Collective couplings: rectification and supertransmittance

TL;DR

This paper explores how a large spin system coupled to two thermal reservoirs can exhibit enhanced heat rectification and supertransmittance, functioning effectively as a heat diode due to cooperative effects.

Contribution

It introduces a model combining Dicke superradiance with pure-dephasing coupling, revealing how these interactions lead to amplified rectification and supertransmittance effects.

Findings

Heat currents scale quadratically with N, indicating supertransmittance.

The system acts as a heat diode with significant current asymmetry.

Rectification persists even with locally dissipative couplings.

Abstract

We investigate heat transport between two thermal reservoirs that are coupled via a large spin composed of N identical two level systems. One coupling implements the dissipative Dicke super- radiance. The other coupling is locally of the pure-dephasing type and requires to go beyond the standard weak-coupling limit by employing a Bogoliubov mapping in the corresponding reservoir. After the mapping, the large spin is coupled to a collective mode with the original pure-dephasing interaction, but the collective mode is dissipatively coupled to the residual oscillators. Treating the large spin and the collective mode as the system, a standard master equation approach is now able to capture the energy transfer between the two reservoirs. Assuming fast relaxation of the collective mode, we derive a coarse-grained rate equation for the large spin only and discuss how the original Dicke superradiance is affected by the presence of the additional reservoir. Our main finding is a cooperatively enhanced rectification effect due to the interplay of supertransmittant heat currents (scaling quadratically with $N$) and the asymmetric coupling to both reservoirs. For large $N$, the system can thus significantly amplify current asymmetries under bias reversal, functioning as a heat diode. We also briefly discuss the case when the couplings of the collective spin are locally dissipative, showing that the heat-diode effect is still present.