595 research outputs found
Fidelity and coherence measures from interference
By utilizing single particle interferometry, the fidelity or coherence of a pair of quantum states is identified with their capacity for interference. We consider processes acting on the internal degree of freedom (e.g., spin or polarization) of the interfering particle, preparing it in states ρA or ρB in the respective path of the interferometer. The maximal visibility depends on the choice of interferometer, as well as the locality or nonlocality of the preparations, but otherwise depends only on the states ρA and ρB and not the individual preparation processes themselves. This allows us to define interferometric measures which probe locality and correlation properties of spatially or temporally separated processes, and can be used to differentiate between processes that cannot be distinguished by direct process tomography using only the internal state of the particle
Operations and single particle interferometry
Interferometry of single particles with internal degrees of freedom is
investigated. We discuss the interference patterns obtained when an internal
state evolution device is inserted into one or both the paths of the
interferometer. The interference pattern obtained is not uniquely determined by
the completely positive maps (CPMs) that describe how the devices evolve the
internal state of a particle. By using the concept of gluing of CPMs, we
investigate the structure of all possible interference patterns obtainable for
given trace preserving internal state CPMs. We discuss what can be inferred
about the gluing, given a sufficiently rich set of interference experiments. It
is shown that the standard interferometric setup is limited in its abilities to
distinguish different gluings. A generalized interferometric setup is
introduced with the capacity to distinguish all gluings. We also connect to
another approach using the well known fact that channels can be realized using
a joint unitary evolution of the system and an ancillary system. We deduce the
set of all such unitary `representations' and relate the structure of this set
to gluings and interference phenomena.Comment: Journal reference added. Material adde
Onset of Rotational Damping in Superdeformed Nuclei
We discuss damping of the collective rotational motion in
superdeformed nuclei by means of a shell model combining the cranked Nilsson
mean-filed and the surface-delta two-body residual force. It is shown that,
because of the shell structure associated with the superdeformed mean-field,
onset energy of the rotational damping becomes MeV above yrast
line, which is much higher than in normal deformed nuclei. The mechanism of the
shell structure effect is investigated through detailed analysis of level
densities in superdeformed nuclei. It is predicted the onset of damping varies
in different supedeformed nuclei along with variation in the single-particle
structure at the Fermi surface.Comment: 24 pages, latex, 14 figures (compressed and uuencoded
Shell Model for Warm Rotating Nuclei
In order to provide a microscopic description of levels and E2 transitions in
rapidly rotating nuclei with internal excitation energy up to a few MeV, use is
made of a shell model which combines the cranked Nilsson mean-field and the
residual surface delta two-body force. The damping of collective rotational
motion is investigated in the case of a typical rare-earth nucleus, namely \Yb.
It is found that rotational damping sets in at around 0.8 MeV above the yrast
line, and the levels which form rotational band structures are thus limited. We
predict at a given rotational frequency existence of about 30 rotational bands
of various lengths, in overall agreement with the experimental findings. The
onset of the rotational damping proceeds quite gradually as a function of the
internal excitation energy. The transition region extends up to around 2 MeV
above yrast and it is characterized by the presence of scars of discrete
rotational bands which extend over few spin values and stand out among the
damped transitions, and by a two-component profile in the
correlation. The important role played by the high-multipole components of the
two-body residual interaction is emphasized.Comment: 28 pages, LaTe
Changes over time in the Chronic Liver Disease risk score predict liver-related outcomes: longitudinal analysis of the Whitehall II study
BACKGROUND AND AIMS: The Chronic Liver Disease (CLivD) risk score was recently shown to predict future advanced liver disease in the general population. We here investigated the impact of individual CLivD-score changes over time. METHODS: Participants of both phase 3 (baseline, 1991-1994) and phase 5 (follow-up, 1997-1999) examinations of the Whitehall II study were followed for liver-related outcomes (hospitalization, cancer, death) until December 2019 through linkage with electronic healthcare registers. The CLivD score, its modifiable components (alcohol use, waist-hip ratio [WHR], diabetes, and smoking), and their individual changes were studied. RESULTS: Among 6590 adults (mean age 50 years, 30% women) with a median 21-year follow-up, there were 80 liver outcomes. A rise in the CLivD score between baseline and follow-up examinations significantly increased the risk for liver-related outcomes (adjusted hazard ratio [aHR] 1.62, 95% confidence interval [CI] 1.01-2.60), more so in subjects with baseline intermediate-high CLivD scores (HR 2.4 for a CLivD-change) compared to minimal-low CLivD scores. Adverse changes over time in alcohol use and WHR, and new-onset diabetes also predicted liver outcomes. In contrast to WHR, changes in body weight (kg) showed a U-shaped association with liver outcomes. CONCLUSIONS: A change in the CLivD score over time corresponds to a true change in the risk for liver-related outcomes, suggesting the usefulness of the CLivD score for assessing response to liver-directed lifestyle interventions. Changes in WHR predicted liver outcomes better than changes in body weight or waist circumference, independent of body mass index, supporting the WHR in assessing risk for future liver disease
Operational approach to the Uhlmann holonomy
We suggest a physical interpretation of the Uhlmann amplitude of a density
operator. Given this interpretation we propose an operational approach to
obtain the Uhlmann condition for parallelity. This allows us to realize
parallel transport along a sequence of density operators by an iterative
preparation procedure. At the final step the resulting Uhlmann holonomy can be
determined via interferometric measurements.Comment: Added material, references, and journal reference
Barrier penetration and rotational damping of thermally excited superdeformed nuclei
We construct a microscopic model of thermally excited superdeformed states
that describes both the barrier penetration mechanism, leading to the decay-out
transitions to normal deformed states, and the rotational damping causing
fragmentation of rotational E2 transitions. We describe the barrier penetration
by means of a tunneling path in the two-dimensional deformation energy surface,
which is calculated with the cranked Nilsson-Strutinsky model. The individual
excited superdeformed states and associated E2 transition strengths are
calculated by the shell model diagonalization of the many-particle many-hole
excitations interacting with the delta-type residual two-body force. The effect
of the decay-out on the excited superdeformed states are discussed in detail
for Dy, Eu and Hg.Comment: 33pages, 32 figures, submitted to Nucl.Phys.
Adiabatic Approximation for weakly open systems
We generalize the adiabatic approximation to the case of open quantum
systems, in the joint limit of slow change and weak open system disturbances.
We show that the approximation is ``physically reasonable'' as under wide
conditions it leads to a completely positive evolution, if the original master
equation can be written on a time-dependent Lindblad form. We demonstrate the
approximation for a non-Abelian holonomic implementation of the Hadamard gate,
disturbed by a decoherence process. We compare the resulting approximate
evolution with numerical simulations of the exact equation.Comment: New material added, references added and updated, journal reference
adde
Holonomy for Quantum Channels
A quantum holonomy reflects the curvature of some underlying structure of
quantum mechanical systems, such as that associated with quantum states. Here,
we extend the notion of holonomy to families of quantum channels, i.e., trace
preserving completely positive maps. By the use of the Jamio{\l}kowski
isomorphism, we show that the proposed channel holonomy is related to the
Uhlmann holonomy. The general theory is illustrated for specific examples. We
put forward a physical realization of the channel holonomy in terms of
interferometry. This enables us to identify a gauge invariant physical object
that directly relates to the channel holonomy. Parallel transport condition and
concomitant gauge structure are delineated in the case of smoothly parametrized
families of channels. Finally, we point out that interferometer tests that have
been carried out in the past to confirm the rotation symmetry of the
neutron spin, can be viewed as early experimental realizations of the channel
holonomy.Comment: Minor changes, journal reference adde
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