Energy Fluctuations in One Dimensional Classical Magnets

The time- and frequency dependent energy fluctuations in the Heisenberg chain are studied by means of a continued fraction representation. In a broad wave vector and temperature range, the energy fluctuations are found to display dominant oscillatory behavior.

Quantum Computer Emulator

We describe a quantum computer emulator for a generic, general purpose quantum computer. This emulator consists of a simulator of the physical realization of the quantum computer and a graphical user interface to program and control the simulator. We illustrate the use of the quantum computer emulator through various implementations of the Deutsch-Jozsa and Grover's database search algorithm.Comment: 28 pages, 4, figures, see also http://rugth30.phys.rug.nl/compphys/qce.htm ; figures updated, instructions change

Event-based simulation of quantum physics experiments

We review an event-based simulation approach which reproduces the statistical distributions of wave theory not by requiring the knowledge of the solution of the wave equation of the whole system but by generating detection events one-by-one according to an unknown distribution. We illustrate its applicability to various single photon and single neutron interferometry experiments and to two Bell test experiments, a single-photon Einstein-Podolsky-Rosen experiment employing post-selection for photon pair identification and a single-neutron Bell test interferometry experiment with nearly $100\%$ detection efficiency.Comment: Lectures notes of the Advanced School on Quantum Foundations and Open Quantum Systems, Jo\~ao Pessoa, Brazil, July 2012, edited by T. M. Nieuwenhuizen et al, World Scientific, to appea

Discrete-event simulation of uncertainty in single-neutron experiments

A discrete-event simulation approach which provides a cause-and-effect description of many experiments with photons and neutrons exhibiting interference and entanglement is applied to a recent single-neutron experiment that tests (generalizations of) Heisenberg's uncertainty relation. The event-based simulation algorithm reproduces the results of the quantum theoretical description of the experiment but does not require the knowledge of the solution of a wave equation nor does it rely on concepts of quantum theory. In particular, the data satisfies uncertainty relations derived in the context of quantum theory

Event-based simulation of neutron experiments: interference, entanglement and uncertainty relations

We discuss a discrete-event simulation approach, which has been shown to give a unified cause-and-effect description of many quantum optics and single-neutron interferometry experiments. The event-based simulation algorithm does not require the knowledge of the solution of a wave equation of the whole system, yet reproduces the corresponding statistical distributions by generating detection events one-by-one. It is showm that single-particle interference and entanglement, two important quantum phenomena, emerge via information exchange between individual particles and devices such as beam splitters, polarizers and detectors. We demonstrate this by reproducing the results of several single-neutron interferometry experiments, including one that demonstrates interference and one that demonstrates the violation of a Bell-type inequality. We also present event-based simulation results of a single neutron experiment designed to test the validity of Ozawa's universally valid error-disturbance relation, an uncertainty relation derived using the theory of general quantum measurements.Comment: Invited paper presented at the EmQM13 Workshop on Emergent Quantum Mechanics, Austrian Academy of Sciences (October 3-6, 2013, Vienna

Thermodynamics of a two-level system coupled to bosons

We study the thermodynamic properties of a system described by two discrete energy levels, coupled to a bath of phonons. We derive a discrete path-integral representation for the partition function that is convenient for numerical evaluation and allows us to calculate in a unified manner the model properties in the whole coupling range. As a function of the coupling strength the system exhibits a transition from the weak-coupling regime to the self-trapped state. In the weak-coupling regime there is a periodic motion, similar to the tunneling of a particle in a double-well potential. In the strong-coupling regime, the periodicity is lost and the motion turns into a stochastic process.

Event-based computer simulation model of Aspect-type experiments strictly satisfying Einstein's locality conditions

Inspired by Einstein-Podolsky-Rosen-Bohm experiments with photons, we construct an event-based simulation model in which every essential element in the ideal experiment has a counterpart. The model satisfies Einstein's criteria of local causality and does not rely on concepts of quantum and probability theory. We consider experiments in which the averages correspond to those of a singlet and product state of a system of two $S=1/2$ particles. The data is analyzed according to the experimental procedure, employing a time window to identify pairs. We study how the time window and the passage time of the photons, which depends on the relative angle between their polarization and the polarizer's direction, influences the correlations, demonstrating that the properties of the optical elements in the observation stations affect the correlations although the stations are separated spatially and temporarily. We show that the model can reproduce results which are considered to be intrinsically quantum mechanical

Irrelevance of Bell's Theorem for experiments involving correlations in space and time: a specific loophole-free computer-example

John Bell is generally credited to have accomplished the remarkable "proof" that any theory of physics, which is both Einstein-local and "realistic" (counterfactually definite), results in a strong upper bound to the correlations that are measured in space and time. He thus predicts that Einstein-Podolsky-Rosen experiments cannot violate Bell- type inequalities. We present a counterexample to this claim, based on discrete-event computer simulations. Our model-results fully agree with the predictions of quantum theory for Einstein-Podolsky-Rosen-Bohm experiments and are free of the detection- or a coincidence-loophole