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Quantum Information Science Outputs
| Title | Category | Date | Authors |
| Generating two-photon entangled states in a driven two-atom system University of Calgary | Publication | 2011-07-01 | K. Almutairi, R. Tanaś, Z. Ficek | | Two-photon dipole-dipole blockadeWe describe a mechanism for a controlled generation of a pure Bell state with correlated atoms that involve two or zero excitations. The mechanism inhibits transitions into singly excited collective states of a two-atom system by shifting them from their unperturbed energies. The shift is accomplished by the dipole-dipole inter- action between the atoms. The creation of the Bell state is found to be dependent on the relaxation of the atomic excitation. When the relaxation is not present or can be ignored, the state of the system evolves harmonically between a separable to the maximally entangled state. We follow the temporal evolution of the state and find that the concurrence can be different from zero only in the presence of the dipole-dipole interaction. Furthermore, in the limit of a large dipole-dipole interaction, the concurrence reduces to that predicted for an X-state of the system. A general inequality is found which shows that the concurrence of an X-state system is a lower bound for the concurrence of the two-atom system. With the relaxation present, the general state of the system is a mixed state that under a strong dipole-dipole interaction reduces the system to an X-state form. We find that mixed states admit of lower level of entanglement, and the entanglement may occur over a finite range of time. A simple analytical expression is obtained for the steady-state concurrence which shows that there is a threshold value for the dipole-dipole interaction relative to the Rabi frequency of the driving field above which the atoms can be entangled over the entire time of the evolution. University of Calgary | Presentation | 2011-06-17 | K. Almutairi, R. Tanas, Z. Ficek | | Optical self-phase modulation via nonlinear spin-wave dynamics in a BECLight can be stored in Bose-Einstein condensates for more than one second using quantum memory techniques based on electromagnetically induced transparency [1]. In recent theoretical work [2], Rispe et al. proposed a method for storing photons in Bose-Einstein condensates to create a photon-photon gate. This gate uses the collisions between atoms in order to generate a phase shift that is dependent on the presence or absence of photons. We go beyond the single photon case considered in the previous scheme [2] to the many-photon case in the mean-field treatment and under the Thomas-Fermi approximation, where this scheme leads to strong phase self-modulation. That medium will allow superposition of an arbitrary number of photons to undergoing nonlinear evolution and in particular produce "cat states" [3]. We generate "cat states" [3] from coherent states through the collision-induced interaction.
References: [1] R. Zhang, S. R. Garner, and L.V. Hau, Phys. Rev. Lett. 103, 233602 (2009). [2] A. Rispe, B. He, and C. Simon ,Phys. Rev. Lett. 107, 043601 (2011). [3] B. Yurke, and D. Stoler, Phys. Rev. Lett. 57, 13 (1986). University of Calgary | Presentation | 2012-07-27 | K. Almutairi, C. Trail, C. Simon, B. C. Sanders | | Nonlinear phase shifts of light trapped in a two-component Bose-Einstein condensate University of Calgary | Publication | 2014-01-01 | C. Trail, K. Almutairi, D. Feder, B. C. Sanders |
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