors.affiliation: Department of Physics, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel.
authors.forename: Shimon
authors.initials: S
authors.lastname: Machluf
authors.affiliation: Department of Physics, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel.
authors.forename: Daniel
authors.initials: D
authors.lastname: Rohrlich
authors.affiliation: Department of Physics, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel.
authors.forename: Yonathan
authors.initials: Y
authors.lastname: Japha
authors.affiliation: Department of Physics, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel. folman@bgu.ac.il.
authors.forename: Ron
authors.initials: R
authors.lastname: Folman