Angel Rivas 19/04

Measures of non-Markovianity for quantum evolutions

Angel Rivas (Institut fur Theoretische Physik, Universitat Ulm, Germany)

The actual dynamics of any real open quantum system is expected to deviate to some extent from the idealized Markovian evolution. While quantum optics provides realizations that are extremely well approximated by such an evolution, soft or condensed matter systems evolve subject to conditions for which the Born-Markov framework is generally unsuitable. The exact details of what makes a given quantum evolution non-Markovian may be complicated, and in many cases an accurate microscopic model of the system-bath interaction may actually be unfeasible. It would therefore be very useful to define some simple measure that captures, in some form, the fact that the evolution departs from strict Markovianity (which is defined here as the quantum counterpart of a classical Markov process). We will deal with this problem by introducing two different measures of non-Markovianity that exploit the specifc traits of quantum correlations and are suitable for opposite experimental contexts, one requiring complete tomographic knowledge about the evolution and the other one requiring no knowledge at all.

LUGAR: Facultad de Ciencias Fisicas, UCM
DIA: 5 DE MAYO 2010 (miercoles)
HORA: 14:30
AULA: 8A (planta baja)

Marcus Muller 21/04

Digital Quantum Simulation with Rydberg Atoms
Marcus Muller (IQOQI, U. Innsbruck Austria)

We propose and analyze a scheme where laser excited Rydberg atoms in large spacing lattices provide an efficient implementation of a universal quantum simulator for spin models. This includes the simulation of Hamiltonian dynamics of spin models involving n-particle interaction terms such as in Kitaev's toric code, color code, and lattice gauge theories. In addition, it provides the ingredients for dissipative preparation of entangled states based on engineering n-particle reservoir couplings. The key building blocks of our architecture are efficient and high-fidelity n-qubit entangling Rydberg gates, which combine electromagnetically induced transparency with strong and long-range Rydberg-Rydberg interactions. Including a possible dissipative time step via optical pumping, this allows to mimic both the coherent and dissipative time  evolution of the spin system by a sequence of fast, parallel and high-fidelity n-particle gates.

LUGAR: Facultad de Ciencias Fisicas, UCM
DIA: 21 DE ABRIL 2010 (miercoles)
HORA: 14:30
AULA: 5B (planta baja)

Curso de criptografía

Sistemas cuánticos de comunicaciones para distribución de claves criptográficas
Marcos Cuty

Debido al crecimiento continuo de las redes abiertas de ordenadores, con millones de usuarios accediendo a las mismas desde terminales diferentes, la protección de la información se ha vuelto imprescindible, especialmente en las operaciones de índole comercial y financiero que realizan las empresas a través de la red. La protección de la información está fuertemente relacionada con uno de los principales servicios criptográficos: La confidencialidad. Su objetivo es garantizar la transmisión de información secreta a través de una canal de comunicaciones abierto.

En este curso se introducen diversos sistemas cuánticos de comunicaciones que permiten garantizar confidencialidad absoluta en la transmisión de información, gracias a la explotación de efectos cuánticos de la luz. Asimismo, se presenta el principal protocolo implementado en los prototipos comerciales, denominado protocolo BB84. Se analiza su seguridad, tanto en el caso de una realización fotónica ideal, como en el caso de una implementación basada en pulsos de luz coherente fuertemente  atenuados. Finalmente, se evalúan diversos prototipos comerciales desarrollados recientemente por las principales empresas de Telecomunicación.

Duración: 12/4 a 16/4 de 2010

El curso se imparte de forma redundante en dos sedes.

En la Complutense (horario de 10:30 a 12:30)
Seminario 222
Departamento de Análisis Matemático
Facultad de Matemáticas
Universidad Complutense

En la Politecnica (horario de 16:00 a 18:00)
Aula 6302
Facultad de Informatica - UPM
Campus de Montegancedo
Universidad Politecnica.

Norbert Schuch 7/4/2010

How symmetries determine the properties of quantum many-body systems
Norbert Schuch, Caltech

In this talk, I will explain how one can understand the properties of quantum many-body states based on a local description with so-called projected entangled pair states (PEPS). In particular, I will highlight the importance of symmetries in this description, by showing how local symmetries of the PEPS determine the global properties of the state. More specifically, all properties characterizing the topological order of these states -- ground state degeneracy, topological entropy, local indistinguishability, and anyonic excitations -- emerge naturally from the symmetry.

Miercoles 7 de marzo, 2010, 16:30-17:30
Sala de Seminarios del Centro de Física
c/ Serrano 121, Madrid