by
𝜋
Realizing a strong interaction between individual photons is the key ingredient for scalable photon-based quantum processing. Since photons in free space do not interact, a medium which introduces a photon number dependent phase shift is required for this purpose. However, standard optical media cause a nonlinear response which is orders of magnitude too week for implementing high-fidelity quantum logic operations.
I will report on the realization of a fiber-integrated optical Kerr-nonlinearity on the single photon level that imprints the maximal nonlinear phase shift .
In our experiment, we couple single
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Rbatoms to a bottle microresonator [1] a novel type of whispering-gallery-mode microresonator. By making use of the particular polarization properties of our resonator we can obtain the ideal situation, where the atom exclusively interacts with one of the two counterpropagating resonator modes [2]. The presence of the single atom in the evanescent field of the resonator results in a strong nonlinear response of the coupled atom-resonator system to the photon number in the incident light field. This causes a nonlinear phase shift on the light passing the resonator.
Analyzing the transmitted light, we observe a nonlinear phase shift close to the maximum value of 𝜋 between the cases where one or two photons pass the resonator [3]. This results in entanglement between the two previously independent fiber guided photons, which we verify by performing a full quantum state tomography of the transmitted two-photon polarization state.
References
[1] M. Pöllinger et al., PRL 103 , 053901 (2009)
[2] C. Junge et al., PRL 110 , 213604 (2013)
[3] J. Volz et al., Nature Photonics (2014) doi:10.1038/nphoton.2014.253