Measurement master equation

We derive a master equation describing the evolution of a quantum system subjected to a sequence of observations. These measurements occur randomly at a given rate and can be of a very general form. As an example, we analyse the effects of these measurements on the evolution of a two-level atom driven by an electromagnetic field. For the associated quantum trajectories we find Rabi oscillations, Zeno-effect type behaviour and random telegraph evolution spawned by mini quantum jumps as we change the rates and strengths of measurement.Comment: 14 pages and 8 figures, Optics Communications in pres

The Evolving Status of Fellowships and Mini-Fellowships in Diagnostic Radiology: A Survey of Program Directors and Chief Residents

RATIONALE AND OBJECTIVES: Recent changes in radiology fellowships include musculoskeletal radiology adopting a match system, interventional radiology transitioning away from diagnostic radiology to offer direct-entry programs, and a common fellowship application timeline created by the Society for Chairs of Academic Radiology Departments (SCARD). The concept of mini-fellowships has also emerged with the elimination of the oral American Board of Radiology examinations that had been administered in the final year of residency training prior to 2014. This paper seeks to assess the opinions of fellowship program directors, residency program directors, and chief residents regarding these recent changes. MATERIALS AND METHODS: This is a cross-sectional study using a web-based survey posed to fellowship program directors, residency program directors, and chief residents in 2020. Questions sought to explore current attitudes toward the following topics: (1) a common fellowship application timeline; (2) a common fellowship match; and (3) the status of mini-fellowships in diagnostic radiology. In addition, the number of fellowship positions for each subspecialty was estimated using subspecialty society directories, Accreditation Council for Graduate Medical Education (ACGME) data, and individual program websites. RESULTS: Deidentified responses were collected electronically and aggregated. The three respondent groups preferred a common fellowship application timeline at rates of 67% among fellowship program directors, 80% residency program directors, and 74% residents. A common match system across all subspecialties was preferred at rates of 50% fellowship program directors, 74% residency program directors, and 26% chief residents. There was widespread reported compliance with the SCARD fellowship timeline policy. Subspecialty programs using the match system reported interviewing greater numbers of applicants per position. Fellowship directors and chief residents reported that the most common duration of mini-fellowship experiences was 2 to 3 months. CONCLUSION: There is a division between chief residents and program directors regarding the preference for a common radiology match. Adopting a radiology-wide fellowship match would increase the number of interviews required. The SCARD fellowship timeline policy has been successful, and there is support across stakeholders regarding the common timeline. Mini-fellowships are highly variable in length and structure

Bitwise Bell inequality violations for an entangled state involving 2N ions

Following on from previous work [J. A. Larsson, Phys. Rev. A 67, 022108 (2003)], Bell inequalities based on correlations between binary digits are considered for a particular entangled state involving 2N trapped ions. These inequalities involve applying displacement operations to half of the ions and then measuring correlations between pairs of corresponding bits in the binary representations of the number of centre-of-mass phonons of N particular ions. It is shown that the state violates the inequalities and thus displays nonclassical correlations. It is also demonstrated that it violates a Bell inequality when the displacements are replaced by squeezing operations.Comment: 12 pages, 5 figures, accepted for publication in Phys. Rev.

Structural basis of meiotic telomere attachment to the nuclear envelope by MAJIN-TERB2-TERB1.

Meiotic chromosomes undergo rapid prophase movements, which are thought to facilitate the formation of inter-homologue recombination intermediates that underlie synapsis, crossing over and segregation. The meiotic telomere complex (MAJIN, TERB1, TERB2) tethers telomere ends to the nuclear envelope and transmits cytoskeletal forces via the LINC complex to drive these rapid movements. Here, we report the molecular architecture of the meiotic telomere complex through the crystal structure of MAJIN-TERB2, together with light and X-ray scattering studies of wider complexes. The MAJIN-TERB2 2:2 hetero-tetramer binds strongly to DNA and is tethered through long flexible linkers to the inner nuclear membrane and two TRF1-binding 1:1 TERB2-TERB1 complexes. Our complementary structured illumination microscopy studies and biochemical findings reveal a telomere attachment mechanism in which MAJIN-TERB2-TERB1 recruits telomere-bound TRF1, which is then displaced during pachytene, allowing MAJIN-TERB2-TERB1 to bind telomeric DNA and form a mature attachment plate

Wave function recombination instability in cold atom interferometers

Cold atom interferometers use guiding potentials that split the wave function of the Bose-Einstein condensate and then recombine it. We present theoretical analysis of the wave function recombination instability that is due to the weak nonlinearity of the condensate. It is most pronounced when the accumulated phase difference between the arms of the interferometer is close to an odd multiple of PI and consists in exponential amplification of the weak ground state mode by the strong first excited mode. The instability exists for both trapped-atom and beam interferometers.Comment: 4 pages, 5 figure

A Quantum Langevin Formulation of Risk-Sensitive Optimal Control

In this paper we formulate a risk-sensitive optimal control problem for continuously monitored open quantum systems modelled by quantum Langevin equations. The optimal controller is expressed in terms of a modified conditional state, which we call a risk-sensitive state, that represents measurement knowledge tempered by the control purpose. One of the two components of the optimal controller is dynamic, a filter that computes the risk-sensitive state. The second component is an optimal control feedback function that is found by solving the dynamic programming equation. The optimal controller can be implemented using classical electronics. The ideas are illustrated using an example of feedback control of a two-level atom

Teleportation-based number state manipulation with number sum measurement

We examine various manipulations of photon number states which can be implemented by teleportation technique with number sum measurement. The preparations of the Einstein-Podolsky-Rosen resources as well as the number sum measurement resulting in projection to certain Bell state may be done conditionally with linear optical elements, i.e., beam splitters, phase shifters and zero-one-photon detectors. Squeezed vacuum states are used as primary entanglement resource, while single-photon sources are not required.Comment: 9 pages, 4 figures, Misprints are corrected. 3 figures for number sum measurement are added. Discussion on manipulations are expanded. Calculations for success probabilities are added. Fig.4 is adde

Fermilab E791

Fermilab E791, a very high statistics charm particle experiment, recently completed its data taking at Fermilab's Tagged Photon Laboratory. Over 20 billion events were recorded through a loose transverse energy trigger and written to 8mm tape in the the 1991-92 fixed target run at Fermilab. This unprecedented data sample containing charm is being analysed on many-thousand MIP RISC computing farms set up at sites in the collaboration. A glimpse of the data taking and analysis effort is presented. We also show some preliminary results for common charm decay modes. Our present analysis indicates a very rich yield of over 200K reconstructed charm decays.Comment: 4 pages, 1 figure, LaTe