A self-interfering clock as a "which path" witness

TL;DR

This paper introduces a novel interferometry method using a self-interfering clock, demonstrating how entanglement between time and path affects interference visibility, with implications for quantum mechanics and relativity.

Contribution

It experimentally demonstrates a self-interfering clock that links time and path information, revealing new insights into quantum interference and the role of time.

Findings

Successful creation of a self-interfering clock with stable phase

Entanglement between clock time and path affects interference visibility

First proof-of-principle experiment linking time, interference, and relativity

Abstract

We experimentally demonstrate a new interferometry paradigm: a self-interfering clock. We split a clock into two spatially separated wave packets, and observe an interference pattern with a stable phase showing that the splitting was coherent, i.e., the clock was in two places simultaneously. We then make the clock wave packets "tick" at different rates to simulate a proper time lag. The entanglement between the clock's time and its path yields "which path" information, which affects the visibility of the clock's self-interference. By contrast, in standard interferometry, time cannot yield "which path" information. As a clock we use an atom prepared in a superposition of two spin states. This first proof-of-principle experiment may have far-reaching implications for the study of time and general relativity and their impact on fundamental quantum effects such as decoherence and wave packet collapse.