# Unifying quantum heat transfer and superradiant signature in a nonequilibrium collective-qubit system: a polaron-transformed Redfield approach

## TL;DR

This paper develops a unified theoretical framework to analyze quantum heat transfer and superradiant effects in a collective-qubit system, revealing how system size influences superradiance and bridging weak and strong coupling regimes.

## Contribution

It introduces a polaron-transformed Redfield approach with an auxiliary counting field to study heat transfer and fluctuations across different coupling strengths.

## Key findings

- Heat current and fluctuations unify weak and strong coupling results.
- Superradiant heat transfer depends on system size and diminishes with more qubits.
- Large qubit numbers suppress superradiant signatures in nonequilibrium conditions.

## Abstract

We investigate full counting statistics of quantum heat transfer in a collective-qubit system, constructed by multi-qubits interacting with two thermal baths. The nonequilibrium polaron-transformed Redfield approach embedded with an auxiliary counting field is applied to obtain the steady state heat current and fluctuations, which enables us to study the impact of the qubit-bath interaction in a wide regime. The heat current, current noise and skewness are all found to clearly unify the limiting results in the weak and strong couplings, respectively. Moreover, the superradiant heat transfer is clarified as a system-size-dependent effect, and large number of qubits dramatically suppresses the nonequilibrium superradiant signature.