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arXiv:2005.11046 · Journal of the Physical Society of Japan

Long-Time Correlations in Single-Neutron Interferometry Data

Madita Willsch, Dennis Willsch, Kristel F. L. Michielsen, Fengping Jin, Tobias Denkmayr, Stephan Sponar, Yuji Hasegawa, Hans A. De Raedt

Published May 22, 2020• 0 citations
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Abstract

We present a detailed analysis of the time series of time-stamped neutron counts obtained by single-neutron interferometry.The neutron counting statistics display the usual Poissonian behavior, but the variance of the neutron counts does not.Instead, the variance is found to exhibit a dependence on the phase-shifter setting which can be explained by a probabilistic model that accounts for fluctuations of the phase shift.The time series of the detection events exhibit long-time correlations with amplitudes that also depend on the phase-shifter setting.These correlations appear as damped oscillations with a period of about 2.8 s.By simulation, we show that the correlations of the time differences observed in the experiment can be reproduced by assuming that, for a fixed setting of the phase shifter, the phase shift experienced by the neutrons varies periodically in time with a period of 2.8 s.The same simulations also reproduce the behavior of the variance.Our analysis of the experimental data suggests that time-stamped data of singleparticle interference experiments may exhibit transient features that require a description in terms of non-stationary processes, going beyond the standard quantum model of independent random events.

DOI
10.7566/jpsj.89.064005

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We present a detailed analysis of the time series of time-stamped neutron counts obtained by single-neutron interferometry.The neutron counting statistics display the usual Poissonian behavior, but the variance of the neutron counts does not.Instead, the variance is found to exhibit a dependence on the phase-shifter setting which can be explained by a probabilistic model that accounts for fluctuations of the phase shift.The time series of the detection events exhibit long-time correlations with amplitudes that also depend on the phase-shifter setting.These correlations appear as damped oscillations with a period of about 2.8 s.By simulation, we show that the correlations of the time differences observed in the experiment can be reproduced by assuming that, for a fixed setting of the phase shifter, the phase shift experienced by the neutrons varies periodically in time with a period of 2.8 s.The same simulations also reproduce the behavior of the variance.Our analysis of the experimental data suggests that time-stamped data of singleparticle interference experiments may exhibit transient features that require a description in terms of non-stationary processes, going beyond the standard quantum model of independent random events.
We present a detailed analysis of the time series of time-stamped neutron counts obtained by single-neutron interferometry. The neutron counting statistics display the usual Poissonian behavior, but the variance of the neutron counts does not. Instead, the variance is found to exhibit a dependence on the phase-shifter setting which can be explained by a probabilistic model that accounts for fluctuations of the phase shift. The time series of the detection events exhibit long-time correlations with amplitudes that also depend on the phase-shifter setting. These correlations appear as damped oscillations with a period of about 2.8 s. By simulation, we show that the correlations of the time differences observed in the experiment can be reproduced by assuming that, for a fixed setting of the phase shifter, the phase shift experienced by the neutrons varies periodically in time with a period of 2.8 s. The same simulations also reproduce the behavior of the variance. Our analysis of the experimental data suggests that time-stamped data of single-particle interference experiments may exhibit transient features that require a description in terms of non-stationary processes, going beyond the standard quantum model of independent random events.
A discrete-event approach, which has already been shown to give a cause-and-effect explanation of many quantum optics experiments, is applied to single-neutron interferometry experiments. The simulation algorithm yields a logically consistent description in terms of individual neutrons and does not require the knowledge of the solution of a wave equation. It is shown that the simulation method reproduces the results of several single-neutron interferometry experiments, including experiments which, in quantum theoretical language, involve entanglement. Our results demonstrate that classical (non-Hamiltonian) systems can exhibit correlations which in quantum theory are associated with interference and entanglement, also when all particles emitted by the source are accounted for.
A discrete-event approach, which has already been shown to give a cause-and-effect explanation of many quantum optics experiments, is applied to single-neutron interferometry experiments. The simulation algorithm yields a logically consistent description in terms of individual neutrons and does not require the knowledge of the solution of a wave equation. It is shown that the simulation method reproduces the results of several single-neutron interferometry experiments, including experiments which, in quantum theoretical language, involve entanglement. Our results demonstrate that classical (non-Hamiltonian) systems can exhibit correlations which in quantum theory are associated with interference and entanglement, also when all particles emitted by the source are accounted for.
Abstract This chapter describes a rather broad selection of neutron interferometry experiments whose theoretical description requires an understanding of the mutual coherence function, and the sensitive experimental techniques utilized. Within the interferometer the coherent beams can be influenced by interactions with fields and material media in space and time causing phase shifts and wave packet delays that substantially affect the outgoing beams. Post-selection experiments involving spectral filtering and time-of-flight analysis are described. The phase-echo effect is described; it is a generalization of the spin-echo effect. Placing statistical or deterministic absorbers within the interferometer affects the outgoing coherence properties of beams quite differently. Low counting rate interference experiments show time pair-correlation effects characteristic of Poissonian statistical beams. Decoherence effects are investigated to study the transition from a quantum to a classical regime.
We have demonstrated in our experiments that important additional information can be won even from a stationary neutron beam by registering the detection time. Time selection was performed by registering the time of arrival of neutrons with respect to reference events. It was thus possible to measure the time-dependent neutron-neutron pair correlation function of a statistical beam. The sequence of time-correlated pairs is more strongly correlated than the Poissonian distribution of the initial events. Using this method it is possible to enhance the contrast and the phase resolution.
We analyse the coherence properties of neutron wavepackets, after they have interacted with a phase shifter undergoing different kinds of statistical fluctuation. We give a quantitative (and operational) definition of decoherence and compare it to the standard deviation of the distribution of the phase shifts. We find that in some cases the neutron ensemble is more coherent, even though it has interacted with a wider (i.e. more disordered) distribution of shifts. This feature is independent of the particular definition of decoherence: this is shown by proposing and discussing an alternative definition, based on the Wigner function, that displays a similar behaviour. We briefly discuss the notion of entropy of the shifts and find that, in general, it does not correspond to that of decoherence of the neutron.