Search

The temperature dependence of spectra can reveal important insights into the structural and dynamical behavior of the system being probed. In the case of linear spectra, this has been exploited to investigate the thermodynamic driving forces governing the spectral response. Indeed, the temperature derivative of a spectrum can be used to obtain effective energetic and entropic profiles as a function of the measured frequency. The former can further be used to predict the temperature-dependent spectrum via a van't Hoff relation. However, these approaches are not directly applicable to nonlinear, complex-valued spectra, such as vibrational sum-frequency generation (SFG) or two-dimensional infrared (2D-IR) photon echo spectra. Here, we show how the energetic and entropic driving forces governing such nonlinear spectra can be determined and used within a generalized van't Hoff relation to predict their temperature dependence. The central idea is to allow the underlying energetic profiles to themselves be complex-valued. We illustrate this approach for 2D-IR spectra of water and SFG spectra of the air–water interface and demonstrate the accuracy of the generalized van't Hoff relationship and its implications for the origin of temperature-dependent spectral changes. [ABSTRACT FROM AUTHOR]

Previously [A.O. Savostianov, I.Yu. Eremchev, T. Plakhotnik, and A.V. Naumov, Phys. Rev. B 110, 045430 (2024)], we have shown that the zero-phonon line broadening of single tetra-tert-butylterrylene molecules embedded in the matrix of amorphous polyisobutylene is a result of coupling with resonant vibrational modes arising due to the impurity effect on the host normal modes. However, the question remained whether this model would be compatible with the extensive single-molecule spectroscopy and photon echo data previously obtained for the same host/guest system. In the present work we demonstrate the high predictive power of the resonant mode model treated in the framework of the non-perturbative theory of electron–phonon coupling, and good agreement with all experimental data. Furthermore, for single-molecule data we find an unexpectedly large dispersion of the force constants for impurity molecules. To explain this dispersion, we propose a simple microscopic model that assumes fluctuations in the distance between the impurity molecule and its nearest surroundings. [ABSTRACT FROM AUTHOR]

According to the theory of atmospheric transmission, the atmospheric optical characteristics of a 700 mm laser ranging telescope system are obtained by the inversion of the experimental data through the telescopic multi-elevation method, and a modified model of the ranging equation of laser diffuse radar is proposed. The variation in the Aerosol Optical Depth and atmospheric transmittance under the multi-elevation method, visibility and the oblique transmission atmospheric stratification model are analyzed and discussed. The model is numerically simulated and compared with the measured data of some space debris. The results show that the relative errors of the average echo photon number obtained by the multi-elevation method are less than 15%, and the average relative errors are 4.643% and 7.934%, respectively. The model improves the calculation accuracy of the laser ranging radar equation to a certain extent. [ABSTRACT FROM AUTHOR]

The dynamics of a liquid and its coupling to a solute are crucial for a better understanding of chemical processes in the liquid phase. In isotropic and homogeneous solutions, the time-correlation function of a solute is expected to vanish over time due to the translational and diffusive motions of the solvent. The three-pulse photon echo peak shift (3PEPS) is a third-order nonlinear spectroscopy technique that records the time-correlation function of a solute molecule in a solution, including an offset (inhomogeneity). In this work, we utilized a diffractive optics-based 3PEPS apparatus to fully resolve the dynamics in liquids from femtoseconds to nanoseconds while varying the temperature in the range of 80–298 K and the probe solute molecules. Our observations reveal dynamics slower than the dielectric relaxation of n-alcohols, even at room temperature, consisting of a ∼0.5 ns time constant that persists below the melting points and a static component (offset) on a nanosecond timescale. Based on the experiments, we suggest that locally formed glass-like clusters in liquids can be responsible for the slow dynamics. Our results may provide new insights into the dynamics of liquids and related phenomena such as liquid-glass and liquid-liquid phase transitions. [ABSTRACT FROM AUTHOR]

Phonon dispersion in crystals determines many important material properties, but its measurement usually requires large-scale facilities and is limited to bulk samples. Here, we demonstrate the measurement of full phonon dispersion along the stacking direction in nanoscale systems by using picosecond acoustics. A heterostructure sample was prepared consisting of layers of hexagonal boron nitride (hBN) sandwiching a thin layer of black phosphorus (BP), within which a strain pulse was generated by photoexcitation and observed with an optical probe in the BP layer. The strain pulse traverses to the few nanometer thick hBN layers, where it propagates to the edge and echoes back, like acoustic waves in Newton's cradle. The echoes returning to the BP layer provide information on the frequency-dependent time-of-flight and group velocity dispersion of the sample system. The microscopic origin of the photoinduced strain pulse generation and its propagation is revealed from first principles. Phonon frequency combs observed in the Fourier transform spectrum confirm the strain wave round trips and demonstrate the feasibility of determining group velocity dispersion through photoacoustics. [ABSTRACT FROM AUTHOR]

Delay lines that store quantum information are crucial for advancing quantum repeaters and hardware efficient quantum computers. Traditionally, they are realized as extended systems that support wave propagation but provide limited control over the propagating fields. Here, we introduce a parametrically addressed delay line for microwave photons that provides a high level of control over the stored pulses. By parametrically driving a three-wave mixing circuit element that is weakly hybridized with an ensemble of resonators, we engineer a spectral response that simulates that of a physical delay line, while providing fast control over the delay line's properties. We demonstrate this novel degree of control by choosing which photon echo to emit, translating pulses in time, and even swapping two pulses, all with pulse energies on the order of a single photon. We also measure the noise added from our parametric interactions and find it is much less than one photon. Delay lines for quantum information are key for quantum networking and hardware efficient quantum computers. Here, the authors present a virtual delay line for microwave pulses where data is stored in the excitations of a collection of resonators, demonstrating translation and swapping of data pulses. [ABSTRACT FROM AUTHOR]

Iron pentacarbonyl is a textbook example of fluxionality. We trap the molecule in cryogenic matrices to study the vibrational dynamics of CO stretching modes involved in the fluxional rearrangement. The infrared spectrum in Ar and N2 is composed of about ten narrow bands in the spectral range of interest, indicating the population of various lattice sites and a lowering of the molecular symmetry in the trapping sites. The vibrational dynamics is explored by means of infrared stimulated photon echoes at the femtosecond scale. Vibrational dephasing and population relaxation times are obtained. The non-linear signals exhibit strong oscillations useful to disentangle the site composition of the absorption spectrum. The population relaxation involves at least two characteristic times. An evolution of the photon echo signals with the waiting time is observed. The behavior of all the signals can be reproduced within a simple model that describes the population relaxation occurring in two steps: relaxation of v = 1 (population time T1 < 100 ps) and return to v = 0 (recovery time > 1 ns). These two steps explain the evolution of the oscillations with the waiting time in the photon echo signals. These results discard fluxional rearrangement on the time scale of hundreds of ps in our samples. Dephasing times are of the same order of magnitude as T1: dephasing processes due to the matrix environment are rather inefficient. The photon echo experiments also reveal that intermolecular resonant vibrational energy transfers between guest molecules occur at the hundreds of ps time scale in concentrated samples (guest/host > 104). [ABSTRACT FROM AUTHOR]

We present a partially linearized method based on spin-mapping for computing both linear and nonlinear optical spectra. As observables are obtained from ensembles of classical trajectories, the approach can be applied to the large condensed-phase systems that undergo photosynthetic light-harvesting processes. In particular, the recently derived spin partially linearized density matrix method has been shown to exhibit superior accuracy in computing population dynamics compared to other related classical-trajectory methods. Such a method should also be ideally suited to describing the quantum coherences generated by interaction with light. We demonstrate that this is, indeed, the case by calculating the nonlinear optical response functions relevant for the pump–probe and 2D photon-echo spectra for a Frenkel biexciton model and the Fenna–Matthews–Olsen light-harvesting complex. One especially desirable feature of our approach is that the full spectrum can be decomposed into its constituent components associated with the various Liouville-space pathways, offering a greater insight beyond what can be directly obtained from experiments. [ABSTRACT FROM AUTHOR]

High-resolution optical multidimensional coherent spectroscopy (MDCS) requires frequency-stable laser sources and high-resolution heterodyne spectra. Fully phase-locked dual-comb spectroscopy (DCS) enables the achievement of high resolution, high accuracy, broad bandwidth, and a rapid multi-heterodyne spectrum, which results in the DCS's potential to replace the spectrometer and phase detection system in MDCS. We verified the phase measurement capability of the MDCS system based on fully phase-locked fiber DCS by studying phase-sensitive photon echoes and double-quantum processes. The accurate phase and frequency of linear and nonlinear signals were obtained simultaneously using a single detector without subsequent frequency drift correction. Subsequently, the acquisition of longtime quantum beat signals demonstrates the high phase coherence between excitation pulses. Additionally, the two-dimensional coherent spectrum (2DCS) with high signal-to-noise-ratio and 100 MHz resolution was obtained via the MDCS system based on fully phase-locked fiber DCS. These results exhibit that fully phase-locked fiber DCS is an effective method for high-resolution 2DCS measurement, which facilitates further research on cold atoms, higher-order nonlinear spectra, and molecular fingerprint vibrational spectroscopy. [ABSTRACT FROM AUTHOR]

A time-multiplexing technique is proposed and demonstrated for single-photon imaging lidar, utilizing a large-area single-pixel single-photon detector to simultaneously detect the multi-pixel echoes. In this time-division multiplexing lidar, the echo signals from different pixels of the fiber array are delayed through fibers of varying lengths, merged into a fiber bundle, and then sequentially detected by the large-area single-pixel detector. In the experimental demonstration, a two-detector system capable of imaging 122 pixels using single-photon imaging lidar was showcased in three-dimensional imaging. Furthermore, the spectral broadening caused by multimode fiber dispersion was analyzed. Imaging of four different targets at a distance of 80 m was experimentally validated. This time-multiplexing technique can greatly reduce the number of single-photon detectors required in imaging lidar systems, making it suitable for low-cost lidar applications. [ABSTRACT FROM AUTHOR]

The rationality of the minimum electrophilicity principle (MElP) as a companion of minimum polarizability principle and maximum hardness principle is studied for simple diatomic, triatomic, and tetratomic molecules. The applicability is further justified considering organic molecules (e.g., pyrene and acridine yellow) are known for their photophysical properties and accordingly their excited state properties. Single excitation CI (CIS) and time‐dependent density functional theory (TDDFT) are employed to study the excited state reactivity. Two types of excitations, namely vertical and adiabatic, are considered. Processes involving conservation and change in spin multiplicity are included during excitation. The general trend is that the molecules are less electrophilic in the ground state than those in the corresponding excited states. It is found that adiabatic excitation validates the principle even for the triplet ground state molecules undergoing an excitation where spin multiplicity gets altered. The TDDFT method explains the validity of the MElP augmenting the CIS method. This study echoed the MElP during molecular electronic excitation. [ABSTRACT FROM AUTHOR]

The time-correlated single-photon-counting (TCSPC) three-dimensional (3D) imaging lidar system has broad application prospects in the field of low-light 3D imaging because of its single-photon detection sensitivity and picoseconds temporal resolution. However, conventional TCSPC systems always limit the echo photon flux to an ultra-low level to obtain high-accuracy depth images, thus needing to spend amounts of acquisition time to accumulate sufficient photon detection events to form a reliable histogram. When the echo photon flux is increased to medium or even high, the data acquisition time can be shortened, but the photon pile-up effect can seriously distort the photon histogram and cause depth errors. To realize high accuracy TCSPC depth imaging with a shorter acquisition time, we propose a high-flux fast photon-counting 3D imaging method based on empirical depth error correction. First, we derive the photon flux estimation formula and calculate the depth error of our photon-counting lidar under different photon fluxes with experimental data. Then, a function correction model between the depth errors and the number of echo photons is established by numerical fitting. Finally, the function correction model is used to correct depth images at high photon flux with different acquisition times. Experimental results show that the empirical error correction method can shorten the image acquisition time by about one order of magnitude while ensuring a moderate accuracy of the depth image. [ABSTRACT FROM AUTHOR]

Atomic-like emitters in the solid state serve as important resources in the advancement of future quantum networks. In particular, intra-4f optical transitions of rare earth ions exhibit excellent coherence properties thanks to the shielding effect of outer electrons. Still, the presence of various dephasing channels in solid state hosts introduces additional decoherence beyond the radiative decay, causing the coherence time of most rare earth doped materials to be over an order of magnitude lower than the radiative limit. Such obstacle prevents the emission of indistinguishable photons from rare earth ions, which is an essential requirement for various quantum applications. In this work, we perform optical coherence study on erbium ions doped in thin-film lithium niobate by patterning photonic crystal resonators with quality factor around 100 k and sub- λ 3 mode volume. Leveraging the combination of long coherence and strong Purcell enhancement in the cavity, we show that the coherence time measured with photon echo approaches the radiative limit (80%), representing a 50-fold improvement compared to the waveguide case. Our results present promising prospects toward utilizing rare earth doped materials as quantum repeaters and sources of indistinguishable photons. [ABSTRACT FROM AUTHOR]

This paper is devoted to an acoustical method of measuring mesoscale sea and ocean currents. Due to the fact that such currents exhibit variability, long-term studies are of great interest. The aim of this study is to prepare a physical foundation to organize current measurements in an automated way using stationary mounted underwater echosounding systems. An acoustic system operating at a frequency of 1–3 kHz (lower than commercial frequencies) that is capable of sensing echo signals from natural inhomogeneities located at distances of 1 to 10 km was tested. The test was conducted during a two-week marine experiment on the northern shelf of the Black Sea. The acoustic system was mounted on a platform together with a weather station and other tools that provided reference values for further comparison. Scattering from moving particles, as well as from wind waves, provides a general opportunity for sensing of currents at remote points. Since most scatterers exist at a depth of at least 2 m or on the surface, the proposed sensing method is going specialized for currents in upper layers. However, analysis of Doppler spectra of the actual returning (reverberation) signal showed that this kind of scattering was mixed with bottom reverberation (which contains no additional frequency shift), and other signal distortions were present. Thus, we proposed a new method of signal processing that is aware of the regional environment. The described method is based on machine learning, namely on gradient boosting to build decision trees, which compute water current properties. Such a computational routine is preceded by an original acoustic signal feature extraction process. Finally, a precision of an order of magnitude was achieved, and a sensing distance of at least 2 km was proven as a result of this study carried out with available instruments. [ABSTRACT FROM AUTHOR]

This paper proposes a single-photon-counting lidar based on time coding that can obtain the target's spatial location and measure the distance and azimuth angle in real time without needing a scanning device. Multiple optical fibers were used to introduce laser echo photons into a single-pixel single-photon detector. According to the deviation in the detection time of the echo photons passing through different optical fibers, multiple distances can be obtained simultaneously. Combining the measured distances with the fiber spacing allows the calculation of the distance, azimuth angle, and spatial coordinates of the target. This lidar has the advantages of high photon detection efficiency, short signal acquisition time, and low cost compared to array detectors. [ABSTRACT FROM AUTHOR]

A major goal of time-resolved spectroscopy is to resolve the dynamical processes that follow photoexcitation. This amounts to identifying all the quantum states involved and the rates of population transfer between them. Unfortunately, such quantum state and kinetic reconstructions are ambiguous using one-dimensional methods such as transient absorption even when all the states of the system are fully resolved. Higher-dimensionality methods like two-dimensional spectroscopy lift some of the ambiguity, but unless the spectral features are well-separated, current inversion methods generally fail. Here, we show that, using both coherence and population signals of the nonlinear response, it is indeed possible to accurately extract both static and dynamic information from the 2D spectrum even when features are highly congested. Coherences report on the positions of the vibronic states of the system, providing a useful constraint for extracting the full kinetic scheme. We model time-resolved 2D photon echo spectra using a sum-over-states approach and show in which regimes the Hamiltonian and kinetic schemes may be recovered. Furthermore, we discuss how such algorithms may be applied to experimental data and where some of the underlying assumptions may fail. The ability to systematically extract the maximal information content of multidimensional spectroscopic data is an important step toward utilizing the full power of these techniques and elucidating the structure and dynamics of increasingly complex molecular systems. [ABSTRACT FROM AUTHOR]

Optically coupling quantum emitters to nanoparticles provides the foundation for many plasmonic applications. Including quantum mechanical effects within the calculations can be crucial for designing new devices, but classical approximations are sometimes sufficient. Comprehending how the classical and quantum mechanical descriptions of quantum emitters alter their calculated optical response will lead to a better understanding of how to design devices. Here, we describe how the semiclassical Maxwell-Liouville method can be used to calculate the optical response from inhomogeneously broadened states. After describing the Maxwell-Liouville algorithm, we use the method to study the photon echoes from quantum dots and compare the results against analytical models. We then modify the quantum dot's state distribution to match a PbS 850 nm quantum dot's absorption spectra to see how the complete quasi-band structure affects their coupling to gold nanoislands. Finally, we compare the results with previously published work to demonstrate where the complete quantum dot description is necessary. [ABSTRACT FROM AUTHOR]

The memory effect in the form of hysteresis has been detected in the measured dependence of the intensity of the photon echo in YLiF4 and LuLiF4 samples with Er3+ impurity ions on the orientation, strength, and variation direction of the magnetic field. The prehistory of the location of a sample in the magnetic field with a certain direction and strength is written and stored for no less than 6 h at a temperature of 2 K. The effect crucially depends on the orientation of the optical axis of the sample with respect to the external magnetic field. [ABSTRACT FROM AUTHOR]

The memory effect in the form of hysteresis has been detected in the measured dependence of the intensity of the photon echo in YLiF4 and LuLiF4 samples with Er3+ impurity ions on the orientation, strength, and variation direction of the magnetic field. The prehistory of the location of a sample in the magnetic field with a certain direction and strength is written and stored for no less than 6 h at a temperature of 2 K. The effect crucially depends on the orientation of the optical axis of the sample with respect to the external magnetic field. [ABSTRACT FROM AUTHOR]

Existing laser active imaging detection methods are limited by the detection mechanism, which can only capture the intensity image and distance image of the target, and lack practical detection solutions for acquiring images of the target motion state characteristics (non-macroscopic centroid motion, such as rotation, rolling, and other motion characteristics around the centroid). In this paper, a detection method using Geiger mode avalanche photodiode (GM-APD) array detector for heterodyne imaging to obtain images of the target motion state is proposed. An innovative method based on photon counting time interval calculation (PCTIC) is proposed to obtain the Doppler frequency shift of the target echo for each GM-APD pixel, which effectively eliminates useless data unrelated to the signal. With limited data storage and processing speed, the heterodyne imaging performance has been effectively improved to achieve high-precision heterodyne imaging detection of very weak target echoes and to support heterodyne imaging detection of large arrays with more image pixels in parallel. Experiments show that the method can achieve video-level detection at an imaging resolution of 32×32, and with a paucity of echo photons (detection probability of echo is 0.0032), a millimetre-level velocimetry measurement error can be achieved by accumulating only 6 echo photons per image element. The system also shows good resistance to turbulence interference, with target motion state characteristics detected based on velocity images remaining virtually unaffected under turbulence conditions caused by strong flames. This advancement is crucial for target detection in complex working environments such as smart manufacturing and autonomous driving. • Supports a larger array of heterodyne imaging detection with more image pixels in parallel. • Velocity images provide features of the target motion dimension in addition to distance and intensity. • PCTIC method can break the limitation of phase noise on conventional heterodyne imaging detection. [ABSTRACT FROM AUTHOR]

• This article proposes a sparse adaptive matching pursuit (SAMP) algorithm. • The SAMP algorithm achieves high-precision and fast imaging of targets without prior information. • 3.Under low light conditions and acquisitio time of 4us per pixel, high-precision facial reconstruction has been achieved. Photon counting lidar has the ability to detect weak echo photons. However, in imaging applications, a small number of echo signals obtained in a very short acquisition time cannot get an accurate image estimation through the photon arrival time distribution histogram. Therefore, high-precision and fast imaging of an object using a small amount of weak echo photon signals is urgent to be solved. In this work, a sparse adaptive matching pursuit (SAMP) algorithm is proposed to process the echo photons without prior information to obtain the effective photon interval, which improves the reconstruction quality and imaging speed. By constructing a non-coaxial scanning imaging system to detect the face model, it has been experimentally proven that the proposed algorithm can achieve depth and reflectance image estimation under the condition of low power and low acquisition time of 4µs per pixel on average, and the mean absolute error (MAE) value is reduced by about 10 times compared to conventional reconstruction algorithm. [ABSTRACT FROM AUTHOR]

Over the last two decades, quantum memories have been intensively studied for potential applications of quantum repeaters in quantum networks. Various protocols have also been developed. To satisfy no noise echoes caused by spontaneous emission processes, a conventional two-pulse photon-echo scheme has been modified. The resulting methods include double-rephasing, ac Stark, dc Stark, controlled echo, and atomic frequency comb methods. In these methods, the main purpose of modification is to remove any chance of a population residual on the excited state during the rephasing process. Here, we investigate a typical Gaussian rephasing pulse-based double-rephasing photon-echo scheme. For a complete understanding of the coherence leakage by the Gaussian pulse itself, ensemble atoms are thoroughly investigated for all temporal components of the Gaussian pulse, whose maximum echo efficiency is 26% in amplitude, which is unacceptable for quantum memory applications. [ABSTRACT FROM AUTHOR]

Strong nonlinear interactions between single photons have important applications in optical quantum information processing. Demonstrations of these interactions in cold atomic ensembles have largely been limited to exploiting slow light generated using electromagnetically induced transparency (EIT). However, these EIT implementations have limited achievable phase shifts due to spontaneous emission. Here, we demonstrate and characterize a scheme free from these limitations using gradient echo memory with inferred single photon phase shifts of 0.07 ± 0.02 μ rad. Excellent agreement with theoretical modelling was observed. Degradation of memory efficiency was observed for large phase shifts but strategies to overcome that are presented. [ABSTRACT FROM AUTHOR]

Copyright of Study on Optical Communications / Guangtongxin Yanjiu is the property of Study on Optical Communications Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A quantum memory protocol has been implemented on the basis of the revival of silenced echo (ROSE) in the 167Er3+:Y2SiO5 crystal at the telecommunication wavelength for input light fields with a small number of photons. An efficiency of storage of 44% has been reached at a storage time of 40 μs. The input pulse contains ~340 photons on average, the reconstructed echo signal includes ~150 photons, and the signal-to-noise ratio is 4. It has been shown that the main source of noise is the spontaneous emission of atoms remaining in the excited state because the parameters of two rephasing pulses are imperfect. Methods of increasing the signal-to-noise ratio for the implementation of the efficient quantum memory for single-photon fields have been discussed. [ABSTRACT FROM AUTHOR]

The laser transmitter and photoelectric receiver are the core modules of the detector in a laser proximity fuse, whose performance variability can affect the accuracy of target detection and identification. In particular, there is no study on the effect of detector's component performance variability on frequency-modulated continuous-wave (FMCW) laser fuse under smoke interference. Therefore, based on the principles of particle dynamic collision, ray tracing, and laser detection, this paper builds a virtual simulation model of FMCW laser transmission with the professional particle system of Unity3D, and studies the effect of performance variability of laser fuse detector components on the target characteristics under smoke interference. Simulation results show that the difference in the performance of the fuse detector components causes the amplitude variation and peak migration of the beat signal spectrum, and the change in the visibility of the smoke can also affect the results, which indicates that the factors affecting the signal-to-noise ratio (SNR) of the echo signal are related to the smoke interference and performance variability of the detector. The proposed simulation model is supported by experimental results, which reflect the reliability of the proposed findings. Therefore, this study can be used for the optimization of the parameters in the laser fuse antismoke interference to avoid false alarms. [ABSTRACT FROM AUTHOR]

We report an eye-safe aerosol and cloud lidar with an Erbium-doped fiber laser (EDFL) and a free-space intracavity upconversion detector as the transmitter and receiver, respectively. The EDFL was home-made, which could produce linearly-polarized pulses at a repetition rate of 15 kHz with pulse energies of ~70 μJ and pulse durations of ~7 ns centered at 1550 nm. The echo photons were upconverted to ~631 nm via the sum frequency generation process in a bow-tie cavity, where a Nd:YVO4 and a PPLN crystal served as the pump and nonlinear frequency conversion devices, respectively. The upconverted visible photons were recorded by a photomultiplier tube and their timestamps were registered by a customized time-to-digital converter for distance-resolved measurement. Reflected signals peaked at ~6.8 km from a hard target were measured with a distance resolution of 0.6 m for an integral duration of 10 s. Atmospheric backscattered signals, with a range of ~6 km, were also detectable for longer integral durations. The evolution of aerosols and clouds were recorded by this lidar in a preliminary experiment with a continuous measuring time of over 18 h. Clear boundary and fine structures of clouds were identified with a spatial resolution of 9.6 m during the measurement, showing its great potential for practical aerosol and cloud monitoring. [ABSTRACT FROM AUTHOR]

The ability to extend the time scale of the coherent optical response from large ensembles of quantum emitters is highly appealing for applications in quantum information devices. In semiconductor nanostructures, spin degrees of freedom can be used as auxiliary, powerful tools to modify the coherent optical dynamics. Here, we apply this approach to negatively charged (In,Ga)As/GaAs self-assembled quantum dots which are considered as excellent quantum emitters with robust optical coherence and high bandwidth. We study three-pulse spin-dependent photon echoes subject to moderate transverse magnetic fields up to 1 T. We demonstrate that the timescale of coherent optical response can be extended by at least an order of magnitude by the field. Without magnetic field, the photon echo decays with T2 = 0.45 ns which is determined by the radiative lifetime of trions T1 = 0.26 ns. In the presence of the transverse magnetic field, the decay of the photon echo signal is given by spin dephasing time of the ensemble of resident electrons T2,e ∼ 4 ns. We demonstrate that the non-zero transverse g-factor of the heavy holes in the trion state plays a crucial role in the temporal evolution and magnetic field dependence of the long-lived photon echo signal. Semiconductor nanostructures are central to the implementation of quantum communication and information technologies. The authors leveraged spin degrees of freedom in quantum dot ensembles to increase optical coherence timescales, thereby disclosing intriguing solutions for future quantum memories. [ABSTRACT FROM AUTHOR]

General relativity admits a plethora of exact compact object solutions. The augmentation of Einstein's action with non-minimal coupling terms leads to modified theories with rich structure, which, in turn, provide non-trivial solutions with intriguing phenomenology. Thus, assessing their viability under generic fluctuations is of utmost importance for gravity theories. We consider static and spherically-symmetric solutions of a Horndeski subclass which includes a massless scalar field non-minimally coupled to the Einstein tensor. Such theory possesses second-order field equations and admits an exact black hole solution with scalar hair. Here, we study the stability of such solution under axial gravitational perturbations and find that it is linearly stable. The qualitative features of the ringdown waveform depend solely on the ratio of the two available parameters of spacetime, namely the black hole mass m and the non-minimal coupling strength ℓ η . Finally, we demonstrate the gravitational-wave ringdown transitions between three distinct patterns as the ratio m / ℓ η increases; a state which is dominated by photon-sphere excitations and maintains a typical quasinormal ringdown, an intermediate long-lived state which exhibits gravitational-wave echoes and, finally, a state where the ringdown and echoes are depleted rapidly to turn to an exponential tail. [ABSTRACT FROM AUTHOR]

We present the results from investigation of spectra of polar mesospheric summer echoes (PMSE) observed with EISCAT VHF 224 MHz radar during energetic particle precipitation events in the summer of 2019. We used the sudden enhancements in electron densities derived from the VHF observations above 90 km as indicators of particle precipitation. We find that the altitude extent of the PMSE increased along with an enhancement of the strength of the pre-existing PMSE. On some occasions, PMSE suddenly appeared during particle precipitation events. After the particle precipitation subsided, the PMSE intensities continued to be stronger for a few minutes and then decreased. At the altitudes where the maximum enhancement in PMSE backscatter occurred, there is no corresponding broadening in the spectral widths. Interestingly, the most intense PMSE echoes almost always coincided with the lower values of spectral widths both during particle precipitations and other times. In some cases, the spectral widths show well separated regimes between the upper and lower parts of the PMSE layers and this also happened irrespective of particle precipitation. The frequency Doppler shifts showed alternating upward and downward motions without much difference before and after the particle precipitation. Based on these observations, we conclude that the sudden enhancement in the electron densities during particle precipitation intensifies PMSE structures that match the Bragg scale of the incident radio wave thereby enabling an enhancement in the backscatter strength. Similarly, PMSE backscattering may get initiated in the altitudes in which the structures were already present but where electron density was not sufficient before the onset of precipitation. Spectral widths and Doppler velocities does not show sudden variations with particle precipitation because they depend on the neutral dynamics. [ABSTRACT FROM AUTHOR]

Monolayers of transition metal dichalcogenides display a strong excitonic optical response. Additionally encapsulating the monolayer with hexagonal boron nitride allows to reach the limit of a purely homogeneously broadened exciton system. On such a MoSe2‐based system, ultrafast six‐wave mixing spectroscopy is performed and a novel destructive photon echo effect is found. This process manifests as a characteristic depression of the nonlinear signal dynamics when scanning the delay between the applied laser pulses. By theoretically describing the process within a local field model, an excellent agreement with the experiment is reached. An effective Bloch vector representation is developed and thereby it is demonstrated that the destructive photon echo stems from a destructive interference of successive repetitions of the heterodyning experiment. [ABSTRACT FROM AUTHOR]

Analogues of 2D photon echo methods in which two population times are sampled have recently been used to expose heterogeneity in chemical kinetics. In this work, the two population times sampled for a transition metal complex are transformed into a 2D rate spectrum using the maximum entropy method. The 2D rate spectrum suggests heterogeneity in the vibrational cooling (VC) rate within the ensemble. In addition, a cross peak associated with VC and back electron transfer (BET) dynamics reveals correlation between the two processes. We hypothesize that an increase in the strength of solute-solvent interactions, which accelerates VC, drives the system toward the activationless regime of BET. [ABSTRACT FROM AUTHOR]

Over the last two decades, quantum memories have been intensively studied for potential applications of quantum repeaters in quantum networks. Various protocols have also been developed. To satisfy no noise echoes caused by spontaneous emission processes, a conventional two-pulse photon-echo scheme has been modified. The resulting methods include double-rephasing, ac Stark, dc Stark, controlled echo, and atomic frequency comb methods. In these methods, the main purpose of modification is to remove any chance of a population residual on the excited state during the rephasing process. Here, we investigate a typical Gaussian rephasing pulse-based double-rephasing photon-echo scheme. For a complete understanding of the coherence leakage by the Gaussian pulse itself, ensemble atoms are thoroughly investigated for all temporal components of the Gaussian pulse, whose maximum echo efficiency is 26% in amplitude, which is unacceptable for quantum memory applications.

Photon echo is a fundamental tool for the manipulation of electromagnetic fields. Unavoidable spontaneous emission noise is generated in this process due to the strong rephasing pulse, which limits the achievable signal-to-noise ratio and represents a fundamental obstacle towards their applications in the quantum regime. Here we propose a noiseless photon-echo protocol based on a four-level atomic system. We implement this protocol in a Eu3+:Y2SiO5 crystal to serve as an optical quantum memory. A storage fidelity of 0.952 ± 0.018 is obtained for time-bin qubits encoded with single-photon-level coherent pulses, which is far beyond the maximal fidelity achievable using the classical measure-and-prepare strategy. In this work, the demonstrated noiseless photon-echo quantum memory features spin-wave storage, easy operation and high storage fidelity, which should be easily extended to other physical systems. Photon echo techniques are difficult to implement in the quantum regime due to coherent and spontaneous emission noise. Here, the authors propose a low-noise photon-echo quantum memory approach based on all-optical control in a four-level system, and demonstrate it using a Eu3+:Y2SiO5 crystal. [ABSTRACT FROM AUTHOR]

Тhe realization of logical operations for images using an accumulated echo hologram in the presence of external spatially inhomogeneous electric fields is considered. It is shown that the photon echo locking effect allows controlling the type of logical operations (from uniting the sets to their symmetric difference and superposition) by varying the values of gradients of external spatially inhomogeneous electric fields. [ABSTRACT FROM AUTHOR]

Following the scheme proposed by Eberly and Wodkiewicz for the physical spectrum, we calculate the fluorescence spectrum of the Jaynes–Cummings model when the two-level system interacts with an electromagnetic field that initially is in a squeezed coherent state. We show the appearing of "ringing lines" in the fluorescence spectrum that are echoes of the oscillations in the photon distribution of the compressed field. These ringing lines may be a similar effect as the ringing revivals of the atomic inversion that are a signature of squeezed states. [ABSTRACT FROM AUTHOR]

Assigning absolute phase to two-dimensional (2D) third-order nonlinear optical signals generally requires acquiring both the rephasing and the non-rephasing signals and comparing the sum of the two to spectrally resolved pump-probe spectra. To date, however, Gradient Assisted Photon Echo Spectroscopy (GRAPES) has only been able to acquire rephasing spectra. Such a constraint requires a new phasing protocol. Here, we analytically prove that the rephasing and non-rephasing spectra can be phased independently using pump-probe signal. We verify this result holds even for finite duration pulses by simulation. This relationship holds for all 2D spectroscopies, not only GRAPES. In addition, we present improvements to GRAPES that enable acquisition of rephasing and non-rephasing signals in different phase-matched directions. We employ our phasing protocol to phase the data for laser dye IR-144, leading to reconstruction of purely absorptive 2D spectrum. [ABSTRACT FROM AUTHOR]

We consider the implementation of the logical operation of disjunction of signals using accumulated stimulated echo holography. We study the processing of information embedded in the laser pulses of a pulse pair, with one of the pulses in the pair being an object and the other one having a wide frequency spectrum. We show that, taking the pulse spectra as narrow frequency regions within the inhomogeneously broadened resonance transition line, it is possible to implement the disjunction operation in the frequency domain. [ABSTRACT FROM AUTHOR]

The article present the first hybrid quantum memory-enabled network by demonstrating the interconnection and simultaneous operation of two types of quantum memory including an atomic ensemble-based memory and an all-optical Loop memory. It observes a well-preserved quantum correlation and a violation of Cauchy-Schwarz inequality by interfacing the quantum memories at room temperature.

We study the localization of dressed Dirac electrons in a cylindrical quantum dot (QD) formed on monolayer and bilayer graphene by spatially different potential profiles. Short lived excitonic states which are too broad to be resolved in linear spectroscopy are revealed by cross peaks in the photon-echo nonlinear technique. Signatures of the dynamic gap in the two-dimensional spectra are discussed. The effect of the Coulomb induced exciton-exciton scattering and the formation of biexciton molecules are demonstrated. [ABSTRACT FROM AUTHOR]

We have investigated the dynamics of the hydrogen bonds that connect the components of a [2]rotaxane in solution. In this rotaxane, the amide groups in the benzylic-amide macrocycle and the succinamide thread are connected by four equivalent N-H···O=C hydrogen bonds. The fluctuations of these hydrogen bonds are mirrored by the frequency fluctuations of the NH-stretch modes, which are probed by means of three-pulse photon-echo peak shift spectroscopy. The hydrogen-bond fluctuations occur on three different time scales, with time constants of 0.1, 0.6, and >=200 ps. Comparing these three time scales to the ones found in liquid formamide, which contains the same hydrogen-bonded amide motif but without mechanical constraints, we find that the faster two components, which are associated with small-amplitude fluctuations in the strength of the N-H···O=C hydrogen bonds, are very similar in the liquid and the rotaxane. However, the third component, which is associated with the breaking and subsequent reformation of hydrogen bonds, is found to be much slower in the rotaxane than in the liquid. It can be concluded that the mechanical bonding in a rotaxane does not influence the amplitude and time scale of the small-amplitude fluctuations of the hydrogen bonds, but strongly slows down the complete dissociation of these hydrogen bonds. This is probably because in a rotaxane breaking of the macrocycle-axle contacts is severely hindered by the mechanical constraints. The hydrogen-bond dynamics in rotaxane-based molecular machines can therefore be regarded as liquidlike on a time scale 1 ps and less, but structurally frozen on longer (up to at least 200 ps) time scales. [ABSTRACT FROM AUTHOR]

We have studied the temperature dependence of the vibrational frequency fluctuation of the antisymmetric stretching mode of N3- in D2O by three-pulse infrared (IR) photon echo experiments. IR pump-probe measurements were also carried out to investigate the population relaxation and the orientational relaxation of the same band. It was found that the time-correlation function (TCF) of the frequency fluctuation of this mode is well described by a biexponential function with a quasistatic term. The faster decay component has a time constant of about 0.1 ps, and the slower component varies from 1.4 to 1.1 ps in the temperature range from 283 to 353 K. This result indicates that liquid dynamics related to the frequency fluctuation are not highly sensitive to temperature. We discuss the relationship between the temperature dependence of the vibrational frequency fluctuation and that of the molecular motion of the system to investigate the molecular origin of the frequency fluctuation of the solute. We compare the temperature dependence of the frequency fluctuation with that of other dynamics such as dielectric relaxation of water. In contrast to the Debye dielectric relaxation time of D2O, the two time constants of the TCF of the frequency fluctuation do not exhibit strong temperature dependence. We propose a simple theoretical model for the frequency fluctuation in solutions based on perturbation theory and the dipole-dipole interaction between the vibrational mode of the solute and the solvent molecules. This model suggests that the neighboring solvent molecules in the vicinity of the solute play an important role in the frequency fluctuation. We suggest that the picosecond component of the frequency fluctuation results from structural fluctuation of the hydrogen-bonding network in water. [ABSTRACT FROM AUTHOR]

The role of weakly chirped pulses (time bandwidth product, ΔνΔτ<0.61) on three-pulse photon echo signals has been systematically studied. Pulses with varying chirp were characterized with frequency resolved optical gating (FROG) and used to measure spectrally resolved three-pulse photon echoes of a dye in solution. The weakly chirped pulses give rise to markedly different echo signals for population times below ∼100 fs. The chirped pulses can decrease or enhance spectral signatures of an excited state absorption transition in the echo signal. Furthermore, the observed dephasing dynamics depend on the phase of the electric fields. Simulations based on a three-level model and the electric fields retrieved from the FROG traces give a good agreement for photon echo experiments with both transform limited and chirped pulses. The simulations also allow for a numerical investigation of effects of chirp in two-dimensional spectroscopy. For a two-level system, the chirped pulses result in nonelliptical two-dimensional spectra that can erroneously be interpreted as spectral heterogeneity with frequency dependent dephasing dynamics. Furthermore, chirped pulses can give rise to “false” cross peaks when strong vibrational modes are involved in the system-bath interaction. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) photon-echo spectra of a single subunit of the Fenna–Matthews–Olson (FMO) bacteriochlorophyll trimer of Chlorobium tepidum are simulated, employing the equation-of-motion phase-matching approach (EOM-PMA). We consider a slightly extended version of the previously proposed Frenkel exciton model, which explicitly accounts for exciton coherences in the secular approximation. The study is motivated by a recent experiment reporting long-lived coherent oscillations in 2D transients [Engel et al., Nature 446, 782 (2007)] and aims primarily at accurate simulations of the spectroscopic signals, with the focus on oscillations of 2D peak intensities with population time. The EOM-PMA accurately accounts for finite pulse durations as well as pulse-overlap effects and does not invoke approximations apart from the weak-field limit for a given material system. The population relaxation parameters of the exciton model are taken from the literature. The effects of various dephasing mechanisms on coherence lifetimes are thoroughly studied. It is found that the experimentally detected multiple frequencies in peak oscillations cannot be reproduced by the employed FMO model, which calls for the development of a more sophisticated exciton model of the FMO complex. [ABSTRACT FROM AUTHOR]

We report a three-pulse photon echo peak shift (3PEPS) apparatus adopting a diffractive beam splitter to generate triplets of femtosecond pulses with tilted wave front, which enhances the overlap over the entire aperture in a noncollinear geometry while preserving femtosecond pulse duration. The apparatus provides highly reproducible 3PEPS data including the long time peak shift, a critical parameter to recognize the spectral inhomogeneity in condensed phases. To demonstrate the high performance of our setup and to examine the inhomogeneous line broadening in liquids, we measured 3PEPS of a carbocyanine dye IR125 in several solvents. The solvation dynamics becomes slower for IR125 compared to the typical values reported previously probably due to the multipolar nature of the excitation in this large and flexible probe molecule. More importantly, inhomogeneity was observed unambiguously in all solvents, and it is excitation energy dependent. It was speculated that slow dielectric relaxation and conformational heterogeneity may be responsible for the inhomogeneity. [ABSTRACT FROM AUTHOR]

We theoretically investigate intermolecular motions in liquid water in terms of third-order infrared (IR) spectroscopy. We calculate two-dimensional (2D) IR spectra, pump-probe signals, and three-pulse stimulated photon echo signals from the combination of equilibrium and nonequilibrium molecular dynamics simulations. The 2D IR spectra and the three-pulse photon echo peak shift exhibit that the frequency correlation of the librational motion decays with a time scale of 100 fs. The two-color 2D IR spectra and the pump-probe signals reveal that the energy transfer from the librational motion at 700 cm-1 to the low frequency motion below 300 cm-1 occurs with a time scale of 60 fs and the subsequent relaxation to the hot ground state takes place on a 500 fs time scale. The time scale of the anisotropy decay of the librational motion is found to be ∼115 fs. The energy dissipation processes are investigated in detail by using the nonequilibrium molecular dynamics simulation, in which an electric field pulse is applied. We show that the fast energy transfer from the librational motion to the low frequency motion is mainly due to the librational-librational energy transfer. We also show that the fast anisotropy decay mainly arises from the rapid intermolecular energy transfer. [ABSTRACT FROM AUTHOR]

By means of integrated and dispersed IR photon echo measurement methods, the vibrational dynamics of C–N stretch modes in 4-cyanophenol and 4-cyanophenoxide in methanol is investigated. The vibrational frequency-frequency correlation function (FFCF) is retrieved from the integrated photon echo signals by assuming that the FFCF is described by two exponential functions with about 400 fs and a few picosecond components. The excited state lifetimes of the C–N stretch modes of neutral and anionic 4-cyanophenols are 1.45 and 0.91 ps, respectively, and the overtone anharmonic frequency shifts are 25 and 28 cm-1. At short waiting times, a notable underdamped oscillation, which is attributed to a low-frequency intramolecular vibration coupled to the CN stretch, in the integrated and dispersed vibrational echo as well as transient grating signals was observed. The spectral bandwidths of IR absorption and dispersed vibrational echo spectra of the 4-cyanophenoxide are significantly larger than those of its neutral form, indicating that the strong interaction between phenoxide and methanol causes large frequency fluctuation and rapid population relaxation. The resonance effects in a paradisubstituted aromatic compound would be of interest in understanding the conjugation effects and their influences on chemical reactivity of various aromatic compounds in organic solvents. [ABSTRACT FROM AUTHOR]

We explore how the width of the three-pulse photon echo signal at long population times can be used to determine the strength of the system-bath interaction. Using simulation with finite pulses we show that a simple relation exist between the width of the echo signal, the coupling strength, and the pulse autocorrelation. The derived model is applied to Rhodamine 6G in alcoholic solution, a paradigm system for the study of solvation dynamics, and the results are compared to conventional methods. The independently determined coupling strength forms the basis for a computationally inexpensive route to determine the entire spectral density, the key parameter when considering system-bath interactions. Our method allows us to accurately estimate the relative amplitude of fast and slow components in the correlation function using only impulsive limit simulations. We show that the peak shift significantly overestimates the amplitude of the fastest decay component for our experimental data. Changing solvent from methanol to 1-hexanol we observe a narrowing of the width of the echo profile. The changes in the echo width allow us to estimate the changes of the coupling strength in various solvents. [ABSTRACT FROM AUTHOR]

We present the theory and the selection procedure of phase-cycling schemes for phase coherent multidimension optical spectroscopy. We apply our selection procedure to determine the phase-cycling schemes with the least number of steps needed to measure the two-dimensional spectra of various time resolved four wave mixing optical processes. The phase-cycling scheme selection procedure presented in this paper can be applied to higher order nonlinear optical experiments involving more optical pulses that measure higher dimensional optical spectra. [ABSTRACT FROM AUTHOR]

Effects of the exciton-exciton coherence transfer (EECT) in strongly coupled molecular aggregates are investigated from the reduced time-evolution equation which we have developed to describe EECT. Starting with the nonlinear response function, we obtained explicit contributions from EECT to four-wave-mixing spectrum such as photon echo, taking into account double exciton states, static disorder, and heat-bath coupling represented by arbitrary spectral densities. By using the doorway-window picture and the projection operator technique, the transfer rates between two different electronic coherent states are obtained within a framework of cumulant expansion at high temperature. Applications of the present theory to strongly coupled B850 chlorophylls in the photosynthetic light harvesting system II (LH2) are discussed. It is shown that EECT is indispensable in properly describing ultrafast phenomena of strongly coupled molecular aggregates such as LH2 and that the EECT contribution to the two-dimensional optical spectroscopy is not negligible. [ABSTRACT FROM AUTHOR]