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Seminars 2009-2013


The Tokyo QKD Network

posted May 11, 2015, 6:22 AM by QUITEMAD   [ updated May 11, 2015, 6:22 AM ]

Invitado: : Kiyoshi Tamaki 
NTT Basic Research Laboratories,Japan.

Date:19 de diciembre, 2013 
Time:14:30 
Place:3rd floor seminar lecture room. Dpt. Física Teórica I. Facultad de Ciencias Físicas UCM.

ABSTRACT

 In!the!first!part!of!my!talk,!I!will!present!activities!of!the!project!in Tokyo!QKD!network.!In!particular,!I!introduce!a!recent!long!term field!test!of!our!QKD!system.!The!second!part!of!the!talk!will!be!devoted!to sideZchannel!issues!of!QKD.!QKD!is!said!to!be!unconditionally!secure, but!it!is!based!on!some!assumptions!on!the!users’!devices.!That!is,!the! actual devises!have!to!operate!as!the mathematical!models!that!the! security proof!requires.!Unfortunately,!there!is!a!gap!between!the!theory! and the!actual!devices,!and!I!will!introduce!some!counterZmeasures!to! close!this!gap.

Testing universality of topological defect formation: an update

posted May 11, 2015, 6:18 AM by QUITEMAD   [ updated May 11, 2015, 6:19 AM ]

Invitado: : Adolfo del Campo 
Los Alamos National Laboratory, Theoretical Division, Los Alamos, USA

Date:16 de diciembre, 2013 
Time:14:30 
Place:3rd floor seminar lecture room. Dpt. Física Teórica I. Facultad de Ciencias Físicas UCM.

ABSTRACT

In the course of a nonQequilibrium!continuous!phase!transition,!the! dynamics!ceases!to!be!adiabatic!in!the!vicinity!of!the!critical!point!as!a! result!of!the!critical!slowing!down!(the!divergence!of!the!relaxation!time!in! the!neighborhood!of!the!critical!point).!This!enforces!a!local!choice!of!the! broken!symmetry!and!can!lead!to!the!formation!of!topological!defects.! The!KibbleQZurek!mechanism!(KZM)!was!developed!to!describe!the! associated!nonequilibrium!dynamics!and!to!estimate!the!density!of! defects!as!a!function of!the!quench!rate!through!the!transition.!During! recent!years,!several!new!experiments!investigating!formation!of!defects! in!phase!transitions!induced!by!a!quench!both!in!classical!and!quantum! mechanical!systems!were!carried!out.!At!the!same!time,!some!established! results!were!called!into!question.!We!review!and!analyze!the!KibbleQZurek! mechanism!focusing!in!particular!on!this!surge!of!activity,!and!suggest! possible!directions!for!further!progress.

Quantum Field Theory in Quantum Information

posted May 11, 2015, 6:13 AM by QUITEMAD   [ updated May 11, 2015, 6:16 AM ]

Invitados: Hal Haggard, Carlo Rovelli y Jakob Yngvason


Date: 2nd , 3rd, 4th December 2013 
Time:10-13  & 15 -18:30
Place:3rd floor seminar lecture room. Dpt. Física Teórica I. Facultad de Ciencias Físicas UCM.


Quantum agents, simulation and biology

posted May 11, 2015, 6:07 AM by QUITEMAD   [ updated May 11, 2015, 6:08 AM ]

INVITADO: Hans Briegel 
University of Innsbruck, and Institute for Quantum Optics and Quantum Information (IQOQI), Innsbruck, Austria

Date:23 de octubre, 2013 
Time:14:30 
Place:3rd floor seminar lecture room. Dpt. Física Teórica I. Facultad de Ciencias Físicas UCM.

ABSTRACT 

The"ultimate"scope"and"power"of"computers"are"determined"by"the"laws" of"physics. Quantum"computers"exploit"the"rules"of"quantum"mechanics," using"quantum"coherence"and"superposition"for"new"ways"of"information" processing."The"question,"to"what"extent"quantum"effects"could"also"be" employed"in"learning"systems,"including"biological"ones,"is"exciting"but"still" open."In"this"talk,"I"will"discuss"some"of"our"recent"work"on"physical"and" biologically"inspired"models"of"(quantum)"information"processing"and" artificial"intelligence.

Exploring synthetic quantum materials with ultracold fermions in a tunable-geometry optical lattice

posted May 11, 2015, 5:59 AM by QUITEMAD   [ updated May 11, 2015, 6:03 AM ]

INVITADO: Leticia Tarruell 
ICFO1The Institute of Photonic Sciences, Barcelona (Spain)

Date:26 de septiembre, 2013 
Time:14:30 
Place:3rd floor seminar lecture room. Dpt. Física Teórica I. Facultad de Ciencias Físicas UCM.


ABSTRACT 

Ultracold"atomic"gases"in"optical"lattices"provide"the"opportunity"of" engineering"synthetic"quantum"materials"in"a"clean"and"highly"controlled" environment."On"the"one"hand,"these"systems"can"be"viewed"as" experimental"quantum"simulators"for"exploring"challenging"problems"of" condensed"matter"physics."On"the"other"hand,"they"also"allow"for"the" realization"of"completely"novel"materials"of"interesting"properties,"without" counterpart"in"solid1state"systems. In"my"talk,"I"will"present"recent"experiments"where"an"ultracold"Fermi"gas" trapped"in"an"optical"lattice"of"tunable"geometry"is"used"to"explore"both" aspects. By"loading"non1interacting"atoms"into"a"honeycomb"structure,"we"realize" artificial"graphene"and"observe"the"presence"of"two"Dirac"points"in"the" band"structure"[1]."The"flexibility"of"our"experimental"approach"allows"us" to"adjust"the"properties"of"these"Dirac"points"at"will,"moving"them"inside" the"Brillouin"zone"and"changing"the"effective"mass"of"the"associated"Dirac" fermions."Furthermore,"we"observe"how"the"two"Dirac"points"annihilate" each"other"when"coming"too"close"together,"a"situation"which"is"presently" out"of"reach"in"solid1state"samples. Preparing"instead"a"repulsively"interacting"gas"of"atoms"in"two"different" internal"states,"we"implement"the"Fermi1Hubbard"model"and"aim"at" simulating"quantum"magnetism"in"this"system."In"particular,"we"explore" experimentally"how"certain"crystal"geometries"favor"the"emergence"of" short1range"magnetic"order,"and"directly"probe"the"nearest1neighbor"spin" correlations"of"the"system"[2]."In"a"dimerized"lattice,"the"correlations" manifest"as"an"excess"number"of"singlets"as"compared"to"triplets,"whereas" in"an"anisotropic"simple"cubic"lattice"we"observe"the"appearance"of" antiferromagnetic"correlations"along"one"spatial"axis."

Physics of underdoped cuprate superconductors:Evolution of spin states from the Mott insulator

posted May 11, 2015, 5:56 AM by QUITEMAD   [ updated May 11, 2015, 5:57 AM ]

INVITADO:Sanjoy Sarker 
University of Alabama,US

Date:8 de mayo, 2013 
Time:14:30 
Place:3rd floor seminar lecture room. Dpt. Física Teórica I. Facultad de Ciencias Físicas UCM.

ABSTRACT.

 The"origin"of"the"highly"unusual"behavior"of"a cuprate"superconductor"is thought"to"be"due"to"its"proximity"to"the"Mott"insulator."Anderson argued"quite"early"that"spin"structure"of"the"doped"region"is"intimately connected"to"that"of"the"insulator."However,"attempts"to construct"a"theory"based"on"such a"connection"have"run"into"serious difficulties."I"will"discuss"some"recent"progress"made"in"this direction."Specifically,"we"have"derived"a"renormalized"Hamiltonian"from the"parent"tZJ"model,"which"is"charaterized"by"a"spin"gap. The"model"is"analyzed"by"continuing"the"known"spin"states"from"the insulator,"which"constraints"the"theory."This"leads"to"the"correct"phase diagram:"a"strange"metal,"a"pseudogap"metal"and"a"dZwave" superconductor. These"results"follow"directly" from"the"symmetry"of"the" known valenceZbond""vacuum""which"is"continued"from"half"filling."Not" much calculation"is"needed."Additionally,"the"twoZdimensional"nature"of" the metallic"state"emerges"from"the"theory.

Protected qubits and digital methods in ion traps

posted May 11, 2015, 5:49 AM by QUITEMAD   [ updated May 11, 2015, 5:54 AM ]

INVITADO: Antonio Mezzacapo
Universidad"del"País"Vasco,"Bilbao

Date:9 de abril, 2013 
Time:14:30 
Place:3rd floor seminar lecture room. Dpt. Física Teórica I. Facultad de Ciencias Físicas UCM.

ABSTRACT Decoherence"protected"qubits"are"one"of"the"major"paths"towards"the" achievement"of"scalable,"fault"tolerant,"quantum"computers."Though"their" realization"in"physical"systems"remains"an"hard"task,"trapped"ions"may" provide"a"feasible"implementation,"together"with"a"set"of"quantum"gates" acting"on"them."Recent"technology"developments"in"digital"approximation" methods"in"ion"traps"may"also"be"useful"to"demonstrate"implementations" of"correlated"bosonic[fermionic"systems,"such"as"the"Holstein"lattice" model,"and"formation"of"polarons,"encoded"in"the"motional"and"internal" degrees"of"freedom"of"the"ions." 

Projective simulation for learning agents: formalism and performances

posted May 11, 2015, 5:44 AM by QUITEMAD   [ updated May 11, 2015, 5:53 AM ]

INVITADO: Adi Makmal
Institute for Quantum Optics and Quantum Information, Innsbruck, Austria

Date:23 de enero, 2013 
Time:14:30 
Place:3rd floor seminar lecture room. Dpt. Física Teórica I. Facultad de Ciencias Físicas UCM.

ABSTRACT:

 In this Talk I will describe the model of projective simulation (PS), a novel  approach to artificial intelligence (AI) based on the stochastic processing  of episodic memory, which was first introduced in [1]. The underlying formalism will be explained, and the main features"of"the"model"will"be" highlighted."This"will"be"followed"by"presenting"the"performance"of"the" model"in"terms"of"``learning"time”"and"``efficiency”"(defined"during"the" talk),"where"a"variety"of"learning"scenarios"will"be"considered."In"addition," the"performance"of"the"PS"model"will"be"compared"with"those"of"Q\ learning"and"``learning"classier"systems”,"two"popular"representatives"of" AI"models"[2]."Finally,"some"of"our"recent"observations"will"be"discussed," together"with"a"future"outlook

Quantum organization in indistinguishable groups: a route towards nonJAbelian states of matter

posted May 5, 2015, 5:52 AM by QUITEMAD   [ updated May 11, 2015, 5:35 AM ]

INVITADO:Belén Paredes.
Universidad Autónoma de Madrid / CSIC


Date:30 de enero, 2013 
Time:14:30 
Place:3rd floor seminar lecture room. Dpt. Física Teórica I. Facultad de Ciencias Físicas UCM.


ABSTRACT

Topological  states of matter represent  an exotic organizational form of quantum matter  that contradicts the traditional paradigms of condensed matter physics. Our understanding of how topological order emerges from
the microscopic  degrees of freedom of  a  quantum manyXbody system  is far from complete. Especially intriguing is the possible formation of nonX Abelian  topological phases, whose  excitations display nonXAbelian braiding properties with potential application for quantum computing.
In  this talk  I  will propose  a  physical  mechanism for the formation of topological states: the organization of particles into identical indistinguishable groups. I will argue that such global organization can give rise to topological quasiparticles obeying nonXAbelian statistics.To illustrate the construction, I will present a physical realization of this type of order in a spin lattice model.In theground state, spins are organized in 
two  identical quantum  loop condensates. Excitations with  nonXAbelian braiding properties are created by opening loops in each of the copies.
My  proposal  might  open  a  door  for  the  understanding  of  the origin  of topological states of matter and for the experimental realization of nonX Abelian anyons in the laboratory.

Atomic Quantum Simulation of U(N) and SU(N) Non-­‐Abelian Lattice Gauge Theories

posted Oct 14, 2014, 3:12 AM by Juan Jose Garcia-Ripoll   [ updated Oct 14, 2014, 3:12 AM ]

Enrique Rico, Institute for Quantum Optics and Quantum Information (IQOQI), Innsbruck, Austria

Using ultracold alkaline-­‐earth atoms in optical lattices, we construct a quantum simulator for U(N) and SU(N) lattice gauge theories with fermionic matter based on quantum link models. These systems share qualitative features with QCD, including chiral symmetry breaking and restoration at non-­‐zero temperature or baryon density. Unlike classical simulations, a quantum simulator does not suffer from sign problems and can address the corresponding chiral dynamics in real time.

arXiv:1211.2242

Date: 20 december, 2012
Time: 14:30 h
Place: 3rd floor seminar lecture room. Dpt. Física Teórica I. Facultad de Ciencias Físicas UCM.

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