Page 66 - ILL Annual Report 2019

NUCLEAR AND PARTICLE PHYSICS
Armin Danner. Austrian
Atominstitut, TU Wien
‘We perform neutron interferometer experiments to give new insights and interpretations on quantum mechanics. Coming to Grenoble for this purpose is always exciting—it gives and takes a lot at each visit.’
Inertia of intrinsic spin observed in neutron interferometry
Interferometer S18
Inertia is a key property in both
general relativity and quantum theory. While inertia is usually associated
with mass, intrinsic spin can exhibit similar behaviour in the form of spin- rotation coupling. This coupling is a quantum mechanical extension of the Sagnac effect and manifests itself as
an additional phase in the neutron
wave function. Such experiments were proposed as far back as thirty years ago. With the instrument S18, we were finally able to conduct a high-precision experiment using the technique of neutron interferometry to confirm the effect.
AUTHORS
A. Danner, B. Demirel, W. Kersten, R. Wagner and S. Sponar (TU Wien, Austria)
H. Lemmel (ILL and TU Wien, Austria)
Y. Hasegawa (TU Wien, Austria and Hokkaido University, Japan)
ARTICLE FROM
npj Quantum Information 6, 23 (2020) - doi:10.1038/s41534-020- 0254-8
REFERENCES
[1] G. Sagnac, Comptes Rendus Acad. Sci. 157 (1913) 1410 [2] H. Rauch and S.A. Werner, Oxford University Press (2000)
[3] B. Mashhoon, Phys. Rev. Lett. 61 (1988) 2639
[4] B. Mashhoon and H. Kaiser, Physica B 385–386 (2006) 1381
When Georges Sagnac conducted his famous interferometer experiment with light [1], he was convinced that he had found proof of the ether. In his rotatable set-up, a light wave is split in an interferometer where both partial waves propagate through a ring interferometer in opposite directions. The relative phase shift at recombination is linearly dependent on the rotation frequency. Although
we strongly favour the framework of special relativity to describe his results today, the experiment itself is still an interesting one: without external reference, observers in
a rotating frame are able to measure the rotation of their system. This was also demonstrated in the rotating frame of the Earth in the Michelson–Gale experiment with light and by Werner et al. with neutrons [2].
In the rotating system, we can express the phase shift in
⃑⃑⃑
the Sagnac interferometer as a coupling ~Ω • A, where
Ω is the rotation vector and A the oriented area of the ⃑⃑
interferometer. Alternatively, one can write this as ~Ω • L,
with the orbital angular momentum L. For an observer in the
rotating frame, accelerations of particles require different
forces depending on the direction of their orbital angular
momentum and linear to their mass. When extending the
orbital angular momentum to the total angular momentum,
an additional spin contribution ~ Ω • S naturally appears, called spin-rotation coupling. To confirm this effect, various neutron interferometer experiments have been suggested
[2, 3]. The coupling has been used in NMR to describe the rotation of the polarisation vector in rotating magnetic fields for a long time. However, semi-classical Bloch equations suffice to describe those experimental results where only the orientation of the polarisation vector is observed.
⃑⃑
⃑⃑
© L. Thion
ANNUAL REPORT 2019
Figure 1
The neutron interferometry station S18.