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We have studied the pump-probe spectroscopy of graphene oxide quantum dots. In the presence of gold nanoparticles, strong modifications of pump-probe spectra have been observed. We develop a theoretical model to explain the observed features of the pump-probe spectra. The model takes into account self-consistently the interaction of exciton with surface plasmonic waves excited in the gold nanoparticles, and it provides a qualitative agreement with the observed pump-probe spectra. We have demonstrated that the using gold nanoparticles can increase sensitivity, and potentially to have a broader range of applications to both spectroscopy and microscopy.

The adaptation of systems to external influences is of broad interest. We study the influence of microwave signals of different shapes on the magnetoacoustic wave system with a giant nonlinearity in canted antiferromagnet FeBO3 at room temperature, which is close to its phase transition to the paramagnetic state. The classical nonlinear system obeys external deterministic signals; the modulation response describes the shape of these signals. In response to a noisy spectrum, the system shows self-organization, and mode competition selects one excited mode while suppressing others. With an increase in the power of the external signal, another self-organization is observed in the form of a narrow peak at the frequency of the fundamental minimum. This represents the first observation of the macroscopic quantum statistical phenomenon, Bose-Einstein condensation of magnetoacoustic wave quanta in a wave system with a high level of thermal fluctuations. The resulting picture of adaptation can analogously be transferred to many other adaptive wave systems, including large scale adaptive wave systems in the natural environment.

Hydrogen-bonded mixtures with varying concentration are a complicated networked system that demands a detection technique with both time and frequency resolutions. Hydrogen-bonded pyridine–water mixtures are studied by a time-frequency resolved coherent Raman spectroscopic technique. Femtosecond broadband dual-pulse excitation and delayed picosecond probing provide sub-picosecond time resolution in the mixtures temporal evolution. For different pyridine concentrations in water, asymmetric blue versus red shifts (relative to pure pyridine spectral peaks) were observed by simultaneously recording both the coherent anti-Stokes and Stokes Raman spectra. Macroscopic coherence dephasing times for the perturbed pyridine ring modes were observed in ranges of 0.9–2.6 ps for both 18 and 10 cm − 1 10\hspace{0.33em}{{\rm{cm}}}^{-1} broad probe pulses. For high pyridine concentrations in water, an additional spectral broadening (or escalated dephasing) for a triangular ring vibrational mode was observed. This can be understood as a result of ultrafast collective emissions from coherently excited ensemble of pairs of pyridine molecules bound to water molecules.

Air quality control is an important task in prevention of human exposure to toxic and harmful gases and requires reliable gas sensors. During last decades many gas sensing mechanisms, based on different physical or chemical interactions with sensitive materials, have been developed, but the problem of precise analysis of gas mixtures still remains. The problem can be solved by introducing new sensing mechanism based on an adiabatically changing electric field interacting with the rotational structure of the molecules with dipole moments. We have theoretically demonstrated a single low frequency gas detector that can be used for sensing of gas mixtures with high selectivity, accuracy, and sensitivity. The enhancement of the population difference between corresponding molecular levels and reached the theoretical maximum of absorption have been shown.

Using quantum coherence effects, we have developed a new technique of detection of motion of single atoms or ions in an optical cavity. We have theoretically demonstrated that the presence of a sin...

For most three centuries after Hooke introduced optical microscopy, refinement of the instrumentation made microscopes more convinient than anything else. As in modern microscopy, a light source, an objective lens, and an eyepiece were used to project an image magnified from a 100-fold to 1,000-fold into a human eye. This range of magnifications and resolution (of the order of 200 nm) has brought cellular morphology and tissue structure into view and made optical microscopy the perfect partner for biological investigations. A resolution constraint in optical imaging is imposed by the diffraction limit discovered by Lord Rayleigh in the 19th century. Fundamentally, this restricts the ability to resolve two distant point sources, such as stars or planets, with an angular resolution α smaller than the wavelength of light λ divided by the numerical aperture of the imaging system

During last decades many gas sensing mechanisms, based on different physical or chemical interactions with sensitive materials, have been developed, but the problem of precise analysis of gas mixtures still remains. New sensing mechanism has been suggested that is based on an adiabatically changing electric field interacting with the rotational structure of the molecules with dipole moments. A single low frequency gas detector, that can be used for sensing of gas mixtures with high selectivity, accuracy, and sensitivity, has been theoretically demonstrated. The enhancement of the population difference between corresponding molecular levels and reached the theoretical maximum of absorption have been shown.

The propagation of quantum field interacting with a single two-level atom has been studied. Using the Gaussian quantum mode functions, we calculate evolution of the quantum state that includes atomic and field variable. We demonstrated the phase and group velocities of the single photon propagation that can be of great importance for long quantum communications. The results can be used for controlling quantum field propagation, and for design of optical elements such as a quantum prism and a quantum lens.

Spontaneous emission from individual atoms in vapor lasts nanoseconds, if not microseconds, and beatings in this emission involve only directly excited energy sublevels. In contrast, the superfluorescent emissions burst on a much-reduced timescale and their beatings involve both directly and indirectly excited energy sublevels. In this work, picosecond and femtosecond superfluorescent beatings are observed from a dense cesium atomic vapor. Cesium atoms are excited by 60-femtosecond long, 800 nm laser pulses via two-photon processes into their coherent superpositions of the ground 6S and excited 8S states. As a part of the transient four wave mixing process, the yoked superfluorescent blue light at lower transitions of 6S - 7P are recorded and studied. Delayed buildup time of this blue light is measured as a function of the input laser beam power using a high-resolution 2 ps streak camera. The power dependent buildup delay time is consistently doubled as the vapor temperature is lowered to cut the number of atoms by half. At low power and density, a beating with a period of 100 picoseconds representing the ground state splitting is observed. The autocorrelation measurements of the generated blue light exhibit a beating with a quasi-period of 230 fs corresponding to the splitting of the 7P level primarily at lower input laser power. Understanding and, eventually, controlling the intriguing nature of superfluorescent beatings may permit a rapid quantum operation free from the rather slow spontaneous emission processes from atoms and molecules., Comment: 7 pages, 5 figures

Additional spectral broadening for pyridine-water complexes was observed that cooperative phenomenon is in effect. Probe pulse delay measurements in coherent Raman spectroscopy differentiated spectral dephasing rates for cooperative species among others.

The Raman scattering of Cisplatin (the first generation of anticancer drugs) has been studied. In the presence of silver nanoparticles, strong modifications of Raman spectra have been observed. The Raman frequencies have been shifted and the line profiles are broadened. We develop a theoretical model to explain the observed features of the Raman scattering. The model takes into account self-consistently the interaction of molecules with surface plasmonic waves excited in the silver nanoparticles, and it provides a qualitative agreement with the observed Raman spectra. We have demonstrated that the using silver nanoparticles can increase sensitivity of the technique, and potentially it has a broader range of applications to both spectroscopy and microscopy.

The absorption in quantum dots (QDs) embedded within a semiconductor matrix can be manipulated by resonant optical excitation of phonons. The far-field interaction of the light leading to dressed phonon states within reduced graphene oxide quantum dots has been coherently modified by a near-field optical driving field at the nanoscale limit. The near-field optical excitation was introduced by resonant excitation of localized plasmons in metal nanoparticles coupled to QDs for ultrafast light manipulation. The coherent interaction of photons due to localized plasmon induced a change in the transient absorption of graphene oxide quantum dots conjugated to silver nanoparticles. Resonant pumping of plasmons and phonons with 400 nm pump photons induces a coherent change in excitonic absorption within QDs which results in phonon-assisted plasmon induced transparency at room temperature. This novel effect can be related to the appearance of the coherent effects such as forming dark states and coherent population ...

We consider the motion of a quantum particle in a free space. Introducing an explicit measurement procedure for velocity, we demonstrate that the measured velocity is related to the group and phase velocities of the corresponding matter waves. We show that for long distances the measured velocity coincides with the matter wave group velocity. We discuss the possibilities to demonstrate these effects for the optical pulses in coherently driven media or for radiation propagating in waveguides.

We have considered the Raman scattering in molecular media. Applying two laser fields in a two-photon resonance with vibrational transition, we have studied the role of rotational levels for excitation of vibrational coherence. It is shown that the molecular vibrational coherence strongly depends on the effect of coherent population trapping for rotational levels. The obtained results are important for applications of Raman spectroscopy to molecular detection in engineering, chemical, and biological applications.

Using the Magnus expansion to the fourth order, we obtain analytic expressions for the atomic state of a two-level system driven by a laser pulse of arbitrary shape with small pulse area. We also determine the limitation of our obtained formulas due to limited range of convergence of the Magnus series. We compare our method to the recently developed method of Rostovtsev et al. (PRA 2009, 79, 063833) for several detunings. Our analysis shows that our technique based on the Magnus expansion can be used as a complementary method to the one in PRA 2009., 12 pages, 4 figures

This study reports the optimized structures and lowest-energy conformations/stereochemistry of five currently used platinum-based drugs: cisplatin, carboplatin, nedaplatin, oxaliplatin, and heptaplatin. Normal Raman and IR spectra of each drug are experimentally obtained and have been compared to various levels of density functional theory (DFT). Although some combination of structure, reactivity, or spectroscopy for these drugs has been studied by various groups, there are no known experimental normal Raman and IR spectra for nedaplatin, oxaliplatin, and heptaplatin in the literature. The detailed structural and vibration findings of these drugs are very important to understanding platinum behavior and drug dynamics. The following work explores the vibrational frequencies of these drugs particularly by focusing on the low-energy modes between 200 and 600 cm

The absorption due to phonon vibrations in graphene oxide quantum dots (GO-QDs) has been modified by localized plasmons induced by Ag nanoparticles (NPS). The interference of phonons and plasmons results in coherent interaction that leads to the formation of "dark states" and "coherent population trapping" related to Fano like effect. The localized electric field effectively drives the phonons which in turn modifies the coherent interaction in exciton absorption states of graphene oxide. A quantum optical theory is used to qualitatively explain the differential absorption spectra measured using pump-probe spectroscopy demonstrating the formation of dark states.

We present a study of the interaction of coherent field effects on population of two bound atomic states of a dense atomic gas interacting in a cooperative regime. We provide a theoretical description of this phenomenon using density matrix equations. We discuss the implications and applications of the present studies to quantum amplification by superradiant emission of radiation action. A classical model is developed to gain physical insights into qaser physics.

We investigate cooperative emission from a rubidium vapor, and demonstrate a controlled transition from yoked superfluorescence to three-photon-induced superradiance by driving the medium with co-propagating ultrashort laser pulses. We study temporal emission profiles and time delays on a picosecond time scale and compare the measured pulse shapes with simulations. Our results suggest strategies to improve efficiency of mirrorless lasers and superradiant light sources.

The absorption due to phonon vibrations in graphene oxide quantum dots (GO-QDs) has been modified by localized plasmons induced by Ag nanoparticles (NPS). The interference of phonons and plasmons results in coherent interaction that leads to the formation of “dark states” and “coherent population trapping” related to Fano like effect. A quantum optical theory is used to qualitatively explain the differential absorption spectra measured using pump-probe spectroscopy demonstrating the formation of dark states.

We report an analytic solution for a three-level atom driven by arbitrary time-dependent electromagnetic pulses. In particular, we consider far-detuned driving pulses and show an excellent match between our analytic result and the numerical simulations. We use our solution to derive a pulse area theorem for three-level $\mathsf{V}$ and $\mathrm{\ensuremath{\Lambda}}$ systems without making the rotating wave approximation. Formulated as an energy conservation law, this pulse area theorem can be used to understand pulse propagation through three-level media.

We consider an opto-mechanical effect that is related to the appearance of additional optical phase due to motion of an ultra-dispersive medium, the enhanced Fizeau effect. We have theoretically shown that the enhanced Fizeau effect on a single atom in a cavity can be observed. It has been shown that the change of phase is sensitive to the mechanical motion and can be applied to measurement of possible displacements as small as cm Hz. One of application can be the detection of weak forces exerted on a single atom.

We devise an approximate and fast converging iterative approach to solve the Riccati equation. This solution provides a systematic way to generate isospectral potentials in quantum mechanics. The proposed solutions derived by our approach are compared with exact solutions for various potentials.

The vibrational molecular excitation by strong laser fields have been studied. Starting with the molecular Hamiltonian, we derive the vibrational excitation rate due to a gradient of laser field and show that the rate can be two to three orders of magnitude larger than the regular Raman rates. The developed theory contributes to understanding of interaction of powerful laser pulses with molecular systems, and it might be used in developing quantitative coherent Raman spectroscopy. Copyright © 2013 John Wiley & Sons, Ltd.

Quantum optics with X-rays has long been a somewhat exotic activity, but it is now rapidly becoming relevant as precision x-ray optics and novel X-ray light sources, and high-intensity lasers are becoming available. This article gives an overview of the current state of the field and an outlook to future prospects.

We study Raman scattering in molecular media by applying two laser fields in a two-photon resonance with vibrational transition. The role of rotational levels has been investigated. It is shown that the molecular vibrational coherence strongly depends on the effect of coherent population trapping for rotational levels. The obtained results are important for application of Raman spectroscopy to molecular detection for engineering, chemical, and biological applications.

We introduce and theoretically demonstrate a quantum metamaterial made of dense ultracold neutral atoms loaded into an inherently defect-free artificial crystal of light, immune to well-known critical challenges inevitable in conventional solid-state platforms. We demonstrate an all-optical control, on ultrafast time scales, over the photonic topological transition of the isofrequency contour from an open to closed topology at the same frequency. This atomic lattice quantum metamaterial enables a dynamic manipulation of the decay rate branching ratio of a probe quantum emitter by more than an order of magnitude. Our proposal may lead to practically lossless, tunable, and topologically reconfigurable quantum metamaterials, for single or few-photon-level applications as varied as quantum sensing, quantum information processing, and quantum simulations using metamaterials.

We propose a novel architecture for topologically reconfigurable quantum metamaterial by engineering the response of dense ultracold atoms loaded in an artificial crystal of light. Our atomic lattice quantum metamaterial opens the door for applications at single-photon level with metamaterials.

We have derived an analytical solution of the 3D Schrequation where the mass varies with position. Our solution is a general solution for any massive particle with a position dependent mass m(r) scattered by an arbitrary potential V(r)

It was shown some time ago that when the excitation of an ensemble of two-level atoms is swept in the direction of lasing, so that atoms are prepared in the excited state just as the radiation from previously excited atoms reaches them, the resulting laser amplifier is “highly anomalous” and yields superradiant emission without population inversion. We here show that transient gain in a three-level system has common features with Dicke superradiance and can yield strong extreme ultraviolet lasing in, for example, He atoms (at 58 nm) or He-like ions such as B3+ (at 6.1 nm).

We study the statistics of the emitted light from a single two-level atom in a cavity. We explore the effects of counter-rotating terms. We show that the virtual processes destroy the antibunching effect in the low-frequency regime.

It is well-known that strong Coulomb effects in carbon nanotubes lead to formation of the so-called "bright" and "dark" (forbidden one-photon optical transition) exciton states, and dramatically decrease the efficiency of one-photon light emission via trapping of the carriers by "dark" states. We suggest and demonstrate that the proper use of these "bright" and "dark" exciton states with distinctively different recombination times may turn the situation around: the use of quantum coherence and multiphoton schemes of excitation potentially not only allow one to efficiently manipulate the dark states, but can also create conditions for efficient light generation in different frequency regions, produce "slow" or "fast" light, implement quantum light storage, and media with a negative refractive index. We discuss possible applications of the quantum coherent effects to quantum-optical carbon nanotube devices that have a potential for suitable performance at elevated temperatures, because the binding energies of excitons in single-walled nanotubes are hundreds-of-meV high.

Excitation of induced coherent Smith–Purcell (SP) radiation by relativistic magnetized electron beam in the absence of the resonator is considered within the framework of the dispersion equation. We have found that the dispersion equation for the SP instability is a quadratic equation for frequency. The first-step approximation for solution of the dispersion equation, giving the SP-spectrum of frequency, corresponds to the mirror boundary case, when the electron beam propagates above a plane metal surface (mirror). It was found that the conditions for both the Thompson and the Raman regimes of excitation do not depend on beam current and depend on the height of the beam above the grating surface. The growth rate of the instability in both cases is proportional to the square root of the electron beam current. No feedback is needed to provide the coherent emission.

Coupled super- and sub- radiant emission of dye fluorescence near the plasmonic surface is shown to be an intrinsic property of the hybrid system. The bi-exponential decay is demonstrated for Au\SiO2\ATTO655 core-shell nanoparticles, which persists even when averaging over a broad range of the coupling parameter. The superradiant and subradiant states are distinct and exclusive by the identical permutational symmetry of the atom-field interaction Hamiltonian of the two-level system. Our analytical approach shows that starting from two emitters, coupled for example via the plasmon modes, the symmetry breaking occurs, making detectable the simultaneous existence of the fast super-radiance and the slow sub-radiance. The relaxation in the sub-radiant system occurs mainly due to the interaction with the plasmon modes. Our theory shows that the relaxation leads to the population of the sub-radiant states by dephasing the super-radiant Dicke states giving rise to the bi-exponential decay in agreement with the experiments. Even if we have a group of many coupled emitters or many groups of coupled emitters with different coupling parameters, the averaging will affect the emission among the super-radiant fast transitions and the sub-radiant slow transitions and keep these two group distinct.

We have studied electromagnetically induced transparency (EIT) in diatomic cesium molecules in a vapor cell by using tunable diode lasers. We have observed a sub-natural Lambda-resonance in an absorption molecular band at different cesium vapor pressures. The width of the EIT resonance shows a linear dependence on cesium vapor pressure. Narrow Lambda-resonances in molecules can be used as frequency references for femtosecond laser frequency combs.

Motivated by the recent experiment [Sautenkov, V.A.; Rostovtsev, Yu.V.; Scully, M.O. Phys. Rev. A 2005, 72, 065801], we study the field intensity fluctuations due to interaction between a laser with a finite bandwidth and a dense atomic medium. The intensity–intensity cross-correlation of two orthogonal, circular polarized beams can be controlled by the applied external magnetic field. A smooth transition from perfect correlations to anti-correlations (at zero delay time) of the outgoing beams is observed.

Nuclear quantum optics deals with the resonant interaction of gamma-radiation and nuclei, generally incorporated in a solid-state material. Single gamma-rays interact with an ensemble of nuclei. The properties of the resonantly forward-scattered gamma-radiation depend on the details of the interaction. An external modification of the nuclear energies will influence the interactions, and hence the properties of the radiation. Several techniques are proposed to reduce the resonant absorption of the gamma-rays, creating a nuclear medium that is partially transparent: nuclear-level-mixing induced transparency, modification of nuclear levels by means of an optical laser, phase-shift-induced transparency. Interference is crucial in all this. The partial transparency could be exploited to study special effects such as slow gamma-radiation and gain without population inversion. It could alsa be of importance for the realization of a gamma-ray laser.

We study population transfer in a two-level system interacting with a strong off-resonant electromagnetic field. We show that the effects of tunneling in an electric field enhances the probability of excitation. We discuss the possible applications of results obtained to the generation of XUV radiation.

We have studied a time response of electromagnetically induced transparency (EIT) in a rubidium vapor to a rapid variation of optical phase. We have observed a very fast growth of the absorption when the phase of the optical field has been abruptly changed, followed by a slow return to the level of steady-state absorption. The recovery time decreases with increasing optical power. A simple theoretical analysis shows that under our experimental conditions the low power limit of the recovery time is determined by the ground relaxation time. In our case it is defined by a time-of-flight of rubidium atoms through laser beam. The obtained value of the ground state relaxation time is in a good agreement with result of direct measurements by ‘relaxation in the dark’ method. Our technique based on phase dynamics in EIT can be used for investigation of the ground state relaxation and the fast control of EIT.

We have studied the intensity correlations between two orthogonally linearly polarized components of a laser field propagating through a resonant atomic medium. These experiments have been performed in a rubidium atomic vapor. We observe that the correlations between the orthogonally polarized components of the laser beam are maximal in the absence of a magnetic field. The magnitude of the correlations depends on the applied magnetic field, and the magnitude first decreases and then increases with increasing magnetic field. Minimal correlations and maximal rotation angles are observed at the same magnetic fields. The width of the correlation function is directly proportional to the excited state lifetime and inversely proportional to the Rabi frequency of laser field.

We have studied phase dynamics in EIT in a dense rubidium vapor. We have observed a very fast growth of the absorption when the phase of the optical field was abruptly changed, followed by a slow return to the steady state absorption. Then the transmission was slowly restored to stationary magnitude. The recovery time is on the order of the transit time of the atom flying through the laser beam and decreases with increasing optical power. The fast variation of the transparency is proportional to the phase deviation. The obtained result can be used for the fast control of EIT, for example, in an optical switch.

We find that intense short pulses of XUV radiation can be produced by cooperative spontaneous emission from visible or IR laser pulses driving atoms or ions. The process depends on the generation and utilization of atomic coherence as is the case in lasing without inversion. However, the radiation process is not stimulated emission, but is rather cooperative spontaneous emission in the sense of Dicke. More precisely, the many atom mathematics of superradiance has much in common with coherent anti-Stokes Raman scattering. †It is a pleasure to dedicate this article to Professor Lorenzo Narducci: scientist, scholar, savant. All who were touched by him were enriched. The generation of Raman coherence is considered from the perspectives of multi-photon excitation and breaking of adiabaticity. In particular, we find that the advent of an ultrashort (e.g. single cycle) pulse rewards rethinking of conventional (nanosecond) nonlinear optics with new insights.

We study population transfer in a three-level system interacting with a strong off-resonant electromagnetic field consisting of radiation with two optical frequencies. We show that the presence of the second frequency broadens multi-photon resonances and even for higher than 3-photon resonances the probability of excitation weakly depends on optical frequency. We discuss possible applications of results obtained for generation of XUV radiation.

We have studied a scheme of lasing without inversion (LWI) that uses the Pauli exclusion principle. We perform simulations to demonstrate the gain at 58 nm using parameters for 3He. The usage of the Pauli principle allows us to meet the necessary condition for LWI and provides also the efficient control of the coupling between X-ray radiation and atomic system. This approach can be extended to other atoms and ions to obtain lasing at shorter wavelengths.