Programm Wintersemester 2021/2022
Mo. 29.10.2021, 16:15, Hörsaal 28 D 001
Dr. Christian Wagner (RWTH Aachen University)
Towards nanofabrication with molecular building blocks
In the last half century, a multitude of ideas for the application of individual organic molecules in non-biological contexts emerged. As mechanical and electronic devices shrunk in size and the complex space of chemical compounds became increasingly accessible, the visions of molecular machines and molecular electronics took shape. More recent are ideas to utilize the quantum states of individual molecules in quantum technologies. To realize any of these visions, it is essential to precisely understand and quantify the physical interactions that govern molecular behavior and to reach a new level of control over the mechanical manipulation of individual molecules. With its unique imaging and manipulation capabilities, the low-temperature scanning probe microscope (SPM) is our tool of choice to work towards this goal. In my talk I will cover the range from basic considerations of stability to SPM-fabricated single-molecule devices. Specifically, I will outline how the stabilizing potential of a fragile standing molecule can be quantified with few-meV accuracy by a combination of thermal-excitation experiments and theory; introduce an autonomous agent which controls the SPM and masters a nanoscale robotic task of molecule manipulation using reinforcement learning; and present a new microscopy technique, scanning quantum dot microscopy, which uses a single-molecule sensor to image and quantify electrostatic surface potentials at the atomic scale.
Host: Markus Morgenstern
Mo, 20.12.2021, 16:15, Hörsaal 28 D 001
Prof. David DiVincenzo (RWTH Aachen University)
Many body localization, quantum chaos, and superconducting quantum computers
Solid state quantum computers have arrived! -- a 53-qubit system from Google, 56 qubits from the Chinese Ac. Sci, and 127 qubits from IBM-Q. Can they really work? Our recent work examines these devices from the perspective of many body physics, where we begin with the identification of the above devices as systems of coupled nonlinear quantum resonators. A certain amount of intentional frequency detuning (`disorder') is crucially required to protect individual qubit states against the destabilizing effects of nonlinear resonator coupling. I will discuss the stability of the resulting many-body localized (MBL) phase for system parameters relevant to the current quantum processors. We find that some of these quantum computing platforms are dangerously close to a phase of uncontrollable chaotic fluctuations.