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Sol-Gel Synthesis and Spectral Characterizations of (35-x)B2O3-65Bi2O3-x Fe2O3 Glass System
摘要： Sol-gel technique was used to prepare glasses of the (35-x)B2O3-65Bi2O3-x Fe2O3 (0.1≤ x ≤ 0.4) system (A1-A4: x = 0.1, 0.2, 0.3, 0.4). The local structure and symmetry around trivalent iron were determined by studying X-band powder EPR spectra at room temperature. The EPR spectra of trivalent iron in glass samples are characterized by a more intense line at g = 4.2 and a less intense line at g = 2.0. The EPR line at g = 4.2 is attributed to trivalent iron in rhombic octahedral environment. The line at g = 2.0 is because of two or more trivalent iron coupling through dipole-dipole interactions in distorted octahedral symmetry. The intensity of EPR lines is dependent of Fe2O3 content in the glass samples. At higher concentration of Fe2O3, EPR line at g = 4.2 is less intense whereas the line at g = 2.0 is more intense which is ascribed to the formation of clusters of trivalent iron. The electronic spectra of glass samples show two broad bands corresponding to d-d transition in the range 410-450 nm and in the range 530-570 nm, respectively which are assigned to trivalent iron in distorted octahedral environment.
关键词： Glass samples,Dipole-dipole interaction,Electronic spectra,Sol-gel technique
更新于2025-09-19 17:15:36
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Coherence turned on by incoherent light
摘要： One of the most pertinent problems in the debate on non-trivial quantum effects in biology concerns natural photosynthesis. Since sunlight is composed of thermal photons, it was argued to be unable to induce quantum coherence in matter, and that quantum mechanics is therefore irrelevant for the dynamical processes following photoabsorption. Our present analysis of a toy 'molecular aggregate'—composed of two dipole–dipole interacting two-level atoms treated as an open quantum system—however shows that incoherent excitations indeed can trigger persistent, coherent dynamics in both the site and the exciton bases: we demonstrate that collective decay processes induced by the dipole–dipole interactions create coherent intermolecular transport—regardless of the coherence properties of the incoming radiation. Our analysis shows that the steady state coherence is mediated by the population imbalance between the molecules and, therefore, increases with the energy difference between the two-level atoms. Our results establish the importance of collective decay processes in the study of ultrafast photophysics, and especially their potential role to generate stationary coherence in incoherently driven quantum transport.
关键词： molecular aggregate,energy transfer,coherence,dipole–dipole interaction,thermal photons
更新于2025-09-19 17:15:36
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Improving photon antibunching with two dipole-coupled atoms in whispering-gallery-mode microresonators
摘要： In the two-atom or multiatom system, the atoms can interact with each other through exchange of virtual photon. This kind of energy exchange is often referred as the dipole-dipole interaction (DDI). Here we consider this DDI system consisting of a pair of two-level atoms strongly coupled with a bimodal whispering-gallery-mode (WGM) microresonator which is driven by an external laser field. Our aim is to explore the photon correlation characteristics of the proposed architecture using realistic experimental parameter values. We compare in detail the quality of photon antibunching (i.e., the smallness of the second-order correlation function) from three involved configurations in cavity quantum electrodynamics (QED): (i) only one two-level atom, (ii) two far apart two-level atoms without DDI, and (iii) two DDI (dipole-coupled) two-level atoms are respectively coupled to the driven WGM microresonator through the evanescent field. We clearly show that the DDI between both atoms can distinctly enhance the photon antibunching even in the weak-coupling regime in configuration (iii) with feature-rich line shapes. We also find that the photon antibunching can be modulated by properly adjusting the atom-cavity coupling strength. In addition, we display that this strong photon antibunching is robust against the cooperative atomic decay. Our DDI-based cavity QED scheme may provide an alternative way to the construction of integrated on-chip single-photon sources.
关键词： photon antibunching,whispering-gallery-mode microresonators,single-photon sources,dipole-dipole interaction,cavity quantum electrodynamics
更新于2025-09-19 17:13:59
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Laser-induced self-assembly of quantum dots: Deterministic case versus brownian case
摘要： The process of aggregation of two colloidal quantum dots in the field of quasiresonant laser radiation is investigated via computer simulation. The cases of either completely deterministic movement of particles or the movement with the account for random forces are considered. The conditions of pair formation are determined in dependence on initial interparticle distance, on laser wavelength, and on their initial orientation with respect to polarization plane of laser radiation. It is shown that despite velocity of thermal motion dominates over the velocity of directional diffusion of quantum dots, the account for random forces weakly influences on the probability of pair formation, the latter being close to results obtained in the deterministic case. The reason for this weak influence of Brownian movement is the resonant increase of electrodynamics attraction force during certain time interval within the laser pulse.
关键词： Self-assembly of nanostructures,Laser field,Dipole-dipole interaction,Brownian dynamics
更新于2025-09-19 17:13:59
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Dynamics of Quantum States in a System of 3 Quantum Dots with Dipole-Dipole Interaction
摘要： We present the results of simulation of the dynamics of a 3 quantum dot array by means of numerical solution of the von Neumann equation. The trace over the states of phonon bath was taken by Feynman path integral numerical calculation. It is shown that simplistic system of 3 quantum dots with common phonon bath can implement XOR logic operation. The results of our model can be applied to the development of different quantum simulators, quantum gates, and quantum neural networks implemented in arrays of quantum dots.
关键词： Feynman path integral,quantum neural networks,dipole-dipole interaction,quantum dots,von Neumann equation
更新于2025-09-16 10:30:52
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Subradiance dynamics in a singly excited chirally coupled atomic chain
摘要： We investigate theoretically the subradiance dynamics in a nonreciprocal chirally coupled atomic chain, in which infinite-range dipole-dipole interaction emerges in the dissipation. We find that super- and subradiance are both present in the dissipation process following single-photon excitation, and the decay dynamics shows burst emissions from uniform initial excitations, which reflects the influence of atomic ordering on the propagation of light-induced atom-atom correlations. By tuning the nonreciprocal couplings in the chirally coupled atomic system, we show that the subradiance dynamics can be greatly modified. We further study the effect of atomic local disorder and find the occurrence of plateaus on the decay curve dependent on the defect locations, as well as persistent localized excitations induced by disorder. We also discuss the effect of imperfections of systems on the subradiance dynamics. Our results show rich opportunities in the chirally coupled system toward photon storage and routing.
关键词： subradiance,chiral coupling,photon storage,dipole-dipole interaction,atomic chain
更新于2025-09-16 10:30:52
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Entanglement versus cooling in the system of a driven pair of two-level qubits longitudinally coupled with a boson mode field
摘要： The relationship among the entanglement creation within coherently pumped and closely spaced two-level emitters longitudinally coupled with a single-mode boson field, and the subsequent quantum cooling of the boson mode is investigated. Even though the two-level qubits are resonantly driven, we have demonstrated an efficient cooling mechanism well below limits imposed by the thermal background. Furthermore, the cooling effect is accompanied by entanglement of the qubit pair components when the dipole-dipole frequency shift is close to the frequency of the boson mode. The maximum boson mode cooling efficiency realizes on the expense of the entanglement creation. Importantly, this occurs for rather weak external pumping fields protecting the sample from the deteriorations. Finally, the conditions to effectively optimize these effects are described as well.
关键词： entanglement,boson mode,dipole-dipole interaction,two-level qubits,cooling
更新于2025-09-11 14:15:04
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Specific Features of Interatomic Dipole–Dipole Interaction near a Perfectly Conducting Charged Surface
摘要： Specific features of dipole–dipole interaction between two motionless point atoms located near a perfectly conducting charged plate are investigated theoretically within a consistent quantum microscopic approach. These features are analyzed on the basis of the dynamics of cooperative spontaneous decay of excited states of a diatomic quasimolecule. The decay rate is investigated as a function of the interatomic distance, the orientation angle of the quasimolecule with respect to the plane of the plate, and the distance between the quasimolecule and the plate. It is shown that the conducting plate significantly modifies the character of dipole–dipole interaction even when the plate is not charged. When the plate is charged, the Stark splitting of atomic levels leads to an additional modification of the interatomic interaction. The features observed are explained on the basis of the analysis of the spectrum of collective states of diatomic molecules.
关键词： dipole–dipole interaction,quantum microscopic approach,Stark splitting,cooperative spontaneous decay
更新于2025-09-10 09:29:36
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Near-threshold bound states of the dipole-dipole interaction
摘要： We study the two-body bound states of a model Hamiltonian that describes the interaction between two field-oriented dipole moments. This model has been used extensively in the many-body physics of ultracold polar molecules and magnetic atoms, but its few-body physics has been explored less fully. With a hard-wall short-range boundary condition, the dipole-dipole bound states are universal and exhibit a complicated pattern of avoided crossings between states of different character. For more realistic Lennard–Jones short-range interactions, we consider parameters representative of magnetic atoms and polar molecules. For magnetic atoms, the bound states are dominated by the Lennard–Jones potential, and the perturbative dipole-dipole interaction is suppressed by the special structure of van der Waals bound states. For polar molecules, we find a dense manifold of dipole-dipole bound states with many avoided crossings as a function of induced dipole or applied field, similar to those for hard-wall boundary conditions. This universal pattern of states may be observable spectroscopically for pairs of ultracold polar molecules.
关键词： Lennard–Jones potential,bound states,ultracold polar molecules,dipole-dipole interaction,magnetic atoms
更新于2025-09-09 09:28:46