Some results concerning the extended CMV matrix

Speaker: 

Darren Ong

Institution: 

Rice

Time: 

Thursday, January 17, 2013 - 2:00pm to 3:00pm

Host: 

Location: 

RH 306

The CMV matrix is a unitary operator on $\ell^2(\mathbb N)$ that is a central tool in the study of orthogonal polynomials on the unit circle. One may view it as a unitary analogue of the Jacobi matrix. We may extend the CMV matrix to be a unitary operator on $\ell^2(\mathbb Z)$. It is more natural to consider the extended CMV matrix in certain contexts: for example, if we wish to generate CMV matrices dynamically. The extended CMV matrix also plays an important role in the study of quantum random walks.

In this talk, we will discuss a Gordon lemma for the CMV matrix (The Gordon lemma is an important tool in the study of Jacobi matrices, used to rule out the possibility pure point spectrum). We will also discuss some results pertaining to the H\"older-continuity of the spectrum of the extended CMV matrix.

Dissipative Properties of Systems Composed of High-Loss and Lossless Components

Speaker: 

Aaron Welters

Institution: 

MIT

Time: 

Thursday, August 30, 2012 - 2:00pm to 3:00pm

Host: 

Location: 

RH 306

We study dissipative properties of systems composed of two components one of which is highly lossy and the other is lossless. One of the principal result is that the dissipation causes modal dichotomy, i.e., splitting of the eigenmodes into two distinct classes according to their dissipative properties: high-loss and low-loss modes. Interestingly, larger losses in the lossy component make the entire composite less lossy, the dichotomy more pronounced, low-loss modes less lossy, and high-loss modes less accessible to external excitations. We also have carried out an exhaustive analytical study of the system quality factor. This is joint work with Alexander Figotin.

Symmetry breaking in quasi-1D Coulomb systems

Speaker: 

Paul Jung

Institution: 

UAB

Time: 

Thursday, September 27, 2012 - 2:00pm to 3:00pm

Host: 

Location: 

RH 306

Quasi one-dimensional particle systems have domains which are infinite
in one direction and bounded in all other directions, e.g. an infinite
cylinder. We will show that for such particle systems with Coulomb
interactions and a neutralizing background, the so-called jellium,
there is translation symmetry breaking in the Gibbs measures at any
temperature. This extends a previous result on Laughlin states in
thin, two-dimensional strips by Jansen, Lieb and Seiler (2009). The
structural argument is akin to that employed by Aizenman and Martin
(1980) for a similar statement concerning symmetry breaking at all
temperatures in strictly one-dimensional Coulomb systems. The
extension is enabled through bounds which establish tightness of
finite-volume charge fluctuations. We will also discuss an
application to quantum one-dimensional jellium which extends an old
result of Brascamp and Lieb (1975).

Local estimates of exponential polynomials

Speaker: 

Christoph Marx

Institution: 

Caltech

Time: 

Thursday, August 23, 2012 - 2:00pm to 3:30pm

Host: 

Location: 

RH 306

A classical result by Pál Turán, estimates the global behavior
of an exponential polynomial on an interval by its supremum on any
arbitrary subinterval. In this talk we discuss Nazarov's extension of this
``global to local reduction'' to arbitrary Borel sets of positive Lebesgue
measure.

Local estimates of exponential polynomials

Speaker: 

Christoph Marx

Institution: 

UCI

Time: 

Thursday, June 21, 2012 - 2:00pm to 3:00pm

Location: 

RH 306

A classical result by Pál Turán, estimates the global behavior
of an exponential polynomial on an interval by its supremum on any
arbitrary subinterval. In this talk we discuss Nazarov's extension of this
``global to local reduction'' to arbitrary Borel sets of positive Lebesgue
measure.

Measure of the spectrum of the almost Mathieu operator

Speaker: 

Rajinder Mavi

Institution: 

UCI

Time: 

Thursday, May 3, 2012 - 2:00pm to 3:00pm

Location: 

RH 306

We calculate the measure if the phase-intersected spectrum of the almost
Mathieu operator for rational frequencies. We follow the proof of Avron,
Mouche and Simon using Chambers formula and truncated Hamiltonians.

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