An effective force induced by spatially depending decoherence is predicted. The phenomenon is illustrated by a simple model of a 1/2-spin particle subjected to distributed unselective measurement of noncommuting spin components.
The effects of fluctuating boundaries on a superposition state of a quantum particle in a box is studied. We consider a model in one space dimension in which the initial state is a coherent superposition of two energy eigenstates. The locations of the walls of the box are assumed to undergo small fluctuation with a Gaussian probability distribution. The spatial probability density of the particle contains an interference term, which is found to decay in time due to the boundary fluctuations. At late times, this term vanishes and the quantum coherence is lost. The system is now described by a density matrix rather than a pure quantum state.This model gives a simple illustration of how environment-induced decoherence can take place in quantum systems. It can also serve as an analog model for the effects of spacetime geometry fluctuations on quantum systems.
Measurement-induced decoherence and its consequent effect on the time evolution of the measured system is investigated via the Wigner representation W. Using a discrete-state computer model put forward by Wallace [D. Wallace, Phys. Rev. A 63, 022109 (2001)], we simulate a free particle moving in a periodic space, which is subjected to repeated projection-valued measurements of position. The measurements are made at rapid intervals, such as to induce a Zeno effect in the motion of the particle. We construct a discrete form of the Wigner distribution, which is used to represent the system ensemble at various times during its evolution. In addition, we calculate the entropy of the system ensemble and compare its time development with the Wigner distribution of the system state. We conclude that, in accordance with the findings of other similar investigations, the attenuation of negative W is a measure of the increasing decoherence in the system density operator, and is characteristic of the transition from the quantum to the classical descriptions of the system.
Recent ab initio lattice studies have found that the interactions between alpha particles (^{4}He nuclei) are sensitive to seemingly minor details of the nucleon-nucleon force, such as interaction locality. In order to uncover the essential physics of this puzzling phenomenon without unnecessary complications, we study a simple model involving two-component fermions in one spatial dimension. We probe the interaction between two bound dimers for several different particle-particle interactions and measure an effective potential between the dimers using external point potentials which act as numerical tweezers. We find that the strength and range of the local part of the particle-particle interactions play a dominant role in shaping the interactions between the dimers and can even determine the overall sign of the effective potential.