Engineering competing nonlinearities

Weak modulation of a quasi-phase-matching (QPM) grating opens possibilities for engineering both the average quadratic nonlinearity and the incoherent average cubic nonlinearity induced by QPM. The relative strength of the average quadratic and effective (intrinsic plus induced) cubic nonlinearity is studied for LiNbO(3) . We show how the induced average cubic nonlinearity can be engineered to dominate the intrinsic material cubic nonlinearity and how doing so will allow the intensity at which the quadratic and cubic nonlinearities balance and thus compete to be decreased to a few gigawatts per square centimeter.     

Solitons in a diatomic chain with competing nonlinearities

A one-dimensional diatomic chain whose energy contains cubic and quartic terms in the atomic displacements is considered. A modified asymptotic method is proposed for finding soliton solutions to equations describing systems with nonlinearities of various symmetry. It is shown that the dynamics of the model in question can be described in terms of equations that are similar to the dynamic equations for a diatomic chain with an even potential function. Soliton solutions of a new, unusual type are found in the specific case of a free diatomic chain with a purely cubic anharmonic potential.     

Quantum correlated twin beams

We discuss recent progress in the study of the non-classical properties of light beams generated by non-degenerate parametric splitting in ⁽²⁾ nonlinear birefringent crystals, with special emphasis on their quantum correlation (twin beams). We describe experimental results using successively pure parametric fluorescence, parametric amplification of a weak signal beam pumped by a pulsed laser, and parametric oscillation in a cavity pumped by a cw laser. In this review, we compare the respective advantages and drawbacks of the different approaches.     

Experimental characterization of quantum-correlated twin beams and a quantum channel with twin beams

We report the generation and characterization of quantum-correlated twin beams and their application to a quantum channel. Compared with our previous results, the characterization of twin beams and the quantum channel have been studied with 7.0-dB intensity difference squeezing. The measured inference variance of twin beams is decreased to 0.40 ± 0.02. For the quantum channel, the bit error rate will be 0.035 by using 7.0-dB intensity difference squeezing compared with our previous result of 0.067 by using 4.9-dB intensity difference squeezing.     

Phase sensitivity with a coherent beam and twin beams via intensity difference detection

We focus on the Mach–Zehnder interferometer(MZI) with the input of a coherent beam and one of the bright entangled twin beams with an external power reference beam employed for measurement. The results show that the phase sensitivity can reach sub-Heisenberg limit and approach quantum Cramer–Rao bound by changing the squeezing parameters and the photon number of the coherent beam, under the phase-matching condition. The absence of the external power reference beam will degrade the performance of...     

Robust propagation of two-color soliton clusters supported by competing nonlinearities

We reveal numerically the remarkably robust propagation of quasistationary two-color soliton clusters in media with competing quadratic and cubic nonlinearities. We predict that such clusters carrying nonzero angular momentum can propagate over any practically feasible crystal length before they decay, even in the presence of input random perturbations.     

Absolute detector calibration using twin beams

A method for the determination of absolute quantum detection efficiency is suggested based on the measurement of photocount statistics of twin beams. The measured histograms of joint signal-idler photocount statistics allow us to eliminate an additional noise superimposed on an ideal calibration field composed of only photon pairs. This makes the method superior above other approaches presently used. Twin beams are described using a paired variant of quantum superposition of signal and noise.     

Quantum interference of ultrastable twin optical beams

We report the first measurement of the quantum phase-difference noise of an ultrastable nondegenerate optical parametric oscillator that emits twin beams classically phase locked at exact frequency degeneracy. The measurement illustrates the property of a lossless balanced beam splitter to convert number-difference squeezing into phase-difference squeezing, and thus provides indirect evidence for Heisenberg-limited interferometry using twin beams. This experiment is a generalization of the Hong-Ou-Mandel interference effect for continuous variables and constitutes a milestone towards continuous-variable entanglement of bright, ultrastable nondegenerate beams.     

Solutions to the equations describing materials with competing quadratic and cubic nonlinearities

The Lie group theoretical method is used to study the equations describing materials with competing quadratic and cubic nonlinearities. The equations share some of the nice properties of soliton equations. From the elliptic functions expansion method, we obtain large families of analytical solutions, in special cases, we have the periodic, kink and solitary solutions of the equations. Furthermore, we investigate the stability of these solutions under the perturbation of amplitude noises by numerical simulation.     

QND-measurement of twin beams by phase sensitive preamplification

We propose a QND-measurement of twin beams to improve the noise suppression achieved with squeezed states, which is currently limited by the finite sensitivity of the photo detectors. The scheme can be implemented with existing fiber technology. Received: 31 January 1996 / Revised version: 24 June 1996     

Tailoring optical nonlinearities via the Purcell effect

We predict that the effective nonlinear optical susceptibility can be tailored using the Purcell effect. While this is a general physical principle that applies to a wide variety of nonlinearities, we specifically investigate the Kerr nonlinearity. We show theoretically that using the Purcell effect for frequencies close to an atomic resonance can substantially influence the resultant Kerr nonlinearity for light of all (even highly detuned) frequencies. For example, in realistic physical systems, enhancement of the Kerr coefficient by one to two orders of magnitude could be achieved.     

Transfer of intensity quantum correlation with twin beams

We demonstrate experimentally a protocol of transferring nonclassical quantum properties using two pairs of quantum-correlated twin beams in the continuous variable regime. The intensity quantum correlation from one twin beam is transferred to two initially independent idler beams with the help of a displacement transformation. It makes two originally independent beams exhibit an intensity quantum correlation of 0.8 dB below shot-noise level.     

Secure quantum channels with correlated twin laser beams

A quantum cryptographic protocol based on the use of a strongly correlated pair of laser beams is proposed. The properties of the corresponding states are described in detail. The protocol is based on the strong correlation of photon numbers in both beams in each measurement. The protocol stability against basic interception attempts is analyzed.     

Method for generating solitons sustained by competing nonlinearities by use of optical rectification

We put forward a method for generating engineerable competing quadratic and cubic nonlinearities in suitable settings in which frequency generation is accompanied by optical rectification. The novel scheme is based on the full exploitation of the geometrical conditions that determine the magnitude of the rectified fields and translates the different orientations of an elliptical pump beam into tunable nonlinearities, which can be used to act on the spectral composition and overall features of optical solitons.     

Sub-Poissonian shot noise in graphene

We calculate the mode-dependent transmission probability of massless Dirac fermions through an ideal strip of graphene (length L, width W, no impurities or defects) to obtain the conductance and shot noise as a function of Fermi energy. We find that the minimum conductivity of order e2/h at the Dirac point (when the electron and hole excitations are degenerate) is associated with a maximum of the Fano factor (the ratio of noise power and mean current). For short and wide graphene strips the Fano factor at the Dirac point equals 1/3, 3 times smaller than for a Poisson process. This is the same value as for a disordered metal, which is remarkable since the classical dynamics of the Dirac fermions is ballistic.     

竞争型非线性介质中艾里-高斯光束交互作用的调控

基于分步傅里叶法研究了艾里-高斯光束在三次聚焦和五次散焦竞争型非线性介质中交互作用的调控.结果表明:当入射角度为零时,同相位艾里-高斯光束相互吸引,五次散焦非线性强度较弱时,可形成周期逐渐缩短的呼吸孤子或强度不变的孤子.五次散焦非线性强度较强时,呼吸孤子的平均宽度变大甚至出现光束分叉现象,形成孤子对.反相位艾里-高斯光束相互排斥,排斥力随五次散焦非线性强度单调递增.当入射角度不为零时,通过控制光束入射角度的正负和初始间距.同相位和反相位艾里-高斯光束交互作用时可以同时表现出相互吸引和排斥的现象.     

Generation of spatially broadband twin beams for quantum imaging

We generate spatially multimode twin beams using 4-wave mixing in a hot atomic vapor in a phase-insensitive traveling-wave amplifier configuration. The far-field coherence area measured at 3.5 MHz is shown to be much smaller than the angular bandwidth of the process and bright twin images with independently quantum-correlated subareas can be generated with little distortion. The available transverse degrees of freedom form a high-dimensional Hilbert space that we use to produce quantum-correlated twin beams with finite orbital angular momentum.     

Tunable twin beams generated by a type-I LNB OPO

We present a novel scheme to separate spatially twin beams generated by a type-I lithium niobate (LNB) optical parametric oscillator near frequency degeneracy. The system is based on a holographic diffraction grating acting as a beam splitter in a balanced detector. The fast and easy temperature tuning of LNB index of refraction allows an easy control of the twin-beam wavelength distance in a range of the order of ∼100 nm. We report correlation spectra measured for different twin-beam wavelength separations (15–60 nm) with a maximum noise reduction of 3.2 dB at 3.5 MHz. The described system exhibited a pump resonance stability longer than 6 h with infrared output power fluctuations within 4% around an average value of ≃2 mW in each beam. The measured oscillation threshold pump power was lower than 31 mW. Received: 7 June 2001 / Revised version: 17 July 2001 / Published online: 10 October 2001