Electron-photon Interaction Research Articles

Ab initio quantum approach to electron-hole exchange for semiconductors hosting Wannier excitons

We propose a quantum approach to ``electron-hole exchange,'' better named electron-hole pair exchange, that makes use of the second quantization formalism to describe the problem in terms of Bloch-state electron operators. This approach renders transparent the fact that such singular effect comes from interband Coulomb processes. We first show that, due to the sign change when turning from valence-electron destruction operator to hole creation operator, the interband Coulomb interaction only acts on spin-singlet electron-hole pairs, just like the interband electron-photon interaction, thereby making these spin-singlet pairs optically bright. We then show that, when written in terms of reciprocal lattice vectors ${\mathbf{G}}_{m}$, the singularity of the interband Coulomb scattering in the small wave-vector transfer limit entirely comes from the ${\mathbf{G}}_{m}=\mathbf{0}$ term, which renders its singular behavior easy to calculate. Comparison with the usual real-space formulation in which the singularity appears through a sum of ``long-range processes'' over all ${\mathbf{R}}_{\ensuremath{\ell}}\ensuremath{\ne}\mathbf{0}$ lattice vectors once more proves that periodic systems are easier to handle in terms of reciprocal vectors ${\mathbf{G}}_{m}$ than in terms of lattice vectors ${\mathbf{R}}_{\ensuremath{\ell}}$. Well-accepted consequences of the electron-hole exchange on excitons and polaritons are reconsidered and refuted for different major reasons.

Thermoelectric Rectification and Amplification in Interacting Quantum-Dot Circuit-Quantum-Electrodynamics Systems.

Thermoelectric rectification and amplification were investigated in an interacting quantum-dot circuit-quantum-electrodynamics system. By applying the Keldysh nonequilibrium Green's function approach, we studied the elastic (energy-conserving) and inelastic (energy-nonconserving) transport through a cavity-coupled quantum dot under the voltage biases in a wide spectrum of electron-electron and electron-photon interactions. While significant charge and Peltier rectification effects were found for strong light-matter interactions, the dependence on electron-electron interaction could be nonmonotonic and dramatic. Electron-electron interaction-enhanced transport was found under certain resonance conditions. These nontrivial interaction effects were found in both linear and nonlinear transport regimes, which manifested in charge and thermal currents, rectification effects, and the linear thermal transistor effect.

First principle calculation of the photocurrent in a short carbon nanotube: the effect of an external bias

We studied the transport properties of a short carbon nanotube between two different metal electrodes. Specifically, the photocurrents under a series of bias voltages are investigated. The calculations are completed within the non-equilibrium Green’s function method, where the photon–electron interaction is taken as a perturbation. The rule-of-thumb that a forward bias decreases while a reverse bias increases the photocurrent under the same illumination is verified. The first principle results demonstrate the characteristic of the Franz–Keldysh effect, where the photocurrent response edge shows a clear red-shift trend in electric fields along both axial directions. An obvious Stark splitting is observed when some reverse bias is applied to the system due to the huge field strength. In this short-channel situation, intrinsic nanotube states are strongly hybridized with metal electrode states, which results in dark current leakage and specific features such as a long tail and fluctuations in the photocurrent response.

Radiative Recombination Plasma Rate Coefficients for Multiply Charged Ions

Radiative recombination (RR) plasma rate coefficients are often applied to estimate electron densities and temperatures under quite different plasma conditions. Despite their frequent use, however, these rate coefficients are available only for selected (few-electron) ions and isoelectronic sequences, mainly because of the computational efforts required. To overcome this limitation, we report here a (relativistic) cascade model which helps compute fine-structure and shell-resolved as well as total RR plasma rate coefficients for many, if not most, elements of the periodic table. This model is based on Jac, the Jena Atomic Calculator, and supports studies on how the electron is captured in selected levels of the recombined ion, a relativistic (Maxwellian) electron distribution, or how the multipoles beyond the electric-dipole field in the electron-photon interaction affect the RR rate coefficients and, hence, the ionization and recombination dynamics of hot plasma. As a demonstration of this model, we compute, compare, and discuss different RR plasma rate coefficients for initially helium-like ions, with an emphasis especially on Fe24+ ions.

Electron‒Photon Interactions under the Size Limitation of the Conductivity in Single Semiconductor Quantum-Sized Particles in an Interelectrode Nanogap

Electron‒Photon Interactions under the Size Limitation of the Conductivity in Single Semiconductor Quantum-Sized Particles in an Interelectrode Nanogap

Phase-locked photon–electron interaction without a laser

Ultrafast photon–electron spectroscopy in electron microscopes commonly requires ultrafast laser setups. Photoemission from an engineered electron source is used to generate pulsed electrons, interacting with a sample excited by the laser pulse at a known time delay. Thus, developing an ultrafast electron microscope demands the exploitation of extrinsic laser excitations and complex synchronization schemes. Here we present an inverse approach to introduce internal radiation sources in an electron microscope based on cathodoluminescence spectroscopy. Our compact method is based on a sequential interaction of the electron beam with an electron-driven photon source and the investigated sample. Such a source in an electron microscope generates phase-locked photons that are mutually coherent with the near-field distribution of the swift electron. We confirm the mutual frequency and momentum-dependent correlation of the electron-driven photon source and sample radiation and determine a degree of mutual coherence of up to 27%. With this level of mutual coherence, we were able to perform spectral interferometry with an electron microscope. Our method has the advantage of being simple, compact and operating with continuous electron beams. It will open the door to local photon–electron correlation spectroscopy of quantum materials, single-photon systems and coherent exciton–polaritonic samples with nanometre resolution.

First-principles study on tuning electronic and optical properties in graphene rotation on h-BN

Graphene rotation on hexagonal boron nitride(h-BN) is of great significance in fundamental research and device exploration for its unique energy band structure, rich physical and chemical properties. Twisting angle technique of Graphene/h-BN heterojunction(G/h-BN) is considered as effective approach for modulating band and optoelectronic properties. In this work, G/h-BN heterojunction with different twist angles are discussed based on density functional theory and a critical angle of ∼13.17° is found which tends to rotate towards 21.79° or 7.34°. Band gap at the primary Dirac point is opened by 44 meV, and it changes from 0.7 meV to 7.1 meV when the rotation angle is twisted from 21.79° to 7.34°, which is related to the motion properties of carriers in different directions. Meanwhile, the optical properties of the twisting G/h-BN are very sensitive to the atom bonding. The calculated electron-photon interactions show that reflectivity and energy loss function have significant changes at different twist angles, indicates that the twisting angle can tuning the optical absorption spectrum and reflectivity.

Potential controlled redox cycling of 4-aminothiophenol by coupling plasmon mediated chemical reaction with electrochemical reaction

The plasmon-mediated chemical reaction (PMCR) is a promising new direction for photocatalysis. By harvesting light through photon-electron interactions using nanostructures of plasmonic metals, chemical reactions of immobilized molecules on the metal surface can be activated. As demonstrated in recent years, the electrode potential (E) applied to the metal surface also provides a unique means for electrosynthesis by changing the local electrostatic field and controlling the electron transfer and redistribution in the molecules immobilized on the electrode surface. Here, as a case study, we studied the E-modulated PMCR of 4-aminothiophenol (4-ATP) confined in the nano junction formed between the gold nanoparticle (AuNP) and gold nanoelectrode (AuNE) by using the time-resolved electrochemical-surface-enhanced Raman spectroscopy (EC-SERS), a powerful tool to track the chemical reaction in-situ on the plasmonic metal surfaces in solution. We demonstrated that the negative E can effectively suppress the plasmon-mediated photo-oxidation of 4-ATP to 4,4-dimercaptoazobenzene (DMAB) and meanwhile activate the EC reduction of DMAB to 4-ATP. We are able to use E to regulate the competition between photo-oxidation and EC reduction and achieve the redox cycling between 4-ATP and DMAB in continuous E cycles. By analyzing the E-modulated dynamic SERS signal changes, we also found the applied E could affect the SERS changes through two intertwined nonreaction and reaction mechanisms. This approach can improve our understanding of the photon-electron-molecule interactions and the interplay between PMCR and EC reactions in plasmonic molecular junctions.

Compton scattering driven by intense quantum light.

Compton scattering is a cornerstone of quantum physics, describing the fundamental electron-photon interaction. Inverse Compton scattering can create attosecond x-ray pulses by high-intensity lasers driving free electrons. So far, in all theory and experiments, the observables of Compton scattering and its generalizations could be described by treating the driving electromagnetic field classically. Motivated by advances in the generation of squeezed light with high intensity, we consider driving the Compton effect with nonclassical light. We develop a framework to describe the nonperturbative interaction of a charged particle with driving fields of an arbitrary quantum light state. We obtain analytical results for the Compton emission spectrum when driven by intense thermal and squeezed vacuum states, showing noticeably broader emission spectra relative to a classical drive, thus reaching higher emission frequencies for the same average intensity. We envision quantum light properties such as squeezing and entanglement as degrees of freedom to control various radiation phenomena.

Tailoring near-field-mediated photon electron interactions with light polarization

Inelastic interaction of free-electrons with optical near fields has recently attracted attention for manipulating and shaping free-electron wavepackets. Understanding the nature and the dependence of the inelastic cross section on the polarization of the optical near-field is important for both fundamental aspects and the development of new applications in quantum-sensitive measurements. Here, we investigate the effect of the polarization and the spatial profile of plasmonic near-field distributions on shaping free-electrons and controlling the energy transfer mechanisms, but also tailoring the electron recoil. We particularly show that polarization of the exciting light can be used as a control knop for disseminating the acceleration and deceleration path ways via the experienced electron recoil. We also demonstrate the possibility of tailoring the shape of the localized plasmons by incorporating specific arrangements of nanorods to enhance or hamper the transversal and longitudinal recoils of free-electrons. Our findings open up a route towards plasmonic near-fields-engineering for the coherent manipulation and control of slow electron beams for creating desired shapes of electron wavepackets.

Electron-photon interactions in the conditions of dimensional conductivity restrictions in semiconductor single quantum-size particles in interelectrodic nanogap

For quantum-size particles of the InSb, PbS, HgSe, CdSe semiconductors, a model of competition of dimensional quantum restrictions and blocking with a single-electron current and Coulomb restriction, as well as heating electrons with an electric field of the light wave, is proposed. This made it possible to explain the highly multiplicity (up to two orders of order) of a change in photoconductivity observed in conditions of tunnel conductivity, and in the conditions of the confinement --- the absence of inter-zone and inter-level photoconductivity. The resonant current peaks of quantum conductivity observed on the V-I characteristics when irritating with light of any wavelength (in the interval of 0.4-1.2 μm) are reset or shifted towards smaller voltage values. The energy minimum of quanta recorded in this case is estimated as 100 meV. The results can be useful in resolving issues of application in uncooled IR detectors, including single-photon registration. Keywords: Quantum-size particle, dimensional quantification, one-electron current, single-photon process, inter-zone and intra-zone transitions, tunnel conductivity, Coulomb restriction, quantum conductivity.

Photon angular distribution of radiative electron capture into high-Z projectiles: A brief review

With the revolutionary development in the design of heavy-ion cooler storage rings and detectors, increasing interest is being focused on ion-atom collisions, in which the projectiles with a velocity comparable to the speed of light and the electronic transitions in inner shells of high-[Formula: see text] ions are involved. For this purpose, a fundamental interaction mechanism between a photon and an atomic electron in the presence of a strong Coulomb field is reviewed from the perspective of radiative electron capture into highly-charged ions. This is followed by the discussions of photon-electron interactions beyond the dipole approximation, which can be unambiguously visible in the photon angular distributions. In addition, the interference between the leading electric dipole transition [Formula: see text] and the magnetic multipole transition [Formula: see text] for the case of Lyman-[Formula: see text] radiation in hydrogen-like projectiles is also discussed.

Orbital-angular-momentum fluorescence emission based on photon–electron interaction in a vortex field of an active optical fiber

Abstract We develop a model of interaction between photons and electrons in an active vortex field, which can generate a fluorescence spectrum with the characteristics of orbital angular momentum (OAM). In an active optical fiber, our findings generalize the notion of photon–electron interaction and point to a new kind of OAM-mode broad-spectrum light source, which could be interpreted in two processes: one microscopically is the excitation of OAM-carrying photons based on the photon–electron interaction; the other macroscopically is the emission and transmission of a donut-shaped fluorescence in a vortex field with a spiral phase wavefront in a ring-core active fiber. Here we present a straightforward experimental method that the emission of broad-spectrum fluorescence with an OAM feature is actualized and validated in a ring-core erbium-doped fiber. The spectrum has a broad spectral width up to 50 nm. Furthermore, four wavelengths are extracted from the fluorescence spectrum and superimposed with their corresponding Gaussian beams, from which the spiral-shaped interferograms of OAM modes in a broad spectrum are identified with high purity. The application of the OAM-based fluorescence light source may range from classical to quantum information technologies, and enable high-capacity communication, high-sensitivity sensing, high-resolution fluorescence imaging, etc.

The effect of Bi2O3/PbO substitution on physical, optical, structural, and gamma shielding properties of boro-tellurite glasses

Boro-tellurite glasses with molar compositions 60TeO2–20B2O3-(20-x)Bi2O3-xPbO, where x = 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 mol% were fabricated using a standard melt quenching technique and studied in term of their physical, optical, structural and gamma shielding properties. As PbO concentration increases from 0 to 10 mol% (Bi2O3 decreases), the density and molar volume of the present samples decrease from 6.08 to 5.93 gr/cm3 and 33.37 to 30.27 cm3/mol, respectively. The optical packing density increases from 71.91 to 72.67% as PbO is added to the network to substitute Bi2O3. With the increase of PbO concentration, the refractive index, molar refractivity, and ionic polarizability decrease from 1.9137 to 1.8306, 18.531 to 16.884 cm3, and 7.3534 to 6.7000 Å3, respectively. The percentage of [TeO3] (tp) and [TeO3+1] polyhedra in the glass network increase with the rise of PbO concentration. The gamma radiation shielding features were analyzed theoretically using Phy-X PSD software with photon energies varied between 0.015 and 15 MeV. For all glasses, the highest linear attenuation coefficient (LAC) values are observed at 0.015 MeV while the lowest values are observed around 5 MeV, a turning point at which pair production starts to dominate the gamma photon-electron interaction. At all photon energies, the LAC values decrease with the increase in PbO concentration (the decrease in Bi2O3). The LAC values at 0.015 MeV vary from 413.2183 to 12.4962 cm−1. At low photon energies (0.015–0.04 MeV), this compositional dependence is high. Above 0.04 MeV, this dependence is low. This LAC result suggests that adding Bi2O3 to the glasses is favorable for gamma shielding material as compared to PbO.

Resonant tunneling diodes in semiconductor microcavities: Modeling polaritonic features in the terahertz displacement current

We develop in this work a simple qualitative quantum electron transport model, in the strong light-matter coupling regime under dipole approximation, able to capture polaritonic signatures in the time-dependent electrical current. The effect of the quantized electromagnetic field in the displacement current of a resonant tunneling diode inside an optical cavity is analyzed. The original peaks of the bare electron transmission coefficient split into two new peaks due to the resonant electron-photon interaction, leading to coherent Rabi oscillations among the polaritonic states that are developed in the system in the strong coupling regime. This mimics known effects predicted by a Jaynes-Cummings model in closed systems, and shows how a full quantum treatment of electrons and electromagnetic fields may open interesting paths for engineering new THz electron devices. The computational burden involved in the multi-time measurements of THz currents is tackled by invoking a Bohmian description of the light-matter interaction. We also show that the traditional static transmission coefficient used to characterize DC quantum electron devices has to be substituted by a new displacement current coefficient in high-frequency AC scenarios.

Directional Chiral Optical Emission by Electron-Beam-Excited Nano-Antenna

Manipulating directional chiral optical emissions on a nanometer scale is significant for material science research. The electron-beam-excited nanoantenna provides a favorable platform to tune optical emissions at the deep subwavelength scale. Here we present an L-shaped electron-beam-excited nanoantenna (LENA) with two identical orthogonal arms. By selecting different electron-beam impacting sites on the LENA, either the left-handed circularly polarized (LCP) or the right-handed circularly polarized (RCP) emission can be excited. The LCP and RCP emissions possess different emission directionality, and the emission wavelength depends on the arm length of the LENA. Further, we show a combined nanoantenna with two LENAs of different arm lengths. Induced by the electron beam, LCP and RCP lights emit simultaneously from the nanoantenna with different wavelengths to different directions. This approach is suggested to be informative for investigating electron-photon interaction and electron-beam spectroscopy in nanophotonics.

Directional Chiral Optical Emission by Electron-Beam-Excited Nano-Antenna

Abstract Manipulating directional chiral optical emissions on a nanometer scale is significant for material science studies. The electron-beam-excited nanoantenna provides a favorable platform to tune optical emissions at the deep subwavelength scale. Here we present an L-shaped electron-beam-excited nanoantenna (LENA) with two identical orthogonal arms. By selecting different electron-beam impacting sites on the LENA, either the left-handed circularly polarized (LCP) or the right-handed circularly polarized (RCP) emission can be excited. The LCP and RCP emissions possess different emission directionality, and the emission wavelength depends on the arm length of the LENA. Further, we show a combined nanoantenna with two LENAs of different arm lengths. Induced by the electron beam, LCP and RCP lights emit simultaneously from the nanoantenna with different wavelengths to different directions. We suggest this approach is informative for investigating electron-photon interaction and electron-beam spectroscopy in nanophotonics.

Full counting statistics of the photocurrent through a double quantum dot embedded in a driven microwave resonator

Detection of single, itinerant microwave photons is an important functionality for emerging quantum technology applications as well as of fundamental interest in quantum thermodynamics experiments on heat transport. In a recent experiment [W. Khan et al., Nat. Commun. 12, 5130 (2021)], it was demonstrated that a double quantum dot (DQD) coupled to a microwave resonator can act as an efficient and continuous photodetector by converting an incoming stream of photons to an electrical photocurrent. In the experiment, average photon and electron flows were analyzed. Here we theoretically investigate, in the same system, the fluctuations of the photocurrent through the DQD for a coherent microwave drive of the resonator. We consider both the low frequency full counting statistics as well as the finite-frequency noise (FFN) of the photocurrent. Numerical results and analytical expressions in limiting cases are complemented by a mean-field approach neglecting dot-resonator correlations, providing a compelling and physically transparent picture of the photocurrent statistics. We find that for ideal, unity efficiency detection, the fluctuations of the charge current reproduce the Poisson statistics of the incoming photons, while the statistics for non-ideal detection is sub-Poissonian. Moreover, the FFN provides information of the system parameter dependence of detector short-time properties. Our results give novel insight into microwave photon-electron interactions in hybrid dot-resonator systems and provide guidance for further experiments on continuous detection of single microwave photons.

Silicon/graphene–ITO multiple heterojunctions and 1D PhC waveguide-based photodetection for mid-NIR IPE with high responsivity

A nanophotonic photodetector is proposed with a multi-heterojunction structure based on silicon–ITO (Indium Tin Oxide) slot waveguide covered with 2D (two-dimensional) graphene sheets. A heavily n-doped ITO layer covers the whole device and works as an electrode to reduce the light loss at the metal–graphene interfaces. Different waveguides are arranged to design a one-dimensional photonic crystal (1D PhC) and the slot is defined by creating a defect in it. The PhC provides strong confinement of light, increasing the light–matter interaction, and thus generating more electron–hole (e–h) pairs or charge carriers under light illumination. Moreover, the multiple heterojunctions enhance the e–h generation and help enhancing the transportation of charge carriers. As a result, high photocurrent, fast response across a large bandwidth, strong electron-photon interaction, and also enhancement of photocarrier multiplications can be achieved. The photodetector realizes a photoresponsivity beyond 0.6 A/W at around 1550 nm wavelength. From 0.5 V–2 V of the bias voltage, the difference between the photocurrent and the dark current for the device with the PhC is more than 5 times that for the device without the PhC. Moreover, a 25 Gbit/s non-return to zero optical transmission is measured at 10 km transmission. The proposed device has diverse applications such as telecommunications, optical computing, interconnects, laser radar, lab-on-chip for sensing, and on-chip quantum photonics.

Reduced-density-matrix-based ab initio cavity quantum electrodynamics

A reduced-density-matrix (RDM)-based approach to {\em ab initio} cavity quantum electrodynamics (QED) is developed. The expectation value of the Pauli-Fierz Hamiltonian is expressed in terms of one- and two-body electronic and photonic RDMs, and the elements of these RDMs are optimized directly in polynomial time by semidefinite programming techniques, without knowledge of the full wave function. QED generalizations of important ensemble $N$-representability conditions are derived and enforced in this procedure. The resulting approach is applied to the description of classic ground-state strong electron correlation problems, augmented by the presence of ultrastrong light-matter coupling. First, we assess cavity-induced changes to the singlet-triplet energy gap of the linear oligoacene series; for a heptacene molecule, this gap can change by as much as 1.9 kcal mol$^{-1}$ (or 15\%) when the molecule is aligned along the cavity mode polarization axis. We also explore the metal-insulator transition in linear hydrogen chains and demonstrate that strong electron-photon interactions increase the insulating character of these systems under all coupling strengths considered.