Conditional quantum dynamics with several observers

We consider several observers who monitor different parts of the environment of a single quantum system and use their data to deduce its state. We derive a set of conditional stochastic master equations that describe the evolution of the density matrices each observer ascribes to the system under the Markov approximation, and show that this problem can be reduced to the case of a single "super-observer", who has access to all the acquired data. The key problem - consistency of the sets of data acquired by different observers - is then reduced to the probability that a given combination of data sets will be ever detected by the "super-observer". The resulting conditional master equations are applied to several physical examples: homodyne detection of phonons in quantum Brownian motion, photo-detection and homodyne detection of resonance fluorescence from a two-level atom. We introduce {\it relative purity} to quantify the correlations between the information about the system gathered by different observers from their measurements of the environment. We find that observers gain the most information about the state of the system and they agree the most about it when they measure the environment observables with eigenstates most closely correlated with the optimally predictable {\it pointer basis} of the system.Comment: Updated version: new title and contents. 22 pages, 8 figure

Relativistic quantum clocks

The conflict between quantum theory and the theory of relativity is exemplified in their treatment of time. We examine the ways in which their conceptions differ, and describe a semiclassical clock model combining elements of both theories. The results obtained with this clock model in flat spacetime are reviewed, and the problem of generalizing the model to curved spacetime is discussed, before briefly describing an experimental setup which could be used to test of the model. Taking an operationalist view, where time is that which is measured by a clock, we discuss the conclusions that can be drawn from these results, and what clues they contain for a full quantum relativistic theory of time.Comment: 12 pages, 4 figures. Invited contribution for the proceedings for "Workshop on Time in Physics" Zurich 201

The LHCb upgrade I

The LHCb upgrade represents a major change of the experiment. The detectors have been almost completely renewed to allow running at an instantaneous luminosity five times larger than that of the previous running periods. Readout of all detectors into an all-software trigger is central to the new design, facilitating the reconstruction of events at the maximum LHC interaction rate, and their selection in real time. The experiment's tracking system has been completely upgraded with a new pixel vertex detector, a silicon tracker upstream of the dipole magnet and three scintillating fibre tracking stations downstream of the magnet. The whole photon detection system of the RICH detectors has been renewed and the readout electronics of the calorimeter and muon systems have been fully overhauled. The first stage of the all-software trigger is implemented on a GPU farm. The output of the trigger provides a combination of totally reconstructed physics objects, such as tracks and vertices, ready for final analysis, and of entire events which need further offline reprocessing. This scheme required a complete revision of the computing model and rewriting of the experiment's software

A similar 24-h blood pressure control is obtained by zofenopril and candesartan in primary hypertensive patients

Objective. To compare the antihypertensive effect of treatment with zofenopril vs candesartan by office and ambulatory blood pressure (BP). Design and methods. Following a 2-week wash-out from previous treatment, 236 grade I-II primary hypertensive patients were randomized double-blind to 12 weeks treatment with zofenopril 30 mg or candesartan 8 mg od. After 4 weeks, treatment was doubled in responder non-normalized (office systolic BP≥140 mmHg and office diastolic BP reduction ≥10 mmHg) or non-responder patients (office systolic BP≥140 mmHg and office diastolic BP reduction <10 mmHg). Following a further 4 weeks, non-responder non-normalized patients were withdrawn. Results. In the intention-to-treat population, office systolic BP and diastolic BP reductions after 12 weeks of treatment were similar between the two groups (zofenopril: 21±11/15±8 mmHg, n=114 vs C: 20±11/15±7 mmHg (candesartan; p=NS). Also 24-h ambulatory BPs were equally reduced by zofenopril and candesartan (7±13/ 5±8 mmHg vs 7±12/5±8 mmHg; p=NS). The trough-to-peak ratio and smoothness index were not sigficantly different between zofenopril and candesartan. Tolerability of both drugs was good. Conclusions. Monotherapy with zofenopril and candesartan similary reduced office and 24-h BPs. Since almost 90% of patiens were normalized by either zofenopril or candesartan, this result suppots the importance of considering low- or high-dose monotherapies as initial for most hypertensive patients of mild degree