Coherent Pump Research Articles

Coherent superconducting quantum pump

We demonstrate nonadiabatic charge pumping utilizing a sequence of coherent oscillations between a superconducting island and two reservoirs. The pumping rate for each elementary cycle is limited by the coupling between the island and the reservoirs given by the Josephson energy. Our experimental and theoretical studies show that relaxation can be employed to reset the pump in order to avoid accumulation of errors due to nonideal control pulses. Thus our results demonstrate the effects of nonadiabatic quantum pumping and dissipation.

Role of pump coherence in the evolution of continuous-wave supercontinuum generation initiated by modulation instability

We report in detail, both experimentally and using numerical simulation, the efficiency of generation of supercontinua in optical fiber driven by modulation instability of a continuous-wave (CW) pump source. It is shown that the degree of pump coherence has a dramatic effect on the resulting spectral expansion and it is discussed how this can be explained by having the proper conditions for efficient modulation instability to break the CW pump light into a train of fundamental solitons that subsequently undergo self-Raman shift to longer wavelengths. It is proposed that an optimal pump bandwidth exists corresponding to the optimal degree of pump incoherence, defined as a function of the modulation instability period.

Four-Wave Mixing in Nonlinear Fiber With Two Intracavity Frequency-Shifted Laser Pumps

We experimentally study Bragg-type four-wave mixing frequency conversion in highly nonlinear fibers by using two independent frequency-shifted-feedback lasers. We obtain frequency conversion with partial coherent pumps when both lasers operate in the continuous-wave regime. Our experimental results compare well with numerical simulations, which take into account partial coherence of the two pumps.

Detection of Sum and Difference Squeezing

Sum and difference squeezing was defined by Hillery who showed that these turn into normal squeezing in sum and difference frequency generation. We re-examine this using an intense coherent pump mode and with a much better approximation. Our results are valid for much larger interaction times and therefore enable detection of smaller sum and difference squeezings, in principle., Moreover, if both, our and Hillary's results are regarded holding, our results lead to more squeezing.

Bragg-Scattering Four-Wave Mixing in Nonlinear Fibers with Intracavity Frequency-Shifted Laser Pumps

We experimentally study four-wave mixing in highly nonlinear fibers using two independent and partially coherent laser pumps and a third coherent signal. We focus our attention on the Bragg-scattering frequency conversion. The two pumps were obtained by amplifying two Intracavity frequency-shifted feedback lasers working in a continuous wave regime.

Dissipation-driven generation of two-qubit entanglement mediated by plasmonic waveguides

We study the generation of entanglement between two distant qubits mediated by the surface plasmons of a metallic waveguide. We show that a V-shaped channel milled in a flat metallic surface is much more efficient for this purpose than a metallic cylinder. The role of the misalignments of the dipole moments of the qubits, an aspect of great importance for experimental implementations, is also studied. A careful analysis of the quantum-dynamics of the system by means of a master equation shows that two-qubit entanglement generation is essentially due to the dissipative part of the effective qubit-qubit coupling provided by the surface plasmons. The influence of a coherent external pumping, needed to achieve a steady state entanglement, is discussed. Finally, we pay attention to the question of how to get information experimentally on the degree of entanglement achieved in the system.

Parametric polariton solitons in coherently pumped semiconductor microcavities

The investigation of exciton-polaritons in semiconductor microcavities operating in the strong-coupling regime is attracting growing interest because of their extraordinary optical properties [1]. Together with the strong excitonic nonlinearities, originating from the Coulomb interaction between excitons, the peculiar dispersion relation of these quasi-particles allows a variety of fundamental effects like optical bistability, low threshold parametric oscillations [2] and formation of robust self-localized states, so-called, cavity polariton solitons (CPSs) [3,4]. It was shown that the inclination of the coherent optical pump (plane wave) endows exciton-polaritons with a kinetic momentum (k x ) along one of the orthogonal directions in the plane of the microcavity. It even allows controlling their dispersion. As a result moving 2D CPSs can exist despite the opposite dispersion signs along (x) and orthogonal (y) to the pump momentum directions [4]. In this contribution we provide theoretical evidence of self-localization of polaritons in the direction orthogonal to the pump tilt (y), which is unusual for the defocusing nonlinearity. We study the formation of 1D CPSs excising due to the parametric four-wave mixing of polaritons.

Coherent spectroscopy of a Λ atomic system and its prospective application to tunable frequency offset locking

We investigate the coherent pump–probe spectroscopy of a three-level Λ system, , in the hyperfine manifold of D2 transition (852 nm) of cesium with particular reference to the sub-Doppler linewidth resonance arising from Aulter–Townes (AT) splitting and the possibility of using it for realizing a scheme for tunable atomic frequency offset locking (AFOL). We discuss here the theoretical framework for a Λ system interacting with a coherent pump and probe and use it to describe the process of modulation transfer in the AT and electromagnetically induced transparency regimes. We further employ an experimental scheme consisting of a strong pump and a pair of weak probes to resolve the sub-Doppler linewidth (∼8 MHz) AT resonance and study its dependence on pump intensity and detuning. In order to explore the possibility of using such a sub-Doppler linewidth resonance for AFOL, we use its first derivative signal as a frequency discriminator to stabilize the probe laser. The frequency stability of the probe is characterized by means of error signal analysis. This study reveals that while the frequency stability of the AT locked laser is limited by the pump laser, the tuning range of the offset frequency lock can cover the entire Doppler profile and its immediate neighbourhood, thereby providing a simple and cost effective alternative to the external modulator. The study described in this paper contributes to the discussion on the subtle link between dressed state spectroscopy and AFOL, which is relevant for developing a master–slave-type laser system in the domain of coherent photon–atom interaction.

Controllable spontaneous emission from a double Λ-type four-level atom in an anisotropic photonic crystal

The spontaneous emission behavior of a double Λ-type four-level atom embedded in a photonic crystal (PC) with anisotropic dispersion relations is investigated. It is shown that some interesting phenomena such as the spectral-line enhancement, the spectral-line narrowing, the spectral-line suppression and the spontaneous emission cancellation can be observed by adjusting the density of states of the photonic-band-gap (PBG) reservoir and the combination of two pump intensities. The proposed scheme can be achieved by use of coherent pump fields into the transitions from the upper levels to the ground level in rubidium atom confined in a PC. These theoretical investigations may provide more degrees of freedom to manipulate the atomic spontaneous emission.

Role of pump coherence in two-photon interferometry

We use a parametric down-conversion source pumped by a short coherence-length continuous-wave (CW) diode laser to perform two-photon interferometry in an intermediate regime between the more familiar Franson-type experiments with a long coherence-length pump laser, and the short pulsed pump "time-bin" experiments pioneered by Gisin's group. The use of a time-bin-like Mach-Zehnder interferometer in the CW pumping beam induces coherence between certain two-photon amplitudes, while the CW nature of the experiment prevents the elimination of remaining incoherent ones. The experimental results highlight the role of pump coherence in two-photon interferometry.

Laser-launched evanescent surface plasmon polariton field utilized as a direct coherent pumping source to generate emitted nonlinear four-wave mixing radiation

We develop a concept of surface plasmon polaritons (SPPs) based four-wave mixing (4WM), in which a laser-launched evanescent SPP field is utilized as a coherent pumping source to involve directly in a nonlinear 4WM process at the dielectric/metal interface. Conversion efficiency of the resulting 4WM radiation is expected to be dramatically increased due to the local-field enhancement effect. Feasibility of implementing this concept at the air/gold film and graphene flake/gold film interfaces is further examined by numerical simulations. The concept shows intriguing promise for applications in newly emerging nanophotonics, optoelectronics, and active plasmonics.

Stimulated Raman scattering in natural crystals of SrSO4, BaSO4 and PbSO4: High-order Stokes and anti-Stokes generation with single-wavelength UV, visible, and near-IR excitation, as well as cascaded up-conversion nonlinear χ (3)↔χ (3) lasing effects under dual-wavelength picosecond collinear coherent pumping

Orthorhombic crystals of SrSO4, BaSO4, and PbSO4, known as natural crystals celestine, barite, and anglesite, were found to be attractive χ(3)-active nonlinear optical materials. High-order Stokes and anti-Stokes picosecond generation that spans almost two octaves has been recorded with single-wavelength laser excitation in the UV, visible, and near-IR ranges. All recorded Raman induced lasing components were identified and attributed to the SRS-promoting vibration modes of the studied crystals (ωSRS≈999 cm−1 for SrSO4,ωSRS≈985 cm−1 for BaSO4 and ωSRS≈977 cm−1 for PbSO4). Under dual-wavelength (λf1=1.06415 μm + λf2=0.53207 μm) collinear coherent picosecond pumping several new manifestations of cascaded χ(3)↔χ(3) nonlinear up-conversion lasing effects were observed in BaSO4 and SrSO4 crystals. We classify all three studied sulfate crystals as promising SRS-active materials for Raman laser frequency converters and as efficient χ(3)-crystals that efficiently generate Stokes and anti-Stokes frequency combs, which can enable experiments of ultra-short pulse syntheses.

Manifestations of new χ(3)‐ and χ(2)‐nonlinear optical interactions and χ(2)‐properties of orthorhombic bis(guanidinium) zirconium bis(nitrilotriacetate) hydrate, [C(NH2)3]2Zr[N(CH2COO)3]2·H2O crystal

AbstractUsing single‐ and dual‐wavelength coherent collinear picosecond pumping we observed in semi‐organic heterodesmic orthorhombic [C(NH2)3]2Zr[N(CH2COO)3]2·H2O manifestations of several new χ(3)‐ and χ(2)‐nonlinear optical effects, among them self‐frequency doubling, “Cherenkov”‐type second harmonic generation (SHG), cascaded self‐frequency tripling and self‐sum‐frequency generation, as well as more than two‐octave Stokes and anti‐Stokes generation under one‐micron excitation. All newly recorded nonlinear optical frequency components were identified and attributed to stimulated Raman scattering (SRS) promoting modes of the crystal. All three tensor components of the second order nonlinear optical susceptibility tensor (SHG tensor) were determined at the wavelength 1.064 µm using the Maker fringe technique. The maximal value of the SHG tensor is 0.6 pm V−1. SHG phase matching directions of type‐I/II and effective nonlinear susceptibilities are given for 0.7–1.4 µm fundamental wavelengths.

3-(2-Benzimidazolyl)coumarin derivatives —highly effective laser media

New laser dyes based on derivatives of 3-(2-benzimidazolyl)coumarin are proposed that lase under lamp and coherent (nanosecond and microsecond) pumping in the spectral range 420–700 nm and feature a high generation efficiency reaching 40% under coherent pumping (1% when lamp-pumped) and an increased operational life that surpasses that for most popular laser dyes. The nature of the substituents in the 6- and 7-positions of the coumarin ring and the ionic structure of the dyes are found to influence their spectral and lasing characteristics.

Regular and stochastic motion of dissipative optical solitons

Investigations of the motion of dissipative optical solitons and their complexes in wide-aperture nonlinearly optical (with coherent pump radiation) and laser (with incoherent pump radiation) systems have been reviewed. An important characteristic of dissipative solitons is the topology of the energy fluxes, which determines the internal structure of individual solitons and makes it possible to certainly separate the cases of the weak and strong interactions between the solitons. It has been shown that the character of the regular motion of dissipative soliton structures in a homogeneous system is determined by the symmetry of the transverse distributions of the intensity and energy flux; the motion of asymmetric structures is curvilinear. This is also valid for complexes of three-dimensional dissipative optical solitons, “laser bullets.” The extreme possibilities of localization of solitons are determined by quantum noises. The corresponding Brownian motion of the center of the dissipative optical soliton is characterized by a much lower level of the statistic dispersion of the coordinates of its center and velocity than that in the case of conservative solitons.

Pulsed Nuclear Pumping and Spin Diffusion in a Single Charged Quantum Dot

We report the observation of a feedback process between the nuclear spins in a single charged quantum dot under coherently pulsed optical excitation and its trion transition. The optical pulse sequence intersperses resonant narrow-band pumping for spin initialization with off-resonant ultrafast pulses for coherent electron-spin rotation. A hysteretic sawtooth pattern in the free-induction decay of the single electron spin is observed; a mathematical model indicates a competition between optical nuclear pumping and nuclear spin-diffusion. This effect allows dynamic tuning of the electron Larmor frequency to a value determined by the pulse timing, potentially allowing more complex coherent control operations.

Practical tests for distinguishing slow light from saturable absorption

A series of practical tests of slow light (light with reduced group velocity) in saturable absorbers is proposed. These include experimental tests for saturable absorption, which can mimic slow light effects in saturable media, the dependence of slow light on the mutual coherence of pump and probe, since both slow and fast light effects can be simulated with incoherent sources, and the influence of polarization. The principal requirements for practical observation of spectral hole burning are reviewed and shown to be achievable for a wide range of saturable media with the narrow line sources now available.

Vortex Lattices in Coherently Pumped Polariton Microcavities

We propose a new class of vortex lattices supported by the parametric conversion of polaritons in wide aperture semiconductor microcavities operating in the strong coupling regime and pumped by a coherent beam. We present numerical and analytical results confirming the existence and robustness of the polaritonic vortex lattices in practically relevant settings and discuss their melting scenarios.

Spatial two-photon coherence of the entangled field produced by down-conversion using a partially spatially coherent pump beam

We study the spatial coherence properties of the entangled two-photon field produced by parametric down-conversion (PDC) when the pump field is, spatially, a partially coherent beam. By explicitly treating the case of a pump beam of the Gaussian Schell-model type, we show that in PDC the spatial coherence properties of the pump field get entirely transferred to the spatial coherence properties of the down-converted two-photon field. As one important consequence of this study, we find that, for two-qubit states based on the position correlations of the two-photon field, the maximum achievable entanglement, as quantified by concurrence, is bounded by the degree of spatial coherence of the pump field. These results could be important by providing a means of controlling the entanglement of down-converted photons by tailoring the degree of coherence of the pump field.

How to achieve lasing in a system with the strong lifetime broadening of working levels?

To minimize and put into an experimentally reachable domain the coherent optical pump intensity needed for radiation amplification on a transition between strongly lifetime broadened levels, an inversionless lasing scheme is suggested. Such a scheme can be used, for example, to achieve lasing in quantum dots with lifetime broadened levels.