Spontaneous parametric down-conversion
![](http://upload.wikimedia.org/wikipedia/commons/thumb/7/74/Spontaneous_Parametric_Downconversion.png/350px-Spontaneous_Parametric_Downconversion.png)
Spontaneous parametric down-conversion (also known as SPDC, parametric fluorescence or parametric scattering) is a nonlinear instant optical process that converts one photon of higher energy (namely, a pump photon), into a pair of photons (namely, a signal photon, and an idler photon) of lower energy, in accordance with the
Basic process
![](http://upload.wikimedia.org/wikipedia/commons/thumb/d/df/Scheme_of_spontaneous_parametric_down-conversion.pdf/page1-350px-Scheme_of_spontaneous_parametric_down-conversion.pdf.jpg)
A
The conversion efficiency of SPDC is typically very low, with the highest efficiency obtained on the order of 4x10-6 incoming photons for
Example
![](http://upload.wikimedia.org/wikipedia/commons/thumb/2/2d/SPDC_figure.png/350px-SPDC_figure.png)
In a commonly used SPDC apparatus design, a strong
Another crystal is KDP (
Some of the characteristics of effective parametric down-converting nonlinear crystals include:
- Nonlinearity: The refractive index of the crystal changes with the intensity of the incident light. This is known as the nonlinear optical response.
- Periodicity: The crystal has a regular, repeating structure. This is known as the lattice structure, which is responsible for the regular arrangement of the atoms in the crystal.
- Optical anisotropy: The crystal has different refractive indices along different crystallographic axes.
- Temperature and pressure sensitivity: The nonlinearity of the crystal can change with temperature and pressure, and thus the crystal should be kept in a stable temperature and pressure environment.
- High nonlinear coefficient: Large nonlinear coefficient is desirable, this allow to generate a high number of entangled photons.
- High optical damage threshold: Crystal with high optical damage threshold can endure high intensity of the pumping beam.
- Transparency in the desired wavelength range: It is important for the crystal to be transparent in the wavelength range of the pump beam for efficient nonlinear interactions
- High optical quality and low absorption: The crystal should be high optical quality and low absorption to minimize loss of the pump beam and the generated entangled photons.
History
SPDC was demonstrated as early as 1967 by S. E. Harris, M. K. Oshman, and R. L. Byer,[7] as well as by D. Magde and H. Mahr.[8] It was first applied to experiments related to coherence by two independent pairs of researchers in the late 1980s: Carroll Alley and Yanhua Shih, and Rupamanjari Ghosh and Leonard Mandel.[9][10] The duality between incoherent (Van Cittert–Zernike theorem) and biphoton emissions was found.[11]
Applications
SPDC allows for the creation of
SPDC is widely used to create pairs of entangled photons with a high degree of spatial correlation.[13] Such pairs are used in ghost imaging, in which information is combined from two light detectors: a conventional, multi-pixel detector that does not view the object, and a single-pixel (bucket) detector that does view the object.
Alternatives
The newly observed effect of
See also
References
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- ISBN 978-1-4299-6379-4.
- ^ Reck, M H A, Quantum Interferometry with Multiports: Entangled Photons in Optical Fibers (page 115) (PDF), retrieved 16 February 2014
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- ^ Y. Shih and C. Alley, in Proceedings of the 2nd Int'l Symposium on Foundations of QM in Light of New Technology, Namiki et al., eds., Physical Society of Japan, Tokyo, 1986.
- PMID 10035364.
- ^ http://pra.aps.org/abstract/PRA/v62/i4/e043816 - Duality between partial coherence and partial entanglement
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