Response to "Verifying quantum superpositions at metre scales"

TL;DR

This paper defends the interpretation that a half-metre-scale atom interferometer demonstrates quantum superpositions at macroscopic distances, countering claims that it does not test quantum mechanics at such scales.

Contribution

The authors argue that their experiment provides evidence for macroscopic quantum superpositions and effectively tests quantum mechanics at large length scales, addressing prior criticisms.

Findings

Interference contrast constrains modifications to quantum mechanics

Experiment demonstrates quantum superposition at half-metre scale

No known mechanism prevents future differential measurements

Abstract

The preceding BCA (Stamper-Kurn et. al., arXiv:1607.01454) asserts that our observation of interference contrast in a half-metre-scale atom interferometer (Kovachy et. al., Nature 528, 530-3 (2015)) does not prove the existence of macroscopic quantum superpositions and hence does not test quantum mechanics at long length scales. Moreover, the BCA implies that intrinsic atomic interactions or technical imperfections could prevent the application of our work to future differential measurements. On the contrary, we argue the following: i) in standard quantum mechanics, there is no known mechanism in our system that prohibits its use in future differential measurement applications; ii) our experiment tests quantum mechanics in that it constrains any modifications that would reduce contrast in an interferometer with arms that propagate over widely separated trajectories; and iii) using a standard definition of superposition, our observation of interference results from quantum superposition at the half-metre scale. In particular, quantum superposition is a more general concept than first-order coherence.