Investigating laser induced phase engineering in MoS2 transistors

Phase engineering of MoS2 transistors has recently been demonstrated and has led to record low contact resistances. The phase patterning of MoS2 flakes with laser radiation has also been realized via spectroscopic methods, which invites the potential of controlling the metallic and semiconducting phases of MoS2 transistors by simple light exposure. Nevertheless, the fabrication and demonstration of laser patterned MoS2 devices starting from the metallic polymorph has not been demonstrated yet. Here, we study the effects of laser radiation on 1T/1T'-MoS2 transistors with the prospect of driving an in-situ phase transition to the 2H-polymorph through light exposure. We find that although the Raman peaks of 2H-MoS2 become more prominent and the ones from the 1T/1T' phase fade after the laser exposure, the semiconducting properties of the laser patterned devices are not fully restored and the laser treatment ultimately leads to degradation of the transport channel

Multi-mode ultra-strong coupling in circuit quantum electrodynamics

With the introduction of superconducting circuits into the field of quantum optics, many novel experimental demonstrations of the quantum physics of an artificial atom coupled to a single-mode light field have been realized. Engineering such quantum systems offers the opportunity to explore extreme regimes of light-matter interaction that are inaccessible with natural systems. For instance the coupling strength $g$ can be increased until it is comparable with the atomic or mode frequency $\omega_{a,m}$ and the atom can be coupled to multiple modes which has always challenged our understanding of light-matter interaction. Here, we experimentally realize the first Transmon qubit in the ultra-strong coupling regime, reaching coupling ratios of $g/\omega_{m}=0.19$ and we measure multi-mode interactions through a hybridization of the qubit up to the fifth mode of the resonator. This is enabled by a qubit with 88% of its capacitance formed by a vacuum-gap capacitance with the center conductor of a coplanar waveguide resonator. In addition to potential applications in quantum information technologies due to its small size and localization of electric fields in vacuum, this new architecture offers the potential to further explore the novel regime of multi-mode ultra-strong coupling.Comment: 15 pages, 9 figure