An asymptotical von-Neumann measurement strategy for solid-state qubits

A measurement on a macroscopic quantum system does in general not lead to a projection of the wavefunction in the basis of the detector as predicted by von-Neumann's postulate. Hence, it is a question of fundametal interest, how the preferred basis onto which the state is projected is selected out of the macroscopic Hilbert space of the system. Detector-dominated von-Neumann measurements are also desirable for both quantum computation and verification of quantum mechanics on a macroscopic scale. The connection of these questions to the predictions of the spin-boson modelis outlined. I propose a measurement strategy, which uses the entanglement of the qubit with a weakly damped harmonic oscillator. It is shown, that the degree of entanglement controls the degree of renormalization of the qubit and identify, that this is equivalent to the degree to which the measurement is detector-dominated. This measurement very rapidly decoheres the initial state, but the thermalization is slow. The implementation in Josephson quantum bits is described and it is shown that this strategy also has practical advantages for the experimental implementation.Comment: 4 pages, 3 figures, accepted for publication as a rapid communication in Phys. Rev.

Phase locking in quantum and classical oscillators: polariton condensates, lasers, and arrays of Josephson junctions

We connect three phenomena in which a coherent electromagnetic field could be generated: polariton condensation, phase-locking in arrays of underdamped Josephson junctions, and lasing. All these phenomena have been described using Dicke-type models of spins coupled to a single photon mode. These descriptions may be distinguished by whether the spins are quantum or classical, and whether they are strongly or weakly damped.Comment: 6 pages, RevTex. To appear in a special edition of Solid State Communications on "Quantum Phases at the Nanoscale

Waarde van lichte en intensieve begeleiding van patienten met hartfalen; resultaten van het COACH-onderzoek.

OBJECTIVE: To determine the efficacy of 2 nurse-directed programmes of different intensity for the counselling and follow-up of patients hospitalised for heart failure, compared with standard care by a cardiologist. DESIGN: Multicentre randomised clinical trial (www.trialregister.nl: NCT 98675639). METHOD: A total of 1023 patients were randomized after hospitalisation for heart failure to 1 of 3 treatment strategies: standard care provided by a cardiologist, follow-up care from a cardiologist with basic counselling and support by a nurse specialising in heart failure, or follow-up care from a cardiologist with intensive counselling and support by a nurse specialising in heart failure. Primary end points were the time to rehospitalisation due to heart failure or death and the number of days lost to rehospitalisation or death during the 18-month study period. Data were analysed on an intent-to-treat basis. RESULTS: Mean patient age was 71 years, 38% were women, 50% had mild heart failure and 50% had severe heart failure. During the study, 411 patients (40%) were rehospitalised due to heart failure or died from any cause: 42% in the control group, and 41% and 38% in the basic and intensive support groups, respectively (differences not significant). The time to rehospitalisation or death was similar in the 3 groups: hazard ratios for the basic and intensive support groups versus the control group were 0.96 (95% CI: 0.76-1.21; p = 0.73) and 0.93 (95% CI: 0.73-1.17; p = 0.53), respectively. The number of days lost to rehospitalisation or death was 39,960 in the control group; this number was 15% less in the intervention groups, but the difference was not significant. However, there was a trend toward lower mortality in the intervention groups. In all 3 groups, more visits occurred than planned, which may have had a considerable effect on care, notably in the control group. CONCLUSION: The results of this study indicated that the provision of additional counselling and support by a nurse specialising in heart failure as an adjuvant to intensive follow-up care provided by a cardiologist does not always lead to a reduction in rehospitalisation frequenc

Quantum bits with Josephson junctions

Already in the first edition of this book (Barone and Paterno, "Fundamentals and Physics and Applications of the Josephson Effect", Wiley 1982), a great number of interesting and important applications for Josephson junctions were discussed. In the decades that have passed since then, several new applications have emerged. This chapter treats one such new class of applications: quantum optics and quantum information processing (QIP) based on superconducting circuits with Josephson junctions. In this chapter, we aim to explain the basics of superconducting quantum circuits with Josephson junctions and demonstrate how these systems open up new prospects, both for QIP and for the study of quantum optics and atomic physics.Comment: 30 pages, 10 figures. Book chapter for a new edition of Barone and Paterno's "Fundamentals and Physics and Applications of the Josephson Effect". Final versio