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 $A\sim 150$ 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 $E_x \sim 2-3$ 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 $E_\gamma -E_\gamma$ 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 $^{152}$Dy, $^{143}$Eu and $^{192}$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 $4\pi$ rotation symmetry of the neutron spin, can be viewed as early experimental realizations of the channel holonomy.Comment: Minor changes, journal reference adde