Spontaneous parametric down-conversion

Abstract

Spontaneous Parametric Down-Conversion (SPDC), also known as parametric fluorescence, parametric noise, parametric scattering and all various combinations of the abbreviation SPDC, is a non-linear optical process where a photon spontaneously splits into two other photons of lower energies. One would think that this article is about particle physics and yet it is not, as this process can occur fairly easily on a day to day basis in an optics laboratory. Nowadays, SPDC is at the heart of many quantum optics experiments for applications in quantum cryptography, quantum simulation, quantum metrology but also for testing fundamentals laws of physics in quantum mechanics. In this article, we will focus on the physics of this process and highlight few important properties of SPDC. There will be two parts: a first theoretical one showing the particular quantum nature of SPDC and the second part, more experimental and in particular focusing on applications of parametric down-conversion. This is clearly a non-exhaustive article about parametric down-conversion as there is a tremendous literature on the subject, but it gives the necessary first elements needed for a novice student or researcher to work on SPDC sources of light.

Perspectives for Applications of Quantum Imaging

“…The development of nonlinear crystals with a large aperture is a key requirement toward high‐resolution quantum imaging applications . Furthermore, since the crystal length affects the spatial correlations of biphotons, these crystals should be of limited thickness . Hence, to achieve a significant photon flux, the crystals must thus also exhibit a large nonlinearity.…”

“…A practical way to distinguish different types of light is by means of their photon number statistics. Any given state of light can be characterized by its mean photon number n and its variance ( n) 2 , where we first consider only a single spatial mode. While classical light is associated with a super-Poissonian distribution with ( n) 2 > n , non-classical light, which can only be described using quantum optics, is linked with a sub-Poissonian one, that is, ( n) 2 < n .…”

“…[44] Furthermore, since the crystal length affects the spatial correlations of biphotons, these crystals should be of limited thickness. [2] Hence, to achieve a significant photon flux, the crystals must thus also exhibit a large nonlinearity. At present, aperture sizes for commercially available periodically poled nonlinear crystals are approximately 1-2 mm.…”

“…In doing so, entanglement plays a central role. In particular, momentum‐, energy‐, and position correlations of entangled photon pairs are crucial . They allow for spectroscopy and imaging in spectral ranges where no efficient detection is possible or even imaging with light that actually never interacted with a sample .…”

“…In particular, momentum-, energy-, and position correlations of entangled photon pairs are crucial. [1,2] They allow for spectroscopy and imaging in spectral ranges where no efficient detection is possible or even imaging with light that actually never interacted with a sample. [3][4][5][6] Furthermore, by utilizing certain quantum states of light and their photon number statistics, sensing and imaging beyond classical limitations, like the shot noise level, become possible.…”