Manipulation of gravitational quantum states of a bouncing neutron with the GRANIT spectrometer

TL;DR

This paper discusses methods to manipulate and select specific gravitational quantum states of bouncing neutrons using the GRANIT spectrometer, advancing quantum gravity research with precise neutron state control.

Contribution

It introduces novel techniques for selecting gravitational quantum states of neutrons and quantifies the neutron wave function extension using the GRANIT apparatus.

Findings

Effective methods to favor specific GQS using mirrors and absorbers

Increased GQS separation efficiency with absorber roughness

Measured neutron wave function extension as 5.9±0.3 μm

Abstract

The bouncing neutron is one of the rare system where gravity can be studied in a quantum framework. To this end it is crucial to be able to select some specific gravitational quantum state (GQS). The GRANIT apparatus is the first physics experiment connected to a superthermal helium UCN source. We report on the methods developed for this instrument showing how specific GQS can be favored using a step between mirrors and an absorbing slit. We explore the increase of GQS separation efficiency by increasing the absorber roughness amplitude, and find it is feasible but requires a high adjustment precision. We also quantify the transmission of the absorbing slit leading to a measurement of the spatial extension of the neutron vertical wave function $z_0 = \hbar^{2/3}\left(2m^2g\right)^{-1/3} = 5.9\pm0.3\,\mu$m.