Experimental realization of a quantum heat engine based on dissipation-engineered superconducting circuits

  1. Tuomas Uusnäkki,
  2. Timm Mörstedt,
  3. Wallace Teixeira,
  4. Miika Rasola,
  5. and Mikko Möttönen
Quantum heat engines (QHEs) have attracted long-standing scientific interest, especially inspired by considerations of the interplay between heat and work with the quantization of energy
levels, quantum superposition, and entanglement. Operating QHEs calls for effective control of the thermal reservoirs and the eigenenergies of the quantum working medium of the engine. Although superconducting circuits enable accurate engineering of controlled quantum systems, beneficial in quantum computing, this framework has not yet been employed to experimentally realize a cyclic QHE. Here, we experimentally demonstrate a quantum heat engine based on superconducting circuits, using a single-junction quantum-circuit refrigerator (QCR) as a two-way tunable heat reservoir coupled to a flux-tunable transmon qubit acting as the working medium of the engine. We implement a quantum Otto cycle by a tailored drive on the QCR to sequentially induce cooling and heating, interleaved with flux ramps that control the qubit frequency. Utilizing single-shot qubit readout, we monitor the evolution of the qubit state during several cycles of the heat engine and measure positive output powers and efficiencies that agree with our simulations of the quantum evolution. Our results verify theoretical models on the thermodynamics of quantum heat engines and advance the control of dissipation-engineered thermal environments. These proof-of-concept results pave the way for explorations on possible advantages of QHEs with respect to classical heat engines.

Theory of an autonomous quantum heat engine based on superconducting electric circuits with non-Markovian heat baths

  1. Miika Rasola,
  2. Vasilii Vadimov,
  3. Tuomas Uusnäkki,
  4. and Mikko Möttönen
We propose and theoretically analyze a realistic superconducting electric circuit that can be used to realize an autonomous quantum heat engine in circuit quantum electrodynamics. Using
a quasiclassical, non-Markovian theoretical model, we demonstrate that coherent microwave photon generation can emerge solely from heat flow through the circuit and its nonlinear internal dynamics. The predicted generation rate is sufficiently high for experimental observation in circuit quantum electrodynamics, making this work a significant step toward the first experimental realization of an autonomous quantum heat engine in superconducting circuits.