34810669
Quantum approach to a derivation of the second law of thermodynamics.
We reinterpret the microcanonical conditions in the quantum domain as constraints for the interaction of the "gas subsystem" under consideration and its environment ("container"). The time average of a purity measure is found to equal the average over the respective path in Hilbert space. We then show that for typical (degenerate or nondegenerate) thermodynamical systems almost all states within the allowed region of Hilbert space have a local von Neumann entropy S close to the maximum and a purity P close to its minimum, respectively. Typically, thermodynamical systems should obey the second law.
17564383
Measurement models for time-resolved spectroscopy: a comment
We present an exactly solvable model for photon emission, which allows us to examine the evolution of the photon wavefunction in space and time. We apply this model to coherent phenomena in three-level systems with a special emphasis on the effects of the photon detection process.
16125330
Pattern formation in quantum Turing machines
We investigate the iteration of a sequence of local and pair unitary transformations, which can be interpreted to result from a Turing-head $(\mathrm{pseudospin}S)$ rotating along a closed Turing tape $(M$ additional pseudospins). The dynamical evolution of the Bloch vector of S, which can be decomposed into ${2}^{M}$ primitive pure state Turing-head trajectories, gives rise to fascinating geometrical patterns reflecting the entanglement between head and tape. These machines thus provide intuitive examples for quantum parallelism and, at the same time, means for local testing of quantum network dynamics.
18424039
Quantum control of atomic systems by time resolved homodyne detection
We describe the light-matter interaction of a single two level atom with the electromagnetic vacuum in terms of field and dipole variables by considering homodyne detection of the emitted fields. Spontaneous emission is then observed as a continuous fluctuating force acting on the atomic dipole. The effect of this force may be compensated and even reversed by feedback.
37474263
Quantum control by compensation of quantum fluctuations.
We show that the influence of quantum fluctuations in the electromagnetic field vacuum on a two level atom can be measured and consequently compensated by balanced homodyne detection and a coherent feedback field. This compensation suppresses the decoherence associated with spontaneous emissions for a specific state of the atomic system allowing complete control of the coherent state of the system.
15461480
Moving Quantum Agents in a Finite Environment
We investigate an all-quantum-mechanical spin network, in which a subset of spins, the K “moving agents”, are subject to local and pair unitary transformations controlled by their position with respect to a fixed ring of M “environmental”-spins. We demonstrate that a “flow of coherence” results between the various subsystems. Despite entanglement between the agents and between agent and environment, local (non-linear) invariants may persist, which then show up as fascinating patterns in each agent’s Bloch-sphere. Such patterns disappear, though, if the agents are controlled by different rules. Geometric aspects thus help to understand the interplay between entanglement and decoherence.
118056950
The RHIC p‐Carbon CNI Polarimeter Upgrade For The Beam Polarization And Intensity Measurements
Proton polarization measurements in the AGS and RHIC (Relativistic Heavy Ion Collider at the beam energies 24–250 GeV) are based on proton‐carbon and proton‐proton elastic scattering in the Coulomb Nuclear Interference (CNI) region. Polarimeter operation in the scanning mode also gives polarization profile and beam intensity profile (beam emittance) measurements. Bunch by bunch emittance measurement is a very powerful tool for machine setup. Presently, the polarization and beam intensity profile measurements (in both vertical and horizontal planes) are restricted by the long target switching time and possible target destruction during this complicated motion. The RHIC polarimeters were operated near the limit of the counting rate for present silicon strip detectors. The ongoing polarimeter upgrade for the 2009 run will address all these problems. The upgrade should allow significant reduction of the polarization measurement errors by making feasible the complete polarization measurements, which includes p...
121340242
Stripped electron collection at the Spallation Neutron Source
One of the main sources of electrons in the Spallation Neutron Source's Accumulator Ring is the stripped electrons in the injection region. A magnetic field guides the stripped electrons to the bottom of the beam pipe, where an electron catcher with overhanging surface traps them. This paper describes the stripped electrons' motion, the optimization of the catcher, and the build up of an electron cloud in this region.
26164616
A new relative proton polarimeter for RHIC
An innovative polarimeter based on proton carbon elastic scattering in the Coulomb nuclear interference (CNI) region has been installed and commissioned in the Blue ring of RHIC during the first RHIC polarized proton commissioning in September, 2000. The polarimeter consists of ultra-thin C targets and four Si detectors. All elements are in a 1.6 meter vacuum chamber. This paper summarizes the polarimeter design issues and recent commissioning results.