Light and Atoms: How Anisotropy Controls Heat express
Light and atoms, like dancers, can move in sync or out of step. When their interaction is anisotropic (that is, direction-dependent) the dance gets trickier. In a new study, physicists considered a model where many atoms (qubits) collectively interact with an anisotropic light field, and each component is connected to a thermal reservoir. It turns out that anisotropy can drastically change the heat flow through the system.
The number of atoms acts as an amplifier: as it grows, the peaks in heat current become higher and the valleys deeper. In the limit of an infinite number of atoms (the thermodynamic limit), simple formulas were derived that set an upper bound on the heat current for finite systems. These formulas describe a process akin to cotunneling — where heat is transferred not in single quanta but in coordinated chunks.
A thermal diode, a device that conducts heat better in one direction than the other, also depends on anisotropy. Tuning the light–atom interaction opens a path to controlling heat at the quantum level, which could prove useful in future microelectronics.
Original abstract
as written by the authors arXiv:2603.29180
Nonequilibrium heat transport and quantum thermodynamics in light-matter interacting systems have received increasing attention. Quantum thermal devices, e.g., heat valve and head diode, have been realized. Recently, it has been discovered that the anisotropic light-matter interactions can greatly modify the eigenvalues and eigenvectors of hybrid quantum systems, leading to nontrivial quantum phase transitions, quantum metrology, and nonclassicality of photons. To explore the influences of anisotropic light-matter interactions on quantum transport, we investigate heat flow in the nonequilibrium anisotropic Dicke model. In this model, an ensemble of qubits collectively interacts with an anisotropic photon field. Each component interacts with bosonic thermal reservoirs. Quantum dressed master equation (DME) is included to properly study dissipative dynamics of the anisotropic Dicke model. Within the eigenbasis of the reduced anisotropic Dicke system, strong qubit-photon couplings can be properly handled. Our results demonstrate that anisotropic qubit-photon interactions are crucial for modulating steady-state heat flow. In particular, it is found that under strong coupling the heat flow is dramatically suppressed by a large anisotropic qubit-photon factor. While under moderate coupling, the anisotropic qubit-photon interactions enhance the heat flow. Moreover, the increase in the number of qubits amplifies the flow characteristics, with the peaks increasing and the valleys decreasing. Besides, we derive two analytical expressions of heat flows in thermodynamic limit approximation with limiting anisotropic factors. These heat currents exhibit the cotunneling heat transport pictures. They also serve as the upper boundaries for the heat flows in the finite-size anisotropic Dicke model. We also analyze the thermal rectification effect in the anisotropic Dicke model.
In the Dicke model, interaction anisotropy can lead to exotic quantum phase transitions, where the system's properties change abruptly as parameters are varied smoothly.