Coherent Superposition Research Articles

Structured light reconstruction by Computer-Generated hologram in defect state

The generation of structured light from Computer-Generated Hologram (CGH) using spatial light modulators (SLM) has a wide range of applications, but there is currently a lack of research on localized defects in SLM devices. Considering that the local damage of SLM can lead to hologram defect, its result can be equivalent to the process of normal hologram generated structured beam with its near field being blocked. In this paper, CGH loaded onto digital micromirror device (DMD) is used to generate structured beams, and two cases of local defect states at the center and edge of the DMD are discussed. The results show that the reconstructed light field obtained by central defect is quite similar to the original light field, while the reconstructed light field obtained by edge defect is a much similar to the lower case of the original light field. The article further demonstrates the reconstructed results in coherent superpositions of Hermite-Gaussian modes using DMD-generated structured beams based on the single mode regime. This study expands the application scenarios for the generation of structured light beams with SLM.

Symmetry Breaking: A Classic Example of Quantum Interference Captured by Mixed Quantum/Classical Theory.

The phenomena of propensity and inverse propensity are explored using time-dependent mixed quantum classical theory, MQCT, in which the rotational motion of the molecule is treated quantum mechanically, whereas the scattering process is described classically. Good agreement with the results of accurate full-quantum calculations is reported for a closed shell approximation to the NO + Ar system. It is shown that MQCT reproduces both phenomena in a broad range of the final states of the molecule and for various initial rotational states, offering a unique time-dependent insight. It permits seeing that both propensity and inverse propensity occur due to efficient depopulation of some states at the early postcollisional stage of the scattering process, when the molecule exists in a coherent superposition of many excited states that span a very broad range of angular momentum quantum numbers, populated by an efficient stepladder process of many consecutive transitions with small Δj.

Carbon monoxide ionization in femtosecond bicircular laser pulses

The CO ionization by 7.8 fs bicircular laser field consisting of the coherent superposition of two coplanar circularly polarized laser pulses is studied in the framework of the time-dependent Hartree–Fock method. Six different superpositions composed of a near-infrared pulse with wavelength of 780 nm and an ultraviolet pulse with wavelength ranging from 244 to 390 nm are considered. The intensity of the near-infrared laser pulse is 1.0 × 1014 W cm−2 and the intensity of the ultraviolet laser pulse runs from 5.0 × 1013 to 2.0 × 1014 W/cm2. Numerical results reveal that the ionization probabilities for counter-rotating field are enhanced compared to the ionization probabilities for co-rotating field only for the coherent superposition of 780 and 390 nm circularly polarized laser pulses. Our computations also emphasize that the highest occupied molecular orbital mainly contributes to CO ionization. The contribution of the inner valence molecular orbitals can be significantly increased by adjusting the intensity ratio and the relative phase between the two colors. Note that the co-rotating laser field consisting of the coherent superposition of two circularly polarized laser pulses of wavelengths 780 and 390 nm yields higher ionization probability when the positive direction of the electric field component along molecular axis points to the O nucleus.

Generation of complex structured laser beams based on the coherent superposition of Hermite-Gaussian eigenmodes

Structured beams have been extensively studied in the last ten to twenty years. Due to its excellent spatial characteristics, it has been widely used in the fields of optical communication, optical tweezer and particle manipulation. This paper first analyzes and summarizes the formation mechanism of structured beams. Then, based on the eigenmode superposition theory, the numerical simulation was carried out for the first three-orders of Hermitian-Gaussian (HG) eigenmodes. At the same time, some complex structured beams were obtained through experiments. The structured beams obtained from experiments are in good agreement with the numerical simulation results, which further verifies that the eigenmode superposition method is an effective way to realize complex structured beams.

Massive particle interferometry with lattice solitons

We discuss an interferometric scheme employing interference of bright solitons formed as specific bound states of attracting bosons on a lattice. We revisit the proposal of Castin and Weiss [Phys. Rev. Lett. vol. 102, 010403 (2009)] for using the scattering of a quantum matter-wave soliton on a barrier in order to create a coherent superposition state of the soliton being entirely to the left of the barrier and being entirely to the right of the barrier. In that proposal, it was assumed that the scattering is perfectly elastic, i.e. that the center-of-mass kinetic energy of the soliton is lower than the chemical potential of the soliton. Here we relax this assumption: By employing a combination of Bethe ansatz and DMRG-based analysis of the dynamics of the appropriate many-body system, we find that the interferometric fringes persist even when the center-of-mass kinetic energy of the soliton is above the energy needed for its complete dissociation into constituent atoms.

High Efficiency and Flexible Modulation of Spintronic Terahertz Emitters in Synthetic Antiferromagnets.

Spintronic terahertz (THz) emitters based on synthetic antiferromagnets (SAFs) of FM1/Ru/FM2 (FM: ferromagnet) have shown great potential for achieving coherent superposition and significant THz power enhancement due to antiparallel magnetization alignment. However, key issues regarding the effects of interlayer exchange coupling and net magnetization on THz emissions remain unclear, which will inevitably hinder the performance improvement and practical application of THz devices. In this work, we have investigated the femtosecond laser-induced THz emission in Pt (3)/CoFe (3)/Ru (tRu = 0-3.5)/CoFe (tCoFe = 1.5-10)/Pt (3) (in units of nm) films with compensated and uncompensated magnetic moments. Antiferromagnetic (AF) coupling occurs in the Ru thickness ranges of 0.2-1.1 and 1.9-2.3 nm, with the first peak (tRu = 0.4 nm) of the AF coupling field (Hex) significantly higher than that of the second peak (2.0 nm). Rather high THz amplitude is found for the samples with strong AF coupling. Nevertheless, despite the same remanence ratio of zero, the THz amplitude for the symmetric SAF films declines significantly as the tRu decreases from 0.8 to 0.4 nm, which is mainly ascribed to the noncolinear magnetization vectors due to the increased biquadratic coupling term. Specifically, we demonstrate that an asymmetric SAF structure with a dominant FM layer is more favored than the completely compensated one, which could generate significantly enhanced THz electric field with well-controlled polarity and intensity. In addition, as the temperature decreases, the THz emission intensity increases for the SAF samples of tRu = 0.9 nm with negligible biquadratic coupling, which is contrary to the decreasing trend of the tRu = 0.4 nm sample and has been attributed to the greatly enhanced Hex.

A wide-beam NCS algorithm for multi-receiver SAS based on azimuth spectrum superposition

The existing multi-receiver synthetic aperture sonar (SAS) imaging algorithms are suitable for narrow-beam width, which will lead to a decrease in imaging quality under wide-beam condition and are not in line with the development needs of SAS. We propose a non-linear chirp scaling algorithm (NCSA) for wide beam multi-receiver SAS. Firstly, the point target reference spectrum (PTRS) of each receiver is obtained by the Lagrange inversion theorem (LIT), and then the under-sampled signal in the azimuth frequency domain is obtained through azimuth spectrum extension; Then, considering the cubic term of range frequency in the PTRS and the linear variation of equivalent frequency modulation slope with range, each receiver is imaged using the NCSA, and coherent superposition is performed in the azimuth frequency domain to eliminate spectrum aliasing caused by azimuth spectrum extension; Finally, the azimuth inverse transform is performed on the superimposed signal to obtain the focusing imaging. Computer simulation experiments and field data verify that this method is superior to the existing SAS imaging algorithm, improving the quality of wide-beam imaging, avoiding the interpolation operation of the traditional range-Doppler algorithm, and saving computation cost.

Heterodyne dynamic light scattering for the characterization of particle dispersions.

Particle self-diffusivities in unimodal and bimodal aqueous dispersions are characterized by dynamic light scattering (DLS) applying a heterodyne detection scheme. For unimodal dispersions close to infinite dilution, it could be evidenced that pure homodyne conditions cannot be realized, leading to an increasing underestimation of diffusivity with a decreasing concentration. Even for bimodal dispersions and neglecting any local oscillator field, the coherent superposition of scattered light from different particle species hinders a clear assignment of the measured signals and their evaluation for diffusivity. In this case, the impact of a crossterm on the determined diffusivities cannot be neglected. The results emphasize that the use of a heterodyne detection scheme in DLS experiments is a key aspect for an accurate determination of particle diffusivities in low-concentrated unimodal and bimodal dispersions.

Three-dimensional measurement of laser-induced thermal mirror dynamics using photothermal vortex interferometer with azimuthal phase spectra analysis

Measurement of the thermal mirror caused by laser heating provides direct access to the optical, thermophysical, and mechanical properties of solid materials. However, the nanoscale time-dependent three-dimensional (3D) thermal mirror hinders the existing photothermal techniques to obtain the thermal mirror dynamics without sacrificing the spatial profile of the thermal mirror. To fill the gap of 3D measurement of laser-induced thermal mirror dynamics, a photothermal vortex interferometer (PTVI) is proposed. The PTVI produces a multi-ring petal-like interferogram by the coaxial coherent superposition of the high-order conjugated Laguerre-Gaussian beams. The nanoscale 3D thermal mirror with a rotationally symmetric surface profile can be encoded into different azimuthal phase shifts at the different radii of the interferogram. An azimuthal phase spectra analysis is proposed to extract the azimuthal phase shifts from the continuously captured interferograms, enabling reconstruction of the 3D thermal mirror dynamics. The experimental results verified that the PTVI can measure the surface deformation due to the thermal mirror at an accuracy of picometer scale, and the optical and thermophysical properties of an optical glass sample can be determined with the assistance of the thermophysical model of the 3D thermal mirror dynamics. The approach can be an effective tool for characterization of solid materials.

Mechanisms of chiral plasmonics-Scattering, absorption, and photoluminescence.

Chirality is a concept that one object is not superimposable on its mirror image by translation and rotation. In particular, chiral plasmonics have been widely investigated due to their excellent optical chiral properties, and have led to numerous applications such as optical polarizing element etc. In this study, we develop a model based on the concept of the interaction between harmonic oscillators to investigate and explain the optical chiral mechanisms of strongly coupled metal nanoparticles (MNPs). The chirality of the scattering, absorption, and photoluminescence spectra are carefully discussed in detail. The results show that the chirality of the system originates not only from the orientations of the MNPs, but also from the different eigen parameters between them. Specifically, the derived three factors contribute to the chirality: the symmetry, the coupling strength, and the coherent superposition of the emitted electric field. This work provides a deeper understanding on the chiral plasmonics and may guide relevant applications in theory.

Harnessing optical vortices to control current flow via quantized torque in coherently prepared multilevel atoms

This study delves into the interaction between coherently prepared trapped atoms and optical vortices, focusing on the intriguing phenomenon of light-induced torque enhancement and the resultant persistent current flow. Beginning with a three-level atom ensemble in the Λ configuration, we initiate a coherent superposition of lower levels to establish a coherent population trapping medium. The atoms interact with a pair of optical vortices, producing a quantized torque on each trapped atom that is directly proportional to the topological charge of the inhomogeneous coupling beams. This torque imparts a rotation to the entire ensemble, thereby generating a striking ring-shaped atomic current flow. With careful manipulation of the initial internal state of the atoms and the strength of the vortex pair, we can control the magnitude of the torque. Extending the model to include more complex level schemes with additional laser beams offers even greater potential for enhancing light-induced torque and refining our control over the current flow.

Probing the Twist-Controlled Interlayer Coupling in Artificially Stacked Transition Metal Dichalcogenide Bilayers by Second-Harmonic Generation.

Interlayer coupling plays a critical role in the electronic band structures and optoelectronic properties of van der Waals (vdW) materials and heterostructures. Here, we utilize optical second-harmonic generation (SHG) measurements to probe the twist-controlled interlayer coupling in artificially stacked WSe2/WSe2 homobilayers and WSe2/WS2 and WSe2/MoS2 heterobilayers with a postannealing procedure. In the large angle twisted WSe2/WSe2 and WSe2/WS2, the angular dependence of the SHG intensity follows the interference relations up to angles above 10°. For lower angles, the SHG is significantly suppressed. Furthermore, for the twisted WSe2/MoS2 the SHG intensity largely deviates from the coherent superposition model and shows consistent quenching for all the stacking angles. The suppressed SHG in twisted transition metal dichalcogenide (TMDC) bilayers is predominantly attributed to the interlayer coupling between the two adjacent monolayers. The evolution of the interlayer Raman mode in WSe2 demonstrates that the interlayer coupling in the twisted WSe2/WSe2 and WSe2/WS2 is highly angle-dependent. Alternatively, the interlayer coupling generally exists in the twisted WSe2/MoS2, regardless of the different angles. The interlayer coupling is further confirmed by the quenching and red-shift of the photoluminescence of WSe2 in the twisted TMDC bilayers. Combined with density functional theory calculations, we reveal that the stacking-angle-modulated interlayer coupling originates from the variation of the interlayer spacing and the binding energy in the twisted TMDC bilayers.

Spatially structured optical effects in semiconductor quantum dots via biexciton coherence

In this paper, we study the spatially structured optical effects that occur when weak laser lights interact with coherently prepared semiconductor quantum dots (SQDs). Initially, the SQD is prepared in a coherent superposition of the lower exciton states. By utilizing two weak optical vortex fields that couple to a biexciton state, we observe spatially dependent effects of the absorption of probe fields. Using the well-established Maxwell–Bloch equations, we analyze the generation of composite optical vortex beams within this system. Our investigation revolves around the formation of different types of spatially dependent beams, exploring their properties and characteristics. Additionally, the transfer of optical vortices through the parametric generation process is examined, for the case where only one vortex beam is present at the beginning of the medium. This study provides insights into the spatially structured optical phenomena in coherently prepared SQDs and contributes to the understanding of light–matter interactions in such systems.

Sensitive detection of electric field-induced second harmonic signals.

We demonstrate sensitive electric field measurements by coherent homodyne amplification of the electric field induced second harmonic generation (E-FISH) technique. In the process of E-FISH, an applied electric field breaks the centrosymmetry of an otherwise homogeneous medium, in turn promoting the generation of the second harmonic frequency of an incident field. Due to weak third-order hyperpolarizability and the requirement of an applied field to break the symmetry, the E-FISH technique has been mainly used to study high fields, also requiring a strong optical field and sensitive detection. Here we superimpose the E-FISH signal with an auxiliary beam, also termed a local oscillator (LO), at double the incident frequency. Coherent superposition of the LO and the E-FISH output (LOE-FISH) allows for a homodyne amplification of the otherwise weak nonlinear signal. We have demonstrated an increase of signal-to-noise by a factor of seven, which results in a measurement time reduction of a factor of 49. This technique, LOE-FISH, has a number of advantages: detection with intensified detectors is not required. Furthermore, instead of millijoule pulsed lasers, we can work with microjoule pulsed lasers, which allows measuring at repetition rates of megahertz and opens single shot and real-time capability. The LOE-FISH technique increases in sensitivity at lower electric field values. Our work is a demonstration of the principle. Already with our first results from the demonstration, one can see the high potential of LOE-FISH.

On-chip multi-dimensional multiplexing communication using tapered adiabatic micro-ring resonators

Multi-dimensional multiplexing plays a vital role in on-chip optical communication for enhancing capacity density. However, the mode (de)multiplexer based on multimode interferometer is generally wavelength dependent, which brings a non-negligible conundrum to fabricate multi-dimensional (de)multiplexers. Herein, we propose an on-chip multi-dimensional (de)multiplexer by designing a tapered adiabatic micro-ring resonator (TAMR), and perform a 4-mode bending transmission via a pixelated meta-structure. The TAMR is designed with a negligible wavelength dependence because of non-coherent superposition (No-coherent superposition mechanism based on directional coupling avoids the coherent superposition of light-waves, which will not reduce the working bandwidth.of device.), but employs the periodic energy exchange of evanescent wave between two waveguides to achieve an equal phase velocity for the fundamental and higher-order modes (mode conversion), where a micro-ring resonator array is exploited for resonance frequency selection. A pixelated meta-structure implemented by writing nano airholes in the silicon slab is employed for addressing the mode distortion induced by the bending of transverse electric (TE) modes. Consequently, we construct a 12-channel multi-dimensional (de)multiplexer composed of 3 wavelengths and 4 TE modes. We show that all the channels are successfully (de)multiplexed with crosstalk less than − 19 dB, and bit error rates lower than 3.8 × 10−3 at the signal to noise ratio of 17 dB.

Creation of galaxy-shaped vortex relief structures in azo-polymers with petal-like beams.

We demonstrate the formation of surface relief structures in azo-polymers which exhibit multiple spiral arms, through irradiation of a rotating petal-like beam formed by the coherent superposition of Laguerre-Gaussian modes with opposite handedness. Intriguingly, the fabricated relief structures reflect full geometric parameters of the irradiated petal beam, such as handedness, topological charge, initial azimuthal phase and even ellipticity, corresponding to azimuthal and polar angles along equator and meridian planes of an orbital Poincaré sphere. The handedness, or direction of rotation, of the fabricated structures with multiple spiral arms could be controlled via the rotation and polarization directions of the irradiating laser field. This effect highlights an exotic coupling between the optical intensity gradient induced mass transport of the irradiated material and the spin angular momentum characteristics of the irradiating optical field. The azimuthal orientation of the surface relief structures could also be tuned by altering the initial relative phase between the coherently superposed Laguerre-Gaussian modes with opposite handedness, constituting the irradiating petal laser field. This work offers new insights into fundamental interactions which occur between light and matter, and we believe, will pave the way towards advanced technologies, such as ultrahigh density optical data storage.

Optical channel aggregation based on modulation format conversion by coherent spectral superposition with electro-optic modulators

Spectrally efficient modulation formats become essential for optical network scaling as the demand for routed data streams exceeds the present wavelength-division multiplexing systems’ throughput. However, achieving high spectral efficiency at high data rates requires complex and bandwidth-intensive electronics. In this study, we propose an all-optical aggregation scheme that combines multiple low spectral efficiency optical wavelength channels from an optical frequency comb based transmitter into fewer channels with higher spectral efficiency. Our method utilizes coherent spectral superposition and optical vector summation, eliminating the need for optical nonlinearities and relying on linear signal processing with an electro-optic modulator. By adjusting the phase of the radio frequency signal driving the modulator, we can easily achieve the required optical phase tuning for vector addition in the I-Q plane. Through experimental demonstrations, we show that the proposed approach enables the generation of 10 GBd PAM-4 and 10 GBd quadrature phase shift keying (QPSK) signals by aggregating two 10 GBd binary phase shift keying signals. Similarly, we aggregate two 10 GBd QPSK signals into one 10 GBd quadrature amplitude modulation-16 (QAM-16) signal. The experiments employ both conventional and sinc-shaped Nyquist signals. Our in-line, all-optical aggregation concept significantly enhances operational capacity while reducing complexity. It offers a promising solution for realizing flexible integrated optical transmitters for advanced modulation format signals using lower-quality electronics. Additionally, it aligns with the requirements of future dynamically reconfigurable optical networks that leverage spectral traffic aggregation. Given its reliance on linear signal processing with an electro-optic modulator, the integration of the method into any integrated photonic platform is straightforward.

Electromagnetically induced grating realization in phaseonium

We propose a method to implement electromagnetically induced grating in a phaseonium medium that has been coherently generated via atomic mechanisms. Phaseonium atoms have a Λ-type structure and three distinct energy levels; such atoms are originally generated in a coherent superposition of two lower levels. The phaseonium system is comprised of three-level atoms with a Λ-type configuration, which are initially prepared in a coherent superposition of two lower levels. To accomplish this spatial modulation based on the susceptibility of phaseonium medium, a standing-wave field is used. By looking at how an optical field diffracts at different relative phases, we find that the zeroth and first order diffraction intensities increase as the relative phase changes. We also investigate the impact of the Rabi frequency of the field on diffraction intensity and notice that an increasing strength of the Rabi frequency leads to amplification in the intensity of both central zeroth order and first-order diffraction. Furthermore, it has been observed that a significant rise in diffraction intensity occurs at longer interaction lengths between external fields and the atomic medium.

Resonance Interaction Due to Quantum Coherence

AbstractThe interaction energy between two atoms is crucially dependent on the quantum state of the two‐atom system. In this paper, it is demonstrated that a steady resonance interaction energy between two atoms exists when the atoms are in a certain type of coherent superposition of single‐excitation states. The interaction is tree‐level classical in the sense of the Feynman diagrams. A quantity called quantum classicality is defined in the present paper, whose nonzero‐ness ensures the existence of this interaction. The dependence of the interatomic interaction on the quantum nature of the state of the two‐atom system may potentially be tested with Rydberg atoms.

Time evolution of quantum correlations induced by atomic state superpositions

In this article, we study the time evolution of Gaussian quantum correlations induced by the superposition of atomic states. Photon-based quantum information and communication are powerful and suitable because the relevant physical mechanisms, the high combination rate of photons, and the sources of coherence can be understood and easily modeled. To this end, coupled photon pairs produced by coherent superposition of atomic states in an atomic laser and influences of spontaneous atomic decay due to vacuum field fluctuations have been considered. The dynamics of the quantum system leads to temporal quantum correlations such as quantum discord, quantum entanglement, and quantum steering, which are treated by the density operator approach. It was found that the generated photon pairs are completely in a separable state in the initial phase of the dynamical processes. The quantum coherences must be given sufficient time to generate quantum correlations that saturate after very short time scales. The strength of these quantum correlations has been improved by increasing the number of superposed atoms per unit of time. In particular, two-way quantum steering, which is a guarantee for the existence of quantum discord and quantum entanglement, can be achieved by increasing the atom injection rate from 10 kHz to 100 kHz when the probability of finding atoms in the excited state is 45%.