The parallel between X-ray and neutron interferometry highlights the considerable challenges of the latter, particularly the need for much larger neutron interferometers, with the first neutron interferometry signal being observed by a team led by Helmut Rauch at the TRIGA research reactor in Vienna in January 1974, almost 10 years after the first X-ray observation.
As a doctoral student of Helmut Rauch, Wolfgang Treimer began to set up an interferometer experiment station at TRIGA in 1972. In the summer of 1973, he visited Ulrich Bonse, whose institute at the University of Dortmund had all the expertise and experimental equipment for X-ray interferometry. On 11 January 1974, he was part of the team who observed the first proof of neutron interference.
Subsequently interferometry experiments were performed in Vienna and conducted on a dedicated instrument at ILL (S18) under more favourable experimental conditions due to the higher neutron flux, although the first experiments were hampered by mechanical vibrations from choppers and pumps destroying the quantum coherence. The optical bench was fitted with vibration dampers - and the interferometer worked from then on.
In particular, in the 1980s, Anton Zeilinger, active over decades at ILL, published a paper that marked the physics of quantum entanglement, inspired by neutron interferometry, that would lead to the physics Nobel prize being awarded to Zeilinger and colleagues in 2022.
The latest and highly promising development in neutron interferometry is the use of a split crystal, rather than a single crystal, for which the orientation of the two parts has to be controlled to better than 10-9 rad. This will allow neutron path lengths of metres to be used to investigate fundamental symmetries and new forces for dark energy fields with exquisite sensitivity.
Left: From 1972 to 1974, the first experimental station for a neutron interferometer was built at the Atomic Institute in Vienna.
Right: Image from: W. Treimer, Dissertation, Universität Wien, März 1975, S. 115, ubdata.univie.ac.at/AC03293949
Reference: W. Treimer Physik Journal 23 (2024) Nr. 10 (link)
To read more about neutron reflectometry at the ILL:
- A Quantum Wave in Two Crystals (2022)
- Experimental demonstration of direct path state characterisation by measuring weak values in a matter-wave interferometer (2017)
Instrument S18 webpage