A scheme of generating controllable (2+1) photons in a double-$% Λ$ atomic system based on active-Raman-gain is presented in this paper. Such (2+1) photons can be a potential candidate to generate a correlated photon pair as the photon `1' acts as a trigger. Compared to other schemes of generating correlated photon pairs, our scheme exhibits a number of advantages due to the exploit of the stimulated Raman process.
Early theoretical works on coherent anti-Stokes Raman scattering in optically active medium consider only heterodyne signal and subsequently, fourth- and fifth-rank tensor averages have been used. In this work, we presented a full signal expression of coherent anti-Stokes Raman scattering in optically active medium with the help of eighth- and ninth-rank tensor averaging for simplest experimental configuration namely, measurements of post-selected circularly polarized components of scattered anti-Stokes field in the presence of three incident laser beams all linearly polarized along the same a…
Using a single channel active Raman gain medium we show a $(220\pm 20)$ns advance time for an optical pulse of $τ_{FWHM}=15.4 μ$s propagating through a 10 cm medium, a lead time that is comparable to what was reported previously. In addition, we have verified experimentally all the features associated with this single channel Raman gain system. Our results show that the reported gain-assisted superluminal propagation should not be attributed to the interference between the two frequencies of the pump field.
We investigate the parametric beating of a quantum probe field with a prepared Raman coherence in a far-off-resonance medium, and describe the resulting multiplexing processes. We show that the normalized autocorrelation functions of the probe field are exactly reproduced in the Stokes and anti-Stokes sideband fields. We find that an initial coherent state of the probe field can be replicated to the Raman sidebands, and an initial squeezing of the probe field can be partially transferred to the sidebands. We show that a necessary condition for the output fields to be in an entangled state or, …
We consider the coherent stimulated Raman process developing in an optically dense disordered atomic medium, which can also incoherently scatter the light over all outward directions. The Raman process is discussed in the context of a quantum memory scheme and we point out the difference in its physical nature from a similar but not identical protocol based on the effect of electromagnetically induced transparency (EIT). We show that the Raman and EIT memory schemes do not compete but complement one another and each of them has certain advantages in the area of its applicability. We include in…
We consider the population transfer process in a Lambda-type atomic medium of unequal oscillator strengths by stimulated Raman adiabatic passage via bright-state (b-STIRAP) taking into account propagation effects. Using both analytic and numerical methods we show that the population transfer efficiency is sensitive to the ratio q_p/q_s of the transition oscillator strengths. We find that the case q_p>q_s is more detrimental for population transfer process as compared to the case where $q_p \leq q_s$. For this case it is possible to increase medium dimensions while permitting efficient populati…
We demonstrate the efficient generation of Raman sidebands in a medium coherently prepared in a dark state by continuous-wave low-intensity laser radiation. Our experiment is performed in sodium vapor excited in $Λ$ configuration on the D$_{1}$ line by two laser fields of resonant frequencies $ω_{1}$ and $ω_{2}$, and probed by a third field $% ω_{3}$. First-order sidebands for frequencies $ω_{1}$, $ω_{2}$ and up to the third-order sidebands for frequency $ω_{3}$ are observed. The generation starts at a power as low as 10 microwatt for each input field. Dependencies of the intensities of both i…
We propose a dual-pump third-order nonlinear scheme for producing pairs of correlated photons that is less susceptible to Raman noise than typical spontaneous four wave mixing methods (SFWM). Beginning with the full multimode Hamiltonian we derive a general expression for the joint spectral amplitude, from which the probability of producing a pair of photons can be calculated. As an example, we demonstrate that a probability of 0.028 pairs per pulse can be achieved in an appropriately designed fused silica microfiber. As compared with single pump SFWM in standard fiber, we calculate that our p…
In this paper, the noise performances of 1.5 um correlated photon pair generations based on spontaneous four wave-mixing in three types of fibers, i.e., dispersion shifted fiber, highly nonlinear fiber, and highly nonlinear microstructure fiber are investigated experimentally. Result of the comparison shows that highly nonlinear microstructure fiber has the lowest Raman noise photon generation rate among the three types of fibers while correlated photon pair generation rate is the same. Theoretical analysis shows that the noise performance is determined by the nonlinear index and Raman respons…
We investigate theoretically the formation of two-component light with superluminal group velocity in a medium controlled by four Raman pump fields. In such an optical scheme only a particular combination of the probe fields is coupled to the matter and exhibits superluminal propagation, the orthogonal combination is uncoupled. The individual probe fields do not have a definite group velocity in the medium. Calculations demonstrate that this superluminal component experiences an envelope advancement in the medium with respect to the propagation in vacuum.
We present a general analysis for the interaction of a probe laser radiation with a coherently prepared molecular Raman medium. We describe a general formalism which includes dispersive effects, such as group velocity and group velocity dispersion (GVD). When dispersion is negligible, the analysis is especially simple and insightful. We show that molecular oscillations result in a modulated instantaneous susceptibility of the medium. The effect of the time-varying susceptibility on a probe laser pulse is two-fold: the output frequency becomes modulated because of the time-varying phase velocit…
We consider the Raman process developing in a disordered medium of alkali-metal atoms when the scattered modes are trapped on a closed transition. Our theoretical analysis, based on numerical simulations of the Bethe-Salpeter equation for the light correlation function, which includes all Zeeman states and light polarization, lets us track the stimulated amplification as well as the losses associated with the inverse anti-Stokes scattering channel. We discuss possible conditions when this process could approach the instability point and enter the regime of random lasing.
Spin-polarised atomic ensembles probed by light based on the Faraday interaction are a versatile platform for numerous applications in quantum metrology and quantum information processing. Here we consider an ensemble of Alkali atoms that are continuously optically pumped and probed. Due to the collective scattering of photons at large optical depth, the steady state of atoms does not correspond to an uncorrelated tensor-product state, as is usually assumed. We introduce a self-consistent method to approximate the steady state including the pair correlations, taking into account the multilevel…
New time-dependent integrals of motion are found for stimulated Raman scattering. Explicit formula for the photon-number probability distribution as a function of the laser-field intensity and the medium parameters is obtained in terms of Hermite polynomials of two variables.
We show that ultra-cold atoms with synthetic spin-orbit coupling in Raman lattices can be used as versatile quantum simulators to explore the connections between correlated Chern insulators and strongly-coupled four-Fermi field theories related to the Gross-Neveu model in (2+1) dimensions. Exploiting this multidisciplinary perspective, we identify a large-$N$ quantum anomalous Hall (QAH) effect in absence of any external magnetic field, and use it to delimit regions in parameter space where these correlated topological phases appear, the boundaries of which are controlled by strongly-coupled f…
We have recently proposed [9], the use of fast-light media to obtain ultrahigh precision rotation sensing capabilities. The scheme relies on producing a critically anomalous dispersion, in a suitable dispersive medium, which is introduced in the arms of a Sagnac interferometer. We present here an experimental investigation of the anomalous dispersion properties of bi-frequency Raman gain in rubidium vapor, with the goal of using this medium for producing the critically anomalous dispersion condition. A heterodyne phase measurement technique is used to measure accurately the index variation ass…
We use a Langevin approach to analyze the quantum noise in Coherent Anti-Stokes Raman Spectroscopy (CARS) in several experimental scenarios: with continuous wave input fields acting simultaneously and with fast sequential pulsed lasers where one field scatters off the coherence generated by other fields; and for interactions within a cavity and in free space. In all the cases, the signal as well as the quantum noise due to spontaneous decay and decoherence in the medium are shown to be described by the same general expression. Our theory in particular shows that for short interaction times, th…
We present the possibility of steering the direction of correlations between the off-resonant Raman scattered photons from the angularly multimode atomic memory based on warm rubidium vapors. Using acousto-optic deflectors (AOD) driven by different modulation frequencies we experimentally change the angle of incidence of the laser beams on the atomic ensemble. Performing correlations measurements for various deflection angles we verify that we can choose the anti-Stokes light propagation direction independently of the correlated Stokes scattered light in the continuous way. As a result we can …
The production of correlated Stokes (S) and anti-Stokes (aS) photons (SaS process) mediated by real or virtual phonon exchange has been reported in many transparent materials. In this work, we investigate the polarization and time correlations of SaS photon pairs produced in a diamond sample. We demonstrate that both S and aS photons have mainly the same polarization of the excitation laser. We also perform a pump-and-probe experiment to measure the decay rate of the SaS pair production, evidencing the fundamental diference between the real and virtual (phonon exchange) processes. In real proc…
By using spontaneous Raman processes in the high gain regime, we produce two independent Raman Stokes fields from an atomic ensemble. Temporal beating is observed between the two directly generated Stokes fields in a single realization. The beat frequency is found to be a result of an AC Stark frequency shift effect. However, due to the spontaneous nature of the process, the phases of the two Stokes fields change from one realization to another so that the beat signal disappears after average over many realizations. On the other hand, the beat signal is recovered in a two-photon correlation me…
We propose a scenario of quantum memory for light based on Raman scattering. The storage medium is a vapor and the different spectral components of the incoming signal are stored in different atomic velocity classes. One uses appropriate pulses to reverse the resulting Doppler phase shift and to regenerate the signal, without distortion, in the backward direction. The different stages of the protocol are detailed and the recovery efficiency is calculated in the semi-classical picture. Since the memory bandwidth is determined by the Raman transition Doppler width, it can be adjusted by changing…
We consider a quantum memory scheme based on the conversion of a signal pulse into a long-lived spin coherence via stimulated off-resonant Raman process. For a storing medium consisting of alkali atoms, we have calculated the Autler-Townes resonance structure created by a strong control field. By taking into account the upper hyperfine states of the D1 optical transition, we show important deviations from the predictions of the usual three-level Lambda-scheme approximation and we demonstrate an enhancement of the process for particular detunings of the control. We estimate the memory efficienc…
We study the formation of off-axis optical vortices propagating inside a double-Raman gain atomic medium. The atoms interact with two weak probe fields as well as two strong pump beams which can carry orbital angular momentum (OAM). We consider a situation when only one of the strong pump lasers carries an OAM. A particular superposition of probe fields coupled to the matter is shown to form specific optical vortices with shifted axes. Such off-axis vortices can propagate inside the medium with sub- or superluminal group velocity depending on the value of the two-photon detuning. The superlumi…
We propose a novel femtosecond stimulated Raman spectroscopy (FSRS) technique that combines entangled photons with interference detection to select matter pathways and enhance the resolution. Following photo excitation by an actinic pump, the measurement uses a pair of broadband entangled photons, one (signal) interacts with the molecule together with a third narrowband pulse induces the Raman process. The other (idler) photon provides a reference for the coincidence measurement. This interferometric photon-coincidence counting detection allows to separately measure Raman gain and loss signals…
We study the generation of correlated photon pairs via spontaneous four wave mixing in a 15 cm long micro/nano-fiber (MNF). The MNF is properly fabricated to satisfy the phase matching condition for generating the signal and idler photon pairs at the wavelengths of about 1310 and 851 nm, respectively. Photon counting measurements yield a coincidence-to-accidental ratio of 530 for a photon production rate of about 0.002 (0.0005) per pulse in the signal (idler) band. We also analyze the spectral information of the signal photons originated from the spontaneous four wave mixing and Raman scatteri…
We propose a scheme to dynamically generate optical flux lattices with nontrivial band topology using amplitude-modulated Raman lasers and radio-frequency (rf) magnetic fields. By tuning the strength of Raman and rf fields, three distinct phases are realized at unit filling for a unit cell. Respectively, these three phases correspond to normal insulator, topological Chern insulator, and semimetal. Nearly nondispersive bands are found to appear in the topological phase, which promises opportunities for investigating strongly correlated quantum states within a simple cold-atom setup. The validit…
Light with high mutual correlations at different frequencies can be used to create heralded single-photon sources, which may serve as the basic elements of existing quantum cryptography and quantum teleportation schemes. One of the important examples in natural systems of light with high mutual correlations is the light produced by spontaneous Raman scattering on an ensemble of molecules. In this paper, we investigate the possibility of using Raman light to create a heralded single-photon source. We show that when using Stokes scattered light for postselection of an anti-Stokes scattered light…
We consider a non-equilibrium system of interacting emitters described by the XXZ model, whose excitonic transitions are spatially and spectrally coupled to a single mode cavity. We demonstrate that the output radiation field is sensitive to an interplay between the hopping ($J$) and the interactions ($U$) of the excitons. Moderate values of the short-ranged interaction are shown to induce laser with maximal output at the Heisenberg point ($U=J$). In the laser regime, charge-charge correlations emerge and they are shown to strongly depend on the interaction-hopping ratio. In particular, the sy…
We study the correlated dynamics of few interacting bosonic impurities immersed in a one-dimensional harmonically trapped bosonic environment. The mixture is exposed to a time-dependent impurity-medium interaction pulse moving it across the relevant phase separation boundary. For modulation frequencies smaller than the trapping one, the system successively transits through the miscible/immiscible phases according to the driving of the impurity-medium interactions. For strong modulations, and driving from the miscible to the immiscible regime, a significant fraction of the impurities is expelle…
We demonstrate a source of correlated photon pairs which will have applications in future integrated quantum photonic circuits. The source utilizes spontaneous four-wave mixing (SFWM) in a dispersion-engineered nanowaveguide made of AlGaAs, which has merits of negligible two-photon absorption and low spontaneous Raman scattering (SpRS). We observe a coincidence-to-accidental (CAR) ratio up to 177, mainly limited by propagation losses. Experimental results agree well with theoretical predictions of the SFWM photon pair generation and the SpRS noise photon generation. We also study the effects f…
We demonstrate the first 1550 nm correlated photon-pair source in an integrated glass platform-a chalcogenide As2S3 waveguide. A measured pair coincidence rate of 80 per second was achieved using 57 mW of continuous-wave pump. The coincidence to accidental ratio was shown to be limited by spontaneous Raman scattering effects that are expected to be mitigated by using a pulsed pump source.
We investigate the propagation of a coherent probe light pulse through a three-level atomic medium (in the $Λ$--configuration) in the presence of a pump laser under the conditions for gain without inversion. When the carrier frequency of the probe pulse and the pump laser are in a Raman configuration, we show that it is possible to amplify a slow propagating pulse. We also analyze the regime in which the probe pulse is slightly detuned from resonance where we observe anomalous light propagation.
