Rovibrational quantum interferometers and gravitational waves

Abstract

We show that the application of atom interferometry techniques to the internal, i.e., rotational-vibrational states of molecules provides a new tool for ultrahigh precision tests of fundamental physics. The measurement principle is based on the fact that the electronic structure of molecules is not spherically symmetric. A diatomic quantum sensor can hence distinguish between the direction along its internuclear axis and the two orthogonal directions and is therefore direction sensitive. As an example we show how a molecular rotational-vibrational quantum interferometer based on the hydrogen deuteride molecular ion $({\text{HD}}^{+})$ may be used to detect gravitational waves. We show that a monochromatic gravitational wave of dimensionless amplitude $h={10}^{\ensuremath{-}19}$ will cause a frequency shift of the order of $30\text{ }\ensuremath{\mu}\text{Hz}$ between appropriately prepared quantum states, a frequency difference likely to be detectable with the next generation atom interferometers in 1 s.