A physical implementation of an entanglement purification protocol is studied using a cavity quantum electrodynamic based proposal, where the quantum information is stored in quantum field states inside cavities. Also a procedure is given for quantifying the degree of entanglement between quantum fields.
We study a physical implementation of an entanglement purification protocol using a cavity quantum electrodynamics based proposal, in both the microwave and the optical domain. The protocol consists of local quantum operations of each particle of an entangled system with one auxiliary particle (ancilla). After the above interaction a measurement on ancillas is carried out. In the microwave region the quantum information is stored in field states inside two distant cavities. We also give a procedure for quantifying the degree of entanglement between quantum fields, which allows verifying the efficiency of the purification process. In the optical domain, we study a setup of cold trapped ions inside cavities, where quantum bits are defined by two electronic levels of ions. This latter proposal is extended to create multiparticle entangled states among distant quantum systems. Entanglement is achieved through a set of local measurements on pairs of entangled particles.
We propose schemes for entanglement concentration and purification for qubit systems encoded in flying atomic pairs. We use cavity-quantum electrodynamics as an illustrative setting within which our proposals can be implemented. Maximally entangled pure states of qubits can be produced as a result of our protocols. In particular, the concentration protocol yields Bell states with the largest achievable theoretical probability while the purification scheme produces arbitrarily pure Bell states. The requirements for the implementation of these protocols are modest, within the state of the art, and we address all necessary steps in two specific setups based on experimentally mature microwave technology.
We give a detailed description of the entanglement purification protocol which generates maximally entangled states with high efficiencies from realistic Gaussian continuous variable entangled states. The physical implementation of this protocol is extensively analyzed using high finesse cavities and cavity enhanced cross Kerr nonlinearities. In particular, we take into account many imperfections in the experimental scheme and calculate their influences. Quantitative requirements are given for the relevant experimental parameters.
In cavity QED, the atoms would be sent through the sequential arrays of cavities for the generation of multi-cavity entanglement, or several atoms would be sent into the same cavity mode one bye one for the generation of multi-atom entanglement. The complexity of these processes will impose limitations on the experimental feasibility of it. So, following our previous publication [International Journal Of Quantum Information 2, 231 (2004)] we will propose an alternative scheme for the preparation of multi-cavity W state via cavity QED, which uses the geometrical method to do what other authors have proposed previously using sequential arrays of cavities. Due to the impossibility that one quantum system can be isolated from the environment absolutely, the entanglement of the entangled objects will decrease exponentially with the propagating distance of the objects, and the practically available quantum entangled states are all non-maximally entangled states or the more general case–-mixed states. Following our previous publications [Phys. Rev. A 72, 042307 (2005), ibid. 71, 012308 (2005)], we will propose an entanglement generation, concentration and purification scheme for atomic or ionic system, which is mainly based on Cavity QED and linear optical elements. This purification process avoids the controlled-NOT (C-NOT) operations needed in the original purification protocol, which simplifies the whole purification process.