Observation of the Schmid-Bulgadaev dissipative quantum phase transition

Abstract

Although quantum mechanics applies to many macroscopic superconducting devices, one basic prediction remained 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 $h/4e^2\approx 6.5\text{k}\Omega$ ($h$ is Planck's constant, $e$ is the electron charge). Here we finally 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.

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Cited by in corpus (6)

• Exact quantization of nonreciprocal quasi-lumped electrical networks
• Resilience of the quantum critical line in the Schmid transition
• Quantum simulation of the microscopic to macroscopic crossover using superconducting quantum impurities
• Revisiting dissipation-driven phase transition in a Josephson junction
• Dissipation and noise in strongly driven Josephson junctions
• Photon-instanton scattering in a superconducting circuit: Beyond the very high impedance regime