Implementation Of An Unconventional Geometric Phase Gate Based On Cavity Quantum Electrodynamics

Quantum logic gate is the basic building block of quantum information pro-cessing.It is crucial for quantum computation to implement a quantum logic gate with a fast rate and a high efficiency.So far,there are primarily two kinds of method to construct the quantum logic gate which are based on dynamical evolution and geometric operation,respectively.The former is sensitive to the parameter fluctua-tions during gate operations,which is the main blockage for a large scale quantum computing.While the latter is determined only by the area enclosed by the evo-lution path in phase space,i.e,it is insensitive to the path shape and the passage rate to traverse the close path,thus is called as the geometric phase gate.In this dissertation,we introduce how to implement a two-qubit unconventional geometric phase gate with atoms trapped in coupled cavities by one step.We implement a two-qubit controlled phase gate based on unconventional ge-ometric phase.During the gate operation,the two atomic systems undergo no transitions,while the cavity modes are displaced along a closed path in the phase s-pace,and the quantum information is encoded in the orthogonal states.In this way,an unconventional geometric phase gate is obtained with a high fidelity and the atomic spontaneous emission is effectively suppressed due to large detuning which makes the scheme robust against decoherence.In the scheme,the unconventional geometric phase gate can be implemented without additional single-qubit operation only by one step,which greatly simplifies the experimental steps.As an expansion,we have proposed an efficient scheme for implementing the above unconventional geometric phase gate using two atomic ensembles trapped in two coupled cavities.Compared with the previous schemes,the gating time is greatly reduced and there is no need for addressing the single-atoms due to the use of atomic ensembles.By numerical simulation a high fidelity can be achieved even if the cavity decay is considered.