Completed Projects

 

Groups Bluhm DiVincenzo Hassler Schuch Terhal

 


 

Bluhm Group

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  Coupled qubits Simon Schaal

B.Sc. Project Long Range
Coupling between Spin Qubits

The Double Quantum Dot system in GaAs can be used for quantum information processing. This thesis benchmarks different ways to couple several qubits to enable good multi-qubit operations.
Thesis (PDF)

  Central spin problem Christian Dickel

M.Sc. Project Nuclear Spin Mediated Landau-Zener Transitions in Double Quantum Dots

The Double Quantum Dot system in GaAs is a promising hardware for quantum information processing. In this thesis, a measurement scheme to probe the dynamics of nuclear spins in GaAs quantum dots is presented. Thesis (PDF)

  Quantum gate Pascal Cerfontaine

M.Sc. Project High-Fidelity Qubit Gates for Two-Electron Spin Qubits

High-fidelity gate operations for manipulating qubits in the presence of decoherence are a prerequisite for fault-tolerant quantum information processing. This work theoretically develops control pulses for singlet-triplet qubits in GaAs double quantum dots with fidelities as high as 99.9%.
Thesis (PDF)

  Measurement sequence Thomas Fink

M.Sc. Project Probing Classical and Quantum-Mechanical Baths with a Qubit

The investigation of deleterious interactions between a qubit and its environment is important for quantum information research. In this thesis, techniques using qubit evolution and readout to investigate interactions with both classical and quantum-mechanical noise baths are introduced.
Thesis (PDF)

 


 

DiVincenzo Group

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B.Sc. Projects

 

M.Sc.-Project Quantum Information Processing with Surface Acoustic Waves ​ Mohammadali Salari

In the first part of the present work, I’m going to investigate the wave propagation in cubic piezoelectric crystals such as GaAs and also wave generation by interdigital transducers. In the second part, I propose and investigate the idea of looking at spiral IDT-like structures, which might permit the simultaneous coupling to two cavities in orthogonal directions. Using COMSOL simulations, I’ve calculated several parameters of the spiral transducer, such as its capacitance, input admittance and response function. The coupling rate of the spiral transducer has also been calculated using semi-classical model for the qubit.Moreover, I have studied the IDT-transmons of Delsing's group. The physics of this is rather different than in conventional "circuit QED", because the transmon capacitor will be much bigger than the wavelength of the bosonic mode, makes it a giant atom. Thesis (PDF)

  Carlin Plot Sander Konijnenberg

M.Sc.-Project Theoretical study of Hall effect gyrators and circulators in the time domain ​

Circulators and gyrators are non-reciprocal circuit elements that play an important role in microwave systems. It would be desirable to keep such elements small in size, so it has been proposed to create such devices that use the Hall effect (as opposed to e.g. the Faraday effect which makes for relatively large devices). It has been shown that by coupling leads capacitively to a 2D Hall conductor, lossless circulators and gyrators can be made. The response of such devices has been studied in the frequency domain, but these results cannot be trivially transformed to the time domain. In this report we study the behaviour of Hall-effect gyrators and circulators in the time domain. Thesis (PDF)

  Energy of dressed states vs detuning Susanne Richer

M.Sc. Project Perturbative analysis of two-qubit gates on Transmon Qubits

This thesis treats different schemes for two-qubit gates on transmon qubits and their per- turbative analysis. The transmon qubit is a superconducting qubit that stands out due to its very low sensitivity to charge noise, leading to high coherence times. However, it is also characterized by its low anharmonicity, making it impossible to neglect the higher transmon levels.

Coupled systems of superconducting qubits and resonators can be treated in cavity QED. In the dispersive regime, where qubit and resonator are far detuned from each other, per- turbative methods can be used for the derivation of effective Hamiltonians. Several such methods are presented here, among which the Schrieffer-Wolff transformation results to be the most adequate. Thesis (PDF)

 

Hassler Group

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B.Sc.-Projects

 

M.Sc.-Projects

  Edge scattering at a graphene boundary Elias Walter

Influence of chiral symmetry on electron scattering at disordered graphene boundaries

In this thesis, we study scattering processes at disordered graphene boundaries. In particular, we investigate how the chiral symmetry of quasiparticles in graphene influences diffusive scattering. We find that a boundary that breaks chiral symmetry behaves like a mirror, in the sense that in the long Fermi wavelength limit diffusive scattering is suppressed and incoming electrons are reflected specularly. However, if the disorder on average preserves chiral symmetry, diffusive scattering increases significantly, leading to a breakdown of the mirror-like behavior. Thesis (PDF)






  Setup photons from QPC Daniel Otten

Second-Order Coherence of Microwave Photons Emitted by a Quantum Point Contact

In this work we present a diagrammatic approach to calculate current cumulants for the electron transport through a quantum point contact. We provide compact expressions for cumulants up to and including the third order. Furthermore, fluctuations in the electronic current lead to emitted radiation in the microwave regime. In this context the current cumulants are linked to the photon counting statistics of the microwave field. For this setup, we calculate the Fano factor F and the second-order coherence function g (2)(τ). Thesis (PDF)






  Aharonov-Bohm interference ring Dominique Dresen

Quantum Transport of Non-Interacting Electrons in 2D Systems of Arbitrary Geometries

The scattering formalism for describing the trans p ort properties of systems is discussed. We apply the formalism to GaAs and graphene with different geometries and types of disorder. For example, we discuss impedance matching of graphene to outside leads, Aharnnov-Bohm effect in a ring geometry, and how strain-fluctuations in graphene manifest themselves in the transport properties. Thesis (PDF)


  electric circuit Sebastian Rubbert

Tuneable Long Range Interactions in an Array of coupled Cooper Pair Boxes

The Kitaev chain emulating the transverse Ising model can be implemented in an array of superconducting islands with semiconducting nanowires. In this thesis, we will show that adding additional capacitances to the system implements a long-range interaction between the Ising degrees of freedom. Thesis (PDF)

 


 

Schuch Group

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  Hamiltonian spectrum Madita Nocon

B.Sc. Project The role of boundaries in gapped one-dimensional phases

Quantum phases in one-dimensional systems can be characterized by the number of ground states. This thesis studies how this classification of phases is affected by the presence of boundaries and the particular way in which the boundary conditions are chosen. Thesis (PDF)

  PEPS Torus Stefan Haßler

M.Sc. Project Entanglement Spectra and Boundary Theories for Gaussian Fermionic PEPS

Entanglement spectra and boundary theories describe the entanglement structure of a correlated quantum system. This thesis develops a framework for studying boundary theories in the context of non-interacting fermionic Projected Entangled Pair States (PEPS).
Thesis (PDF)

  Tensor Network for semionic RVB Mohsin Iqbal

M.Sc. Project Semionic Resonating Valence Bond states on the kagome lattice

Resonating Valence Bond states are a class of states which are well suited to model the physics of Heisenberg antiferromagnets. This thesis shows how Resonating Valence Bond states can be used to describe systems with double semion topological order, as opposed to the toric code order conventionally found in these states, and studies their properties as an ansatz for the Heisenberg antiferromagnet.
Thesis (PDF)

 


 

Terhal Group

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B.Sc. Projects

  Onedimensional circuit Nikolas Breuckmann

M.Sc. Project From quantum circuits to Hamiltonians: analysis of a multi-time construction for QMA

This thesis lies in the area of quantum complexity theory. It proves the QMA-completeness of a class of 2D interacting fermion Hamiltonians.
Thesis (PDF)

  squeezing Eva Kreysing

M.Sc. Project Improving Transmon Qubit Readout Using Squeezed Radiation

The goal of this project has been to analyze whether the use of squeezing in a Mach-Zehnder interferometer can give rise to a faster, high fidelity, measurement of superconducting transmon qubits.
Thesis (PDF)