High impedance superconducting quantum circuits

Contact: Philippe JOYEZ, philippe.joyez@cea.fr, +33 1 69 08 74 44/55 29

Summary: By exploiting the high kinetic inductance of some superconducting materials we should be able to create a new class of quantum electronic circuits

Full description:  By coupling electromagnetism and non-linear quantum circuits it recently became possible to produce more sophisticated quantum states (e.g. "Schrödinger cats", "NOON" states, …) than is possible with atomic physics techniques and also to demonstrate the operation of rudimentary quantum processors. The growth of this field exploiting genuinely quantum phenomena has been amazing.
Even though it is possible to engineer strong light-matter coupling in these systems, the rather weak impedance of vacuum implies an asymmetry in nearly all quantum circuits: Quantum fluctuations of the charge are greater than that of its quantum-conjugate flux, which imposes limitations on the electronic states that can be realized. Our goal is to overcome these limitations by taking advantage of the very high reactance of disordered superconductors to tailor the coupling to the electromagnetic field.
The peculiar properties of these materials (high impedance, non-linearity, …) can indeed be used to develop new devices that are presently lacking such as photon detectors with high quantum efficiency or wideband parametric amplifiers operating at the quantum limit that could be useful in astronomy or other fields. 

The specific goal of the internship (and the PhD to follow) is to test predictions according to which a nanowire made of such a material implements a Quantum Phase Slip Junction (QPSJ) which should be the exact quantum-mechanical dual circuit of the well-known Josephson junction (which is the key component of virtually any quantum circuit). More precisely we will propose to check the striking prediction that the charge of a small superconducting electrode connected by a QPSJ is quantized in units of 2e, realizing the dual of an RF-SQUID.

Technics/methods used during the internship:
The student must like combining experiment and theory. He/she should be at ease with concepts of quantum mechanics and have some knowledge in solid state physics. During the internship the student will familiarize with nanolitography, ultra-low temperatures, ultra low-noise measurements, microwave engineering, modeling, data analysis,…