Quantum Heater Mode

• Quantum heater mode is a regime in quantum thermodynamics where controlled energy conversion dissipates externally supplied work as heat into thermal reservoirs, defined by strict sign conventions.
• It leverages mechanisms such as Floquet heating, micromotion-induced transitions, and non-Markovian dynamics across diverse platforms like superconducting circuits, quantum dots, and cavity QED setups.
• Performance is quantified via a coefficient of performance (COP), balancing optimized drive parameters and system-bath interactions for targeted thermal control and efficient energy management.

A quantum heater mode denotes a specific operational regime in quantum thermodynamics where a device or system, under appropriately configured control and environmental parameters, converts available resource(s)—such as coherent drive, bath energy, or load population—into heat that is deliberately dumped into one or more thermal reservoirs. This regime is defined, both theoretically and experimentally, by sign conventions of heat and work flows in open quantum systems, and it typically emerges in platforms that exploit quantum coherence, many-body localization effects, Floquet engineering, or finite coupling between system and baths. Contemporary quantum heaters have been realized across multiple architectures including driven superconducting qubits, engineered resonator-bath assemblies, non-Markovian Otto cycles, quantum-dot arrays, and collision-model implementations using phase-coherent ancillae.

1. Formal Operational Criteria and Core Models

The quantum heater mode is identified by strict sign patterns of thermodynamic flows, generally within cyclic or steady-state quantum machines. In the context of two-bath engines or Otto/Stirling cycles, the heater mode is mathematically defined by

$Q_h < 0,\qquad Q_c < 0,\qquad W < 0$

where $Q_h$ is the net heat flow from the hot bath (negative when heat is dumped into it), $Q_c$ from the cold bath, and $W$ is the net work per cycle (negative when work is consumed by the system). This sign pattern indicates that the working medium is not extracting heat from any bath, but rather that externally supplied work (or equivalent resource, e.g., population inversion) is fully dissipated as heat into both baths or into a designated reservoir (Alcalá et al., 6 Jan 2026, Suo et al., 25 Jan 2026, S. et al., 2 Jun 2025).

More generally, in autonomous quantum thermal machines interfaced with a load, the heater regime is signified by

$\dot Q_h < 0,\quad \dot Q_c < 0,\quad P_\ell < 0$

with $P_\ell$ the rate of energy loss by the load, i.e., the load powers the heating process (S. et al., 2 Jun 2025).

Specific master equations governing these regimes typically involve weak-to-intermediate coupling, secular or non-secular Redfield/Floquet-Redfield treatments, and include both coherent and dissipative transitions whose balance is tunable via control parameters such as drive amplitude, detuning, or system-bath coupling strength (Satrya et al., 27 Oct 2025, Thomas et al., 2022, Maity et al., 2024, Roy et al., 2019, Amato et al., 2023).

2. Microscopic Mechanisms and Platform Diversity

Microscopically, quantum heater modes can arise in a variety of architectures and via disparate physical mechanisms:

• Driven Two-Level Systems and Floquet Heating: A periodically driven qubit coupled to a resonant bath exhibits sharp heat-current peaks at fractional driving frequencies (e.g., $\omega_d \approx \omega_r / l$) due to interference between Floquet modes. Heating into the bath is maximized when the drive parameters induce a population inversion among Floquet states, with the resonance peak heights and parity (odd vs. even $l$) governed by Fourier components of the drive waveform (Satrya et al., 27 Oct 2025, Thomas et al., 2022).
• Quantum Dots and Micromotion-Induced Heating: In periodically modulated double quantum dots, heater operation is linked directly to nonzero micromotion (additional satellite transitions, $m\neq0$) in the Floquet states, which allow energy from the coherent drive to irreversibly heat the attached reservoirs. The heating power and efficiency can be optimized by tuning Bessel-function-weighted tunnelings and drive frequency (Roy et al., 2019).
• Quantum Heat Valves and Artificial-Atom Systems: In circuit QED platforms, a transmon qubit sandwiched between resonators acts as a controllable spectral filter for heat flow. By tuning qubit frequency (via external flux) into resonance with the resonator, one maximizes heat transfer into a reservoir. Under coherent qubit drive or population inversion protocols, net energy is pumped even against bath temperature gradients, thereby realizing a heater mode (Xu et al., 2020, Ronzani et al., 2018).
• Phaseonium-Driven Cavity Arrays: In collision models where single-mode cavities are repeatedly probed by phase-coherent atoms (phaseonium), the quantum heater mode is realized when atomic parameters (excited-state population and ground-state coherence phase $\phi$) are tuned such that the effective photon creation rate outweighs damping. This enables programmable switching between cooling and heating dynamics (Amato et al., 2023).
• Non-Markovian Otto Cycles and Interaction-Time Engineering: Manipulation of the qubit-bath interaction time in a non-Markovian quantum Otto cycle enables controlled switching into a heater regime. For short interaction times, interaction energy partitioning and detachment work dominate, leading to work consumption and heat emission into both baths (Ishizaki et al., 2022).
• Quantum Heat Transformers (QHT): Multi-qubit networks engineered with resonant, energy-matching Hamiltonians can implement a quantum analog of classical step-up transformers, yielding a steady-state or transient secondary temperature gradient larger than the primary—functioning as a quantum heater, with performance quantified by the “capacity of thermal control” (Maity et al., 2024).
• Disordered and Localized Working Media: In quantum Otto cycles with off-diagonal quasicrystal working media, the onset of many-body localization leads to population inversion effects that generically reverse heat-flow signs, favoring the heater regime and enhancing the coefficient of performance (COP) beyond unity due to the suppression of coherent transport (Suo et al., 25 Jan 2026).

3. Performance Metrics and Efficiency Analysis

Unlike heat engines, heater-mode performance is quantified via a coefficient of performance (COP), defined in several contexts as

$\mathrm{COP}_{\mathrm{heater}} = \frac{|Q_h|}{|W|}$

or in operation with a load,

$$\mathrm{COP}_{\mathrm{heater}} = \frac{|\dot Q_c|}{|W|}$$

This ratio expresses the amount of heat delivered to a targeted bath per unit of invested work. The COP in quantum heater mode can exceed unity, especially in the presence of spectrum localization or finite quantum correlations, although this often comes at the cost of reduced absolute heat currents. For precise comparison among all operational modes, a normalized performance parameter $\kappa = \frac{\mathrm{COP}}{1+\mathrm{COP}}$ (with $0<\kappa<1$) allows direct benchmarking of heater, engine, and refrigerator regimes on the same scale (Alcalá et al., 6 Jan 2026, Suo et al., 25 Jan 2026).

The delivered heating power (for instance $P_b$ in bolometric studies, or $P_\ell$ for load-driven heaters) peaks near the onset of Floquet resonances, large effective coupling (e.g., enhanced by bosonic factors $\sqrt{n_0}$ in oscillator loads), or optimal control configurations (e.g., drive amplitudes $A_d$ maximizing multi-photon transitions) (Satrya et al., 27 Oct 2025, Roy et al., 2019, S. et al., 2 Jun 2025).

4. Control Knobs and Transition Criteria

Operation in the quantum heater mode is highly tunable via various microscopic and macroscopic control parameters:

• Coherent Drive Parameters: Drive amplitude $A_d$ and frequency $\omega_d$ in qubit-resonator systems directly control the order and strength of Floquet-assisted transitions, enabling discrete onsets of heating (via resonance with the $l$-th harmonic, $\omega_d\approx\omega_r/l$) and parity control (even/odd selection rules at symmetry points) (Satrya et al., 27 Oct 2025, Thomas et al., 2022).
• Population Inversion and Atomic Coherence: In phaseonium-driven collision setups, the excited-state population $|α|^2$ and ground-state coherence phase $\phi$ of impinging atoms determine the photon-number steady state and effective temperature. Quantum-heating is achieved when $2|α|^2 > |β|^2(1+\cos\phi)$, with $\phi\rightarrow\pi$ maximizing heating by suppressing damping (Amato et al., 2023).
• Bath and System Couplings: Finite coupling constants $g$ (machine-load or inter-qubit) often control not only the onset but the phase-space extent of the heater regime, with critical values marking transitions where refrigerator or engine operation is suppressed (S. et al., 2 Jun 2025, Alcalá et al., 6 Jan 2026). For bosonic loads, an “effective” $g_{eff}=g\sqrt{n_0}$ introduces quantum enhancement, making the heater mode accessible by increasing initial occupation (S. et al., 2 Jun 2025).
• Frequency Asymmetry and Energy Conservation: Adjusting frequency ratios $r=\bar\omega/\omega$ or enforcing/quenching resonant energy-conserving transitions in QHTs and coupled-qubit machines enables fine-tuned control of heating efficiency, selectivity for targeted junctions, and suppression of non-heater modes (Maity et al., 2024, Alcalá et al., 6 Jan 2026).
• Interaction Time and Non-Markovian Dynamics: In non-Markovian cycles, heater mode is sandwiched between heat-pump and engine regimes as a function of the qubit–bath interaction duration $\tau$. The onset window is analytically demarcated by the roots of $\Delta E_S^\mu(\tau) = 0$ and $W(\tau) = 0$ (Ishizaki et al., 2022).
• Disorder and Localization Degree: In quasicrystalline working media, increasing localization (measured by spectral parameters $r_f/t$ or reduced Wigner entropy $W_S$) systematically pushes the operational mode into the heater domain, associated with sign inversion of heat flows. The “sweet spot” exists just beyond the localization threshold, providing a tradeoff between COP and total power (Suo et al., 25 Jan 2026).

5. Experimental Implementations and Readout Protocols

Experimental realization of quantum heater modes has been achieved in several platforms:

• Superconducting Circuits: Direct measurement of drive-induced heat currents has been accomplished in galvanically coupled flux-qubit–resonator circuits using on-chip bolometric normal-metal resistors. The measurement protocol involves comparison of bath temperatures (extracted via calibrated SINIS thermometer voltages) with and without qubit drive (Satrya et al., 27 Oct 2025). Fractional-resonance peaks and parity selection rules in $P_b(\omega_d,A_d)$ map directly onto heater-mode signatures.
• Atomic and Cavity QED: Collision models with cavity fields bombarded by phaseonium atoms exploit secondary, non-Markovian heating effects via cascaded setups—one cavity achieves programmable heating based on atomic input state, while downstream cavities exhibit feedback-determined non-Markovian temperature dynamics (Amato et al., 2023).
• Quantum Dots and Ultracold Atoms: Periodically driven double-dot systems with tunable drive and reservoir bias have been proposed and characterized for selective heat dumping into chosen baths, with Floquet micromotion directly observed in the heating rates (Roy et al., 2019).
• Mechanical Resonators with NV Centers: In diamond cantilever devices, quantum heater action of a “hot” low-frequency mode coherently cools a higher-frequency mode via a spin-mediated swap mechanism; raising the temperature of the low-frequency bath increases cooling of the high-frequency target—an effect labeled “cooling by heating” (Ma et al., 2016).
• Photonic Heat Valves: Circuit QED devices featuring transmon qubits between resistive-resonator baths operate as tunable quantum heaters, with flux-controlled heat currents reaching modulations up to 80% and “on/off ratios” above $10^2$ (Ronzani et al., 2018, Xu et al., 2020).

6. Parameter Regimes, Optimized Performance, and Limitations

Several explicit parameter regimes and optimization strategies are established for heater-mode operation:

Platform/Device	Key Control Knobs	Performance Markers
Qubit–Resonator–Bath (Floquet)	$\omega_d$, $A_d$, $\varepsilon_0$	$P_b>$0, fractional peaks, Bessel zeros
Double-dot/Ultracold Atomic Gas	$\alpha$ (drive), $\omega$, biasing	$P_{\mathrm{heat}}$, micromotion peaks
Quantum Heat Transformer (QHT)	Initial bath temperatures, $g$, energy gaps	$\mathcal{C}_H<0$, $\Delta T_s>\Delta T_p$
Quasicrystalline Otto Engine	$r_f/t$, $\theta$, $T_h$	$Q_h<0$, $Q_c<0$, COP$\gg1$
Non-Markovian Otto Cycle	Interaction time $\tau$	$Q_h>0$, $Q_c<0$, $W<0$

Peak heating power typically occurs close to transitions where population inversion or localization sends both $Q_h$ and $Q_c$ negative. However, such maxima are often accompanied by diminished total current due to spectral bottlenecks or coherence suppression. Optimization thus requires balancing coupling, drive resonance, and dissipation rates (Satrya et al., 27 Oct 2025, Alcalá et al., 6 Jan 2026, Maity et al., 2024, S. et al., 2 Jun 2025, Roy et al., 2019).

Notably, heater efficiency can be suppressed or enhanced via optional elements (e.g., turning on or off Stirling cycle regeneration sharply narrows or even eliminates the heater domain), and scaling up power may require arraying devices, increasing mode density, or boosting effective coupling via large bosonic occupations (Alcalá et al., 6 Jan 2026, S. et al., 2 Jun 2025, Maity et al., 2024, Xu et al., 2020).

7. Implications, Open Questions and Outlook

Quantum heater modes provide an essential operational class in quantum thermodynamics, revealing the flexibility and nontriviality of energy management in open quantum systems. They underpin the ability of quantum thermal machines to harness coherence, strong coupling, and topology (e.g., via localization phenomena) for targeted heat transfer, moving beyond classical efficiency paradigms.

Current research focuses on optimizing control for maximum heating power under quantum constraints, analyzing the role of strong vs. weak coupling, and understanding heater-to-engine and heater-to-refrigerator transitions in high-dimensional phase diagrams. The impact of non-Markovianity and non-trivial bath correlations is an active area, especially in engineered collision models and strongly-damped circuit QED platforms.

Quantum heater modes are central for next-generation quantum absorption refrigerators, autonomous heat valves, thermal transistors, and dynamic heat management in processors or quantum coherent devices, ultimately pushing the frontier of thermodynamic resource theories and practical solid-state caloritronics (Satrya et al., 27 Oct 2025, S. et al., 2 Jun 2025, Xu et al., 2020, Maity et al., 2024, Amato et al., 2023, Ishizaki et al., 2022, Suo et al., 25 Jan 2026, Ronzani et al., 2018, Ma et al., 2016).