Bachelorprojecten Theoretische Fysica 2011
Electron spin decoherence in quantum dots
begeleider: J.S. Caux
The concrete realization of quantum computers necessitates the practical implementation of qubits which can be consistently prepared in desired states, controllably coupled to each other, coherently evolved and reliably measured. One of the most promising avenues for this is to use electrons confined in quantum dots. This project will consider the spin of dot-confined electrons as a realization of a qubit, by studying the decoherence mechanisms that limit their usefulness.
External links: the Delft spin qubit project,For Link, Delft spin qubit project, click here. For Link to abstract click here
Quantitative evolutionary dynamics
begeleider: J.S. Caux
In this project, we will explore how concepts and methods of many-body physics can be applied in the context of biology, more precisely in the quantitative description of evolutionary dynamics.Holographic superconductors
begeleider: G. Compère
This project will consist in two parts. In the first part, the student will review the essential properties of superconductors such as zero-resistivity, expulsion of magnetic fields and he will review the fundamental equations of superconductors. He will be ask to present briefly some phenomena explained by the standard models of superconductivity as well as some of their limitations. In the second part, he will study holographic superconductors as a model to study high-temperature superconductors. An holographic superconductor is a superconductor that can be described using Einstein gravity. The student will describe the condensation of a field around a black hole in Einstein gravity coupled to electromagnetism as the simplest model for holographic superconductor. He will obtain the drop in the electrical resistivity in the condensate and observe the superconducting phase.
Introduction on superconductivity : Annett, Superconductivity, Superfluids and Condensates, Oxford Master Series in Condensed Matter Physics.
Introduction on holographic superconductors:
For link click here
Main results on holographic superconductors:
For link click here
For link click here
Natuurkunde van extra dimensies
begeleider: J. de Boer
Het is mogelijk dat er naast onze eigen vier dimensies nog meer dimensies bestaan die we tot nu toe niet gezien hebben. In dit projekt kijken we naar de theorie en mogelijke experimentele implicaties van de aanwezigheid van extra dimensies
De Berry fase en het Aharonov-Bohm effect in quantumfysica
begeleider: J. de Boer
De Bell ongelijkheden (is quantummechanica echt quantum)
begeleider: J. de Boer
The arrow of time: waarom tijd maar een kant opgaat.
begeleider: J. de Boer
Coherent states in scattering theory
begeleider: E. Laenen
Scattering theory is very important in quantum mechanics and in quantum field theory. Usually in and out states are defined as single particle states. In this project we will study the benefits of using so-called coherent states instead, especially for scattering in gauge theory such as quantum electrodynamics.
Quarkonia
begeleider: E. Laenen
The heavy quarks "charm" and "bottom" can form "quarkonium" bound states with their anti-particles, just as electrons and positrons can form positronium. These bound states play a crucial role in understanding many LHC processes. We will examine their production and decay, and the remarkable lessons that were learned in understanding this.
Technicolor and other strong dynamics
begeleider: E. Laenen
Although the Higgs mechanism and its accompanying boson is the most popular method of explaining mass generation for elementary particles, another approach, more similar to superconductivity, involves a putative new strong force. Various models exist, with names like technicolor and topcolor. In this project you will lean how they work, and what signals they predict at particle colliders.
Quantum lattice models with super symmetry
begeleider: B. Nienhuis
Super symmetry is a symmetry between bosons and fermions. It is suggested that the laws of nature may respect this symmetry, but this remains indeed a suggestion. Also in condensed matter models have been developed that respect this symmetry, in the form of a symmetry between fermionic states (with an odd number of fermions) and bosonic states (with an even number of fermions).In this project we will focus on some lattice models with this property. THere are a number of questions to investigate: (i) if we introduce an impurity in the system, what are the qualitative differences between impurities that do or do not respect supersymmetry. (ii) Some linear models of this type can be mapped onto models involving spins rather than itinerant fermions. How do these mappings depend on the boundary condition?
Harde magnetische dipolen
begeleider: B. Nienhuis
Er zijn tegenwoordig zeer sterke permanente magneten van diverse vormen en afmetingen te koop. Kleine magnetische balletjes blijken in allerlei verschillende configuraties mechanisch stabiel te zijn. Als je een tijdje met de kogeltjes speelt vallen er allerlei verschijnselen op. Het blijkt dat lange flexibele keten spontaan vormt als je een kogeltje uit een kluwen trekt. Die ketens kunnen gemakkelijk in diverse roosters worden gestapeld.Het is een interessante vraag wat de grondtoestand is van harde bolvormige deeltjes die buiten de harde bollen wisselwerking een pure dipool wisselwerking hebben. Normaal vormen harde bollen een fcc rooster, samen met de dipolaire krachten zijn ook andere roosters denkbaar, en door het empirisch gedrag van de magnetische kogeltjes waarschijnlijk. Harde bollen zijn het model systeem voor bolvormige colloiden in suspensie. Daar worden veel experimenten aan gedaan. Interessante theoretische bevindingen kunnen aanleiding geven om experimenten te doen met colloiden die een magnetisch dipool hebben. Andere interessante vragen betreffen de geschiktheid van het harde dipolen model voor de echte magnetische kogeltjes.Een eerste vraag is of te verwachten is dat de deeltjes ook hogere multipool momenten hebben. Een andere is in hoeverre de magnetiseerbaarheid een rol speelt bij de wisselwerkingen.
Scale invariance of random walks
begeleider: B. Nienhuis
When a particle moves randomly over a lattice, the statistical description of the paths it takes tends to a limit when one zooms out increasingly, i.e. on a sufficiently large scale the paths begin to look similar. In this large scale limit the lattice looses its significance, and the particle effectively moves in a continuum. This so called scaling limit is characterized by power law relations between different quantities. The most well known is the mean distance travelled which grows as the square root of the time (in general dimension). Another example is the perimeter enclosing all sites visited for a walk in 2 dimensions, which grows as the 2/3 power of time. The most prominent fact is that these powers are universal: they do not depend on the lattice or the precise rules of motion for the particle.Nonetheless, it is discovered recently that when a particle moves in three dimensions, but is attracted by a two-dimensional plane, this scaling behavior changes dramatically. The exponents seem to depend continuously on the attracting force. Not many properties have been investigated so far, so many questions remain. The problem can be approached numerically with great ease.
What is a magnetic monopole?
begeleider: K. Skenderis
Magnetic monopoles are fascinating objects. The existence of even a single such object would explain the quantization of electric charge. The aim of this project to explain what magnetic monopoles are and why their existence would imply quantization of electric charge.
Anti-de Sitter spacetime
begeleider: K. Skenderis
A solution of Einstein's equations that played a prominent role in many recent developments in theoretical physics is the so-called Anti-de Sitter spacetime. The aim of this project is to understand the main properties of this spacetime.
Quantization of gauge theories: A primer
begeleider: K. Skenderis
Gauge theories play a prominent role in modern theoretical physics and their path integral quantization is often part of an advanced Quantum Field Theory course. In this project we will study an analogue of the path integral quantization of gauge theories using standard integrals.
Gauge mediation of supersymmetry breaking
begeleider: M. Taylor
Supersymmetry relates particles with one spin to others that differ by a half unit of spin. Theoretically supersymmetry is appealing as it both improves the high energy behavior of the theory and can also potentially explain the scale of the Higgs mass. At the same time, supersymmetry is clearly not an exact symmetry of ourUniverse: since it has not been observed it must be broken at low energies. The goal of this project is to explore one mechanism for supersymmetry breaking, gauge mediation, and discuss how this scenario fits with current constraints from data.
Coleman-de Luccia and false vacua
begeleider: M. Taylor
A false vacuum is a metastable sector of space which is stable against small fluctuations but which can decay by quantum tunnelling to a true vacuum. Is it possible that we are living in a false vacuum? How long would it take for us to decay into the true vacuum? This project will explore false vacua following the seminal work of Coleman and de Luccia.