Engineering a Quantum Thermal Diode with Floquet Driving

Controlling heat flow at the nanoscale is essential for developing quantum thermal devices, such as thermal diodes, which allow heat to flow preferentially in one direction. A significant challenge in static quantum thermal diodes is the trade-off between achieving strong rectification and maintaining a high magnitude of transmitted heat current. This paper investigates whether periodic, time-dependent driving—specifically Floquet control—can overcome this limitation in a minimal system consisting of two Ising-coupled qubits connected to independent thermal reservoirs.

The authors model the system using a microscopic system-bath approach, deriving a Floquet-LGKS master equation. This framework allows them to resolve drive-assisted transition channels, which are categorized by bath, Floquet sideband, and conditional Ising sector. By comparing the undriven resonant device (the reciprocal benchmark) with single-side and dual-side driven configurations, the researchers analyze how periodic modulation reshapes the transition structure to induce thermal rectification.

The study establishes that single-side driving breaks the reciprocal symmetry of the undriven device by creating a Floquet-dressed contact that interacts with a purely thermal contact. This asymmetry allows for the derivation of a compact steady-state current formula and an exact condition for blocking heat flow in one direction while maintaining finite transport in the other.

In the weak-driving regime, the rectification effect emerges quadratically with the modulation amplitude. For dual-side driving, the authors find that the heat current includes a Floquet pumping contribution, necessitating the cancellation of both interaction-mediated and pumping terms to achieve complete blocking. These results provide a design principle for controllable, asymmetric heat transport in minimal quantum systems.

This work provides a theoretical foundation for using Floquet engineering to design active quantum thermal components. By moving beyond static parameters, researchers can gain finer control over heat transport, potentially enabling more efficient thermal logic and information processing at the nanoscale. The analytical criteria derived in the paper offer a clear roadmap for engineering specific diode functionalities in experimental quantum platforms.