## Experimental direct estimation of nonlinear functionals of photonic quantum states via interferometry with a controlled-swap operation |

Optics Express, Vol. 21, Issue 15, pp. 17824-17830 (2013)

http://dx.doi.org/10.1364/OE.21.017824

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### Abstract

We propose a multi-photon interferometer with a generalized C-SWAP operation that can estimate Tr[*ρ*_{1}*ρ*_{2} ⋯*ρ _{n}*], a nonlinear functional of

*n*photonic density matrices. The scheme is demonstrated for three single-photon states whose overlap is experimentally measured as the interference visibility of a control qubit encoded into photonic paths. The validity of this method is verified by comparing the visibility with the results of Hong-Ou-Mandel experiments.

© 2013 OSA

**OCIS Codes**

(270.0270) Quantum optics : Quantum optics

(270.4180) Quantum optics : Multiphoton processes

(270.5585) Quantum optics : Quantum information and processing

**ToC Category:**

Quantum Optics

**History**

Original Manuscript: May 15, 2013

Revised Manuscript: July 12, 2013

Manuscript Accepted: July 12, 2013

Published: July 18, 2013

**Citation**

Sang Min Lee, Sang-Kyung Choi, and Hee Su Park, "Experimental direct estimation of nonlinear functionals of photonic quantum states via interferometry with a controlled-swap operation," Opt. Express **21**, 17824-17830 (2013)

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-15-17824

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