Quantum phase gate Based on Electromagnetically Induced Transparency in Optical Cavities

摘要

We theoretically investigate the implementation of a quantum phase gate in asystem constituted by a single atom inside an optical cavity, based on theelectromagnetically induced transparency effect. Firstly we show that a probepulse can experience a $\pi$ phase shift due to the presence or absence of aclassical control field. Considering the interplay of the cavity-EIT effect andthe quantum memory process, we demonstrated a controlled phase gate between twosingle photons. To this end, firstly one needs to store a (control) photon inthe ground atomic states. In the following, a second (target) photon mustimpinge on the atom-cavity system. Depending on the atomic state, this secondphoton will be either transmitted or reflected, acquiring different phaseshifts. This protocol can then be easily extended to multiphoton systems, i.e.,keeping the control photon stored, it may induce phase shifts in several singlephotons, thus enabling the generation of multipartite entangled states. Weexplore the relevant parameter space in the atom-cavity system that allows theimplementation of quantum phase gates using the recent technologies. Inparticular we have found a lower bound for the cooperativity of the atom-cavitysystem which enables the implementation of phase shift on single photons. Theinduced shift on the phase of a photonic qubit and the controlled phase gatebetween single photons, combined with optical devices, enable to performuniversal quantum computation.