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Laser Physics Letters

Quantum transformation limits in multiwave parametric interactions

M. Yu. Saygin

Published Sep 7, 2016• 2 citations
Publisher

Abstract

Abstract The possibility to realize multiple nonlinear optical processes in a single crystal as means to produce multicolor quantum states favours stability and compactness of optical settings. Hence, this approach can be advantageous compared to the traditional one based on cascaded arrangement of optical elements. However, it comes with an obstacle—the class of accessible quantum states is narrower than that of the cascade counterpart. In this letter, we study this task using an example of three coupled nonlinear optical processes, namely, one parametric down-conversion and two of sum-frequency generation. To this end, the singular value decomposition has been applied to find the cascade representation of the compound field evolution. We have found the link between the parameters of the multiwave processes and the relevant cascade parameters—beam-splitting and squeezing parameters, by means of which the generated quantum states have been characterized. The relation between the squeezing parameters that has been found in the course of this work shows that the squeezing resource, produced in the parametric down-conversion, is shared among the modes involved in the compound interactions. Moreover, we have shown that the degree of two-mode entanglement carried by the up-converted frequencies cannot exceed that of the down-converted frequencies.

DOI
10.1088/1612-2011/13/10/105203

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Abstract The possibility to realize multiple nonlinear optical processes in a single crystal as means to produce multicolor quantum states favours stability and compactness of optical settings. Hence, this approach can be advantageous compared to the traditional one based on cascaded arrangement of optical elements. However, it comes with an obstacle—the class of accessible quantum states is narrower than that of the cascade counterpart. In this letter, we study this task using an example of three coupled nonlinear optical processes, namely, one parametric down-conversion and two of sum-frequency generation. To this end, the singular value decomposition has been applied to find the cascade representation of the compound field evolution. We have found the link between the parameters of the multiwave processes and the relevant cascade parameters—beam-splitting and squeezing parameters, by means of which the generated quantum states have been characterized. The relation between the squeezing parameters that has been found in the course of this work shows that the squeezing resource, produced in the parametric down-conversion, is shared among the modes involved in the compound interactions. Moreover, we have shown that the degree of two-mode entanglement carried by the up-converted frequencies cannot exceed that of the down-converted frequencies.
The teleportation of entangled optical images is for the first time considered. The scheme offered is based on process of four-partite state generation in coupled parametric interactions realizing in an aperiodic nonlinear photonic crystal. The coupled nonlinear optical process consists of one parametric down-conversion process which is followed by two up-conversion ones. We study nonclassical properties of the generated fields by analyzing the EPR correlations for different pairs of modes and carry out the comparison of the EPR correlations of the input and images output images and also calculate fidelity of the teleportation exploiting the covariance matrices of the images. We take into account the difference of spatial frequency bandwidths of the entangled images and fields generated in the coupled process. It has been established that under certain parameters of the scheme one can be obtain rather high fidelity of the teleportation and good preservation of the quantum correlations of the input images for all details of the images.
A quantum theory of parametric amplification and frequency conversion of an optical image in coupled nonlinear optical processes that include one parametric amplification process at high-frequency pumping and two up-conversion processes in the same pump field is developed. The field momentum operator that takes into account the diffraction and group velocities of the waves is used to derive the quantum equations related to the spatial dynamics of the images during the interaction. An optical scheme for the amplification and conversion of a close image is considered. The mean photon number density and signal-to-noise ratio are calculated in the fixed-pump-field approximation for images at various frequencies. It has been established that the signal-to-noise ratio decreases with increasing interaction length in the amplified image and increases in the images at the generated frequencies, tending to asymptotic values for all interacting waves. The variance of the difference of the numbers of photons is calculated for various pairs of frequencies. The quantum entanglement of the optical images formed in a high-frequency pump field is shown to be converted to higher frequencies during the generation of sum frequencies. Thus, two pairs of entangled optical images are produced in the process considered.
We study parametric interactions in a new type of nonlinear photonic structure, which is realized in the volume between a pair of nonlinear crystals. In this kind of structure, which we call binary, multiple nonlinear optical processes can be implemented simultaneously, owing to multiple phase-matching conditions, fulfilled separately in the constituent crystals. The coupling between the nonlinear processes by means of modes sharing similar frequency is attained by the spatially broadband nature of the parametric fields. We investigate the spatial properties of the fields generated in the binary structure constructed from periodically poled crystals for the two examples: (1) single parametric downconversion and (2) coupled parametric downconversion and upconversion processes. The efficacy of the fields’ generation in these examples is analyzed through comparison with the cases of a traditional single periodically poled crystal and an aperiodic photonic structure, respectively. For this, we have devised a method that allowed us to solve the field equations numerically without resorting to statistically modeling the input vacuum states. It has been shown that the relative shift between the periodic crystal lattices has a crucial effect on the generated spatial field spectrum and overall efficiency. In addition, the influence of the intercrystal distance on these characteristics has been studied. Therefore, our study suggests that one can construct optical elements with sophisticated nonlinear properties from simpler elements without significant sacrifice of efficacy.
Nonlinear multiphoton conversion processes are theoretically and experimentally challenging systems in quantum optics and related areas. These phenomena bring remarkable quantum properties and can be of fundamental relevance in quantum information and computation applications. Based on recent experimental advances and the possible uses in generalized three-photon squeezing, we investigate degenerate three-photon parametric down-conversion generated inside a cavity fed by a classical pump. In addition, we consider that the process is stimulated by a coherent driving mode and subjected to dissipation by spontaneous emission of the cavity. A treatment using phase-space methods and stochastic differential equations is applied and the stability conditions of its steady states are found. We find that the system does not exhibit multistability, instead it has a limited parameter region leading to a single stable steady branch, alongside multiple unstable branches. Focusing on the stable steady states and linearizing the dynamics around them, we calculate the spectral densities of the quadrature variables. We identify and characterize the squeezing of three-photon down-conversion. Moreover, since the quasi-probability differential equations of the higher-order multiphoton processes have higher-order derivatives, hindering their mapping into stochastic differential equations, we make use of a positive Wigner function approach to calculate two-dimensional spectral densities associated with three-time correlation functions, with the goal of studying non-Gaussian properties of the system.
The search for new methods to produce entangled photons is a subject of great interest in quantum optics. We show theoretically that two_photon entangled states may be generated through a cascaded nonlinear optical process in a quasiperiodic optical superlattice. When an idler photon ωi produced from spontaneous parametric down conversion (ωp=ωs+ωi) combines with a pum p photon to produce a sum frequency photon ωb(ωb=ωi+ω p), the latter is entangled with the remaining signal photon ωi. Both a pulsed and a cw 532nm laser have been used to pump a quasi_phase matched LiTaO 3 crystal to generate simultaneously 630nm signal photons through parametric d own conversion and 460nm sum frequency photons. The advantage of this method is that entangled photons of short wavelength may be produced.
Abstract Three-color continuous-variable (CV) entangled beams can be produced by single-pass cascaded sum-frequency processes of third-harmonic generation by quasi-phase-matching technique in only one optical superlattice. Firstly, second-harmonic field is generated by the first double-frequency process of the fundamental field. Then, the third-harmonic field can be generated by the second cascaded sum-frequency process between the second-harmonic and the fundamental fields by quasi-phase-matching technique in the same optical superlattice. By using the quantum stochastic method, we investigated the conversion dynamics of the cascaded sum-frequency processes and the quantum correlation nature among the fundamental, second-harmonic, and third-harmonic fields. The results show that the higher conversion efficiency of third-harmonic generation can be achieved with the larger nonlinear coupling parameter of the second cascaded sum-frequency process. We also show that the fundamental, second-, and third-harmonic beams are CV entangled with each other according to the necessary and sufficient CV entanglement criterion. This scheme of three-color entanglement generation without involving optical cavity is easy to realize in experiment. Moreover, the three-color entangled beams are separated by an octave in frequency which has potential applications in quantum communication and computation networks.