983 research outputs found
Dispersive regime of the Jaynes-Cummings and Rabi lattice
Photon-based strongly-correlated lattice models like the Jaynes-Cummings and
Rabi lattices differ from their more conventional relatives like the
Bose-Hubbard model by the presence of an additional tunable parameter: the
frequency detuning between the pseudo-spin degree of freedom and the harmonic
mode frequency on each site. Whenever this detuning is large compared to
relevant coupling strengths, the system is said to be in the dispersive regime.
The physics of this regime is well-understood at the level of a single
Jaynes-Cummings or Rabi site. Here, we extend the theoretical description of
the dispersive regime to lattices with many sites, for both strong and
ultra-strong coupling. We discuss the nature and spatial range of the resulting
qubit-qubit and photon-photon coupling, demonstrate the emergence of photon-
pairing and squeezing, and illustrate our results by exact diagonalization of
the Rabi dimer.Comment: 22 pages, 7 figures, 1 table, Published by NJP, Focus Issues "Focus
on Quantum Microwave Field Effects in Superconducting Circuits
Can Auditors Be Independent? - Experimental Evidence
The Sarbanes-Oxley Act of 2002 has transformed the institutional environment in the US by making the audit committee responsible for the appointment, compensation and oversight of the auditor. We examine whether this institutional change successfully resolves the alleged problem of an unconscious favoring of the management (Bazerman et al. 1997, 2002, 2006) by changing the effects of auditors’ economic incentives and psychological pressure. In our experimental design, we make use of the particular features of the German institutional setting as it enables us to manipulate the client of the auditor in a realistic and clear-cut way. 72 German auditors with at least two years of job experience participated in our experiment. Following Turner (2001), we distinguish in our analyses between belief tasks (e.g. evidence evaluation) and action tasks (e.g. audit opinion). Our findings imply that certain institutional features seem to be helpful in ensuring auditor independence. First, we find that auditors demonstrate professional scepticism in belief tasks. This seems to counteract any potentially negative effect of the acceptability heuristic in actions tasks. Second, experience helped auditors in coping with psychological pressure. Third, making the auditor accountable to a supervisory board was helpful in reducing the risk that financial considerations would impair auditor independence.
Resummation for Nonequilibrium Perturbation Theory and Application to Open Quantum Lattices
Lattice models of fermions, bosons, and spins have long served to elucidate
the essential physics of quantum phase transitions in a variety of systems.
Generalizing such models to incorporate driving and dissipation has opened new
vistas to investigate nonequilibrium phenomena and dissipative phase
transitions in interacting many-body systems. We present a framework for the
treatment of such open quantum lattices based on a resummation scheme for the
Lindblad perturbation series. Employing a convenient diagrammatic
representation, we utilize this method to obtain relevant observables for the
open Jaynes-Cummings lattice, a model of special interest for open-system
quantum simulation. We demonstrate that the resummation framework allows us to
reliably predict observables for both finite and infinite Jaynes-Cummings
lattices with different lattice geometries. The resummation of the Lindblad
perturbation series can thus serve as a valuable tool in validating open
quantum simulators, such as circuit-QED lattices, currently being investigated
experimentally.Comment: 15 pages, 9 figure
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