Thermodynamic Resource Research Articles

Experimental Validation of Enhanced Information Capacity by Quantum Switch in Accordance with Thermodynamic Laws.

We experimentally probe the interplay of the quantum switch with the laws of thermodynamics. The quantum switch places two channels in a superposition of orders and may be applied to thermalizing channels. Quantum-switching thermal channels has been shown to give apparent violations of the second law. Central to these apparent violations is how quantum switching channels can increase the capacity to communicate information. We experimentally show this increase and how it is consistent with the laws of thermodynamics, demonstrating how thermodynamic resources are consumed. We use a nuclear magnetic resonance approach with coherently controlled interactions of nuclear spin qubits. We verify an analytical upper bound on the increase in capacity for channels that preserve energy and thermal states, and demonstrate that the bound can be exceeded for an energy-altering channel. We show that the switch can be used to take a thermal state to a state that is not thermal, while consuming free energy associated with the coherence of a control system. The results show how the switch can be incorporated into quantum thermodynamics experiments as an additional resource.

Optical simulation of a quantum cooling engine powered by entangled measurements

Traditional refrigeration is driven either by external forces or by the information-feedback mechanism. Surprisingly, quantum measurement and collapse, typically viewed as detrimental, can also power a quantum cooling engine without requiring any feedback mechanism. In this work, we perform a proof-of-principle demonstration of quantum measurement cooling (QMC) powered by entangled measurements using a highly controllable linear optical simulator. The simulator can simulate qubits with different energy-level spacings and their thermalizing processes at different temperatures, and also allows for arbitrary projections of two qubits at different energy levels. We show the effect of changes in energy levels and measurement bases on the cooling process and demonstrate the robustness of QMC. These results reveal the special role of entangled measurements in quantum thermodynamics, indicate that quantum measurement is not always detrimental but can be a valuable thermodynamic resource. Our setup also offers a highly controllable simulation platform for multiqubit quantum engines.

Energetic Cost for Speedy Synchronization in Non-Hermitian Quantum Dynamics.

Quantum synchronization is crucial for understanding complex dynamics and holds potential applications in quantum computing and communication. Therefore, assessing the thermodynamic resources required for finite-time synchronization in continuous-variable systems is a critical challenge. In the present work, we find these resources to be extensive for large systems. We also bound the speed of quantum and classical synchronization in coupled damped oscillators with non-Hermitian anti-PT-symmetric interactions, and show that the speed of synchronization is limited by the interaction strength relative to the damping. Compared to the classical limit, we find that quantum synchronization is slowed by the noncommutativity of the Hermitian and anti-Hermitian terms. Our general results could be tested experimentally, and we suggest an implementation in photonic systems.

Thermodynamically optimal protocols for dual-purpose qubit operations

Information processing, quantum or classical, relies on channels transforming multiple input states to different corresponding outputs. Previous research has established bounds on the thermodynamic resources required for such operations, but no protocols have been specified for their optimal implementation. For the insightful case of qubits, we here develop explicit protocols to transform two states in an energetically optimal manner. We first prove conditions on the feasibility of carrying out such transformations at all, and then quantify the achievable work extraction. Our results uncover a fundamental incompatibility between the thermodynamic ideal of slow, quasistatic processes and the information-theoretic requirement to preserve distinguishability between different possible output states. Published by the American Physical Society 2024

Annual Energy-Saving Smart Windows with Actively Controllable Passive Radiative Cooling and Multimode Heating Regulation.

Smart windows with radiative heat management capability using the sun and outer space as zero-energy thermodynamic resources have gained prominence, demonstrating a minimum carbon footprint. However, realizing on-demand thermal management throughout all seasons while reducing fossil energy consumption remains a formidable challenge. Herein, an energy-efficient smart window that enables actively tunable passive radiative cooling (PRC) and multimode heating regulation is demonstrated by integrating the emission-enhanced polymer-dispersed liquid crystal (SiO2@PRC PDLC) film and a low-emission layer deposited with carbon nanotubes. Specifically, this device can achieve a temperature close to the chamber interior ambient under solar irradiance of 700W m-2, as well as a temperature drop of 2.3°C at sunlight of 500W m-2, whose multistage PRC efficiency can be rapidly adjusted by a moderate voltage. Meanwhile, synchronous cooperation of passive radiative heating (PRH), solar heating (SH), and electric heating (EH) endows this smart window with the capability to handle complicated heating situations during cold weather. Energy simulation reveals the substantial superiority of this device in energy savings compared with single-layer SiO2@PRC PDLC, normal glass, and commercial low-E glass when applied in different climate zones. This work provides a feasible pathway for year-round thermal management, presenting a huge potential in energy-saving applications.

Quantum Switch as a Thermodynamic Resource in the Context of Passive States.

In recent years, many works have explored possible advantages of indefinite causal order, with the main focus on its controlled implementation known as quantum switch. In this paper, we tackle advantages in quantum thermodynamics, studying whether quantum switch is capable of activating a passive state, either alone or with extra resources (active control state) and/or operations (measurement of the control system). By disproving the first possibility and confirming the second one, we show that quantum switch is not a thermodynamic resource in the discussed context, though it can facilitate work extraction given external resources. We discuss our findings by considering specific examples: a qubit system subject to rotations around the x and y axes in the Bloch sphere, as well as general unitaries from the U(2) group; and the system as a quantum harmonic oscillator with displacement operators, as well as with a combination of displacement and squeeze operators.

A quantum engine in the BEC–BCS crossover

Heat engines convert thermal energy into mechanical work both in the classical and quantum regimes1. However, quantum theory offers genuine non-classical forms of energy, different from heat, which so far have not been exploited in cyclic engines. Here we experimentally realize a quantum many-body engine fuelled by the energy difference between fermionic and bosonic ensembles of ultracold particles that follows from the Pauli exclusion principle2. We employ a harmonically trapped superfluid gas of 6Li atoms close to a magnetic Feshbach resonance3 that allows us to effectively change the quantum statistics from Bose–Einstein to Fermi–Dirac, by tuning the gas between a Bose–Einstein condensate of bosonic molecules and a unitary Fermi gas (and back) through a magnetic field4–10. The quantum nature of such a Pauli engine is revealed by contrasting it with an engine in the classical thermal regime and with a purely interaction-driven device. We obtain a work output of several 106 vibrational quanta per cycle with an efficiency of up to 25%. Our findings establish quantum statistics as a useful thermodynamic resource for work production.

Parabolic Mirror‐Assisted Thermoelectric and Radiative Cooling System for Maximizing Power Generation Utilizing Solar and Outer Space Thermodynamic Resources

AbstractRadiative cooling technology is extensively researched as a green technology, leveraging outer space as a thermodynamic resource. Recently, integrating thermoelectric generators (TEGs) and radiative coolers (RCs) are proposed to generate power using the temperature difference between the ambient and the radiative cooler. However, current TEG‐RC systems only utilize one thermodynamic resource, resulting in suboptimal efficiency. It proposes a parabolic mirror‐assisted TEG‐RC system that fully utilizes both the Sun and outer space as thermodynamic resources. The system places the hot side of the TEG, covered by a solar absorber (SA), at the focal point of the parabolic mirror, while the RC is located on the cold side of the TEG. Theoretical and experimental results reveal the optimal ratio between the RC and SA sizes to balance the power mismatch between cooling and heating powers. It also finds that the number of TEG stacks significantly affects power generation efficiency and determines the optimal number. Outdoor measurements demonstrate exceptional power generation during the daytime, which is an unprecedented achievement. This study also demonstrates the further enhancement in power generation efficiency when the proposed system is integrated with concentrated solar cells instead of the SA.

A smart thermal-gated bilayer membrane for temperature-adaptive radiative cooling and solar heating

Due to the huge energy consumption of traditional cooling- and heating-based electricity, passive radiative cooling and solar heating with a minimum carbon footprint using the outer space and Sun as natural thermodynamic resources have attracted much attention. However, most passive devices are static and monofunctional, and cannot meet the practical requirements of dynamic cooling and heating under various conditions. Here, we demonstrate a smart thermal-gated (STG) bilayer membrane that enables fully automatic and temperature-adaptive radiative cooling and solar heating. Specifically, this device can switch from reflective to absorptive (white to black) in the solar wavelength with the reduction in optical scattering upon ambient temperature, corresponding to a sunlight reflectivity change from 0.962 to 0.059 when the temperature drops below ∼30 °C, whereas its mid-infrared emissivity remains at ∼0.95. Consequently, this STG membrane achieves a temperature of ∼5 °C below ambient (a key signature of radiative cooling) under direct sunlight (peak solar irradiance >900 W m−2) in summer and a solar heating power of ∼550 W m−2 in winter. Theoretical analysis reveals the substantial advantage of this switchable cooling/heating device in potential energy saving compared with cooling-only and heating-only strategies when widely used in different climates. It is expected that this work will pave a new pathway for designing temperature-adaptive devices with zero energy consumption and provide an innovative way to achieve sustainable energy.

EXERGY-BASED SUSTAINABILITY ANALYSIS OF FOOD PRODUCTION SYSTEMS

As the global population continues to grow, the sustainability of food production systems is increasingly critical, coupled with escalating environmental concerns. Traditional sustainability assessments primarily focus on resource consumption and waste generation, often overlooking the overall efficiency and quality of energy and matter flows within these systems. This comprehensive review paper explores the potential of the exergy concept as a holistic and comprehensive approach to assessing the sustainability of food production systems. Exergy analysis offers valuable insights into the thermodynamic efficiency, resource utilization, and environmental impacts of these systems. By incorporating exergy principles into sustainability assessments, researchers and policymakers can better understand the strengths, weaknesses, and opportunities for improvement in food production systems. This paper highlights key studies and applications that have utilized the exergy concept, discussing its benefits and limitations.

A Scalable Microstructure Photonic Coating Fabricated by Roll-to-Roll "Defects" for Daytime Subambient Passive Radiative Cooling.

The deep space's coldness (∼4 K) provides a ubiquitous and inexhaustible thermodynamic resource to suppress the cooling energy consumption. However, it is nontrivial to achieve subambient radiative cooling during daytime under strong direct sunlight, which requires rational and delicate photonic design for simultaneous high solar reflectivity (>94%) and thermal emissivity. A great challenge arises when trying to meet such strict photonic microstructure requirements while maintaining manufacturing scalability. Herein, we demonstrate a rapid, low-cost, template-free roll-to-roll method to fabricate spike microstructured photonic nanocomposite coatings with Al2O3 and TiO2 nanoparticles embedded that possess 96.0% of solar reflectivity and 97.0% of thermal emissivity. When facing direct sunlight in the spring of Chicago (average 699 W/m2 solar intensity), the coatings show a radiative cooling power of 39.1 W/m2. Combined with the coatings' superhydrophobic and contamination resistance merits, the potential 14.4% cooling energy-saving capability is numerically demonstrated across the United States.

Fermionic One-Body Entanglement as a Thermodynamic Resource.

There is ongoing controversy about whether a coherent superposition of the occupied states of two fermionic modes should be regarded entangled or not, that is, whether its intrinsic quantum correlations are operationally accessible and useful as a resource. This has been questioned on the basis that such an entanglement cannot be accessed by local operations on individual modes due to the parity superselection rule which constrains the set of physical observables. In other words, one cannot observe violations of Bell's inequality. Here, we show, however, that entanglement of a two-mode fermionic state can be used as a genuine quantum resource in open-system thermodynamic processes, enabling one to perform tasks forbidden for separable states. We thus demonstrate that quantum thermodynamics can shed light on the nature of fermionic entanglement and the operational meaning of the different notions used to define it.

Passive freezing desalination driven by radiative cooling

•Radiative cooling is used to passively freeze salt water, enabling its desalination •Two-stage desalination is demonstrated to purify water to drinking water standards •System models were validated against experiments and revealed ways to improve performance •Annual performance in a range of climate zones and thermodynamic limits is predicted Increasing water scarcity in the face of climate change has driven significant interest in finding low-carbon-intensity ways of generating fresh water from saline sources. Conventional membrane and thermal desalination techniques require large energy inputs that can become prohibitive as salinity increases. Alternatively, solar desalination is a well-developed passive evaporative approach but is limited seasonally and geographically by solar insolation. Here, we propose and demonstrate a passive approach to a more thermodynamically attractive phase change that can also enable desalination: freezing. We develop a system that uses passive radiative cooling to the ultimate heat sink, outer space, to freeze and desalinate salt water. We experimentally demonstrate the passive desalination of 37.3 g/L salt water to 1.88 g/L after two radiative cooling-driven freezing desalination stages with 50% recovery and 17.5 g/L salt water to 0.7 g/L with 65% recovery. Our results highlight the potential of harnessing untapped thermodynamic resources for water technologies. Increasing water scarcity in the face of climate change has driven significant interest in finding low-carbon-intensity ways of generating fresh water from saline sources. Conventional membrane and thermal desalination techniques require large energy inputs that can become prohibitive as salinity increases. Alternatively, solar desalination is a well-developed passive evaporative approach but is limited seasonally and geographically by solar insolation. Here, we propose and demonstrate a passive approach to a more thermodynamically attractive phase change that can also enable desalination: freezing. We develop a system that uses passive radiative cooling to the ultimate heat sink, outer space, to freeze and desalinate salt water. We experimentally demonstrate the passive desalination of 37.3 g/L salt water to 1.88 g/L after two radiative cooling-driven freezing desalination stages with 50% recovery and 17.5 g/L salt water to 0.7 g/L with 65% recovery. Our results highlight the potential of harnessing untapped thermodynamic resources for water technologies.

Thermodynamics of Quantum Switch Information Capacity Activation.

We address a new setting where the second law is under question: thermalizations in a quantum superposition of causal orders, enacted by the so-called quantum switch. This superposition has been shown to be associated with an increase in the communication capacity of the channels, yielding an apparent violation of the data-processing inequality and a possibility to separate hot from cold. We analyze the thermodynamics of this information capacity increasing process. We show how the information capacity increase is compatible with thermodynamics. We show that there may indeed be an information capacity increase for consecutive thermalizations obeying the first and second laws of thermodynamics if these are placed in an indefinite order and moreover that only a significantly bounded increase is possible. The increase comes at the cost of consuming a thermodynamic resource, the free energy of coherence associated with the switch.

A Perspective on the optical spectral design for passive solar heating and radiative cooling

Heating and cooling, as the basic requirements of human life, account for more than 28% of global energy consumption. To minimize carbon footprint and save energy, various strategies based on passive heating and cooling have attracted much attention. Typically, as the sun and outer space are the natural thermodynamic resources for renewable energy harvesting, passive solar heating and radiative cooling have been widely explored through a precise spectral design to effectively exploit solar energy and thermal radiation. In this Perspective, based on the previous works and principal development of passive solar heating and radiative cooling, the corresponding ideal spectral design under different temperature conditions is proposed and highlighted. As demonstrations, we present several examples of different optical spectral designs for realizing passive solar heating and radiative cooling to fit various scenarios. Finally, possible solutions to the current problems and the directions for future development are discussed.

Thermodynamic machine learning through maximum work production

Adaptive systems—such as a biological organism gaining survival advantage, an autonomous robot executing a functional task, or a motor protein transporting intracellular nutrients—must somehow embody relevant regularities and stochasticity in their environments to take full advantage of thermodynamic resources. Analogously, but in a purely computational realm, machine learning algorithms estimate models to capture predictable structure and identify irrelevant noise in training data. This happens through optimization of performance metrics, such as model likelihood. If such learning is physically implemented, is there a sense in which computational models estimated through machine learning are physically preferred? We introduce the thermodynamic principle that work production is the most relevant performance measure for an adaptive physical agent and compare the results to the maximum-likelihood principle that guides machine learning. Within the class of physical agents that most efficiently harvest energy from their environment, we demonstrate that an efficient agent’s model explicitly determines its architecture and how much useful work it harvests from the environment. We then show that selecting the maximum-work agent for given environmental data corresponds to finding the maximum-likelihood model. This establishes an equivalence between nonequilibrium thermodynamics and dynamic learning. In this way, work maximization emerges as an organizing principle that underlies learning in adaptive thermodynamic systems.

Radiative-cooling-based nighttime electricity generation with power density exceeding 100 mW/m2

SummaryThe outer space (3 K) represents an important thermodynamic resource. It has been known for decades that at nighttime, a sky-facing thermal emitter radiating strongly within the atmospheric transparency window (8–13 μm), can reach below the ambient temperature. In recent studies, thermoelectric generators were used to harness this temperature difference between the emitter and ambient to generate electricity. However, the demonstrated power density has been limited by parasitic thermal losses. Here we show that these parasitic losses can be reduced through thermal engineering. We present a simple model showing the optimum power density can be approached by controlling the relation between the emitter area and the thermal resistance of the thermoelectric generator. We show that the stacking of multiple thermoelectric generators is an effective way to approach this optimum. We experimentally demonstrate a generated electric power density >100 mW/m2, representing > 2-fold improvement over the previous results for nighttime radiative cooling.

Power Generation on Chips: Harvesting Energy From the Sun and Cold Space

AbstractEnvironmental energy source is abundant, inexhaustible, ubiquitous, and free. However, harvesting thermal energy from the environment to generate uninterrupted electricity is still challenging. Herein, a power device to simultaneously harvest energy from the sun and cold space based on a microfabricated thermoelectric generator (TEG) integrated with a solar absorber (SA) and radiative cooling emitter (RCE) is reported. Nano‐channel arrays structure is introduced in SA to achieve high broadband light absorption (≈96%) over the entire solar spectrum. Then, a typical RCE is fabricated to demonstrate the great potential of cooperating with SA to create a continuous temperature difference for thermal energy harvesting. Furthermore, a TEG sandwiched between SA and RCE can convert the thermal energy into electricity, which is proved by a chip‐integrated micro‐TEG experimentally. What is more, two self‐generation power devices are designed, and the power generation of the reverse structure demo device (r‐TEG) is 130% of the forward one (f‐TEG) in the daytime and 260% in the nighttime. The results demonstrate a renewable and sustainable thermodynamic green resource on chips for power generation independent of time and geographical restrictions, which is vital for promoting the sun and cold space as viable energy sources beyond traditional technologies.

Self-adaptive integration of photothermal and radiative cooling for continuous energy harvesting from the sun and outer space.

The sun (∼6,000 K) and outer space (∼3 K) are two significant renewable thermodynamic resources for human beings on Earth. The solar thermal conversion by photothermal (PT) and harvesting the coldness of outer space by radiative cooling (RC) have already attracted tremendous interest. However, most of the PT and RC approaches are static and monofunctional, which can only provide heating or cooling respectively under sunlight or darkness. Herein, a spectrally self-adaptive absorber/emitter (SSA/E) with strong solar absorption and switchable emissivity within the atmospheric window (i.e., 8 to 13 μm) was developed for the dynamic combination of PT and RC, corresponding to continuously efficient energy harvesting from the sun and rejecting energy to the universe. The as-fabricated SSA/E not only can be heated to ∼170 °C above ambient temperature under sunshine but also be cooled to 20 °C below ambient temperature, and thermal modeling captures the high energy harvesting efficiency of the SSA/E, enabling new technological capabilities.

Quantum Coherences and Classical Inhomogeneities as Equivalent Thermodynamics Resources.

Quantum energy coherences represent a thermodynamic resource, which can be exploited to extract energy from a thermal reservoir and deliver that energy as work. We argue that there exists a closely analogous classical thermodynamic resource, namely, energy-shell inhomogeneities in the phase space distribution of a system’s initial state. We compare the amount of work that can be obtained from quantum coherences with the amount that can be obtained from classical inhomogeneities, and find them to be equal in the semiclassical limit. We thus conclude that coherences do not provide a unique thermodynamic advantage of quantum systems over classical systems, in situations where a well-defined semiclassical correspondence exists.