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Abstract
This PhD thesis treats applications of nonlinear optical effects for quantum information
processing. The two main applications are fourwave mixing in the form
of Bragg scattering (BS) for quantumstatepreserving frequency conversion, and
sumfrequency generation (SFG) in secondorder nonlinear materials for heralded
entanglement.
BS is shown to be separable in the input and output modes in the lowconversion regime, the regime of small pump powers or short interaction times. The selective frequency conversion of a signal is found to only depend on one of the pumps, while the temporal output of the converted idler depends on the other pump. This allows for temporalmodemultiplexing. When the effects of nonlinear phase modulation (NPM) are included, the phases of the natural input and output modes are changed, reducing the separability. These effects are to some degree mediated by prechirping the pumps.
In the highconversion regime without the effects of NPM, exact Green functions for BS are derived. In this limit, separability is possible for conversion efficiencies up to 60 %. However, the system still allows for selective frequency conversion as well as reshaping of the output. One way to obtain a 100 % conversion efficiency is to use multiple stages of frequency conversion, but this setup suffers from the combined effects of NPM. This problem is circumvented by using asymmetrically pumped BS, where one pump is continuous wave. For this setup, NPM is found to only lead to linear phase shifts of the input and output modes, corresponding to shifts of the central frequencies of the fields. The tradeoff is that one is only able to select which signals are converted, or change the shape of the output idler.
Finally, entanglement swapping using SFG was investigated. Considering two pairs of entangled photons, the process of upconverting one photon from each pair leads to heralded entangled pairs by successful detection of the upconverted photon. It was seen that this was indeed possible in the case of anticorrelated phasematching in the upconversion crystal. Possible ways of increasing the probability of an upconversion event were investigated briefly.
BS is shown to be separable in the input and output modes in the lowconversion regime, the regime of small pump powers or short interaction times. The selective frequency conversion of a signal is found to only depend on one of the pumps, while the temporal output of the converted idler depends on the other pump. This allows for temporalmodemultiplexing. When the effects of nonlinear phase modulation (NPM) are included, the phases of the natural input and output modes are changed, reducing the separability. These effects are to some degree mediated by prechirping the pumps.
In the highconversion regime without the effects of NPM, exact Green functions for BS are derived. In this limit, separability is possible for conversion efficiencies up to 60 %. However, the system still allows for selective frequency conversion as well as reshaping of the output. One way to obtain a 100 % conversion efficiency is to use multiple stages of frequency conversion, but this setup suffers from the combined effects of NPM. This problem is circumvented by using asymmetrically pumped BS, where one pump is continuous wave. For this setup, NPM is found to only lead to linear phase shifts of the input and output modes, corresponding to shifts of the central frequencies of the fields. The tradeoff is that one is only able to select which signals are converted, or change the shape of the output idler.
Finally, entanglement swapping using SFG was investigated. Considering two pairs of entangled photons, the process of upconverting one photon from each pair leads to heralded entangled pairs by successful detection of the upconverted photon. It was seen that this was indeed possible in the case of anticorrelated phasematching in the upconversion crystal. Possible ways of increasing the probability of an upconversion event were investigated briefly.
Original language  English 

Place of Publication  Kgs. Lyngby 

Publisher  Technical University of Denmark 
Number of pages  258 
Publication status  Published  2014 
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 1 Finished

Optical Signal Processing using Four Wave Mixing
Andersen, L. M. (PhD Student), Rottwitt, K. (Main Supervisor), Willatzen, M. (Examiner), Karlsson, L. M. I. (Examiner) & Qian, L. (Examiner)
Technical University of Denmark
01/10/2011 → 26/01/2015
Project: PhD