Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:quant-ph/0301068 · Physical Review A

Optimization of a neutron-spin test of the quantum Zeno effect

Paolo Facchi A, Yoichi Nakaguro, Hiromichi Nakazato, Saverio Pascazio, Makoto Unoki, Kazuya Yuasa

Published Jul 22, 2003• 9 citations
arXivHTMLPDF

Abstract

A neutron-spin experimental test of the quantum Zeno effect (QZE) is discussed from a practical point of view, where the nonideal efficiency of the magnetic mirrors, used for filtering the spin state, is taken into account. In the idealized case, the number N of (ideal) mirrors can be indefinitely increased, yielding an increasingly better QZE. In contrast, in a practical situation with imperfect mirrors, there is an optimal number of mirrors, ${N}_{\mathrm{opt}},$ at which the QZE becomes maximum: more frequent measurements would deteriorate the performance. However, a quantitative analysis shows that a good experimental test of the QZE is still feasible. These conclusions are of general validity: in a realistic experiment, the presence of losses and imperfections leads to an optimal frequency ${N}_{\mathrm{opt}},$ which is in general finite. One should not increase N beyond ${N}_{\mathrm{opt}}.$ A convenient formula for ${N}_{\mathrm{opt}},$ valid in a broad framework, is derived as a function of the parameters characterizing the experimental setup.

DOI
10.1103/physreva.68.012107

Related papers

QZE and IZE in a Simple Approach and the Neutron Decay

F. Giacosa

We discuss a simple and analytically solvable measurement model which describes the famous Quantum Zeno Effect (QZE) and Inverse Zeno Effect (IZE), that correspond to the slow down and to the increase of the decay rate caused by measurements (or, more in general, by the interaction of an unstable state with the detector and the environment). Within this model one can understand quite general features of the QZE and IZE: by considering an unstable quantum state, such as an unstable particle, whose decay width as function of energy is $Γ(ω)=g^{2}ω^α,$ then -- under quite general assumptions -- the QZE occurs for $α\in(0,1)$, while the IZE for $α\in(-\infty,0)\cup(1,\infty).$ This result is valid also for more realistic measurement models than the one described in this work. We then apply these considerations to the decay of the neutron, for which $α=5.$ Hence, the realization of the IZE for the neutron decay (and for the majority of weak decays) is in principle possible. Indeed, trap experiments find a lifetime that is $8.7\pm2.1$ s shorter than beam experiments, suggesting that the IZE could have taken place.

arXiv:2004.07772•Acta Physica Polonica B•Jan 1, 2020•1 citation

Reflection and transmission in a neutron-spin test of the quantum Zeno effect

Ken Machida, Hiromichi Nakazato, Saverio Pascazio +2 more

The dynamics of a quantum system undergoing frequent ``measurements,'' leading to the so-called quantum Zeno effect, is examined on the basis of a neutron-spin experiment recently proposed for its demonstration. Unlike in all previous studies, the spatial degrees of freedom of the neutron are duly taken into account. Their inclusion in the analysis is important for two reasons: first, neutron-reflection effects are shown to be very important; second, the evolution may turn out to be totally different from the ideal case. Our results can be interpreted in terms of a rigorous theorem due to Misra and Sudarshan: indeed we clarify that, in contrast with a widespread belief, a quantum Zeno effect does not halt the evolution of a quantum system; it rather modifies it, by forcing the system to remain in a certain subspace, defined by the very measurement performed.

arXiv:quant-ph/9903009•Physical Review A•Nov 1, 1999•16 citations

UNAVOIDABLE QUANTUM LOSSES IN ZENO-LIKE NEUTRON EXPERIMENTS

Helmut Rauch

Neutron phase-echo and spin rotation experiments have shown that in all cases of an interaction, parasitic beams are produced that cannot be recombined with the original beam in an ideal way. This means that a complete reconstruction of the original state would, in principle, be impossible. Thus, a kind of intrinsic irreversibility occurs, even when the original quantum state survives to a very high extent. When plane waves are used, completely reversible situations can be constructed in certain cases, but in any physical situation, wave packets have to be used which do not permit complete reversibility. Even small interaction potentials can have huge effects when they are applied periodically, and resonance effects appear. This gives various constraints for repetitive measurements and prevents a complete freezing of a quantum state in Zeno-like experiments. Additionally, a spectral change occurs, due to the dispersive action of the interaction, which has to be taken into account when many repetitive measurements are considered. A dedicated proposal for a repetitive neutron spin rotation experiment within a perfect crystal resonator will be analyzed in detail. Unavoidable losses due to quantum phenomena can be separated from losses caused by experimental imperfections.

Cybernetics & Systems•Apr 1, 2001•2 citations

Unavoidable losses in neutron quantum experiments

H. Rauch

Quantum optics experiments contribute to a deeper understanding of quantum theory. Neutron phase-echo and spin rotation experiments have shown that, in all cases of an interaction, parasitic beams are produced which cannot be recombined with the original beam in an ideal way. This means that a complete reconstruction of the original state would, in principle, be impossible. Thus a kind of intrinsic irreversibility occurs, even when the original quantum state survives to a very high extent. When plane waves are used, completely reversible situations can be constructed in certain cases, but in any physical situation, wave packets have to be used which do not permit complete reversibility. Even small interaction potentials can have huge effects when they are arranged periodically and resonance effects appear. This gives various constraints for repetitive measurements and prevents a complete freezing of a quantum state in Zeno-like experiments. Additionally, a spectral change occurs, due to the dispersive action of the interaction, which has to be taken into account when many repetitive measurements are considered. A dedicated proposal for a repetitive neutron spin rotation experiment within a perfect crystal resonator will be analyzed in detail. Unavoidable losses due to quantum phenomena can be separated from losses caused by experimental imperfections.

Journal of Physics Conference Series•Apr 1, 2006•6 citations

The neutron hidden in quantum waves

H. Rauch

The curious dual nature of the neutron (sometimes a particle, sometimes a wave) is wonderfully manifested in the various non-local interference effects observed in neutron interferometry. Here we deal with unavoidable quantum losses as they appear in neutron phase-echo and spin rotation experiments. In all cases of an interaction, parasitic beams are produced which cannot be recombined with the original beam in an ideal way. This means that a complete reconstruction of the original state would, in principle, be impossible. Thus a kind of intrinsic irreversibility occurs, even when the original quantum state survives to a very high extent. Even small interaction potentials can have huge effects when they are applied periodically and resonance effects appear. This gives various constraints for repetitive measurements and prevents a complete freezing of a quantum state in Zeno-like experiments. Additionally, a spectral change occurs, due to the dispersive action of the interaction, which has to be taken into account when many repetitive measurements are considered. A dedicated proposal for a repetitive neutron spin rotation experiment within a perfect crystal resonator will be analysed in detail. Unavoidable losses due to quantum phenomena can be separated from losses caused by experimental imperfections.

Journal of Optics B Quantum and Semiclassical Optics•Aug 1, 2002•0 citations

Measurement of the neutron lifetime and inverse quantum Zeno effect

Francesco Giacosa, Giuseppe Pagliara

Quantum mechanics predicts that the decay rate of unstable systems could be effectively modified by the process of the measurement of the survival probability. Depending on the intrinsic properties of the unstable system and the experimental setup for the observation, one could obtain the so called (direct) quantum Zeno and inverse quantum Zeno effects corresponding to a slowing down or a speeding up of the decay, respectively. We argue that the inverse quantum Zeno effect is in principle detectable at a percent level for the neutron decay in experiments with trapped ultracold neutrons. Conversely, this effect is basically undetectable in experiments in which the neutron lifetime is measured by measuring the decays of beams of neutrons. As a test of our claim, we propose a simple qualitative correlation between the number of neutrons in the trap and the neutron lifetime: the larger the number, the faster the decay. Finally we discuss also the presently available measurements of the neutron lifetime and address the issue of the possible discrepancy that has been reported among the results obtained by the different experimental techniques.

arXiv:1906.10024•Physical review. D/Physical review. D.•Mar 5, 2020•17 citations
A neutron-spin experimental test of the quantum Zeno effect (QZE) is discussed from a practical point of view, where the nonideal efficiency of the magnetic mirrors, used for filtering the spin state, is taken into account. In the idealized case, the number N of (ideal) mirrors can be indefinitely increased, yielding an increasingly better QZE. In contrast, in a practical situation with imperfect mirrors, there is an optimal number of mirrors, Nopt,{N}_{\mathrm{opt}},Nopt​, at which the QZE becomes maximum: more frequent measurements would deteriorate the performance. However, a quantitative analysis shows that a good experimental test of the QZE is still feasible. These conclusions are of general validity: in a realistic experiment, the presence of losses and imperfections leads to an optimal frequency Nopt,{N}_{\mathrm{opt}},Nopt​, which is in general finite. One should not increase N beyond Nopt.{N}_{\mathrm{opt}}.Nopt​. A convenient formula for Nopt,{N}_{\mathrm{opt}},Nopt​, valid in a broad framework, is derived as a function of the parameters characterizing the experimental setup.
We discuss a simple and analytically solvable measurement model which describes the famous Quantum Zeno Effect (QZE) and Inverse Zeno Effect (IZE), that correspond to the slow down and to the increase of the decay rate caused by measurements (or, more in general, by the interaction of an unstable state with the detector and the environment). Within this model one can understand quite general features of the QZE and IZE: by considering an unstable quantum state, such as an unstable particle, whose decay width as function of energy is Γ(ω)=g2ωα,Γ(ω)=g^{2}ω^α,Γ(ω)=g2ωα, then -- under quite general assumptions -- the QZE occurs for α∈(0,1)α\in(0,1)α∈(0,1), while the IZE for α∈(−∞,0)∪(1,∞).α\in(-\infty,0)\cup(1,\infty).α∈(−∞,0)∪(1,∞). This result is valid also for more realistic measurement models than the one described in this work. We then apply these considerations to the decay of the neutron, for which α=5.α=5.α=5. Hence, the realization of the IZE for the neutron decay (and for the majority of weak decays) is in principle possible. Indeed, trap experiments find a lifetime that is 8.7±2.18.7\pm2.18.7±2.1 s shorter than beam experiments, suggesting that the IZE could have taken place.
The dynamics of a quantum system undergoing frequent ``measurements,'' leading to the so-called quantum Zeno effect, is examined on the basis of a neutron-spin experiment recently proposed for its demonstration. Unlike in all previous studies, the spatial degrees of freedom of the neutron are duly taken into account. Their inclusion in the analysis is important for two reasons: first, neutron-reflection effects are shown to be very important; second, the evolution may turn out to be totally different from the ideal case. Our results can be interpreted in terms of a rigorous theorem due to Misra and Sudarshan: indeed we clarify that, in contrast with a widespread belief, a quantum Zeno effect does not halt the evolution of a quantum system; it rather modifies it, by forcing the system to remain in a certain subspace, defined by the very measurement performed.
Neutron phase-echo and spin rotation experiments have shown that in all cases of an interaction, parasitic beams are produced that cannot be recombined with the original beam in an ideal way. This means that a complete reconstruction of the original state would, in principle, be impossible. Thus, a kind of intrinsic irreversibility occurs, even when the original quantum state survives to a very high extent. When plane waves are used, completely reversible situations can be constructed in certain cases, but in any physical situation, wave packets have to be used which do not permit complete reversibility. Even small interaction potentials can have huge effects when they are applied periodically, and resonance effects appear. This gives various constraints for repetitive measurements and prevents a complete freezing of a quantum state in Zeno-like experiments. Additionally, a spectral change occurs, due to the dispersive action of the interaction, which has to be taken into account when many repetitive measurements are considered. A dedicated proposal for a repetitive neutron spin rotation experiment within a perfect crystal resonator will be analyzed in detail. Unavoidable losses due to quantum phenomena can be separated from losses caused by experimental imperfections.
Quantum optics experiments contribute to a deeper understanding of quantum theory. Neutron phase-echo and spin rotation experiments have shown that, in all cases of an interaction, parasitic beams are produced which cannot be recombined with the original beam in an ideal way. This means that a complete reconstruction of the original state would, in principle, be impossible. Thus a kind of intrinsic irreversibility occurs, even when the original quantum state survives to a very high extent. When plane waves are used, completely reversible situations can be constructed in certain cases, but in any physical situation, wave packets have to be used which do not permit complete reversibility. Even small interaction potentials can have huge effects when they are arranged periodically and resonance effects appear. This gives various constraints for repetitive measurements and prevents a complete freezing of a quantum state in Zeno-like experiments. Additionally, a spectral change occurs, due to the dispersive action of the interaction, which has to be taken into account when many repetitive measurements are considered. A dedicated proposal for a repetitive neutron spin rotation experiment within a perfect crystal resonator will be analyzed in detail. Unavoidable losses due to quantum phenomena can be separated from losses caused by experimental imperfections.
The curious dual nature of the neutron (sometimes a particle, sometimes a wave) is wonderfully manifested in the various non-local interference effects observed in neutron interferometry. Here we deal with unavoidable quantum losses as they appear in neutron phase-echo and spin rotation experiments. In all cases of an interaction, parasitic beams are produced which cannot be recombined with the original beam in an ideal way. This means that a complete reconstruction of the original state would, in principle, be impossible. Thus a kind of intrinsic irreversibility occurs, even when the original quantum state survives to a very high extent. Even small interaction potentials can have huge effects when they are applied periodically and resonance effects appear. This gives various constraints for repetitive measurements and prevents a complete freezing of a quantum state in Zeno-like experiments. Additionally, a spectral change occurs, due to the dispersive action of the interaction, which has to be taken into account when many repetitive measurements are considered. A dedicated proposal for a repetitive neutron spin rotation experiment within a perfect crystal resonator will be analysed in detail. Unavoidable losses due to quantum phenomena can be separated from losses caused by experimental imperfections.
Quantum mechanics predicts that the decay rate of unstable systems could be effectively modified by the process of the measurement of the survival probability. Depending on the intrinsic properties of the unstable system and the experimental setup for the observation, one could obtain the so called (direct) quantum Zeno and inverse quantum Zeno effects corresponding to a slowing down or a speeding up of the decay, respectively. We argue that the inverse quantum Zeno effect is in principle detectable at a percent level for the neutron decay in experiments with trapped ultracold neutrons. Conversely, this effect is basically undetectable in experiments in which the neutron lifetime is measured by measuring the decays of beams of neutrons. As a test of our claim, we propose a simple qualitative correlation between the number of neutrons in the trap and the neutron lifetime: the larger the number, the faster the decay. Finally we discuss also the presently available measurements of the neutron lifetime and address the issue of the possible discrepancy that has been reported among the results obtained by the different experimental techniques.