Time: Thursday, September 26, 2024, 13:00
Location: Civil Engineering Building (B23), Lecture Hall B (https://esviewer.tudelft.nl/space/29/)
Who: Prof. Vladimir Manucharyan, Ecole Polytechnique Federale de Lausanne (EPFL), Switzerland

Although quantum mechanics applies to many macroscopic superconducting devices, one basic prediction remains controversial for decades. Namely, a Josephson junction connected to a resistor must undergo a dissipation-induced quantum phase transition from superconductor to insulator once the resistor’s value exceeds h/(2e)^2 ≈ 6.5 kΩ (h is Planck’s constant, e is the electron charge). Here we demonstrate this transition by observing the resistor’s internal dynamics. Implementing our resistor as a long transmission line section, we find that a junction scatters electromagnetic excitations in the line as either inductance (superconductor) or capacitance (insulator), depending solely on the line’s wave impedance. At the phase boundary, the junction itself acts as ideal resistance: in addition to elastic scattering, incident photons can spontaneously down-convert with a frequency-independent probability, which provides a novel marker of quantum-critical behavior.

References:

[1] C. Altimiras et al. “Absence of a dissipative quantum phase transition in Josephson junctions: Theory” arXiv:2312.14754

[2] R. Kuzmin et al. “Observation of the Schmid-Bulgadaev dissipative quantum phase transition” arXiv:2304.05806

About Prof. Vladimir Manucharyan

Vladimir received his B.S. degree in 2003 from Moscow Institute of Physics and Technology and Ph.D. in 2012 from Yale University. He was a Junior Fellow at the Harvard Society of Fellows for the period of 2010 – 2013. Prior to joining EPFL in 2022 he was a faculty at the University of Maryland. His research interests are mainly in quantum information processing with superconducting qubits.

Host: Leo DiCarlo