Thermal Photons Research Articles

Nanoengineered nickel-based ultrathin metamaterial absorber for the visible and short-infrared spectrum

Nanostructured-based broadband perfect absorbers are of great interest in a wide range of applications, including spectroscopy, energy harvesting, and thermal photonics, etc. Here, a planar square meta-ring of nickel (Ni) is presented, which has the potential to absorb a large operational wavelength starting from 400 nm to 3000 nm. The proposed device model comprises a configuration of three layers with a top and bottom metal of Ni and a middle dielectric layer of aluminium nitride (AlN). The designed square ring metamaterial absorber (SRMMA) can attain an average absorption value of more than 90% over a large waveband from 400-3000 nm. Moreover, it can also maintain its absorption value up to 70% for oblique incident angles for both the wave polarization cases (TE and TM). Furthermore, it also exhibits the polarization-insensitive absorption response under the influence of different polarization angles, which is attributed to the four-fold symmetry in the geometry of the square meta-ring. Furthermore, our SRMMA also reduces fabrication complexity and cost due to its simplified design architecture. These promising features of the proposed SRMMA may have widespread applications in solar energy harvesting, thermal emission, and other optoelectronic devices.

Quantum thermal field fluctuation induced corrections to the interaction between two ground-state atoms

We generalize the formalism proposed by Dalibard, Dupont-Roc, and Cohen-Tannoudji (the DDC formalism) in the fourth order for two atoms in interaction with scalar fields in vacuum to a thermal bath at finite temperature T, and then calculate the interatomic interaction energy of two ground-state atoms separately in terms of the contributions of thermal fluctuations and the radiation reaction of the atoms and analyze in detail the thermal corrections to the van der Waals and Casimir–Polder interactions. We discover a particular region, i.e. with L, β and λ denoting the interatomic separation, the wavelength of thermal photons and the transition wavelength of the atoms respectively, where the thermal corrections remarkably render the van der Waals force, which is usually attractive, repulsive, leading to an interesting crossover phenomenon of the interatomic interaction from attractive to repulsive as the temperature increases. We also find that the thermal corrections cause significant changes to the Casimir–Polder force when the temperature is sufficiently high, resulting in an attractive force proportional to TL −3 in the λ ≪ β ≪ L region, and a force that can be either attractive or repulsive and even vanishing in the β ≪ λ ≪ L region depending on the interatomic separation.

Design of a gradient epsilon-near-zero refractory metamaterial with temperature-insensitive broadband directional emission

Gradient epsilon-near-zero (ENZ) metamaterials offer broadband directional control over thermal emission. Implementing this approach using materials that remain stable in harsh thermo-chemical environments would allow it to be broadly deployed in thermal photonics. Our prior work showed that heterostructures of rock salt MgO and perovskite BaZr0.5Hf0.5O3 (BZHO) are stable up to 1100 °C in air, with no discernible intermixing. In this work, we design a gradient ENZ metamaterial made from three lattice-matched refractory oxides: MgO, BZHO, and NiO. The miscibility of MgO and NiO makes it possible to linearly vary the ENZ frequency of the metamaterial layers. BZHO is used as a thin, interlayer diffusion barrier. We model the emissivity of our gradient ENZ metamaterial at 25 and 1000 °C to demonstrate that the spectral bandwidth of directional emission is preserved at high temperatures despite changes in the optical properties of each material. Finally, we discuss practical fabrication challenges associated with the back reflector and offer potential solutions based on advancements in hetero-integration. Overall, this work shows a pathway toward gradient ENZ metamaterials with ultrahigh-temperature stability.

Metal oxide/2D layered TMDs composites for H2 evolution reaction via photocatalytic water splitting – A mini review

H2 plays a crucial role in the energy demanding economy which makes it essential to develop materials for its production by water splitting using earth abundant resources. Water is split into H2 and O2 by using thermal energy-thermolysis, electrical energy-electrolysis, or photon energy-photocatalysis. Among them, the semiconductor based photocatalytic water splitting is a simple technique to produce H2 fuel utilizing water and solar energy. Several factors such as band gap alignment, light absorption ability, morphology, and stability influence the efficiency of the photocatalyst. The traditional noble metal and metal oxide based catalyst has some practical difficulty in achieving the overall water splitting, due to the fast recombination of photogenerated charges. This made researchers explore the 2D transition metal dichalcogenides as photocatalyst for H2 production by water splitting owing to their large surface area, excessive adsorption catalytic sites, high carrier mobility and short carrier migration distance. In this regard, the discovery of MoS2 especially paved the way to a new class of 2D transition metal dichalcogenides (TMDs) used as co-catalyst in photocatalytic water splitting. This new class of TMDs played a vital role to enhance the photocatalytic water splitting by acting as a medium for fast charge transfer thereby retarding the recombination of the photogenerated holes and electrons. The tunable band gap, wide absorption ranges, and semimetallic to semiconducting properties of the TMDs have attracted great interest as materials for photocatalysis. Further, the construction of metal oxide/TMDs heterostructures enhanced its efficiency by forming a Z-scheme heterojunction facilitating the mobility and separation of photogenerated charges. In this review, we attempt to sum up the different metal oxide/TMDs heterostructure composite based photocatalysts for efficient H2 production. The reason behind the enhancement of H2 production and the mechanisms are viewed very concisely for the constructed heterostructure composites. Further we also highlight some challenges, drawbacks, and the future perspective for the effective photocatalytic water splitting.

Heat diffusion in nanoparticle systems via near-field thermal photons

Near-field radiative heat transfer (NFRHT) in system of nanoparticles is significantly different from that in the far field regime due to the photon tunneling effect and the complex many body interactions, which is not well understood yet till now. The existing particle-scale NFRHT theory cannot be applied to systems of large number of particles directly, due to the enormous computational efforts. To fill the gap, we derived a continuum-scale normal-diffusion type governing equation starting from the particle-scale fluctuational electrodynamics formulation. The radiative thermal conductivity tensor is rigorously derived as a coefficient of the diffusion term. An additional convection-like term appears naturally in the governing equation for system with asymmetric distribution of particles, indicating a violation of the Fourier's law. The derived new formula of radiative thermal conductivity tensor is demonstrated to be useful and powerful in calculating the radiative thermal conductivity in arbitrary multi-dimensional particulate systems with many-body interactions.

Radiative heat transfer in a low-symmetry Bravais crystal

Over the last few years, broken symmetry within crystals has attracted extensive attention since it can improve the control of light propagation. In particular, low-symmetry Bravais crystal can support shear polaritons which has great potential in thermal photonics. In this work, we report a twist-induced near-field thermal control system based on the low-symmetry Bravais crystal medium (\b{eta}-Ga2O3). The near-field thermal radiation (NFTR) between such crystal slabs is nearly four orders of magnitude larger than the blackbody limit, exceeding the NFTR from other traditional dielectric materials. Moreover, we show that this crystal can serve as an excellent platform for twist-induced near-field thermal control. Due to the intrinsic shear effect, the twist-induced modulation supported by low-symmetry Bravais crystal exceeds that by high-symmetry crystal. We further clarify how the shear effect affects the twist-induced thermal-radiation modulation supported by hyperbolic and elliptical polaritons and show that the shear effect significantly enhances the twist-induced thermal control induced by the elliptical polariton mode. These results open new directions for thermal-radiation control in low-symmetry materials, including geological minerals, common oxides, and organic crystals.

Dynamics of a dispersively coupled transmon qubit in the presence of a noise source embedded in the control line

We describe transmon qubit dynamics in the presence of noise introduced by an impedance-matched resistor ($50\,\mathrm{\Omega}$) that is embedded in the qubit control line. To obtain the time evolution, we rigorously derive the circuit Hamiltonian of the qubit, readout resonator and resistor by describing the latter as an infinite collection of bosonic modes through the Caldeira-Leggett model. Starting from this Jaynes-Cummings Hamiltonian with inductive coupling to the remote bath comprised of the resistor, we consistently obtain the Lindblad master equation for the qubit and resonator in the dispersive regime. We exploit the underlying symmetries of the master equation to transform the Liouvillian superoperator into a block diagonal matrix. The block diagonalization method reveals that the rate of exponential decoherence of the qubit is well-captured by the slowest decaying eigenmode of a single block of the Liouvillian superoperator, which can be easily computed. The model captures the often used dispersive strong limit approximation of the qubit decoherence rate being linearly proportional to the number of thermal photons in the readout resonator but predicts remarkably better decoherence rates when the dissipation rate of the resonator is increased beyond the dispersive strong regime. Our work provides a full quantitative description of the contribution to the qubit decoherence rate coming from the control line in chips that are currently employed in circuit QED laboratories, and suggests different possible ways to reduce this source of noise.

Aligned channel Gelatin@nanoGraphite aerogel supported form-stable phase change materials for solar-thermal energy conversion and storage

To overcome the poor shape stability, low thermal conductivity, and weak photo response of phase change materials (PCMs), we designed a kind of Gelatin@nanoGraphite aerogel with aligned channel structure of graphite nanosheets and a new type of stable Paraffin/Gelatin@nanoGraphite composite PCMs was fabricated in this work. The graphite nanosheets were used as thermal conduction and photon absorption fillers. The microstructure, thermal conductivity, thermal stability, and solar-thermal conversion of the composite PCMs have been investigated. The results show that the rich porosity of the prepared Gelatin@nanoGraphite aerogel effectively loads a large amount of paraffin wax (>93.2 wt%). Meanwhile, the composite PCMs had anisotropic solar-thermal conversion and thermal conductivity (radial 3.75 and axial 2.59 W/(m·K)), high melting enthalpy (>146.4 J/g), and excellent phase change cycle and shape stability. This material has intensive application prospects in the fields of building energy saving, human body hyperthermia and solar energy collection system.

Radiative hadronization: Photon emission at hadronization from quark-gluon plasma

We investigate photon emission at the hadronization stage from a quark-gluon plasma created in relativistic heavy-ion collisions. A recombination-model picture suggests that a quark and an antiquark bind into a meson state in hadronization, which would apparently violate the energy conservation if there is nothing else involved. We consider here a hadronization process where the recombination accompanies a photon emission. This is an analog of the "{\it radiative recombination}" known in plasma physics, such as $e^- + p^+ \to {\rm H}^0 +\gamma$, which occurs when an electromagnetic plasma goes back to a neutral atomic gas. The "radiative hadronization" picture will bring about (i) an enhancement of the photon yield, (ii) significant flow of photons similar to that of hadrons, and (iii) the photon transverse momentum ($p_T$) distribution with a thermal profile whose effective temperature is given by blue-shifted temperature of quarks. Here as a simplest and phenomenological realization of the radiative hadronization, we modify the recombination model to involve a photon emission and evaluate the photon yield with this modified model. Adding this contribution to the direct photon yield along with thermal photon contribution calculated with a hydrodynamic model and a parametrized contribution of prompt photons, we study the $p_T$ spectrum and elliptic flow of the photons produced in heavy-ion collisions at RHIC and LHC energies.

Photon emissivity of the quark-gluon plasma: A lattice QCD analysis of the transverse channel

We present results for the thermal photon emissivity of the quark-gluon plasma derived from spatially transverse vector correlators computed in lattice QCD at a temperature of 250 MeV. The analysis of the spectral functions, performed at fixed spatial momentum, is based on continuum-extrapolated correlators obtained with two flavours of dynamical Wilson fermions. We compare the next-to-leading order perturbative QCD correlators, as well as the ${\cal N}=4$ supersymmetric Yang-Mills correlators at infinite coupling, to the correlators from lattice QCD and find them to lie within $\sim10\%$ of each other. We then refine the comparison, performing it at the level of filtered spectral functions obtained model-independently via the Backus-Gilbert method. Motivated by these studies, for frequencies $\omega\lesssim2.5\,$GeV we use fit ans\"atze to the spectral functions that perform well when applied to mock data generated from the NLO QCD or from the strongly-coupled SYM spectral functions, while the high-frequency part, $\omega\gtrsim 2.5\,$GeV, is matched to NLO QCD. We compare our results for the photon emissivity to our previous analysis of a different vector channel at the same temperature. We obtain the most stringent constraint at photon momenta around $k\simeq0.8\,$GeV, for which we find a differential photon emission rate per unit volume of $d\Gamma_\gamma/d^3k = (\alpha_{\rm em}/(\exp(k/T)-1))\times (2.2 \pm 0.8 ) \times 10^{-3}\,{\rm GeV}$.

Nonreciprocal Thermal Photonics for Energy Conversion and Radiative Heat Transfer

Nonreciprocal thermal photonics is an emerging topic in thermal radiation control. Recent advances in using this approach for energy harvesting, thermal management, and even communication have stimulated substantial interest in the subject. The authors review recent developments, challenges, and opportunities in the unidirectional transfer of heat energy via light, to provide a snapshot of the current status of the field, and to advance future research in it.

Effect of the film thickness on electron stimulated desorption yield from Ti-Zr-V coating

With the benefits of evenly distributed pumping, low thermal outgassing rate and low photon-/electron-/ion stimulated desorption yields, non-evaporable getter (NEG) coating has been widely used in particle accelerators for many years. Our earlier work has demonstrated the different thickness of Ti-Zr-V coating in the range of 0.1–1 μm affects its pumping properties. In this study, the electron stimulated desorption (ESD) yields were studied for Ti-Zr-V coating deposited from a twisted target with its thickness less than 0.5 μm, while an uncoated sample was also measured as a reference. The ESD yields for H2, CH4, CO and CO2 were measured as a function of electron accumulated dose up to ∼2 × 1024 e-/m2 followed bakeout/activation by heating to 80, 120, 140, 180 and 250°C. After each ESD experiment the samples were full saturated with a mix of H2, CO and CO2. Both NEG coated samples demonstrate lower values in comparison to the uncoated one after heating/activation to temperatures up to 180°C for H2, up to 250°C for CH4, up to 140°C for CO and 120°C for CO2. The activation to 140°C is the most efficient way to reach lower pressure and avoid quick aging of the NEG coating. The thinner NEG coating provides a significantly lower ESD yield in comparison to the thicker one only after activation to 180°C, while their ESD yields are almost identical for each gas at the lower temperature.

Photon tunneling reconstitution in black phosphorus/ hBN heterostructure

Excitation of hybrid modes constituted by different material-supported polaritons is a common way to enhance the near-field radiative energy transport, which has fascinating promise in applications of thermal photonics. Here, we investigate near--field thermal radiation mechanisms in heterostructure composed of $h\mathrm{BN}$ film and black phosphorus single layer. The results show that this heterostructured system can give rise to a remarkable enhancement for photon tunneling, outperforming the near-field thermal radiation properties of its building blocks, as well as some other representative heterostructures. Moreover, we find that the anisotropic hybrid effect can induce a remarkable topological reconstitution of polaritons for $h\mathrm{BN}$ film and black phosphorus, forming a novel anisotropic hybrid polaritons. Notably, such hybrid modes show significant topological differences compared to $h\mathrm{BN}$ film and black phosphorus in the type-I Reststrahlen band due to the anisotropic anticrossing hybridization effect. Lastly, we systematically analyze the evolution of such hybrid polariton modes as a function of $h\mathrm{BN}$ film thickness and the corresponding influence on radiative properties of the heterostructure. This work may benefit the applications of near-field energy harvesting and radiative cooling based on hybrid polaritons in anisotropic two-dimensional material and hyperbolic film.

Continuous variable quantum discord in a cavity electrooptical down-conversion quantum system

In this paper, we explore continuous variable quantum discord for the stationary microwave–optical output fields in an electrooptical system. We drive the covariance matrix of the system using the quantum Langevin equations for the intera-cavity microwave and optical modes. Employing the input–output theory, we obtained the output microwave and optical resonator variables in the Fourier frequency domain. The properties of the Gaussian quantum discord with respect to electrooptical cooperativity, the normalized cavity wave guides for microwave and optical resonators, and the thermal mean photon number for microwave and optical modes have been analyzed. Henceforth, we obtained that the Gaussian quantum discord can be enhanced by increasing the electrooptical cooperativity and microwave and optical wave guides. The thermal mean photon numbers of the microwave and optical modes have reduction effects on the Gaussian quantum discord.

Counting statistics of energy transport across squeezed thermal reservoirs

A general formalism for computing the full counting statistics of energy exchanged between 'N' squeezed thermal photon reservoirs weakly coupled to a cavity with 'M' photon modes is presented. The formalism is based on the two-point measurement scheme and is applied to two simple special cases, the relaxation dynamics of a single mode cavity in contact with a single squeezed thermal photon reservoir and the steady-state energy transport between two squeezed thermal photon reservoirs coupled to a single cavity mode. Using analytical results, it is found that the short time statistics is significantly affected by noncommutivity of the initial energy measurements with the reservoirs squeezed states, and may lead to negative probabilities if not accounted properly. Furthermore, it is found that for the single reservoir setup, generically there is no transient or steady-state fluctuation theorems for energy transport. In contrast, for the two reservoir case, although there is no generic transient fluctuation theorem, steady-state fluctuation theorem with a non-universal affinity is found to be valid. Statistics of energy currents are further discussed.

Statistical thermodynamics approach for the available work transported by particle fluxes

The theory covers cases when the exergy concept is not fully relevant. An indicator called work content factor is used to quantify the proportion of available work in a given amount of energy. General expressions have been obtained for the flux of available work transported by particles, the rate of work deficiency and the work content factor. More specific results have been obtained for the work content factor of the low-speed and ultra-relativistic particle fluxes, respectively, by using several assumptions concerning the number of energy states, the mean occupation number of the energy states, the entropy and the module and direction of the particles speed. The theory includes extraction of work from particle fluxes governed by classical kinetic theory and heat as particular cases and has been applied to fluxes of fermions (electrons) and bosons (Helium-4) in both the low-speed and ultra-relativistic case. It has been shown that the emission of thermal photons is several orders of magnitude lower than the stimulated particle emission by the primary work extractor. As a result, a unique expression of the work content factor of the ultra-relativistic particle fluxes has been obtained for both fermions and bosons while another expression has been derived for low-speed fermions and bosons. Generally, the work content factor decreases by increasing the temperature Tc of the primary work extractor. In some cases, at large values of Tc and small values of the average directional factor of the source of particle, work cannot be extracted from the energy of the particle flux.

Enhancement and Manipulation of Near-Field Thermal Radiation Using Hybrid Hyperbolic Polaritons

Owing to a high electromagnetic confinement and a strong photonic density of states, hyperbolic surface plasmon polaritons (HSPPs) provide a fascinating promise for applications in thermal photonics. In this work, we theoretically predict a possibility for the improvement of the near-field radiative heat transfer on the basis of tailoring the electromagnetic state of hyperbolic metasurfaces by the uniaxial hyperbolic substrate. By using the photonic tunneling coefficient and the polaritons dispersion, we present a comprehensive study of the hybrid effect of the hyperbolic substrate on HSPPs. We find that due to the hybrid effect of the hyperbolic substrate, the anisotropy surface state of hyperbolic metasurfaces would undergo significant deformations and even topological transition. Moreover, we systematically exhibit the evolution of such hybrid hyperbolic mode with different thicknesses of the hyperbolic substrate and analyze the thickness effect on radiative properties of the hybrid system. It is shown that the resulting heat transfer with the assistance of the hybrid hyperbolic mode by optimizing the substrate parameters is many times stronger than that of monolayer hyperbolic metasurface at the same vacuum gap. Taken together, our results provide a platform to tailor 2D hyperbolic plasmons as a potential strategy toward passive or active control of the near-field heat transfer, and the hybrid hyperbolic mode presented here may facilitate the system design for near-field energy harvesting, thermal imaging, and radiative cooling applications.

Continuous variable quantum teleportation of a thermal state in a thermal environment

The analytical formula for the fidelity of teleportation from Alice to Bob of a thermal state used as an input state is derived using the characteristic function approach. As a resource state it is used a continuous-variable two-mode bosonic state shared between Alice and Bob and the system is placed in a contact with a general environment. The quantum fidelity depends on the average thermal photon number of the input sate and on the parameters of the resource state and environment. In order to evaluate the parameters required for a successful quantum teleportation of a thermal state we estimate the evolution of the entanglement and fidelity of teleportation in the case when Alice and Bob share an initial squeezed thermal state in contact with a thermal bath. We work in the framework of the theory of open quantum systems based on completely positive dynamical semigroups and we use the Gorini–Kossakowski–Lindblad–Sudarshan master equation in order to describe the evolution of the system. The conditions for a successful quantum teleportation are the fidelity of teleportation larger than the threshold value of the classical fidelity of teleportation and entanglement present in the resource state. In order to assure the fulfillment of these conditions it is necessary to select the time of teleportation and to adjust the parameters characterizing the system (squeezing between the modes of the resource state, their average numbers of thermal photons and frequencies), and the temperature of the thermal reservoir. It is shown that in similar physical conditions, the fidelity of teleportation of the thermal states is larger than that one for a coherent state.

Simple way to incorporate loss when modeling multimode-entangled-state generation

We show that the light generated via spontaneous four-wave mixing or parametric down conversion in multiple, coupled, lossy cavities is a multimode squeezed thermal state. Requiring this state to be the solution of the Lindblad master equation results in a set of coupled first-order differential equations for the time-dependent squeezing parameters and thermal photon numbers of the state. The benefit of this semianalytic approach is that the number of coupled equations scales linearly with the number of modes and is independent of the number of photons generated. With this analytic form of the state, correlation variances are easily expressed as analytic functions of the time-dependent mode parameters. Thus, our solution makes it computationally tractable and relatively straightforward to calculate the generation and evolution of multimode entangled states in multiple coupled, lossy cavities, even when there are a large number of modes and/or photons.

GeV Signatures of Short Gamma-Ray Bursts in Active Galactic Nuclei

The joint detection of gravitational waves and the gamma-ray counterpart of a binary neutron star merger event, GW170817, unambiguously validates the connection between short gamma-ray bursts and compact binary object (CBO) mergers. We focus on a special scenario where short gamma-ray bursts produced by CBO mergers are embedded in disks of active galactic nuclei (AGNs), and we investigate the γ-ray emission produced in the internal dissipation region via synchrotron, synchrotron self-Compton, and external inverse Compton (EIC) processes. In this scenario, isotropic thermal photons from the AGN disks contribute to the EIC component. We show that a low-density cavity can be formed in the migration traps, leading to the embedded mergers producing successful GRB jets. We find that the EIC component would dominate the GeV emission for typical CBO mergers with an isotropic-equivalent luminosity of L j,iso = 1048.5 erg s−1 that are located close to the central supermassive black hole. Considering a long-lasting jet of duration T dur ∼ 102–103 s, we find that the future Cherenkov Telescope Array (CTA) will be able to detect its 25–100 GeV emission out to a redshift z = 1.0. In the optimistic case, it is possible to detect the on-axis extended emission simultaneously with GWs within one decade using MAGIC, H.E.S.S., VERITAS, CTA, and LHAASO-WCDA. Early diagnosis of prompt emissions with Fermi-GBM and HAWC can provide valuable directional information for the follow-up observations.