Roadmap on Quantum Thermodynamics

TL;DR

This Roadmap maps the current landscape of quantum thermodynamics, tracing foundational questions, experimental platforms, and device-oriented applications. It integrates information-theoretic perspectives with strong coupling, non-Abelian, and trajectory-based approaches to illuminate how energy, entropy, and information interplay at the quantum scale. The collection highlights diverse platforms—from superconducting circuits and ultracold atoms to quantum dots, NMR, trapped ions, and NV centers—and surveys topics such as quantum heat engines, batteries, thermometry, and the geometry of thermodynamic processes. Together, these perspectives identify core challenges (e.g., strong coupling, non-Markovian dynamics, autonomous control) and outline practical pathways toward energetic-efficient quantum technologies and deeper quantum foundations.

Abstract

The last two decades has seen quantum thermodynamics become a well established field of research in its own right. In that time, it has demonstrated a remarkably broad applicability, ranging from providing foundational advances in the understanding of how thermodynamic principles apply at the nano-scale and in the presence of quantum coherence, to providing a guiding framework for the development of efficient quantum devices. Exquisite levels of control have allowed state-of-the-art experimental platforms to explore energetics and thermodynamics at the smallest scales which has in turn helped to drive theoretical advances. This Roadmap provides an overview of the recent developments across many of the field's sub-disciplines, assessing the key challenges and future prospects, providing a guide for its near term progress.

Figures (13)

• Figure 1: An open quantum system, here visualized as a device on a chip, is composed of the system itself (here symbolically a qubit) interacting with its environment often formed of a resistor in a circuit. This environment, which can typically be described using a weak-coupling master equation, is often treated as classical in nature, acting as a heat bath or a collection of multiple baths. To understand the dynamics of such a device, one can measure either the quantum system itself or its surrounding environment.
• Figure 2: (a) Schematic of the Pauli engine cycle which consist of two work strokes and two statistical strokes Koch2023. A$\rightarrow$B: the trap compression in the molecular BEC phase does work $W_1$. B$\rightarrow$C: through an interaction ramp the molecular bosons are broken up and driven into the unitary Fermi gas limit. This results in a change in energy due to the change in particle statistics $E_2^P$, which is called Pauli energy. C$\rightarrow$D: the unitary Fermi gas is expanded by reducing the trap frequency and extracting work $W_3$. D$\rightarrow$A: the interaction strength is ramped back to its initial value for the gas to return to a molecular BEC state at the cost of Pauli energy $E^P_4$. (b) Pressure-volume diagram of the Pauli cycle for different compression ratios $\bar{\omega}_B/\bar{\omega}_A$. The fermionization process increases the pressure of the gas and allows for work to be extracted from the engine.
• Figure 3: (a) Quantum dot and charge-detector setup. The charging of a QD by a single electron is controlled by the gate voltage $V_g$ and can be probed via the current through a nearby quantum point contact (QPC). (b) From the charging curve and its temperature dependence, the entropy change is extracted using a Maxwell relation. (c) The time-resolved measurement of QPC current constitutes a weak continuous measurement of the QD charge and can be interpreted as a quantum trajectory.
• Figure 4: Experimental setup: a) A sample containing a large number of molecules, represented here by the chloroform molecule, along with an illustration of its energy levels under a magnetic field. b) A typical cryostat that contains the superconducting magnet generating the static magnetic field. c) A typical RF coil used to apply radio-frequency pulses and detect the NMR signal. d) Observed NMR spectra of hydrogen and carbon for the chloroform molecules, where each line reveals partial information about the system density matrix.
• Figure 5: Schematics of a quantum absorption refrigerator with 3 qubits. Heat naturally flows from the hot bath to the cold bath, through qubits $Q_1$ and $Q_2$. However, the qubits' frequencies $\omega_{1/2}$ are designed to be far off-resonance blocking the natural flow. A third qubit $Q_3$ is introduced with a gap $\omega_3$, designed so that $\omega_1+\omega_3 = \omega_2$. This resonance condition allows for two excitations, one in $Q_1$ and one in $Q_3$, to be converted into a single excitation in $Q_2$. Any excitation in $Q_3$ will therefore be sucked off by the hot/cold temperature gradient. The device therefore operates like an autonomous refrigerator helping qubit $Q_3$ cool.