Optics 101

What is Spontaneous Parametric Down Conversion?

Spontaneous parametric down conversion is as an optical quantum process in which an incident photon is converted into pairs of entangled photons by a non-linear medium.

An Introduction to Spontaneous Parametric Down Conversion

Spontaneous parametric down conversion (SPDC) is also known as parametric scattering or parametric fluorescence. The state of the non-linear crystal remains the same after SPDC has occurred.

The basic principle behind the conversion is law of conservation of energy. SPDC is an important phenomenon in the field of quantum optics. The non-linearities of the crystal cause the spontaneous emission of pairs of photons. This article will look into the experimental set up, working and applications of spontaneous parametric down conversion phenomenon.

Experimental Set Up

The apparatus used for SPDC consists of a high power laser beam, called the pump source. The non-linear medium consists of a beta barium borate crystal. The non-linear medium also exhibits birefringence. KDP (potassium dihydrogen phosphate) crystal may also be used as a non-linear medium for SPDC.

Spontaneous parametric down conversion is accomplished by directing a strong laser beam at anon-linear optical medium which is birefringent. By following the law of conservation of energy, the incident photon is converted into a pair of photons whose axes are symmetrically arranged relative to the incident beam.

The pair of photons produced by the process of SPDC has energy and momentum levels that are equal to the energy of the original photon and match the phase of the original photon.

Applications of Spontaneous Parametric Down Conversion

Some of the typical applications of SPDC include:

  • Optical field creation
  • Quantum cryptography
  • Quantum information experiments.

References and Further Reading


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