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arXiv:2407.09307 · Physical Review Research

Measuring the angular momentum of a neutron using Earth's rotation

Niels Geerits, Stephan Sponar, K. Steffen, William Michael Snow, Steven R. Parnell, Giacomo Mauri, Gregory N. Smith, Robert M. Dalgliesh, V.O. de Haan

Published Jan 13, 2025• 5 citations
arXivHTMLPDF

Abstract

A coupling between Earth's rotation and orbital angular momentum (OAM), known as the Sagnac effect, is observed in entangled neutrons produced using a spin-echo interferometer. After correction for instrument systematics the measured coupling is within 5% of theory, with an uncertainty of 7.2%. The OAM in our setup is transverse to the propagation direction and scales linearly with neutron wavelength (4–12.75 Å), so the Sagnac coupling can be varied without mechanically rotating the device, which avoids systematic errors present in previous experiments. The detected transverse OAM of our beam corresponds to 4098 ± 295 ℏ Å − 1 , 10 5 times lower than in the previous neutron experiments. This demonstrates the feasibility of using the Sagnac effect to definitively measure neutron OAM and paves the way towards a future observation of the quantum Sagnac effect.

DOI
10.1103/physrevresearch.7.013046

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A coupling between Earth's rotation and orbital angular momentum (OAM), known as the Sagnac effect, is observed in entangled neutrons produced using a spin-echo interferometer. After correction for instrument systematics the measured coupling is within 5% of theory, with an uncertainty of 7.2%. The OAM in our setup is transverse to the propagation direction and scales linearly with neutron wavelength (4–12.75 Å), so the Sagnac coupling can be varied without mechanically rotating the device, which avoids systematic errors present in previous experiments. The detected transverse OAM of our beam corresponds to 4098 ± 295 ℏ Å − 1 , 10 5 times lower than in the previous neutron experiments. This demonstrates the feasibility of using the Sagnac effect to definitively measure neutron OAM and paves the way towards a future observation of the quantum Sagnac effect.
Lights carrying orbital angular momentum (OAM) have potential applications in precise rotation measurement, especially in remote sensing. Interferometers, especially nonlinear quantum interferometers, have also been proven to greatly improve the measurement accuracy in quantum metrology. By combining these two techniques, we theoretically propose a new atom-light hybrid Sagnac interferometer with OAM lights to advance the precision of the rotation measurement. A rotation sensitivity below standard quantum limit is achieved due to the enhancement of the quantum correlation of the interferometer even with 96% photon losses. This makes our protocol robustness to the photon loss. Furthermore, combining the slow light effect brings us at least four orders of magnitude of sensitivity better than the earth rotation rate. This new type interferometer has potential applications in high precision rotation sensing.
Einstein's theory of general relativity and quantum theory form the two major pillars of modern physics. However, certain inertial properties of a particle's intrinsic spin are inconspicuous while the inertial properties of mass are well known. Here, by performing a neutron interferometric experiment, we observe phase shifts arising as a consequence of the spin's coupling with the angular velocity of a rotating magnetic field. This coupling is a purely quantum mechanical extension of the Sagnac effect. The resulting phase shifts linearly depend on the frequency of the rotation of the magnetic field. Our results agree with the predictions derived from the Pauli-Schrodinger equation.
The physical basis for the description of phenomena by a rotating observer is investigated. A simple, yet tentative, extension of the hypothesis of locality is used to determine the interference phase shift induced by the rotation of a neutron interferometer. The result consists of the Sagnac term, which is due to the coupling of the orbital angular momentum of the neutron with the rotation of the frame, and a new term which arises from a similar coupling because of the neutron spin. The latter effect is generally smaller than the Sagnac phase shift by the ratio of de Broglie wavelength of the neutron to the dimension of the interferometer. The possibility of detecting the new effect is briefly discussed.
Lights carrying orbital angular momentum (OAM) have potential applications in precise rotation measurement, especially in remote sensing. Interferometers, especially nonlinear quantum interferometers, have also been proven to greatly improve the measurement accuracy in quantum metrology. By combining these two techniques, we theoretically propose a new atom-light hybrid Sagnac interferometer with OAM lights to advance the precision of the rotation measurement. A rotation sensitivity below standard quantum limit is achieved due to the enhancement of the quantum correlation of the interferometer even with 96% photon losses. This makes our protocol robustness to the photon loss. Furthermore, combining the slow light effect brings us at least four orders of magnitude of sensitivity better than the earth rotation rate. This new type interferometer has potential applications in high precision rotation sensing.
Abstract Einstein’s theory of general relativity and quantum theory form the two major pillars of modern physics. However, certain inertial properties of a particle’s intrinsic spin are inconspicuous while the inertial properties of mass are well known. Here, by performing a neutron interferometric experiment, we observe phase shifts arising as a consequence of the spin’s coupling with the angular velocity of a rotating magnetic field. This coupling is a purely quantum mechanical extension of the Sagnac effect. The resulting phase shifts linearly depend on the frequency of the rotation of the magnetic field. Our results agree with the predictions derived from the Pauli–Schrödinger equation.
In a Nature LETTER [1], a control of neutron angular momentum was apparently demonstrated using a neutron crystal interferometer. In the meantime, a number of highly interesting articles have been published dealing with the n-OAM and neutron interferometry, citing [1]. We show that the interpretation of [1] having detected a n-OAM is incorrect for several serious reasons and point out inconsistencies. Based only on the theory of dynamical neutron diffraction, we calculate all the interferograms and show perfect agreement with those given in [1]. There was no need to assume an additional n-OAM because no additional effect was observed that could not be explained by standard theory.