## Theoretical Physics

**Condensed Matter Theory & Quantum Computing Group **

We are interested in the physical properties of systems that are candidates for ‘qubits’, the basic building blocks of a ‘quantum computer’. We study questions related to quantum computing, such as the various mechanisms of relaxation and decoherence, physical and logical implementation of elementary quantum gates, or the creation of entangled states.

**Bruder Group**: quantum transport, quantum computing, quantum optomechanics, quantum synchronization, quantum coherence

**Klinovaja Group**: quantum computing, topological states: Majorana fermions and parafermions, topological insulators, graphene, nanotubes, numerical simulations of condensed matter systems

**Loss Group**: quantum computing, qubits, spin qubits, quantum dots, spintronics, (microwave) cavity QED, topological quantum matter and phases, Majorana fermions, parafermions, topological insulators, topological and non-topological superconductivity, proximity effects, integer and fractional quantum Hall effect, chiral and helical edge states, Weyl and Dirac semimetals, Luttinger liquids, bosonization, strong correlations, quantum phase coherence, decoherence, braid statististic and anyons, surface code, quantum memory, magnonics, quantum magnetism, spin currents, skyrmionics, graphene, nanoribbons, nanotubes, nanowires, 2DEGs, quantum gases etc.

## Experimental Physics

**Maletinsky Group **

The Basel Quantum Sensing Group is employing quantum systems for practical sensing applications, where classical approaches fail. Prime examples include magnetic imaging with single spins on the nanoscale and the realization of hybrid quantum systems, such as single spins coupled to mechanical oscillators. Our main focus is to apply our quantum sensors to open problems in condensed matter, mesoscopic physics, both in ambient and cryogenic environments. Recent achievements include the first such nanoscale imaging of individual vortices in high-temperature superconductors, or the imaging of magnetic domains in thin-film antiferromagnets. We are driven both by further pushing sensing performance of such quantum technologies and by their application to various areas of the nanosciences, where their unprecedented sensing performance offers a multitude of highly interesting applications.

**Keywords:** Quantum sensing, coherent spin dynamics, hybrid quantum systems, nano-magnetism, nano-photonics.

**Meyer Group **

Observation of Majorana bound states in Fe networks engineered atom-by atom on superconductors. Majorana bound states at the ends of Fe chains on superconducting surfaces are investigated by scanning tunneling and atomic force microscopy. The atomic structure will be modified by local probes and the consequences for the bound states observed. These novel topological quantum bits are of interest for quantum computation.

**Keywords:** Majorana bound state, scanning tunneling microscopy, atomic force microscopy, superconductors, topological systems

**Poggio Group**

We apply nano-mechanical sensors to ultra-sensitive measurements of force, spin, and charge. We also develop and use scanning magnetometers capable of measuring the stray fields produced by nanometer-scale magnetization configurations or current distributions. Hybrid quantum systems are another an area of investigation; in particular, we investigate systems, in which mechanical modes are coupled to quantized electronic states.

**Keywords:** nanomechanics, nanomagnetism, hybrid quantum systems, scanning SQUID microscopy, skyrmions

**Sangouard Group**

We work in the field of Theoretical Quantum optics, i.e. we study the quantum properties of light and its interaction with atomic, mechanical and biological systems. Our vision is to lay the theoretical ground work that is needed for both fundamental and applied experimental programs aiming i) to probe the limits of quantum theory ii) to make use of quantum technologies for revolutionizing communication, computing and sensing.

**Schönenberger Group **

The nanoelectronic group of the University of Basel does experiments with nanodevices to explore fundamental electrical properties in confined geometries. Experiments are primarily done with novel nanomaterials like carbon nanotubes (CNTs), semiconducting nanowires (NWs) and graphene. We use and develop both top-down and bottom-up processes and combine different contact materials, for example ferromagnets, superconductors and normal metals, to arrive at unconventional hybrid systems. CNTs and NWs are ideal base materials to realize quantum wires and to define quantum dots, while graphene is a gate-tunable two-dimensional electron gas with Dirac properties. Using these systems, we have contributed to the advancement of science with key results in the area of interacting quantum systems, spintronics, superconducting proximity effect, and correlation effects in reduced dimensions. Our current research targets are engineered devices in which unconventional ground-states and excitations appear, such as the Andreev and Majorana bound states, by design. We probe these systems both by DC transport measurements and also at RF by virtue of electromagnetic resonators.

**Treutlein Group **

The Treutlein Group explores the quantum physics of atoms, photons and phonons. In our experiments we use chip-based microtraps to prepare atoms in highly entangled states and investigate their use in quantum metrology. Moreover, we develop quantum interfaces between atoms and solid-state quantum systems such as semiconductor quantum dots or nanomechanical oscillators.

**Keywords:** Ultracold atoms in chip traps, Quantum metrology, Optomechanics, Quantum interfaces

**Warburton Group **

The Nano-Photonics Group is developing solid-state materials for quantum technology applications, mostly involving the generation and detection of single photons in the optical domain, and the development of a spin qubit. A workhorse system is a semiconductor quantum dot which is a close-to-ideal emitter of single photons and a host for a spin qubit.

**Keywords:** Single photon source, spin qubit, solid-state quantum optics, 2D semiconductors, single photon detection

**Willitsch Group**

The Willitsch group is developing quantum technologies for molecules focusing on cold molecular ions in traps as target systems. We explore quantum-logic assisted approaches for precision measurements on single isolated molecules and study the properties and applications of ion-atom, ion-molecule and ion-mechanical hybrid quantum systems. Our research is highly interdisciplinary and combines quantum science, nanoscience, AMO physics and chemistry.

**Keywords:** cold molecular ions, molecular quantum technologies, precision measurements, hybrid quantum systems

**Zardo Group**

The manipulation of phonons is a challenging objective, which holds the promise of a step forward in the understanding of quantum physics and corresponds to the manipulation of sound and heat at the single quantum level. We want to investigate and engineer phonon transport and phonon interference effects in nanostructures by means of a combination of spectroscopy techniques and transport experiments.

**Keywords:** Nanophononics, coherent phonon transport, pump-probe spectroscopy, Raman, phonon-based quantum computation.

**Zumbühl Group **

Research focuses on quantum transport experiments investigating quantum coherence, electron spins and nuclear spins and interactions in semiconductor and graphene nanostructures. Ongoing projects include

- spin qubits in coupled, laterally gated GaAs quantum dots
- microkelvin temperatures in nanoscale sample
- novel quantum states of matter, such as electron or nuclear spin helices, topological states and Majorana fermions
- spin-orbit coupling in GaAs quantum wells – experiments investigating mesoscopic electron transport, including graphene nanoribbon research

We are interested in coherent manipulation of individual quantum systems in solid state nanostructures with quantum computation as a long term goal.

Experiments investigate quantum transport through semiconductor nanostructures which are fabricated in house using high mobility 2D electron gas materials obtained from collaborating molecular beam epitaxy labs. Experiments are typically performed in dilution refrigerators at millikelvin temperatures in magnetic fields. Measurements are done using electronic low-noise techniques and may involve nanosecond-pulsing and microsecond readout schemes.

**Keywords:** Quantum transport, spins, interactions, qubit, semiconductors, graphene, spin-orbit coupling, quantum wells, low temperature physics, nano-physics