From Enemy to Resource: Dissipation in Superconducting Quantum Circuits - Matteo Mariantoni

Superconducting quantum circuits are one of the leading platforms for quantum information processing, combining macroscopic electrical devices with the laws of quantum mechanics. In this colloquium, I will first introduce the basic principles of these circuits and explain how they can be used to implement microwave superconducting qubits at millikelvin temperatures.

I will then discuss two complementary roles of dissipation. In the first part, dissipation appears as an unwanted effect. In particular, I will discuss loss and noise arising from material defects known as two-level systems (TLSs). These microscopic defects absorb energy and generate fluctuations that limit coherence and the creation of quantum states such as entangled states. I will show how TLSs can be characterized both from a materials-science perspective and through low-temperature microwave measurements and present a detailed study of stochastic time fluctuations affecting resonators and qubits [1]. I will also briefly pay homage to Nobel Laurate John Martinis, who first introduced me to the physics of TLSs.

In the second part, I will present a new circuit platform where dissipation is no longer only a limitation but a resource. By engineering a suitable dissipative environment, we aim to generate entangled states through quantum synchronization-the quantum analogue of synchronized pendulum clocks. I will outline a simple theoretical framework for dissipative time quantum evolution that avoids explicit Hamiltonians [2], and conclude with a proposed experiment to demonstrate quantum synchronization.

[1] J.H. Béjanin et al., Phys. Rev. B 104, 094106 (2021).

[2] M. Mariantoni and N. Gorgichuk, arXiv:2403.10474 (2024).