7,639 research outputs found

### On the Curvature of Monotone Metrics and a Conjecture Concerning the Kubo-Mori Metric

It is the aim of this article to determine curvature quantities of an
arbitrary Riemannian monotone metric on the space of positive matrices resp.
nonsingular density matrices. Special interest is focused on the scalar
curvature due to its expected quantum statistical meaning. The scalar curvature
is explained in more detail for three examples, the Bures metric, the largest
monotone metric and the Kubo-Mori metric. In particular, we show an important
conjecture of Petz concerning the Kubo-Mori metric up to a formal proof of the
concavity of a certain function on R_+^3. This concavity seems to be
numerically evident. The conjecture of Petz asserts that the scalar curvature
of the Kubo-Mori metric increases if one goes to more mixed states.Comment: 20 pages, 4 figure

### Connections and Metrics Respecting Standard Purification

Standard purification interlaces Hermitian and Riemannian metrics on the
space of density operators with metrics and connections on the purifying
Hilbert-Schmidt space. We discuss connections and metrics which are well
adopted to purification, and present a selected set of relations between them.
A connection, as well as a metric on state space, can be obtained from a metric
on the purification space. We include a condition, with which this
correspondence becomes one-to-one. Our methods are borrowed from elementary
*-representation and fibre space theory. We lift, as an example, solutions of a
von Neumann equation, write down holonomy invariants for cyclic ones, and ``add
noise'' to a curve of pure states.Comment: Latex, 27 page

### The Scalar Curvature of the Bures Metric on the Space of Density Matrices

The Riemannian Bures metric on the space of (normalized) complex positive
matrices is used for parameter estimation of mixed quantum states based on
repeated measurements just as the Fisher information in classical statistics.
It appears also in the concept of purifications of mixed states in quantum
physics. Here we determine its scalar curvature and Ricci tensor and prove a
lower bound for the curvature on the submanifold of trace one matrices. This
bound is achieved for the maximally mixed state, a further hint for the quantum
statistical meaning of the scalar curvature.Comment: Latex, 9 page

### Geodesic distances on density matrices

We find an upper bound for geodesic distances associated to monotone
Riemannian metrics on positive definite matrices and density matrices.Comment: 10 page

### On the Apparent Orbital Inclination Change of the Extrasolar Transiting Planet TrES-2b

On June 15, 2009 UT the transit of TrES-2b was detected using the University
of Arizona's 1.55 meter Kuiper Telescope with 2.0-2.5 millimag RMS accuracy in
the I-band. We find a central transit time of $T_c = 2454997.76286 \pm0.00035$
HJD, an orbital period of $P = 2.4706127 \pm 0.0000009$ days, and an
inclination angle of $i = 83^{\circ}.92 \pm 0.05$, which is consistent with our
re-fit of the original I-band light curve of O'Donovan et al. (2006) where we
find $i = 83^{\circ}.84 \pm0.05$. We calculate an insignificant inclination
change of $\Delta i = -0^{\circ}.08 \pm 0.07$ over the last 3 years, and as
such, our observations rule out, at the $\sim 11 \sigma$ level, the apparent
change of orbital inclination to $i_{predicted} = 83^{\circ}.35 \pm0.1$ as
predicted by Mislis and Schmitt (2009) and Mislis et al. (2010) for our epoch.
Moreover, our analysis of a recently published Kepler Space Telescope light
curve (Gilliland et al. 2010) for TrES-2b finds an inclination of $i =
83^{\circ}.91 \pm0.03$ for a similar epoch. These Kepler results definitively
rule out change in $i$ as a function of time. Indeed, we detect no significant
changes in any of the orbital parameters of TrES-2b.Comment: 19 pages, 1 table, 7 figures. Re-submitted to ApJ, January 14, 201

### Multi-field modelling and simulation of large deformation ductile fracture

In the present contribution we focus on a phase-ïŹeld approach to ductile fracture applied to large deformation contact problems. Phase-ïŹeld approaches to fracture allow for an eïŹcient numerical investigation of complex three-dimensional fracture problems, as they arise in contact and impact situations. To account for large deformations the underlying formulation is based on a multiplicative decomposition of the deformation gradient into an elastic and plastic part. Moreover, we make use of a fourth-order crack regularization combined with gradient plasticity. Eventually, a demonstrative example shows the capability of the proposed framework

- âŠ