Signatures of Majorana Fermions in Hybrid Superconductor-Semiconductor Nanowire Devices

Majorana fermions are exotic elementary particles predicted in 1937 by Ettore Majorana. Although heavily searched for, they have never been found in nature up to date. In the past decades, with the progress in theory, theoretical physicists predicted that Majorana fermions might emerge in certain exotic classes of condensed matter systems, where...

Adiabatic quantum pumping via Dirac fermions

Quantum Transport in Indium Antimonide Nanowires: Investigating building blocks for Majorana devices

Recently ideas to engineer Majorana fermions in the solid state have been developed. These Majoranas, quasiparticles that are their own antiparticle, have received much attention, as they are expected to fulfill non-Abelian exchange statistics and could potentially function as fault-tolerant quantum bits. This thesis focuses on a Majorana host...

Quantum transport in nanowire networks

Quantum technology is a promising area of research, with the quantum computer as the prime example. Quantum computers can perform calculations thought to be impossible by conventional means. The fundamental building block of a quantum computer is a qubit, which is a quantumsystem which can be used to process and store quantuminformation. Most...

Towards realistic numerical simulations of Majorana devices

By exploiting quantum mechanics, quantum computers are able to solve problems---for example in quantum chemistry---that are far out of reach of classical computers. Conventional approaches to quantum computers use qubits (quantum bits) that can either be made out of superconducting circuits (the currently leading approach used to demonstrate...

Semiconductor Nanowire Josephson Junctions: In the search for the Majorana

Due to the collective behavior of electrons, exotic states can appear in condensed matter systems. In this PhD thesis, we investigate semiconducting nanowire Josephson junctions that potentially have Majorana zero modes (MZM) as exotic states. MZM are expected to form a robust quantum bit and quantum operations are done by interchange, otherwise...

Ballistic Majorana nanowire devices

The dissertation reports a series of electron transport experiments on semiconductor nanowires towards realizing the hypothesized topological quantum computation. A topological quantum computer manipulates information that is stored nonlocally in the topology of a physical system. Such an operation possesses advantages over the current quantum...

Shadow-wall lithography as a novel approach to Majorana devices

The development of quantum computers is perhaps one of the most exciting innovations of our time. The most investigated quantum computers, however, suffer from the fact that quantum information is lost due to interaction between the quantum bits and their environment. As a radically different approach, it has been proposed that one can instead...

Coherent manipulation of normal and Andreev fermions

A large part of condensed matter physics concerns itself with understanding the behaviour of electrons in solids and finding ways to control them. However, in mesoscopic systems (i.e., systems with nanometer to micrometre scale), the behaviour of electrons is difficult to predict through the Schrödinger equation. Instead, it is often more...

Quantum Properties in Hybrid Nanowire Devices

Quantum computing is a flourishing field of scientific and technological research. The development of quantum computing in the past decades is the so-called second quantum revolution, where various aspects of quantum physics, such as entanglement and superposition, are used to form the main building block of computation — the quantum bit, or...

The best people leave to go abroad; interview

The last six months have been rather crazy for Professor Leo van Kouwenhoven (Applied Sciences). Ever since he first reported in late February that he had detected something that resembled the Majorana fermion, an elementary particle that was first predicted in 1937, his telephone has not stopped ringing.

Effects of the electrostatic environment on the Majorana nanowire devices

One of the promising platforms for creating Majorana bound states is a hybrid nanostructure consisting of a semiconducting nanowire covered by a superconductor.Weanalyze the previously disregarded role of electrostatic interaction in these devices. Our main result is that Coulomb interaction causes the chemical potential to respond to an applied...

Hard Superconducting Gap in InSb Nanowires

Topological superconductivity is a state of matter that can host Majorana modes, the building blocks of a topological quantum computer. Many experimental platforms predicted to show such a topological state rely on proximity-induced superconductivity. However, accessing the topological properties requires an induced hard superconducting gap,...

A general algorithm for computing bound states in infinite tight-binding systems

We propose a robust and efficient algorithm for computing bound states of infinite tight-binding systems that are made up of a finite scattering region connected to semi-infinite leads. Our method uses wave matching in close analogy to the approaches used to obtain propagating states and scattering matrices. We show that our algorithm is robust...

Topological Phases without Crystalline Counterparts

We construct a two-dimensional higher-order topological phase protected by a quasicrystalline eightfold rotation symmetry. Our tight-binding model describes a superconductor on the Ammann-Beenker tiling hosting localized Majorana zero modes at the corners of an octagonal sample. In order to analyze this model, we introduce Hamiltonians...

Hard Superconducting Gap and Diffusion-Induced Superconductors in Ge-Si Nanowires

We show a hard superconducting gap in a Ge-Si nanowire Josephson transistor up to in-plane magnetic fields of 250 mT, an important step toward creating and detecting Majorana zero modes in this system. A hard gap requires a highly homogeneous tunneling heterointerface between the superconducting contacts and the semiconducting nanowire. This...

Electric field tunable superconductor-semiconductor coupling in Majorana nanowires

We study the effect of external electric fields on superconductor-semiconductor coupling by measuring the electron transport in InSb semiconductor nanowires coupled to an epitaxially grown Al superconductor. We find that the gate voltage induced electric fields can greatly modify the coupling strength, which has consequences for the proximity...

Qsymm: Algorithmic symmetry finding and symmetric Hamiltonian generation

Symmetry is a guiding principle in physics that allows us to generalize conclusions between many physical systems. In the ongoing search for new topological phases of matter, symmetry plays a crucial role by protecting topological phases. We address two converse questions relevant to the symmetry classification of systems: is it possible to...