# Abstracts

##### Ruben Jaarsma - Hunting New Physics at the LHC High-Precision Frontier

The Standard Model of particle physics is, so far, in excellent agreement with experimental tests. There have been some hints of physics beyond the Standard Model, such as the intriguing signal of a possible new particle with a mass of 750 GeV at the Large Hadron Collider (LHC), but they are not yet conclusive. Decays of B-mesons, bound states of a b-quark and a light antiquark, offer a rich field of high-precision Standard Model tests. Specifically, these decays are useful in studying CP violation, the asymmetry between processes related through parity and the interchange of particles and their antiparticles. The decay of a neutral B-meson to two charged kaons allows for the determination of a CP-violating phase. Moreover, it is governed by quantum fluctuations, where new physics may appear through new virtual particles, allowing for interesting Standard Model tests. In this project a roadmap for the optimal determination of the CP-violating phase from this decay will be given. The theoretical precision is limited by the influence of strong interactions. Theoretical considerations and experimental data will be used to constrain the uncertainties from these effects to achieve the highest possible precision. In this way full advantage can be taken of the future experimental precision that can be reached at the planned upgrade of the LHC.

##### Laura van Huizen- Assessment of breast tumor tissue using THG microscopy

Breast cancer is the most commonly diagnosed cancer among women. One of the treatment possibilities is a surgery. After the operation a pathologist assesses the excised tissue, and determines whether a second surgery is needed. This process takes a long time, at least 24 hours, and uses dyes to stain, which can damage tissue. A faster, non-labeling, intra-operative technique is third harmonic generation (THG) microscopy. THG microscopy is a novel imaging technique which provides 3D-resolved images with a high (sub-micron) resolution via generation of third optical harmonics. The resulting images reveal all the tissue boundaries which can be used to describe different tissue properties, such as cell density, and cellular and nuclear morphology of the tumor. THG microscopy can be combined with other nonlinear imaging modalities, such as second harmonic generation (SHG) and multi-photon excited fluorescence (MPEF) microscopy. Together, they are able to image the majority of the pathological features of breast tumors, which are necessary to assess breast tumor tissue. Our ultimate goal is to implement this technique in a clinical endoscope . a rapid intra-operative tool used during breast surgery . to distinguish tumor from normal tissue and to identify different breast tumor types. The first step is to validate our technique with the histopathology, and that is my goal for this year.

##### Verena Neder - Wide-Angle Graded Metasurface Retroreflector

A retroreflector is a device that reflects light back to the direction of incidence. There are many applications that need higher efficiencies as available in existing designs (e.g. tilted barcode scanning). Present retroreflectors are based on 3D structures which limits the efficiency by shadowing and have a small spectral and angular working range. These drawbacks can be circumvented by using an ultra-thin graded metasurface. The graded index of this metasurface grating allows local modulation of the phase of the incident light and enables to arbitrary shape the wavefront of an optical beam. This leads to a strongly enhanced broadband reflection of the light into the first diffraction order of the grating over a large range of wavelengths. In this project the theoretical concept of planar graded metasurfaces for wavefront shaping was experimentally proved. After fabrication of the retroreflector structure with current nano-lithography techniques, retroreflectivity efficiencies above 80% have been measured. These results match excellently with predicted outcome of simulations. The concept of graded metasurfaces open the way towards the design of novel optical elements for diverse operation possibilities, e.g. as compact lenses, optical cloaks or light trapping layers for thin-film solar cells.

##### Coenraad Neijssel- Period evolution of binaries containing at least one MS massive star.

Stars more than 8 times the mass of our sun are rare but play an important role in the universe. Recent studies show that over 70% of the massive stars will interact with a close companion star during its lifetime. However, there still are open questions considering massive stars. Why are they born in binaries? What are the exact mechanisms in binary interactions. How do these interactions affect the future evolution of these important massive stars? Studying this is problematic since the very young massive stars are shrouded in clouds and later interactions happen on very short time scales (for astronomers). Not all is lost since we do know that the period of a binary system is affected by interactions such as mass transfer and mergers of stars. Therefore the evolution of the period distribution of a population of massive stars harbours important information to constrain the interaction mechanism and the initial conditions of massive stars. To study this I use recent results of a large survey of massive stars and computer simulations that evolves thousands of binary systems simultaneously. I will explain the basics of binary interactions and show preliminary results of my thesis.

##### Namrata Dutta Mazumdar- Towards Quantum Degeneracy: Rebuilding a potassium quantum gas apparatus.

Our lab aims at producing quantum degenerate gases of fermionic potassium atoms using lasers and magnetic fields. The first step consists of confining atoms in a small volume and simultaneously laser cooling them down to few tens of micro.Kelvin. This is usually achieved by use of a magneto optical trap (MOT), a combination of a magnetic quadrupole field and six orthogonal laser beams. During my thesis I am building the laser system required for the MOT. Firstly, we need a laser lock setup for stabilizing the laser frequency on a particular atomic transition. After that we amplify the laser power and shift its frequency for trapping the atoms. I am currently in the process of installing an imaging technique known as absorption imaging for characterizing the cloud of atoms in the MOT. Then, the final step is to get a quantum degenerate gas by loading the atoms inside an optical dipole trap. There the hotter atoms are allowed to leave the trap, and only the cold ones remain to thermalize and form a colder cloud. Once we achieve a quantum degenerate gas of fermions, our group plans to study itinerant ferromagnetism in one dimension. For engineering these magnetic interactions, we make use of an exceptional configuration of feshbach resonances occurring in fermionic potassium. These studies can enhance our understanding of high temperature superconductivity and strongly correlated systems.

##### Wouter Buijsman - Chaoticity in a Generalized Dicke Model

In condensed matter physics, the Dicke model is considered as the simplest description of collective light-matter interactions. Despite its simplicity, the model shows an interesting zero-temperature phase transition that has recently been observed experimentally, which makes this model of great interest in the field of quantum optics. This project studies chaoticity in a generalized Dicke model for which the coupling constants of the co- and counter rotating terms are varied independently. More specific, the project mainly studies the level spacing distribution and ground state fidelity susceptibility as a function of the two coupling parameters both analytically and numerically. Besides their importance in the field of quantum chaoticity, the level spacing distribution and fidelity susceptibility are concepts that are intensively used in studies in the related fields of integrability and phase transitions, respectively.

##### Leon Schoonderwoerd - The power of tensor networks

In this talk, I will try to convince you of the power and usefulness of tensor networks. I will start by introducing the tensor network formalism and the insightful diagrammatical notation that comes with it. I will show how I use tensor network algorithms in my research on one-dimensional spin chains. I will finish by giving an overview of the surprising areas of physics where tensor networks pop up. My research (background): I use tensor networks for numerical computations with one-dimensional spin chains. In particular I am trying to probe the (optimal) entanglement structure of states on these spin chains by minimizing entanglement entropy in a Matrix Product State (MPS). This work is an extension to Density Matrix Renormalization Group (DMRG) algorithms, used frequently for (near-)ground-state calculations on spin chains. Minimization of the entanglement entropy is achieved by applying iterative unitary basis transformations on the MPS, which can be done both in tandem to the DMRG algorithm (.on-the-fly calculations.) as well as separately.