# Stuttgart 2012 – wissenschaftliches Programm

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# Q: Fachverband Quantenoptik und Photonik

## Q 12: Quanteninformation: Photonen und nichtklass. Licht

### Q 12.3: Vortrag

### Montag, 12. März 2012, 14:30–14:45, V7.02

**Distinguishable and Indistinguishable Photons** — •Falk Töppel^{1,2}, Andrea Aiello^{1,2}, and Gerd Leuchs^{1,2} — ^{1}Max Planck Institute for the Science of Light, 91058 Erlangen, Germany — ^{2}Institute for Optics, Information and Photonics, Universität Erlangen-Nürnberg, 91058 Erlangen, Germany

Since the seminal work by Knill, Laflamme and Milburn [Nature 409, 46 (2001)], it is well known that linear optics combined with photon counting offers a promising route towards the realisation of an efficient scalable Quantum Computer. However, most of the proposed experimental schemes require indistinguishable photons. Since photons have many degrees of freedom (e. g. central frequency, spectral width, polarisation, etc.), the single photons produced in laboratories are very likely to become at least partially distinguishable, due to experimental imperfections.

We introduce in an operational manner a rate of distinguishability that quantifies the distinguishability of two photons with respect to a particular degree of freedom and to the particular state the photons are prepared in [arXiv:1108.5036]. Our measure relies on the Hong-Ou-Mandel experiment already widely used to test indistinguishability of photons experimentally. Our exemplary studies of Gaussian wave functions showed that in this instance the rate of distinguishability is universal for all degrees of freedom and that coupling between different degrees of freedoms critically affects the indistinguishability of photons.