Controlling heat flow in small quantum systems is a central goal of quantum thermodynamics and nanoscale transport. A key challenge is to achieve strong thermal rectification without suppressing the transmitted heat current, a tradeoff that often arises in static diode configurations. We establish a Floquet-control mechanism in a minimal quantum thermal diode formed by two longitudinally modulated Ising-coupled qubits, each coupled to an independent thermal reservoir. From a microscopic system--bath model, we derive a Floquet--LGKS master equation that resolves the drive-assisted transition channels. The resonant undriven device with left--right symmetric bath couplings serves as the reciprocal benchmark, while static detuning provides a rectifying reference with reduced heat current. Single-side driving breaks this reciprocal structure by creating a Floquet-dressed contact opposite a purely thermal contact. For this configuration, we obtain a compact steady-state current formula and an exact blocking condition for suppressing one bias direction while retaining finite transport in the opposite direction. In the weak sinusoidal-drive regime, rectification begins quadratically in the modulation amplitude. Dual-side driving adds a Floquet pumping contribution to the interaction-mediated current, so complete blocking requires cancellation of both contributions. These results establish contact-selective Floquet dressing as a design principle for controllable heat-flow asymmetry in minimal quantum thermal devices.
Controlling heat flow in small quantum systems is a central goal of quantum thermodynamics and nanoscale transport. A key challenge is to achieve strong thermal rectification without suppressing the transmitted heat current, a tradeoff that often arises in static diode configurations. We establish a Floquet-control mechanism in a minimal quantum thermal diode formed by two longitudinally modulated Ising-coupled qubits, each coupled to an independent thermal reservoir. From a microscopic system--bath model, we derive a Floquet--LGKS master equation that resolves the drive-assisted transition channels. The resonant undriven device with left--right symmetric bath couplings serves as the reciprocal benchmark, while static detuning provides a rectifying reference with reduced heat current. Single-side driving breaks this reciprocal structure by creating a Floquet-dressed contact opposite a purely thermal contact. For this configuration, we obtain a compact steady-state current formula and an exact blocking condition for suppressing one bias direction while retaining finite transport in the opposite direction. In the weak sinusoidal-drive regime, rectification begins quadratically in the modulation amplitude. Dual-side driving adds a Floquet pumping contribution to the interaction-mediated current, so complete blocking requires cancellation of both contributions. These results establish contact-selective Floquet dressing as a design principle for controllable heat-flow asymmetry in minimal quantum thermal devices.
Quantum heat transport governs energy exchange processes and statistical laws in non-equilibrium quantum systems, and plays a pivotal role in quantum thermodynamics. We investigate the steady-state thermal transport of a noncommuting coupled spin system. We employ the quantum dressed master equation approach within the framework of open quantum system theory to accurately analyze the non-equilibrium dynamics, ensuring the validity of transport results in the strong coupling regime. Our results demonstrate that noncommuting spin coupling serves as a significant resource for modulating the nonlinearity of the heat current. Specifically, in the weak spin-coupling regime, the system exhibits robust negative differential thermal conductance (NDTC) across various spin numbers. By deriving analytical expressions for the heat current in both the single-spin and large-spin limits, we reveal that this NDTC behavior is governed by microscopic cycle fluxes. Physically, this arises because spin excitation channels induced by the cold reservoir are suppressed under a large temperature bias, thereby blocking energy exchange cycles. Conversely, in the strong spin-coupling and large temperature bias regime, the quantum system demonstrates pronounced thermal rectification. This high rectification efficiency originates from the unidirectional saturation of the heat current, rendering the system a promising candidate for high-performance thermal diodes. Furthermore, we extend the model to a three-terminal configuration to construct a quantum thermal transistor. By manipulating the temperature of the gate reservoir, we achieve efficient modulation and amplification of heat flow between the source and drain. The heat amplification factor is shown to far exceed unity in specific operating regions, confirming significant thermal amplification.
Abstract A quantum thermal diode based on strong dispersive coupling between a magnon and a qubit is proposed and analysed. The system utilizes a direct dispersive interaction that leads to asymmetric energy transitions, enabling controllable directional heat flow. Detailed numerical simulations demonstrate the occurrence of nearly perfect rectification under appropriate parameter conditions, with the rectification factor approaching unity in both resonant and off-resonant regimes. Results reveal that factors such as coupling strength, magnon anisotropy, and energy detuning significantly influence both heat current and rectification performance. While increased dispersive coupling enhances both heat transfer and rectification efficiency, purely coherent or combined coupling configurations are shown to degrade performance. Comparative analysis with existing thermal diode models highlights the superior performance of the proposed system, especially its ability to achieve nearly perfect rectification while maintaining appreciable heat currents. This work presents a feasible platform for designing efficient quantum heat management devices.
Developing mechanisms to control transport in correlated quantum systems is essential for advancing quantum circuit technologies. In this work, we establish a rectification mechanism for both particle and energy flow in a fermionic system coupled to external baths, in the presence of a tilted potential modulated locally by a time-periodic drive. The drive generates particle and energy currents even in the absence of chemical or thermal bias between the baths. These drive-induced currents are enhanced at resonant frequencies at which avoided crossings occur in the Floquet quasienergy spectrum, reflecting the role of the Floquet states as intermediate channels for transport. Once a bias between the baths is introduced, the drive-induced current contribution can reinforce, compete with, or even cancel the bias-induced contribution. These effects enable rectification in the non-interacting regime, which we quantify via the rectification coefficient R. This coefficient measures the asymmetry between transport up the tilt (forward bias) and down the tilt (reverse bias). In addition to standard rectification, where transport is reduced under reverse bias, we identify a regime of bipolar rectification, in which the current flows only up the tilt regardless of the bias polarity. At the boundary between standard and bipolar regimes, the system achieves perfect rectification, corresponding to complete suppression of the reverse-bias current. In the presence of interactions between particles, the parameter region that supports bipolar rectification is enlarged and R can be enhanced by many orders of magnitude. Our results establish a rectification mechanism for particle and energy transport that can be experimentally realized in condensed matter and cold atom systems.
We put forward a quantum-optical model for a thermal diode based on heat transfer between two thermal baths through a pair of interacting qubits. We find that if the qubits are coupled by a Raman field that induces an anisotropic interaction, heat flow can become nonreciprocal and undergoes rectification even if the baths produce equal dissipation rates of the qubits, and these qubits can be identical, i.e., mutually resonant. The heat flow rectification is explained by four-wave mixing and Raman transitions between dressed states of the interacting qubits and is governed by a global master equation. The anisotropic two-qubit interaction is the key to the operation of this simple quantum thermal diode, whose resonant operation allows for high-efficiency rectification of large heat currents. Effects of spatial overlap of the baths are addressed. We discuss the possible realizations of the model in various platforms, including optomechanical setups, systems of trapped ions, and circuit QED.
We present a quantum thermal diode model based on a coupled qutrit–qubit system designed to control heat flow between two thermal baths with unprecedented efficiency. This differs from previous models in terms of the asymmetry introduced by spin particles and their interaction. By exploiting the interactions between degenerate states within the coupled qutrit–qubit system, our model demonstrates diode-like behavior that is both robust and energy-efficient. Utilizing the frameworks of open quantum systems and the quantum Markovian master equation, with the Born and rotating wave approximations, we comprehensively analyze the system’s behavior. Numerical simulations reveal significant thermal rectification across a wide temperature range, positioning our model as a groundbreaking solution for nanoscale heat management. In addition, we employ state transition diagrams to elucidate the transition rate characteristics that underpin the diode behavior. Finally, we explore the potential for physical implementation using superconducting circuits, highlighting the practical relevance of our design.
Periodically-driven (Floquet) quantum systems are ubiquitous in science and technology. For example, when a laser illuminates a material or an AC voltage is applied to a device, the system is well-described by a time-periodic Hamiltonian. In recent years, periodic driving has been proposed, not just as a tool to excite and probe devices, but actually as a mechanism of engineering new phases of matter, some of which have no equilibrium analog. However, with this promise comes a serious problem. Intuitively, if energy is injected into and distributed throughout a system, it is no surprise that it tends to heat up indefinitely to infinite temperature. In this thesis, we study the mechanisms of heating, i.e. the process of thermalization, in Floquet systems and propose methods to control them. Specifically, for non-interacting Floquet systems that are coupled to external bosonic and fermionic baths (e.g. laser-driven electrons in a semiconductor that interact with phonons and an external lead), we classify the relevant scattering processes that contribute to cooling/heating in the Floquet bands and suggest methods to suppress heating via bandwidth-restrictions on the baths. We find that is possible, with appropriate dissipative engineering, to stabilize a controlled incompressible nonequilibrium steady-state resembling a ground state - a state we term the "Floquet insulator." We extend this analysis to include short-range interactions that contribute additional heating processes and show, under the same framework, that heating can be controlled with dissipation. In the process, we develop a simple effective model for the Floquet band densities that captures the essence of all the Floquet scattering processes and that is useful for ballparking experimentally-relevant estimates of heating. Next, we turn our attention to strongly-interacting closed Floquet systems and study how heating emerges through a proliferation of resonances. We find a novel integrable point governing the strong-interaction limit of the Floquet system and examine the breakdown of integrability via the proliferation of resonances. We observe two distinct scaling regimes, attributed to non-thermal and thermal behavior, and discover a power-law scaling of the crossover between them as a function of system size. The lingering ergodicity-breaking effects of the conserved quantities in the vicinity (in parameter space) of the integrable point at finite size is a phenomena we term "near-integrability." These results suggest that small quantum systems, which are accessible currently in many platforms (e.g. trapped ions, cold atoms, superconducting devices), intrinsically host non-thermal states that one may be able to utilize to avoid heating. Furthermore, our results suggest a "dual" interpretation, in the thermodynamic limit, that a periodically-driven system exhibits prethermalization as a power-law in interaction strength.