Abstract
Photons are ideal carriers of quantum information yet their use is often largely hampered by the absence of significant photon-photon interactions especially when optical phase-gate mechanisms are to be implemented. Several proposals of universal phase gates exploit circular polarization states of travelling single-photon wave packets whose interactions could be enhanced in the regime of electromagnetically induced transparency (EIT). These proposals are experimentally challenging and owing to various technical difficulties the relevant cross-Kerr nonlinearities could only result in conditional phase shifts far less than the desired π value. On the other hand, Rydberg atoms have attracted extensive attentions in the quantum information field owing to the presence of strong dipole-dipole interactions and long radiative lifetimes. In particular, dipole-dipole interactions manifest themselves via a blockade mechanism prohibiting the simultaneous Rydberg excitations of two or more atoms in one mesoscopic volume. Here, we show that giant Rydberg nonlinearities created by strong dipole-dipole interactions in cold atoms can replace cross-Kerr nonlinearities in conventional polarization phase gates. Our predictions for polarization phase gates based on conditional Rydberg blockade in 87Rb gases show large efficiencies with negligible losses and the possibility of working in a quantum nonlinear regime.
Coffee and tea will be served 20 minutes prior to the seminar.