Steady-State Heat Transport and Work With a Single Artificial Atom Coupled to a Waveguide: Emission Without External Driving

• Main Authors: Bengtsson, A. (Author), Delsing, P. (Author), Funo, K. (Author), Gasparinetti, S. (Author), Kockum, A.F (Author), Lambert, N. (Author), Lu, Y. (Author), Nori, F. (Author)
• Format: Article
• Language: English
• Published: American Physical Society 2022
• Subjects: Artificial atoms; Continuous emission; Emission spectroscopy; External driving; Heat transfer; Heat transport; Non equilibrium; Output lines; Photons; Power; Quantum optics; Spectrometers; Steady state; Superconducting qubits; Thermal photons; Waveguides
• Online Access: View Fulltext in Publisher

 We observe the continuous emission of photons into a waveguide from a superconducting qubit without the application of an external drive. To explain this counterintuitive observation, we build a two-bath model where the qubit couples simultaneously to a cold bath (the waveguide) and a hot bath (a secondary environment). Our results show that the thermal-photon occupation of the hot bath is up to 0.14 photons, 35 times larger than the cold waveguide, leading to nonequilibrium heat transport with a power of up to 132 zW, as estimated from the qubit emission spectrum. By adding more isolation between the sample output and the first cold amplifier in the output line, the heat transport is strongly suppressed. Our interpretation is that the hot bath may arise from active two-level systems being excited by noise from the output line, and that the qubit coherence can be improved significantly by suppressing this noise. We also apply a coherent drive, and use the waveguide to measure thermodynamic work and heat, suggesting waveguide spectroscopy is a useful means to study quantum heat engines and refrigerators. Finally, based on the theoretical model, we propose how a similar setup can be used as a noise spectrometer which provides a solution for calibrating the background noise of hybrid quantum systems. © 2022 authors. Published by the American Physical Society.