Simon Sundelin, Kvantteknologi

Supervisor: Simone Gasparinetti

Co-supervisor: Aamir Ali

Examiner: Per Delsing

Discussion leader: Janine  Splettstoesser

Sammanfattning:

Quantum thermodynamics seeks to determine how quantum resources reshape the fundamental limits of energy flows at the microscopic scale and whether they can be harnessed to achieve a thermodynamic quantum advantage over classical systems. A central challenge is then to realize quantum thermal machines that both demonstrate nonclassical modes of operation and enable experimental tests of thermodynamic bounds. Here, we implement a three-level quantum thermal machine based on superconducting circuits, in which dephasing noise—typically detrimental to quantum devices—becomes a resource for energy transport. The device consists of a superconducting artificial molecule, composed of two transmon qubits, coupled in a symmetry-selectively manner to two engineered physical heat baths. We demonstrate its operation as a refrigerator, accelerator, and heat engine from measurements of photonic heat current at sub-attowatt levels. This constitutes the first-ever experimental demonstration of the operating principles of noise-assisted quantum refrigeration. In a complementary experiment, we measure higher-order moments of the emitted photonic heat current—a technically challenging task—to resolve the current fluctuations and the entropy production of the system. This direct access to current statistics enables us to probe the thermodynamic uncertainty relation (TUR), which in classical systems constrains the trade-off between power output, its fluctuations, and entropy production; and provides a pathway toward demonstrating the theoretically predicted quantum violation of this bound for optimal parameters in our device. Our results establish superconducting circuits as a versatile platform for investigating the energy flows through quantum thermal machines and for testing the ultimate thermodynamic limits of precision and performance.