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arXiv:0810.4063 · Physical Review A

Demonstration of a bright and compact source of tripartite nonclassical light

Alessia Allevi, Maria Bondani, Matteo G. A. Paris, Alessandra Andreoni

Published Dec 1, 2008• 23 citations
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Abstract

We experimentally demonstrate the nonclassical photon number correlations expected in tripartite continuous-variable states obtained by parametric processes. Our scheme involves a single nonlinear crystal, where two interlinked parametric interactions take place simultaneously, and represents a bright and compact source of a sub-shot-noise tripartite light field. We analyze the effects of the pump intensities on the numbers of detected photons and on the amount of noise reduction in some detail, thus demonstrating a good agreement between the experimental data and a single-mode theoretical description.

DOI
10.1103/physreva.78.063801

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We experimentally demonstrate the nonclassical photon number correlations expected in tripartite continuous-variable states obtained by parametric processes. Our scheme involves a single nonlinear crystal, where two interlinked parametric interactions take place simultaneously, and represents a bright and compact source of a sub-shot-noise tripartite light field. We analyze the effects of the pump intensities on the numbers of detected photons and on the amount of noise reduction in some detail, thus demonstrating a good agreement between the experimental data and a single-mode theoretical description.
We demonstrate, by direct measurement of the number of photons in signal and idler, that the twin-beam of light produced by ps-pulsed spontaneous parametric downconversion is endowed with sub-shot-noise photon-number correlations in a mesoscopic intensity regime (more than 1000 detected photons). The noise reduction, calculated from the variance of the difference in the numbers of detected-photons, resulted to be 3.25 dB below the shot-noise level. From experimental data we can recover joint photon-number distribution and a negative-valued joint signal-idler quasi-distributions of integrated intensities, which demonstrates the nonclassical character of the generated field.
We experimentally investigate the parametric down-conversion process in a nonlinear bulk crystal, driven by two non-collinear pump modes. The experiment shows the emergence of bright hot-spots in modes shared by the two pumps, similar to the phenomenology recently observed in 2D nonlinear photonic crystals. By exploiting the spatial walk-off between the two extraordinary pump modes, we have been able to recreate a peculiar resonance condition, reported by a local enhancement of the parametric gain, which corresponds to a transition from a three-mode to a four-mode coupling. From a quantum point of view, this opens the way to the generation of multimode entangled states of light, such as tripartite or quadripartite states, in simple bulk nonlinear sources.
We demonstrate sub-shot-noise photon-number correlations in a (temporal) multimode mesoscopic ($\ensuremath{\sim}{10}^{3}$ detected photons) twin beam produced by picosecond-pulsed spontaneous nondegenerate parametric down-conversion. We have separately detected the signal and idler distributions of photons collected in twin coherence areas and found that the variance of the photon-count difference goes below the shot-noise limit by 3.25dB3.25\phantom{\rule{0.3em}{0ex}}\mathrm{dB}3.25dB. The number of temporal modes contained in the twin beam, as well as the size of the twin coherence areas, depends on the pump intensity. Our scheme is based on spontaneous down-conversion and thus does not suffer from limitations due to the finite gain of the parametric process. Twin beams are also used to demonstrate the conditional preparation of a nonclassical (sub-Poissonian) state.
Entangled state of light is one of the essential quantum resources in quantum information science and technology. Especially, when the fundamental principle experiments have been achieved in labs and the applications of continuous variable quantum information in the real world are considered, it is crucial to design and construct the generation devices of entangled states with high entanglement and compact configuration. We have designed and built an efficient and compact light source of entangled state, which is a non-degenerate optical parametric amplifier (NOPA) with the triple resonance of the pump and two subharmonic modes. A wedged type-II KTP crystal inside the NOPA is used for implementing frequency-down-conversion of the pump field to generate the optical entangled state and achieving the dispersion compensation between the pump and the subharmonic waves. The EPR entangled state of light with quantum correlations of 8.4 dB for both amplitude and phase quadratures are experimentally produced by a single NOPA under the pump power of 75 mW.
The implementation of a bright frequency correlated photon pairs source based on a PPKTP requires two principal parts: the process of Spontaneous Parametric Down-Conversion SPDC taking into account the quasi-phase-matching conditions and a single-frequency-mode laser source with a Gaussian profile. In this project, a theoretical approach of the SPDC process and the conditions needed to have an intense source of correlated photon pairs source are studied; especially, the process dependence of the temperature of the crystal and the pump wavelength. A single-frequency-mode pump laser source is implemented and focused to a PPKTP crystal. The photon pairs source is characterized spatially, in intensity and frequency. Through this, a bright photon pairs source with a coincidence rate per mW of pump power of 199 +- 1 kHz/mW is obtained, which is at least three times bigger than the rate of coincidences of the SPDC process using a traditional nonlinear crystal as a BBO.