One-photon Resonance Research Articles

Floquet Weyl states at one-photon resonance: An origin of nonperturbative optical responses in three-dimensional materials

Electrons driven coherently by laser light can exhibit nonperturbative geometric effects. Drastic deformation and gap openings of the electrons' Floquet bands occur at one-photon resonances since the electron and hole bands hybridize through their replicas at the lowest-order photon exchange. We study the evolution of Floquet bands in three-dimensional (3D) materials driven by circularly polarized light (CPL) using the Dirac model. We find that the light-induced gap closes at a select few points in the momentum space where Floquet Weyl points are formed. The Weyl points are protected by their monopole charge and can merge, separate, or pair annihilate depending on the anisotropy of electrons and the ellipticity of the incident light. In isotropic 3D Dirac electrons driven by CPL, the Weyl points merge to form Floquet double-Weyl points with topological charge ±2. Our results reveal a universal aspect of light-matter interactions in 3D quantum materials and open a route towards controllable versatile electromagnetic responses associated with light-induced Floquet Weyl states. Published by the American Physical Society 2024

Impact of intense laser Bessel beam on excitonic complexes in ellipsoidal quantum dot

This theoretical study investigates the response of a strongly oblate GaAs ellipsoidal quantum dot to an intense laser field with a Bessel intensity profile at non-resonant extreme violet and simultaneously resonant mid-infrared laser irradiation. Mainly, the linear and nonlinear optical properties of biexcitons in quantum dot are observed. Due to the complexity of the considered particle, all calculations are performed in the framework of the variational method. Biexciton variational function is constructed on the one-particle wave functions, which are correlated with each other by exponents with variational parameters. The biexciton energies for different values of applied intense laser field magnitude on the small geometrical parameter of ellipsoidal quantum dot are calculated. The nonlinear optical properties, including the oscillator strength, third-order nonlinear susceptibility, absorption coefficient, and refractive index change, are evaluated. Numerical results reveal the dependence of the exciton and biexciton energies on the intensity of the laser field and the geometrical parameters of the quantum dot. Additionally, the dependencies of the third-order susceptibility, absorption coefficient, and induced refractive index change on photon energy near the one-photon resonance and two-photon resonance are analyzed. The two-photon absorption coefficient of the biexciton in GaAs ellipsoidal quantum dot is computed, and the spectra of refractive index changes induced by biexciton transitions between ground states are analyzed for different magnitudes of the intense laser field. Biexciton recombination radiative lifetime on the small semiaxis of the ellipsoidal quantum dot for the different values of the laser field influence is estimated. Finally, the visualization of the localization region of biexciton in the ellipsoidal quantum dot is performed.

Efficient Kohn–Sham density-functional theory implementation of isotropic spectroscopic observables associated with quadratic response functions

For general exchange–correlation functionals with a dependence on the local spin densities and spin-density gradients, we provide computationally tractable expressions for the tensor-averaged quadratic response functions pertinent to the experimental observables in second-harmonic generation (SHG). We demonstrate how the tensor-averaged quantities can be implemented with reference to a derived minimal number of first- and second-order perturbed Fock matrices. Our consideration has the capability of treating a situation of resonance enhancement as it is based on damped response theory and allows for the evaluation of tensor-averaged resonant-convergent quadratic response functions using only ∼25% (one-photon off-resonance regions) and ∼50% (one-photon resonance regions) of the number of auxiliary Fock matrices required when explicitly calculating all the needed individual tensor components. Numerical examples of SHG intensities in the one-photon off-resonance region are provided for a sample of makaluvamine derivatives recognized for their large nonlinear optical responses as well as a benchmark set of small- and medium-sized organic molecules.

Optical resonance in the inversion [formula omitted] channel of a silicon MOS structure

The features of the manifestation of the self-induced transparency (SIT) effect at intersubband resonance in the inversion n− layer of silicon semiconductor systems (in field-effect transistors (100)Si−MOSFET) are analyzed. The course of the interaction of ultrashort laser pulses with the quantum states of the inversion layer of the MOS structure varies, depending on the concentration of the induced charge, by changing the voltage across the metal gate. The evolution of a pulse in the transient stage of deformation as it propagates in a resonant medium of an inversion channel is discussed. Possible consequences for a non-degenerate one-photon resonance are considered, with controlled changes in the detuning between a fixed pulse frequency and the resonant energy of the intersubband transition, caused by changes in the charge density. The parametric dependence on the concentration of the induced charges in the “area theorem” for the propagation process in the inversion channel is revealed.

Non-Linear Optical Properties of Biexciton in Ellipsoidal Quantum Dot.

We have presented a theoretical investigation of exciton and biexciton states for the ground and excited levels in a strongly oblate ellipsoidal quantum dot made from GaAs. The variational trial wave functions for the ground and excited states of the exciton and biexciton are constructed on the base of one-particle wave functions. The energies for the ground and excited levels, depending on the ellipsoidal quantum dot’s geometrical parameters, are depicted in the framework of the variational method. The oscillator strength of the transition from exciton to biexciton states for ground and excited levels is investigated as a function of the ellipsoidal quantum dot’s small and large semiaxes. The third-order optical susceptibilities of ground and excited biexcitons around one-photon and two-photon resonances are calculated as a function of the photon energy. The dependences of third-order optical susceptibilities for the ground and excited levels on the photon energy for different values of the ellipsoidal quantum dot’s semiaxis are revealed. The absorption coefficients in the ellipsoidal quantum dot, both for ground and excited states of exciton and biexciton, are calculated. The absorption coefficients for the ground level of exciton and biexciton for the fixed value of the large semiaxis and for the different values of the small semiaxis are determined. Finally, the two-photon absorption coefficient of the biexciton in the GaAs ellipsoidal quantum dot is computed.

Three-Photon Ionization with One-Photon Resonance between Excited Levels

Within the framework of a three-level model, the process of three-photon ionization with one-photon resonance between two excited levels (with the lower one being initially unpopulated) is considered using the density matrix method. It is shown that such resonance can result in the appearance of a maximum in the three-photon ionization spectrum when detuning between the resonance wavenumber and the wavenumber of the transition responsible for the lower excited level being populated exceeds the laser radiation linewidth by more than three orders of magnitude.

Evolution of four-wave mixing by controlling Raman coherence in a multi-dressed atomic system

The evolution of enhanced four-wave mixing based on Raman coherence as the probe intensity increases is observed experimentally in an 85 R b atomic vapor system. We propose that for a Doppler-broadened Λ -type level system, the generated anti-Stokes field from one-photon resonance will be suppressed by the dressed-states resonance and can be controlled by the probe intensity, which influences the effective transverse relaxation rate of Raman coherence. When the probe field is not so weak, the double resonance for dressed states will greatly suppress the anti-Stokes emission at the central frequency, and the signal peak will be split. We show that this phenomenon is a result of the destructive polarization interference between atoms with different velocities from the two types of resonance. Based on our model, we present a new, to the best of our knowledge, interpretation of four-wave mixing enhancement in the conventional Λ -type electromagnetically induced transparency system.

Effective inhibit energetic cost in stimulated Raman shortcut-to-adiabatic passage

A shortcut to the adiabatic process is an effective method for quantum information processing. The fast and robust quantum information transfer can be implemented by this method. The energetic cost is an important measurement for the shortcut. In this paper, we investigate how to inhibit the energetic cost in stimulated Raman shortcut-to-adiabatic passage in a three-level system. The energetic cost can be manipulated by adjusting detuning of the system and the energetic cost takes the minimum with one-photon resonance condition.

Efficient implementation of isotropic cubic response functions for two-photon absorption cross sections within the self-consistent field approximation.

Within the self-consistent field approximation, computationally tractable expressions for the isotropic second-order hyperpolarizability have been derived and implemented for the calculation of two-photon absorption cross sections. The novel tensor average formulation presented in this work allows for the evaluation of isotropic damped cubic response functions using only ∼3.3% (one-photon off-resonance regions) and ∼10% (one-photon resonance regions) of the number of auxiliary Fock matrices required when explicitly calculating all the needed individual tensor components. Numerical examples of the two-photon absorption cross section in the one-photon off-resonance and resonance regions are provided for alanine-tryptophan and 2,5-dibromo-1,4-bis(2-(4-diphenylaminophenyl)vinyl)-benzene. Furthermore, a benchmark set of 22 additional small- and medium-sized organic molecules is considered. In all these calculations, a quantitative assessment is made of the reduced and approximate forms of the cubic response function in the one-photon off-resonance regions and results demonstrate a relative error of less than ∼5% when using the reduced expression as compared to the full form of the isotropic cubic response function.

Generation and dynamics of entangled fermion–photon–phonon states in nanocavities

AbstractWe develop the analytic theory describing the formation and evolution of entangled quantum states for a fermionic quantum emitter coupled simultaneously to a quantized electromagnetic field in a nanocavity and quantized phonon or mechanical vibrational modes. The theory is applicable to a broad range of cavity quantum optomechanics problems and emerging research on plasmonic nanocavities coupled to single molecules and other quantum emitters. The optimal conditions for a tripartite entanglement are realized near the parametric resonances in a coupled system. The model includes dissipation and decoherence effects due to coupling of the fermion, photon, and phonon subsystems to their dissipative reservoirs within the stochastic evolution approach, which is derived from the Heisenberg–Langevin formalism. Our theory provides analytic expressions for the time evolution of the quantum state and observables and the emission spectra. The limit of a classical acoustic pumping and the interplay between parametric and standard one-photon resonances are analyzed.

Vibration overtone hyperpolarizability measured for H2.

The second hyperpolarizability (γ) of the H2 molecule was measured by gas-phase electric field induced second harmonic generation at the frequencies of the one-photon resonance for the 3-0 Q(J) overtone transitions (v, J = 0, J → 3, J for J = 0, 1, 2, and 3). The magnitude of the resonant contribution to γ was measured with 2% accuracy using the previously determined non-resonant γ for calibration. Pressure broadening and frequency shift for the transitions were also measured. A theoretical expression for the resonant vibrational γ contribution in terms of transition polarizabilities is compared to the observations. The measured γ resonance strength is 4%-14% larger than the results obtained from this theoretical expression evaluated using ab initio transition polarizabilities.

A gated quantum dot strongly coupled to an optical microcavity.

The strong-coupling regime of cavity quantum electrodynamics (QED) represents the light-matter interaction at the fully quantum level. Adding a single photon shifts the resonance frequencies-a profound nonlinearity. Cavity QED is a test bed for quantum optics1-3 and the basis of photon-photon and atom-atom entangling gates4,5. At microwave frequencies, cavity QEDhas had a transformative effect6, enabling qubit readout and qubit couplings in superconducting circuits. At optical frequencies, the gates are potentially much faster; the photons can propagate over long distances and can be easily detected. Following pioneering work on single atoms1-3,7, solid-state implementations using semiconductor quantum dots are emerging8-15. However, miniaturizing semiconductor cavities without introducing charge noise and scattering losses remains a challenge. Here we present a gated, ultralow-loss, frequency-tunable microcavity device. The gates allow both the quantum dot charge and its resonance frequency to be controlled electrically. Furthermore, cavity feeding10,11,13-17, the observation of the bare-cavity mode even at the quantum dot-cavity resonance, is eliminated. Even inside the microcavity, the quantum dot has a linewidth close to the radiative limit. In addition to a very pronounced avoided crossing in the spectral domain, we observe a clear coherent exchange of a single energy quantum between the 'atom' (the quantum dot) and the cavity in the time domain (vacuum Rabi oscillations), whereas decoherence arises mainly via the atom and photon loss channels. This coherence is exploited to probe the transitions between the singly and doubly excited photon-atom system using photon-statistics spectroscopy18. The work establishes a route to the development of semiconductor-based quantum photonics, such assingle-photon sources and photon-photon gates.

Photoelectron spectra after multiphoton ionization of Li atoms in the one-photon Rabi-flopping regime

We calculate two-dimensional photoelectron momentum distributions and energy spectra after multiphoton ionization of Li atoms subject to intense laser fields in one-photon Rabi-flopping regime. The time-dependent Schr\"{o}dinger equation is solved within the single-active-electron approximation using a model potential which reproduces accurately the binding energies and dipole matrix elements of the Li atom. Interaction with the external electromagnetic field is treated within the dipole approximation. We show that the Rabi oscillations of the population between the ground $2s$ state and the excited $2p$ state in the one-photon resonance regime are reflected in the energy spectra of emitted photoelectrons which manifest interference structures with minima. Transformations of the interference structures in the photoelectron energy spectra caused by the variation of the laser peak intensity and pulse duration are analyzed.

Multiple-peak resonance of optical second harmonic generation arising from band nesting in monolayer transition metal dichalcogenides TX2 on SiO2/Si(001) substrates (T=Mo,W;X=S,Se)

The nonlinear optical response of monolayer transition-metal dichalcogenides $T{X}_{2}\phantom{\rule{0.28em}{0ex}}(T=\mathrm{Mo},\mathrm{W};\phantom{\rule{0.28em}{0ex}}X=\mathrm{S},\phantom{\rule{0.28em}{0ex}}\mathrm{Se})$ on ${\mathrm{SiO}}_{2}/\mathrm{Si}(001)$ substrates was examined using second-harmonic generation (SHG) spectroscopy in combination with differential reflectance (DR) spectroscopy. In the SHG spectroscopy, the second-harmonic intensity corrected by a crystalline quartz reference was obtained for the wavelength of the incident femtosecond laser varied from 750 to 1040 nm. The SHG spectra of all the four ${TX}_{2}$ were dominated by two-photon resonance around the C peaks in the DR spectra that was previously assigned to interband transitions at critical points formed as a result of band nesting. Multiple peaks were observed in each resonance spectrum, which was then decomposed into a few components. The overall feature of the main components---denoted as $\overline{\mathrm{C}1}$ and $\overline{\mathrm{C}2}$---was common among the four ${TX}_{2}$ materials. The optical transitions contributing to these components were concluded to occur at different $k$ points in a ring-shaped area around the \cyrchar\CYRG{} point with the aid of the published results of optical spectrum calculations and the SHG spectrum of bilayer ${\mathrm{MoS}}_{2}$. In addition, one-photon resonance at the $A$ exciton and two-photon resonance at the ${A}^{\ensuremath{'}}$ exciton were observed in ${\mathrm{MoSe}}_{2}$ and ${\mathrm{WSe}}_{2}$, respectively, and their intensities were proven to be significantly lower than those of the resonances around the C peaks.

Wave mixing and high harmonic generation at two-color multiphoton excitation in two-dimensional hexagonal nanostructures

The high-order wave mixing by two-color multiphoton excitation in nonlinear regime along with the harmonics generation in two-dimensional (2D) nanostructures such as graphene, silicene, germanene, and stanene is investigated. We consider the coherent part of the spectra corresponding to high harmonic generation by two-color intense laser pulses. The developed theory of interaction of free carriers with the driving effective field of two-color waves covers the full Brillouin zone of 2D hexagonal nanostructures. We also consider the case when one of the driving waves is in one-photon resonance with the van Hove singularity at the $M$ point of the Brillouin zone. Obtained results show that novel 2D nanostructures can serve as an effective medium for high-order wave mixing and harmonic generation at the two-color multiphoton excitation with strong laser pulses.

Optimal pulse propagation in an inhomogeneously gas-filled hollow-core fiber

We study optical pulse propagation through a hollow-core fiber filled with a radially inhomogeneous cloud of cold atoms. A co-propagating control field establishes electromagnetically induced transparency. In analogy to a graded index fiber, the pulse experiences micro-lensing and the transmission spectrum becomes distorted. Based on a two-layer model of the complex index of refraction, we can analytically understand the cause of the aberration, which is corroborated by numerical simulations for a radial Gaussian-shaped function. With these insights, we show that the spectral distortions can be rectified by choosing an optimal detuning from one-photon resonance.

Universal speeded-up adiabatic geometric quantum computation in three-level systems via counterdiabatic driving

Universal speeded-up adiabatic geometric quantum computation is studied in a system with different coupling cases including time-dependent detuning, large detuning, and one-photon resonance couplings. The counterdiabatic driving method is used to speed up the universal quantum computation. These schemes are feasible in experiment because additional unaccessible ground-state coupling is not needed. Only the shapes and phases of the reference adiabatic classical-field pulse are modified with the aid of effective two-level systems. The speed and robustness against system decay and control errors are discussed, and the performance of the scheme is compared for different coupling cases.

Strong frequency dependence of transport in the driven disordered central-site model

We study a periodically driven central site coupled to a disordered environment. In comparison to the static model, transport features are either enhanced or reduced, depending on the frequency of the drive. We demonstrate this by analyzing the statistics of quasienergies and the logarithmic entanglement growth between bipartitions, which show similar features: For frequencies larger than disorder strength, localization is enhanced due to a reduced effective coupling to the central site. Remarkably, localization can even be increased up to almost perfect freezing at particular frequencies, at which the central site decouples due to the emergence of `dark Floquet states'. This high-frequency domain of our model is bounded by a critical frequency $\omega_c$, where transport increases abruptly. We demonstrate that $\omega_c$ is determined by one-photon resonances, which connect states across the mobility edge. This sensitive frequency dependence allows us to fine tune transport properties of the driven central site model, by unprecented precision.

Nondipole effects in helium ionization by intense soft x-ray laser pulses

We consider the helium atom exposed to laser pulses in soft-x regime at intensities of the order of 1017–1020 W/cm2. Two cases are investigated, first a pulse with a central frequency of 20 a.u. (~522.2eV) and a pulse with a central frequency of 50 a.u. (~1.36keV). We solve the time-dependent Schrodinger equation (TDSE), nondipole (retardation) effects are included up to O(1/c) (c being the velocity of light). We study the single photoionization of helium with a focus on nondipole effects. We calculate the total and partial photoelectron energy spectra, and the photoelectron angular distributions. The nondipole effects associated with the A·P and A2 coupling terms in the Hamiltonian (A denoting the vector potential of the field and P the momentum operator) are thoroughly analyzed in the region of one-photon resonance. We show that the nondipole contribution associated with A·P varies linearly with the intensity I while a three-photon transition involving A2 increases like I3, in agreement with lowest order perturbation theory (LOPT). At high intensities these contributions compete and the nondipole transition becomes nonlinear. The physical mechanisms associated with nondipole couplings are discussed, as well as their effects on photoelectron energy and angular distributions.

Population inversion in laser-driven N2+

The time-dependent population transfer process of N2+ generated in an intense laser pulse has been investigated using the quasi-stationary Floquet theory by assuming that N2+ experiences an intense laser pulse with the sudden turn-on. A light-dressed B state is formed with a significant amount of population when pulse is suddenly turned on and is adiabatically transformed to the vibrational ground state (v = 0) of the field-free B state when the pulse vanishes. In addition, a part of the population is transferred to the electronically excited A state through one-photon resonance, which also contributes to decreasing the final population in the X state, facilitating the population inversion between the B state and the X state.