Decoherence versus entropy in neutron interferometry

Abstract

We analyze the coherence properties of polarized neutrons, after they have interacted with a magnetic field or a phase shifter undergoing different kinds of statistical fluctuations. We endeavor to probe the degree of disorder of the distribution of the phase shifts by means of the loss of quantum-mechanical coherence of the neutron. We find that the notion of entropy of the shifts and that of decoherence of the neutron do not necessarily agree. In some cases the neutron wave function is more coherent, even though it has interacted with a more disordered medium

Decoherence, fluctuations and Wigner function in neutron optics

“…All our results corroborate the ideas expressed elsewhere [4] and make it apparent that the concept of loss of quantum mechanical coherence deserves clarification and additional investigation. It would also be interesting to discuss analogies and differences with conceptual experiments in which decoherence is complemented by Welcher-Weg information [24].…”

“…Essentially, this Wigner function represents the whole ensemble of neutrons in an experimental run. For the double Gaussian state (58), It is therefore possible to define an alternative decoherence parameter [4], that takes into account the coherence properties of the neutron ensemble…”

Interference of Mesoscopic Particles: Quantum–Classical Transition

“…(32) is understood in the r.m.s. sense and H exch = −ξ(t)x, like in (2), we have H exch dt = √ Λt △p d = △p tot d ≤ where △p tot (T ) is the total recoil due to a momentum random walk [9]. In such a case the first inequality in (32) is nothing but Heisenberg's inequality and this clarifies the rationale behind it.…”

Thermal decoherence in mesoscopic interference

“…By (11) and (4), the average over the direction of the emitted photon yields ð d n 4 I Àn! 0 =c ðxÞ ¼ I slit ðxÞ…”

“…The evolution of the spontaneous emission process is readily computed in the Weisskopf-Wigner approximation [10] and yields [11] …”