Toward a quantum advantage in the thermodynamics of precision in a superconducting circuit

The performance of a nanoscale heat engines in the classical regime is fundamentally constrained by the thermodynamic uncertainty relation (TUR). This relation imposes a trade-off among mean power output〈P〉, its fluctuations represented by the variance var(P), and the entropy dissipation σ, expressed as var(P)/〈P〉² ≥ 2k_B/σ, in which k_B is the Boltzmann’s constant. Quantum effects, however, may permit enhanced precision and possibly even a violation of this classical bound, according to recent theoretical studies [1]. Experimentally verifying such quantum-induced violation is challenging, primarily because of the difficulty in detecting minuscule heat currents (order of attowatts) and their even smaller fluctuations. Here, we report our progress in experimentally probing the TUR in a superconducting quantum thermal machine. The device consists of a superconducting artificial molecule — comprising two transmon qubits — coupled in a symmetry-selective way [2] to both a microwave waveguide and a resonator. We coherently drive the transition between the ground state and a specific excited state through the resonator, while coupling the two upper levels via a dephasing channel that serves as an infinite-temperature bath. We measure the statistical moments of the instantaneous output power radiated into the waveguide, which functions as a cold bath, allowing us to assess the TUR at the limit of its classical bound. Our results bring us closer to demonstrating a genuine quantum advantage in thermodynamics.

[1] Kalaee et al., Phys. Rev. E 104, L012103 (2021).

[2] Aamir et al., Phys. Rev. Lett. 129, 123604 (2022)