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International Journal of Quantum Information

Spatio-spectral characterization of twin-beam states of light for quantum state engineering

Alessia Allevi, Marco Lamperti, Ottavia Jedrkiewicz, Justinas Galinis, Radek Machulka, Ondřej Haderka, Jan Peřina, Maria Bondani

Published Nov 1, 2014• 7 citations
Publisher

Abstract

We present an experimental investigation of the spatio-spectral coherence properties of bright twin-beam states (TWBs) as functions of different parameters, such as pump mean power and tuning angle of the employed nonlinear crystal. Our attention is mainly focused on the possible relations among the different quantities under investigation. Particular attention is devoted to the evolution of the number of spatio-spectral modes describing the radiation field, as it represents an interesting property to be controlled in view of possible applications to quantum state engineering protocols.

DOI
10.1142/s0219749915600278

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We present an experimental investigation of the spatio-spectral coherence properties of bright twin-beam states (TWBs) as functions of different parameters, such as pump mean power and tuning angle of the employed nonlinear crystal. Our attention is mainly focused on the possible relations among the different quantities under investigation. Particular attention is devoted to the evolution of the number of spatio-spectral modes describing the radiation field, as it represents an interesting property to be controlled in view of possible applications to quantum state engineering protocols.
We present the experimental investigation of the coherence properties of the light produced by parametric down conversion in the macroscopic regime, also including pump depletion. In particular, we compare the results obtained in very similar geometric conditions by using two nonlinear crystals having different lengths. We observe that the number of generated photons, the size of spatio-spectral coherence areas, and the number of modes in the photon number statistics exhibit a similar behavior in the two crystals as a function of pump mean power, even if we notice that the absolute values are different. The available theory of parametric down conversion cannot account for these differences.
Single-mode quantum optical states represent an interesting resource for the implementation of quantum information protocols. Here, we address the generation of twin-beam (TWB) states characterized by a quasi-single-mode thermal statistics. In more detail, the selection procedure leading to single-mode states is achieved with a strong filtering applied to intense TWBs generated in a single crystal by parametric downconversion. We investigate the role of pump power in the production of the single-mode states and compare the results obtained with nonlinear crystals having different lengths.
Abstract Properties of intense twin beams generated in parametric down-conversion in periodically poled LiNbO3 crystals and their chirped variants by intense pump fields are analyzed along the model of intense parametric down-conversion that allows for pump depletion and uses the dual spatio-spectral Schmidt modes. Spectral and spatial intensity auto- and cross-correlation functions are determined as they depend on the pump power. Temporal correlations in intense twin beams at the fs time scale are investigated using the Hong-Ou-Mandel interferometer and the process of sum-frequency generation.
Waves in the spatio-spectral and -temporal coherence of evolving ultra-intense twin beams are predicted: Twin beams with low intensities attain maximal coherence in the beam center until certain threshold intensity is reached. Then the area of maximal coherence moves with increasing intensity from the beam center towards its edges leaving the beam center with low coherence (the first coherence wave). For even larger intensities, a new coherence maximum is gradually built in the beam center with the increasing intensity and, later, it again moves towards the beam edges forming the second coherence wave. Rotationally-symmetric twin beams are analyzed within a three-dimensional model that couples spectral and spatial degrees of freedom. Relation between the twin-beam coherence and its local density of modes during the nonlinear evolution is discussed.
We observed the spectral coherence structure of twin beam states generated by spontaneous parametric down-conversion by using a simple fiber spectrometer synchronized with a pulsed laser source. The recorded single-shot spectra exhibit a well-defined peak structure, where the peak wavelengths change values from shot to shot. We studied the number and the width of the peaks as a function of the different parameters in the experimental setup (pump power, iris size, iris distance from the BBO crystal). Moreover, we evaluated the number of modes in the intensity distribution of the light in different portions of the spectrum. The experimental results indicate that the number of modes from statistics and the number and width of the peaks evolve differently with the parameters.