Quantum Dipole Research Articles

Identification of molecules through the fluorescence enhancement by a metal tip

A fluorescence enhancement phenomenon, which is realized as a result of a sharp increase in the radiative decay rate of a quantum dipole emitter (QDE) is investigated theoretically in the vicinity of a conical metal tip. The QDE relaxation process is considered as a self-stimulated transition from an excited state into the ground state due to the feedback field formation from the tip. The dynamics of the system shows a stepped relaxation behavior that differs significantly from the conventional exponential decay. This effect can be observed in a small region of the resonance frequency, which is defined by an angle of conical tip. The increase of fluorescence when approaching of molecule to the metal tip on the surface enables one to determine its location.

SPECIFICATIONS OF RABI OSCILLATIONS IN THE QUANTUM EMITTERS SYSTEMS COUPLED TO THE LOCALIZED PLASMON POLARITONS

In this work phenomenon of resonant transfer of the excited energy between quantum dipole emitters (QDE) by the localized plasmon polaritons (LPP) is investigated. In system the molecules or semiconductor quantum dots act as QDEs and the nanometer size metal particles (MNP) care LPPs. The dependence of the frequency of Rabi oscillations on system parameters (the distance between MNP and QDE, the radius of MNP and dielectric permittivity of the surrounding medium) was determined. Conditions when the period of Rabi oscillations is considerably shorter than system relaxation time were defined.

Quasinormal mode theory and modelling of electron energy loss spectroscopy for plasmonic nanostructures

Understanding light–matter interactions using localized surface plasmons (LSPs) is of fundamental interest in classical and quantum plasmonics and has a wide range of applications. In order to understand the spatial properties of LSPs, electron energy loss spectroscopy (EELS) is a common and powerful method of spatially resolving the extreme localized fields that can be obtained with metal resonators. However, modelling EELS for general shaped resonators presents a major challenge in computational electrodynamics, requiring the full photon Green function as a function of two space points and frequency. Here we present an intuitive and computationally simple method for computing EELS maps of plasmonic resonators using a quasinormal mode (QNM) expansion technique. By separating the contribution of the QNM and the bulk material, we give closed-form analytical formulas for the plasmonic QNM contribution to the EELS maps. We exemplify our technique for a split ring resonator, a gold nanorod, and a nanorod dimer structure. The method is accurate, intuitive, and gives orders of magnitude improvements over direct dipole simulations that numerically solve the full 3D Maxwell equations. We also show how the same QNM Green function can be used to obtain the Purcell factor (and projected local density of optical states) from quantum dipole emitters or two level atoms, and we demonstrate how the spectral features differ in general to the EELS spectrum.

Mode coupling and photon antibunching in a bimodal cavity containing a dipole quantum emitter

We study the effect of mode-coupling on a single-photon device in which a dipole-quantum-emitter (DQE) is embedded in a bimodal whispering-gallery-mode cavity (WGMC). A scatterer is used to induce mode coupling between counter-clockwise and clockwise propagating light fields, which interact with the DQE. In contrast to models for the interaction between a DQE and a (one-mode or two-mode) cavity field, we find that strong photon antibunching can occur even for a weak DQE-field coupling and large dephasing of the DQE, when mode coupling is introduced. We also find that mode coupling can make the device robust against either the frequency mismatch between cavity modes and the DQE or the coupling strength mismatch between the DQE and each mode in the two-mode cavity. Moreover, we find that these mismatches can be used to generate better antibunching in the weak DQE-field coupling regime. Our study shows that mode coupling in a bimodal cavity is very important for the realization of a good single-photon device.

Application of Electrodynamic Theory on Quantum Hall Effect

The quantum electrodynamic (QED) behaviour is studied for quantum Hall effect (QHE). Quantum theory with conjecture of fractional charge quantization (quantum dipole moment), eigenfunctions for fractional charge quantization at the surface of a twisted and twigged electron quanta and above its surface, fractional Fourier transform and Hermite function for fractional charge quantization is developed. With energy eigen value equation for QHE and with energy operator on an eigenfunction of a twisted and twigged electron quanta, the corresponding eigenfunctions are normalized with Schrodinger’s quantum wave mechanical equation for electric scalar and magnetic potentials, respectively (QED behavior). The fractional electric and magnetic fields with their corresponding potentials for the quantized fractional states in semiconducting hereto structures are theoretically calculated. Such mathematical expressions are in good agreement with experimental results of Nobel Prize winning scientists Klitzing, Haroche, Peter and Gruebber. Our results can also explain the hybridized states of orbits with emphasis on sigma and pi bonding and their corresponding antibonding orbitals as a manifestation of electrophilic and nucleophilic chemical reactions.

Dipole moments and quantum chemical study of the structure of furan-containing gem-bromonitroethenes

As shown by the dipole moment method and quantum chemical calculations, 1-(furan-2-yl)-2-nitroethene and 1-nitro-2-(5-nitrofuran-2-yl)ethenes exist in solution as E-s-trans isomers while 1-bromo-2- (5-bromofuran-2-yl)-1-nitroethene and 1-bromo-1-nitro-2-(5-nitrofuran-2-yl)ethene have Z-s-cis configuration.

Phosphoryl- and thiophosphoryl-functionalized enamino ketones. Polarity and conformational analysis

The polarity and conformational behavior of some phosphorus-containing enamino ketones have been determined by the dipole moment method, IR spectroscopy, and quantum chemical calculations. 3-[2-[(Diphenylphosphoryl)methyl]phenylamino]-1-phenylprop-2-en-1-one has been found to exist as the single Z isomer. 3-[2-(Diphenylphosphoryl)phenylamino]-1-phenylprop-2-en-1-one and 3-[2-(diphenylphosphorothioyl) phenylamino]-1-phenylprop-2-en-1-one exist in equilibrium between the Z and E isomers, the latter prevailing.

Entanglement of two qubits mediated by a localized surface plasmon

We investigate relaxation dynamics in the system of two identical quantum dipole emitters (QDEs) located near a metal nanoparticle (MNP) exhibiting a dipolar localized surface plasmon (LSP) resonance at the frequency of the QDE radiative transition. Considering one QDE to be brought into an optically active excited state and weakly coupled to the resonant LSP, we show that a stable superposition state of two QDEs is formed during the transition time, which is much shorter than the QDE spontaneous decay time and determined by the efficiency of resonant interaction between the QDEs and induced LSP. It is elucidated that the superposition state is established as a result of redistribution of the energy of the initially excited QDE so that the corresponding steady-state QDE fields induced at the MNP site cancel each other. The degree of steady-state entanglement characterized by the concurrence is found dependent only on the ratio of distances between the QDEs and the MNP, reaching its maximum value of $\ensuremath{\sim}0.65$, when the separation between the MNP and the initially excited QDE is larger by $\ensuremath{\sim}20%$ than the distance from the other QDE to the MNP.

Synthesis, polarity, and structure of 2-chloro-N-[2-(methylsulfanyl)phenyl]- and 2-(diphenylthiophosphoryl)-N-[2-(methylsulfanyl)phenyl]acetamides

Conformations of 2-chloro-N-[2-(methylsulfanyl)phenyl]- and 2-(diphenylthiophosphoryl)-N-[2-(methylsulfanyl)phenyl]acetamides have been studied by the dipole moment method and quantum chemical calculations. 2-(Diphenylthiophosphoryl)-N-[2-(methylsulfanyl)phenyl]acetamide has been found to exist as an equilibrium mixture of two conformers with synclinal and anticlinal orientations of the $${C_{s{p^3}}} - {C_{s{p^2}}}$$ and P=S bonds. 2-Chloro-N-[2-(methylsulfanyl)phenyl]acetamide is represented by one preferred conformer.

Optical antenna enhanced spontaneous emission

Atoms and molecules are too small to act as efficient antennas for their own emission wavelengths. By providing an external optical antenna, the balance can be shifted; spontaneous emission could become faster than stimulated emission, which is handicapped by practically achievable pump intensities. In our experiments, InGaAsP nanorods emitting at ∼ 200 THz optical frequency show a spontaneous emission intensity enhancement of 35 × corresponding to a spontaneous emission rate speedup ∼ 115 ×, for antenna gap spacing, d = 40 nm. Classical antenna theory predicts ∼ 2,500 × spontaneous emission speedup at d ∼ 10 nm, proportional to 1/d(2). Unfortunately, at d < 10 nm, antenna efficiency drops below 50%, owing to optical spreading resistance, exacerbated by the anomalous skin effect (electron surface collisions). Quantum dipole oscillations in the emitter excited state produce an optical ac equivalent circuit current, I(o) = qω|x(o)|/d, feeding the antenna-enhanced spontaneous emission, where q|x(o)| is the dipole matrix element. Despite the quantum-mechanical origin of the drive current, antenna theory makes no reference to the Purcell effect nor to local density of states models. Moreover, plasmonic effects are minor at 200 THz, producing only a small shift of antenna resonance frequency.

Towards a Polarizable Force Field for RNA based on the Classical Drude Oscillator

RNA plays many important roles in the cell, including information transfer, gene regulation, protein synthesis, and catalysis. This diversity in function arises in part from the adoption of complex tertiary structures and interconversion between multiple conformational states in response to bound metabolites or changes in other cellular conditions. Modeling RNA with atomistic resolution using molecular dynamics (MD) simulations requires a high-quality empirical force field that can adequately describe the properties of both canonical and non-canonical structures and is sensitive to environmental conditions. To this end, we are developing a force field for RNA that includes the explicit treatment of electronic polarization using the classical Drude Oscillator model. Optimization is focused on the RNA 2′-hydroxyl group and the phosphodiester backbone targeting 2-D quantum mechanical (QM) potential energy and dipole moment surfaces in combination with condensed phase MD simulations of both canonical and non-canonical RNA structures. Parameter validation involves conducting MD simulations of various RNAs not included in the training set.

Relaxation dynamics of a quantum emitter resonantly coupled to a coherent state of a localized surface plasmon

We investigate the relaxation dynamics of a quantum dipole emitter (QDE), e.g., a molecule or quantum dot, located near a metal nanoparticle (MNP) exhibiting a dipolar localized surface plasmon (LSP) resonance at the frequency of the QDE radiative transition. A generic three-level QDE, which is pumped with an external laser pulse and thereby brought into an optically active excited state, is considered to be weakly coupled to the resonant LSP described by a coherent state. It is shown that, under the condition of the QDE-MNP characteristic relaxation time being much shorter than that of the QDE in free space but much longer than the LSP lifetime, the QDE relaxation dynamics can be described analytically and feature, in general, non-exponential decay with complicated transient behaviour. The main physical consequence of this relaxation process is that the emission, being largely determined by the MNP, comes out with a substantial delay. It is also shown that energy dissipation in the QDE-MNP system is relatively weak with the probability of the photon emission being ∼0.75, a number which, rather surprisingly, does not explicitly depend on the metal absorption characteristics. A large number of QDE-MNP system parameters in our analytical description open new possibilities for controlling quantum emitter dynamics.

Study of the structure of 1-nitro-3,3,3-trifluoro- and 1-nitro-3,3,3-tribromopropenes by the methods of dipole moments and quantum chemistry

Method of dipole moments and quantum-chemical calculations allowed establishing that 1-nitro-3,3,3-trifluoro- and 1-nitro-3,3,3-tribromopropenes have the E-configuration (the nitro group and the trihalomethyl substituent are in the trans-position); the obtained characteristics were compared with the corresponding data for the trichloromethyl-containing analog.

Conformational analysis of 2-aminophenyl-, 2-aminobenzyl-, and 2-nitrobenzyl(diphenyl)phosphine oxides

The polarity and conformations of 2-aminophenyl-, 2-aminobenzyl-, and 2-nitrobenzyl(diphenyl)-phosphine oxides were studied by the dipole moment method, IR spectroscopy, and quantum chemical calculations. 2-Aminophenyl- and 2-aminobenzyl(diphenyl)phosphine oxides were found to exist preferentially as conformers with intramolecular hydrogen bond. 2-Nitrobenzyl(diphenyl)phosphine oxide is likely to be represented by equilibrium mixture of three conformers in which the phosphoryl and nitro groups are oriented syn or anti with respect to the \(PC_{sp^3 } C_{sp^2 } \) fragment.

Relaxation dynamics of a quantum emitter resonantly coupled to a metal nanoparticle

The presence of a metal nanoparticle (MNP) near a quantum dipole emitter, when a localized surface plasmon mode is excited via the resonant coupling with an excited quantum dipole, dramatically changes the relaxation dynamics: an exponential decay changes to step-like behavior. The main physical consequence of this relaxation process is that the emission, being largely determined by the MNP, comes out with a substantial delay. A large number of system parameters in our analytical description opens new possibilities for controlling quantum emitter dynamics.

Conformational analysis of arylphosphine selenides

We have carried out the conformational analysis by the methods of dipole moments and quantum chemistry [DFT B3PW91/6-31G(d), B3PW91/6-311++G(3df, 3pd)] of bis[(4-chlorophenyl)ethyl]phosphine selenide (I) and bis-[(4-tert-butylphenyl)ethyl]phosphine selenide (II), which are promising initial materials for the synthesis of various organophosphoselenium compounds. Their structural formulas are presented in the scheme. The coeffi cients of the calculation equations and the experimental dipole moments of phosphine selenides I, II are compiled in Table 1. The most probable conformers of compounds I, II according to the quantum-chemical calculations are given below (hydrogen atoms are not shown). The energies, theoretical dipole moments and those computed using the vector-additive scheme for the conformational isomers of compounds I, II are presented in Table 2. In phosphine selenide I according to the data of B3PW91/6-31G(d) the energy minimum corresponds to conformer IА possessing a symmetric structure. However the calculation in an extended basis indicates the energy prevalence of conformer IB. Taking into consideration that the dipole moment values of conformer IB calculated in both bases is in better agreement with the experimental fi nding than those of conformer IA the results of B3PW91/6-311++G(3df,3pd) concerning the energy preference of conformer IB apparently should be regarded Table 1. Coeffi cients of calculation equations and experimental dipole moments of compounds I, II

Theoretical study of the structure of N-arylmaleimides and bis-maleimides

Conformational analysis of N-arylmaleimides and bis-maleimides was performed by the dipole moment method and quantum chemical calculations. The aromatic ring and heterocycle in N-arylmaleimides are turned with respect to each other through an angle of 42–44°, which excludes conjugation between these fragments. No conjugation exists between the dioxopyrrole rings in bridged bis-maleimides. The structure of the examined compounds is controlled by steric factors. Pronounced inductive effect of chlorine atoms in chloro-substituted bis-maleimides is responsible for their reduced dipole moments.

Rapidly converging bound state eigenenergies for the two dimensional quantum dipole

We examine the effectiveness of a new spectral method in solving the two dimensional dipole problem (DP), as originally formulated by Dasbiswas et al (2010 Phys. Rev. B: At. Mol. Opt. Phys. 81 064516), and recently analysed by Amore and Fernandez (AF, 2012 Phys. Rev. B: At. Mol. Opt. Phys. 45 235004), through a large, non-orthogonal basis, Rayleigh–Ritz (RR) analysis. This deceptively simple problem has a long history of poorly approximated energy values, particularly for the ground state, until the recent work by AF. In contrast to their approach, we implement an orthogonal polynomial projection quantization (OPPQ) analysis (Handy and Vrinceanu 2013 J. Phys. A: Math. Theor. 46 135202), involving expanding the wavefunction in terms of a complete basis, , where are the orthogonal polynomials relative to the weight . For systems transformable into a moment equation, such as DP, the projection coefficients are determinable in closed form, yielding an efficient quantization procedure, particularly when the weight assumes the asymptotic form of the physical solutions. There are several theoretical reasons why the OPPQ should be more effective than the above RR approach. Indeed, comparable results are achieved with significantly fewer OPPQ variational parameters as compared to RR-variational parameters. For instance, with regards to the delicate ground state energy, 130 OPPQ variables are required to achieve Egr = −0.137 7614 (Egr = −0.137 7514 after a Shanks transform) as opposed to the 821 required within the RR formulation: Egr = −0.137 7478. Despite this, the relative slow convergence for low lying even parity states, within both the OPPQ and RR formulations, suggests that significant logarithmic contributions to the wavefunction, at the origin, have been ignored by all previous investigators. Modifying the RR variational analysis to include log-dependent basis, affirms this through an accelerated RR convergence for the ground state: Egr = −0.137 748 utilizing 68 variational parameters. This result suggests further improvements within either the OPPQ or RR formulation.

Conformational Analysis of 1,3,2-Dioxaphospholane and Pyrocatehine Phosphite with Oc(O)Cf3 Exocyclic Substituents

Conformational analysis of 1,3,2-dioxaphospholane-2-yl-2,2,2-trifluoroacetate and 4,5-benzo-1,3,2-dioxaphosphole-2-yl-2,2,2-trifluoroacetate was carried out by dipole moment method and quantum chemical calculations (DFT B3LYP/6-31G*).

Polarity and Conformational Analysis of Secondary Phosphine Selenides

The polarities of bis(2-phenylethyl) and bis(2-phenylpropyl) phosphine selenides were determined and conformational analysis of these phosphine selenides was carried out by the method of dipole moments, IR spectroscopy, and quantum chemical calculations. They exist as an equilibrium of several conformers, and the preferred conformers have gauche orientation of the P = Se and Csp3 – Csp3 bonds.