# Strong system-bath coupling induces negative differential thermal conductance and heat amplification in nonequilibrium two-qubits systems

## TL;DR

This paper investigates quantum heat transfer in two-qubits systems, revealing that strong system-bath coupling can cause negative differential thermal conductance and significant heat amplification, advancing understanding of nonequilibrium quantum thermal devices.

## Contribution

It demonstrates that strong qubit-bath coupling induces negative differential conductance and heat amplification in nonequilibrium two-qubits systems, unifying weak and strong coupling regimes.

## Key findings

- Negative differential thermal conductance occurs with strong qubit-bath coupling.
- Giant heat amplification factor observed in three-terminal setups.
- Partial strong spin-boson interaction suffices for heat conductance effects.

## Abstract

Quantum heat transfer is analyzed in nonequilibrium two-qubits systems by applying the nonequilibrium polaron-transformed Redfield equation combined with full counting statistics. Steady state heat currents with weak and strong qubit-bath couplings are clearly unified. Within the two-terminal setup, the negative differential thermal conductance is unraveled with strong qubit-bath coupling and finite qubit splitting energy. The partially strong spin-boson interaction is sufficient to show the negative differential thermal conductance. Based on the three-terminal setup, that two-qubits are asymmetrically coupled to three thermal baths, a giant heat amplification factor is observed with strong qubit-bath coupling. Moreover, the strong interaction of either the left or right spin-boson coupling is able to exhibit the apparent heat amplification effect.