Quantum Entanglement Concentration And Preparation Based On Collective Rotating Decoherence-free Subspace

Quantum entanglement is the core of quantum information processing and is commonly used in various quantum information processing tasks.Considering the safety and effectiveness of the task,we often need maximally entangled state.However,in the actual quantum information processing,it is inevitable that the maximally entangled state interact with the environment and are disturbed by noise.Therefore,the maximally entangled state can easily become a partially entangled state.Entanglement concentration is one of the effective methods to concentrate partially entangled states to maximally entangled states.However,when the maximally entangled state obtained by the concentration is in contact with the environment again and is disturbed by noise,it becomes a partially entangled state.In order to solve the problem of noise interference in quantum information processing,this paper is based on the cross-Kerr nonlinearity,and encodes several physical qubits into one logical qubit to construct a collective rotating decoherence-free subspace,such as (?),quantum information processing in this subspace,where the quantum entangled states can resist noise interference and remain unchanged.Based on the collective rotating decoherence-free subspace,this paper mainly does the following researches:(1)Entanglement concentration in decoherence-free subspace,not only can the maximally entangled state be obtained,but the prepared maximally entangled state can also resist noise interference to ensure that the prepared entangled state will not be decoherence again under the interference of the noise.And the proposed scheme can improve the yield through iteration process.Data analysis shows that scheme has high fidelity even considering dissipation,and we also discuss the experimental feasibility of the scheme.(2)Based on the collective rotating decoherence-free subspace,in addition to entanglement concentration to obtain the maximum entangled state,it is also proposed to prepare three logical bits GHZ entangled state and W entangled state,the entangled state prepared in this way is immune to noise by itself,and decoherence will not easily occur.The analysis data show that our preparation scheme has a high probability of success and also has a high fidelity when considering dissipation.Therefore,the proposed entanglement concentration and entanglement state preparation schemes will provide an alternative for quantum information processing based on decoherence-free subspaces.