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Journal of the Physical Society of Japan

Quantum Beat Experiments Using a Cold Neutron Spin Interferometer

Toru Ebisawa, Dai Yamazaki, S. Tasaki, Takeshi Kawai, Masahiro Hino, Tsunekazu Akiyoshi, Norio Achiwa, Yoshié Otake

Published May 15, 1998• 9 citations
Publisher

Abstract

Easy quantum beat experiments have been developed using a new cold neutron spin interferometer, which brings us easy observation of quantum beat phenomena. The quantum beat is created by the coherent superposition of the spin eigenstates of cold neutron with different energy states, which are produced with two radio-frequency flippers. We observed quantum beat phenomena with a range of frequency from 4 kHz to 10 -5 Hz, which correspond to the energy differences from 1.66 ×10 -11 eV to 4.1 ×10 -20 eV. The principle and the arrangement of the quantum beat experiment are discussed, and typical measurement data are presented. Some applications of the quantum beat experiments are briefly proposed.

DOI
10.1143/jpsj.67.1569

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Easy quantum beat experiments have been developed using a new cold neutron spin interferometer, which brings us easy observation of quantum beat phenomena. The quantum beat is created by the coherent superposition of the spin eigenstates of cold neutron with different energy states, which are produced with two radio-frequency flippers. We observed quantum beat phenomena with a range of frequency from 4 kHz to 10 -5 Hz, which correspond to the energy differences from 1.66 ×10 -11 eV to 4.1 ×10 -20 eV. The principle and the arrangement of the quantum beat experiment are discussed, and typical measurement data are presented. Some applications of the quantum beat experiments are briefly proposed.
In continuation of previous work explicitly demonstrating the basic quantum-mechanical principles of the static and the time-dependent superposition of spinors, a new double-resonance coil experiment is described, where a spin-flip process associated with an exchange of energy quanta happens in both beams of a perfect-crystal neutron interferometer. It is shown that under the given circumstances of neutron self-interference coherence is preserved in spite of the energy transfer to every neutron, which may stimulate renewed epistemological discussions about the interpretation of quantum mechanics. Furthermore quantum beating on a macroscopic time scale has been observed by introducing an exceedingly small energy difference of 8.6\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}17}$ eV between the two interfering beams. According to the statistical accuracy of the data thereby an energy sensitivity of 2.7\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}19}$ eV has been achieved.
The perfect crystal neutron interferometer has been used continuously for test measurements on quantum mechanics. Polarized neutrons were used to perform the quantum mechanical spin-superposition experiment on a macroscopic scale. This experiment was continued with two resonance coils in the beams, in which the coherence persisted, even if an energy exchange occurred with certainty between the neutron and the resonator system. A quantum beat effect was observed when slightly different resonance frequencies were applied to both beams. In this case, an extremely high energy sensitivity of 2.7×10 −19 eV was achieved. Neutron spectroscopy is thus able to cover time domains from microscopic to macroscopic scales. All the results obtained until now are in agreement with the formalism of quantum mechanics and stimulate discussion about the interpretation of this basic theory L'interferometre a neutrons a cristal parfait a servi sans discontinuer a faire des mesures tests en mecanique quantique. Des neutrons polarises ont ete utilises pour effectuer une experience de superposition de spins quantiques a l'echelle macroscopique. Cette experience fut reprise, en interposant deux solenoides resonnants dans les faisceaux et la coherence montree persister meme si un echange d'energie s'effectuait de maniere certaine entre le neutron et le systeme resonnant. Un effet de battement quantique a ete observe quand des frequences de resonance legerement differentes sont appliquees aux deux faisceaux. Dans ce cas une sensibilite en energie extremement grande (2,7×10 −19 et) a ete atteinte. La spectroscopie de neutrons peut donc couvrir des domaines temporels allant de l'echelle microscopique a l'echelle macroscopique. Tous les resultats obtenus jusqu'a present sont en accord avec le formalisme de la mecanique quantique et suscite des discussions sur l'interpretation de cette theorie fondamentale
Since the invention of perfect crystal neutron interferometry this technique has become an important tool in the realization of many textbook experiments in quantum mechanics. Widely separated coherent beams of thermal neutrons are produced and superposed by dynamical Bragg diffraction from a properly shaped perfect crystal. The observed interference patterns show the characteristic coherence properties of matter waves which arc influenced by the individual particle and by the properties of the experimental device. The verification of the 4π-periodicity of spinor wavefunctions and the realization of thc spin-superposition experiment on B macroscopic scale has become feasible by this technique. A new kind of a quantum beat effect with an energy sensitivity of 2.7 × 20−-19 eV has been observed in a double coil resonance experiment. The influence of gravity and of the Earth's rotation on the wavefunction become visible at a level of an elementary particle with non-zero mass. All the results are in agreement with the formulation of quantum mechanics but, nevertheless, they stimulate discussion about its interpretation. The particle-wave dualism becomes obvious on a macroscopic scale and with a beam of massive particles.
The object of this report is to review the recent results and some perspectives on cold neutron interferometry using multilayer neutron mirrors developed in KUR.The purposes of our research are to develop new experimental techniques, new devices for controlling neutron spin states for opening up a new world of physics.A multilayer neutron polarizes working under a very low external magnetic field (low field magnetic mirror), Funahashi's interferometer, a cold neutron spin echo instrument, a multilayer neutron spill splitter and a cold neutron pulser were developed.The equiv- alency of the quantum precession induced by the effective gap layer of the multilayer neutron spin splitter and Larmor precession of neutron spin in a magnetic field is established.This idea allows us to develop a cold neutron phase-spin-echo interferometer (a neutron spin interferometer).The neutron spin interferometer and a cold neutron pulser enabled us to carry out the delayed choice experiment for answering the question "how the neutron wave propagates after being split by the semitransparent mirror (wave splitter)".• These matters are reviewed in this paper.•
The coherent superposition of particle quantum states resulting from different spatial paths shows well-known interference effects. Another type of interference is Larmor precession, which can be described as neutron wave interference in spin space, i.e. interference on the same spatial path. Here we show several new manifestations of interference phenomena of the latter type. The interference is produced by coherent population of different I z = ±½ spin states in a polarized neutron beam between two resonant radio-frequency (RF) spin flippers. Their spin flip probability, and thus the occupation numbers of the spin states, can be tuned between 0 and 1 by changing the RF amplitude. This leads to interference effects in the polarization since the energy exchanged between the RF field and spin yields different phase evolution in the spatial parts of the neutron states. Depending on the preparation of the initial neutron states, five values for the time-independent phase difference between the final neutron states can be observed.