Sisyphus cooling and amplification by a superconducting qubit

TL;DR

This paper demonstrates Sisyphus cooling and amplification of a superconducting LC oscillator using a driven qubit, bridging concepts from quantum optics and circuit QED with experimental and theoretical analysis.

Contribution

It introduces the first demonstration of Sisyphus cooling and amplification in a superconducting circuit system, extending quantum optical techniques to circuit QED.

Findings

Successful experimental realization of Sisyphus cooling of a superconducting LC oscillator.

Observation of Sisyphus amplification in the superconducting circuit.

Quantitative agreement between theory and experiment supports the interpretation.

Abstract

Laser cooling of the atomic motion paved the way for remarkable achievements in the fields of quantum optics and atomic physics, including Bose-Einstein condensation and the trapping of atoms in optical lattices. More recently superconducting qubits were shown to act as artificial two-level atoms, displaying Rabi oscillations, Ramsey fringes, and further quantum effects. Coupling such qubits to resonators brought the superconducting circuits into the realm of quantum electrodynamics (circuit QED). It opened the perspective to use superconducting qubits as micro-coolers or to create a population inversion in the qubit to induce lasing behavior of the resonator. Furthering these analogies between quantum optical and superconducting systems we demonstrate here Sisyphus cooling of a low frequency LC oscillator coupled to a near-resonantly driven superconducting qubit. In the quantum optics setup the mechanical degrees of freedom of an atom are cooled by laser driving the atom's electronic degrees of freedom. Here the roles of the two degrees of freedom are played by the LC circuit and the qubit's levels, respectively. We also demonstrate the counterpart of the Sisyphus cooling, namely Sisyphus amplification. Parallel to the experimental demonstration we analyze the system theoretically and find quantitative agreement, which supports the interpretation and allows us to estimate system parameters.