Hund's coupling mediated multi-channel quantum phase transition of a single magnetic impurity in Fe(Se, Te).

Understanding the interplay between individual magnetic impurities and superconductivity is crucial for bottom-up construction of novel phases of matter. Sub-gap bound states that are used in this endeavor are typically considered as independent entities that each result from the exchange scattering between the respective impurity orbitals and electrons of the superconducting condensate. Here we present experimental evidence of individual multi-spin impurities where the sub-gap states are not independent.

Efficient Microwave Photon-to-Electron Conversion in a High-Impedance Quantum Circuit.

We demonstrate an efficient and continuous microwave photon-to-electron converter with large quantum efficiency (83%) and low dark current. These unique properties are enabled by the use of a high kinetic inductance disordered superconductor, granular aluminium, to enhance light-matter interaction and the coupling of microwave photons to electron tunneling processes. As a consequence of strong coupling, we observe both linear and nonlinear photon-assisted processes where two, three, and four photons are converted into a single electron at unprecedentedly low light intensities.

Imaging the Quantum Capacitance of Strained MoS Monolayers by Electrostatic Force Microscopy.

We implemented radio frequency-assisted electrostatic force microscopy (RF-EFM) to investigate the electric field response of biaxially strained molybdenum disulfide (MoS) monolayers (MLs) in the form of mesoscopic bubbles, produced via hydrogen (H)-ion irradiation of the bulk crystal. MoS ML, a semiconducting transition metal dichalcogenide, has recently attracted significant attention due to its promising optoelectronic properties, further tunable by strain. Here, we take advantage of the RF excitation to distinguish the intrinsic quantum capacitance of the strained ML from that due to atomic scale defects, presumably sulfur vacancies or H-passivated sulfur vacancies.

Quantum bath engineering of a high impedance microwave mode through quasiparticle tunneling.

In microwave quantum optics, dissipation usually corresponds to quantum jumps, where photons are lost one by one. Here we demonstrate a new approach to dissipation engineering. By coupling a high impedance microwave resonator to a tunnel junction, we use the photoassisted tunneling of quasiparticles as a tunable dissipative process.

Coherent and Incoherent Tunneling into Yu-Shiba-Rusinov States Revealed by Atomic Scale Shot-Noise Spectroscopy.

The pair breaking potential of individual magnetic impurities in s-wave superconductors generates localized states inside the superconducting gap commonly referred to as Yu-Shiba-Rusinov (YSR) states whose isolated nature makes them promising building blocks for artificial structures that may host Majorana fermions. One of the challenges in this endeavor is to understand their intrinsic lifetime, ℏ/Λ, which is expected to be limited by the inelastic coupling with the continuum thus leading to decoherence. Here we use shot-noise scanning tunneling microscopy to reveal that electron tunneling into superconducting 2H-NbSe_{2} mediated by YSR states is not Poissonian, but ordered as a function of time, as evidenced by a reduction of the noise.