Search

We study the interaction of a V-type atom in a cavity with incident single- and two-photon wavepackets and derive an exact formula, valid in all parameter regimes, relating the spectrum of the outgoing wavepackets to the incident one. We present detailed results for several special input pulses and consider the potential performance of the system as a CPHASE gate for initial pulses in a product state. We find values of the cavity, atomic, and pulse parameters that yield a conditional phase shift of π , albeit with a relatively small overlap between the incoming and outgoing pulse forms. [ABSTRACT FROM AUTHOR]

We investigate a Dicke quantum battery in the dispersive regime, where the photons trapped in a resonant cavity are much more energetic with respect to the two-level systems embedded into it. Under such off-resonant conditions, even an empty cavity can lead to the charging of the quantum battery through a proper modulation of the matter–radiation coupling. This counterintuitive behaviour has its roots in the effective interaction between two-level systems mediated by virtual photons emerging from the fluctuations of the quantum electromagnetic field. In order to properly characterize it, we address relevant figures of merit such as the stored energy, the time required to reach the maximum charging, and the averaged charging power. Moreover, the possibility of efficiently extracting energy in various ranges of parameters is discussed. The scaling of stored energy and power as a function of the number N of two-level systems and for different values of the matter–radiation coupling is also discussed, showing, in the strong coupling regime, performances in line with what is reported for the Dicke quantum battery in the resonant regime. [ABSTRACT FROM AUTHOR]

• Cascade decays of vacancies in inner-shell-photoionized iodine atom are simulated. • Spectra of cascade-produced electrons and photons are calculated. • Dependences of reemitted energy on the incident photon energy are studied. • Mean free paths of cascade electrons and photons in liquid water are estimated. • Roles of photo- and cascade electrons in local energy deposition is discussed. Cascade decays of single K to O vacancies in an isolated iodine atom are simulated by straightforward construction of the cascade decay trees. Cascade-emitted electron and photon spectra are calculated and analyzed to determine the portions of energies (a) absorbed by the iodine atom after ionization and complete cascade relaxation, (b) emitted by cascade electrons, (c) emitted by cascade photons. These quantities are calculated as functions of incident photon energy following photoionization of the iodine atom in the 0.01–100 keV energy range. Cascade electrons and photoelectrons are shown to be principal energy transmitters from an ionized iodine atom to the environment. Presented data are relevant for developing the strategies of photon activation radiation therapy when iodine is used as a radiosensitizing agent. [ABSTRACT FROM AUTHOR]

The effects of the non-ideality (NI) of classical plasmas on the photoionization of helium atoms at high non-relativistic photon energies are investigated within the framework of the dipole approximation. Screened interaction in non-ideal plasmas is represented by an effective potential, deduced from a solution of Bogolyubov's hierarchy equations on discarding the effects of quantum degeneracy. A highly correlated wave function consisting of 715 terms for the ground state of helium has been used to evaluate the dipole matrix element. Changes in the asymptotic cross sections of single, double, and total photoionizations due to varying NI of plasmas have been investigated in detail. Particular emphasis is made to study the changes in the asymptotic ratio of the double-to-single photoionization cross section caused by the variation of non-ideality parameter in a wide range. It is found that increasing plasma NI makes the feasibility of occurrence of double photoionization to broaden. [ABSTRACT FROM AUTHOR]

• Ag q+ photoions production cross sections at 0.07–100 keV are calculated. • Ag q+ ion yields and mean photoion charge are presented against photon energy. • Possible use of Ag as radiosensitizing agent is discussed. The formation of multiply charged Ag q+ ions resulting from photoionization and subsequent cascade decay of inner-shell vacancy states is studied using the method of construction and analysis of the cascade decay trees. Cross sections for the cascade production of Ag q+ ions, yields of Ag q+ ions, and mean photoion charge are calculated as functions of incident photon energy in the range of 70 eV to 100 keV. The results of this study are relevant for developing the strategies of radiotherapy using Ag-based radiosensitizers. [ABSTRACT FROM AUTHOR]

The effects of permanent dipoles, and the relative effects of the direct permanent dipole and the virtual state excitation mechanisms, are discussed for excitations involving the simultaneous absorption of two identical photons. Two molecular models for two-photon excitation, one dominated by the direct permanent dipole mechanism and the other having significant contributions from both excitation mechanisms, are used for this purpose. Resonance profiles, as a function of laser intensity, are evaluated for both models by employing the full Generalized Rotating Wave Approximation method and the recently developed Analytic Generalized Rotating Wave Approximation (AGRWA). The profiles are used to assess (1) the nature of the effects of permanent molecular dipoles, (2) the relative contributions of the two excitation mechanisms, and (3) the validity of the AGRWA for two-photon excitations. The AGRWA is a very useful interpretive/predictive tool even for higher laser intensities where its validity becomes questionable. It can be used to suggest how to exploit the effects of molecular permanent dipoles to enhance two photon excitations using both excitation mechanisms. [ABSTRACT FROM AUTHOR]

In connection to the paper by Kornev and Zon (2019 J. Phys. B: At. Mol. Opt. Phys. 52 075205), we would like to remind that the two-photon laser-assisted electron scattering on hydrogen atom is a subject already studied and analyzed in the literature, and we briefly present the well established situation. We wish to point out a possible limitation in the calculations performed within the perturbation theory in reference to the work by Kornev and Zon (2019 J. Phys. B: At. Mol. Opt. Phys. 52 075205) at high laser intensities and/or at very low photon energies, where the α0| ϵ ⋅ q | ≪ 1 condition is not satisfied. [ABSTRACT FROM AUTHOR]

We experimentally observed a two-photon interference between a squeezed vacuum state from an optical parametric amplifier and a weak coherent state on a beam splitter with continuous variables. The photon statistics properties of the mixed field were investigated by calculating the correlations among four permutations of measured quadratures components, which were obtained by two homodyne detection systems. This also means that the two-photon interference occurred at analysis frequency differing from the previous two-photon interference reports. The nonclassical effect of photon anti-bunching occurred when an amplitude squeezed vacuum state acted as one of interference sources. On the other hand, the photon bunching effect appeared when a phase squeezed vacuum state was employed. Graphical abstract: [ABSTRACT FROM AUTHOR]

[Display omitted] • D. tharense UAM-C/S02 exhibited high biomass productivity and CO 2 bio-fixation. • The strain accumulated 13 % C-PC and reached a maximum productivity of 97 mg L−1 d−1. • 1.81 purity of crude extract C-PC is the highest reported for this genus. • A two-step purification process can increase C-PC purity to biomarker-grade. • C-PC obtained from this strain showed a high capacity for ROS scavenging activity. A native cyanobacterial strain, Desertifilum tharense UAM-C/S02, was studied as a possible C-phycocyanin (C-PC) producer. Photosynthetic activity (PA) assays through oxygen production determined the proper temperature and range of irradiances to be tested in a stirred tank photobioreactor. The highest C-PC productivity (97 mg L−1 d−1), with a yield of 86.46 mg C-PC g B −1 was obtained at 730 µmol photons m−2 s−1 with a biomass productivity of 608 mg L−1 d−1 and the CO 2 fixation rate was 1,194 mg L−1 d−1. The 1.81 crude extract purity value is the highest reported for this genus, which was improved to biomarker-grade purity after a two-step purification strategy comprising precipitation with ammonium sulfate, followed by dialysis. The purified C-PC was almost entirely radical-free using 1 mg mL−1, which validates its potential use in therapeutic formulations. [ABSTRACT FROM AUTHOR]

Two-photon excited fluorescence (TPEF) is a standard technique in modern microscopy, but is still affected by photodamage to the probe. It has been proposed that TPEF can be enhanced using entangled photons, but this has proven challenging. Recently, it was shown that some features of entangled photons can be mimicked with thermal light, which finds application in ghost imaging, subwavelength lithography and metrology. Here, we use true thermal light from a superluminescent diode to demonstrate TPEF that is enhanced compared to coherent light, using two common fluorophores and luminescent quantum dots, which suit applications in imaging and microscopy. We find that the TPEF rate is directly proportional to the measured degree of second-order coherence, as predicted by theory. Our results show that photon bunching in thermal light can be exploited in two-photon microscopy, with the photon statistic providing a new degree of freedom. [ABSTRACT FROM AUTHOR]

Evidence for Bell's nonlocality is so far mainly restricted to microscopic systems, where the elements of reality that are negated predetermine results of measurements to within one spin unit. Any observed nonlocal effect (or lack of classical predetermination) is then limited to no more than the difference of a single photon or electron being detected or not (at a given detector). In this paper, we analyze experiments that report the Einstein-Podolsky-Rosen (EPR) steering form of nonlocality for mesoscopic photonic or Bose-Einstein condensate systems. Using an EPR steering parameter, we show how the EPR nonlocalities involved can be quantified for four-mode states, to give evidence of EPR-nonlocal effects corresponding to a two-mode number difference of 105 photons, or of several tens of atoms (at a given site). Applying to experiments, we also show how the variance criterion of Duan, Giedke, Cirac and Zoller for EPR entanglement can be used to determine a lower bound on the number of particles in a pure two-mode EPR-entangled or steerable state. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to propose quantum filters for a two-level atom driven by two continuous-mode counter-propagating photons and under continuous measurements. Two scenarios of multiple measurements are discussed: (1) homodyne detection plus photodetection and (2) two homodyne detections. Filtering equations for both cases are derived explicitly. As demonstration, the two input photons with rising exponential and Gaussian pulse shapes are used to excite a two-level atom under two homodyne detection measurements. Simulations reveal scaling relations between atom-photon coupling and photonic pulse shape for maximum atomic excitation. [ABSTRACT FROM AUTHOR]

In this paper we want to investigate the possibility of transferring entanglement to two three-level separable atomic states over long distance using the quantum repeater protocol. In detail, our model consists of eight Λ-type three-level atoms where only the pairs (1, 2), (3, 4), (5, 6) and (7, 8) are prepared in maximally entangled states. Performing suitable interaction between non-entangled three-level atoms (2, 3) and (6, 7) in two-mode cavities with photon leakage rates in the presence of spontaneous emission leads to producing entanglement between atoms (1, 4) and (5, 8), separately. Finally, the entanglement between atoms (1, 8) is successfully produced by performing interaction between atoms (4, 5) while spontaneous emission is considered in a dissipative cavity. In the continuation, the effects of detuning, dissipation sources and initial interaction time are evaluated on the negativity and success probability of the processes. It is shown that, the maxima of negativity are decreased by increasing the detuning, in most cases. Also, the time evolution of negativity is non-periodic in the presence of dissipation. In addition, increasing the initial interaction time has a constructive effect on the negativity in all considered cases. The oscillations of negativity are destroyed as time goes on and the produced entanglement becomes stable. The success probability of entangled state of atoms (1, 8) is tunable by controlling the detuning and dissipation. We show that via justifying the involved parameters one can arrive at conditions in which the decoherence effects are fully disappeared; as a result, an ideal quantum repeater can be properly achieved while atomic and field dissipations are taken into account. [ABSTRACT FROM AUTHOR]

The photodouble ionization of the water molecule has been studied at about 20 eV excess energy by detecting in coincidence two photoelectrons of equal energy. Two types of measurements have been performed. In the first one the photon energy has been scanned in order to reconstruct the spectrum of the H2O2+ states; in the second, the photon energy has been fixed, the direction of one photoelectron has been chosen along the direction of the polarization axis of the incident radiation and the coincidence angular distribution of the two photoelectrons has been measured. The angular distributions show that, at variance with previous measurements in diatomic molecules, the emission of the two electrons along the antiparallel direction is highly favored. [ABSTRACT FROM AUTHOR]

We here present the rate analysis and a proof of principle demonstration of a device-independent quantum key distribution protocol requiring the lowest detection efficiency necessary to achieve a secure key compared to device-independent protocols known so far. The protocol is based on a non-maximally entangled state and its experimental demonstration has been performed by two-photon bipartite entangled states. The improvement with respect to protocols involving maximally entangled states has been estimated. [ABSTRACT FROM AUTHOR]