We study an entangled two-mode coherent state within the framework of2×2-dimensional Hilbert space. We investigate the problem of quantum teleportation ofa superposition coherent state via an entangled coherent channel. By three differentmeasures with the titles ``minimum assured fidelity (MASF)”, ``average teleportationfidelity” and ``optimal fidelity (f)” we study the quality of this kind of teleportation.Decoherence properties of the entangled coherent state due to channel losses areanalysed. For a symmetric noise channel, the degradation of optimal fidelity and degreeof entanglement are calculated. Also by two different measures with the titles``concurrence” and ``entanglement of formation” we study the amount of entanglementof a decohered quantum channel and discuss its details. We demonstrate thatentanglement of the decohered entangled coherent state is reduced but not throughlylost. Finally we find that the optimal fidelity of the decohered entangled coherent state ismore than the classical limit and the decohered entangled coherent state may be usefulfor quantum teleportation.
We study an entangled two-mode coherent state within the framework of2×2-dimensional Hilbert space. We investigate the problem of quantum teleportation ofa superposition coherent state via an entangled coherent channel. By three differentmeasures with the titles minimum assured fidelity (MASF)”, average teleportationfidelity” and optimal fidelity (f)” we study the quality of this kind of teleportation.Decoherence properties of the entangled coherent state due to channel losses areanalysed. For a symmetric noise channel, the degradation of optimal fidelity and degreeof entanglement are calculated. Also by two different measures with the titlesconcurrence” and ``entanglement of formation” we study the amount of entanglementof a decohered quantum channel and discuss its details. We demonstrate thatentanglement of the decohered entangled coherent state is reduced but not throughlylost. Finally we find that the optimal fidelity of the decohered entangled coherent state ismore than the classical limit and the decohered entangled coherent state may be usefulfor quantum teleportation.
A scheme of teleporting a superposition of coherent states |α⟩ and | − α⟩ using a beam splitter and two phase shifters was proposed by van Enk and Hirota (2001 Phys. Rev. A 64 022313). The authors concluded that the probability for successful teleportation is 1/2. In this paper, it is shown that the authors' scheme can be altered slightly so as to obtain an almost perfect teleportation for an appreciable value of |α| 2 . For |α| 2 = 5, the minimum of average fidelity, which is the minimum of the sum of the product of probability of occurrence of any case, and the corresponding fidelity is less than 1 by a quantity ∼10 −4 . We also discuss the effect of decoherence on teleportation fidelity. We find that if no photons are counted in both final outputs, the minimum assured fidelity is still non-zero except when there is no decoherence and the information is an even coherent state. For non-zero photon counts, minimum assured fidelity decreases with an increase in |α| 2 for low noise. For high noise, however, it increases, attains a maximum value and then decreases with |α| 2 . The average fidelity depends appreciably on the information for low values of |α| 2 only.
We consider the scheme proposed by Wang [Phys. Rev. A64 (2001) 022302] for teleporting bipartite entangled states, which is a superposition of coherent states |α,α〉 and |-α,-α〉, with our suggested modification [Phys. Rev. A75 (2007) 044305] and discuss the effect of decoherence on teleportation fidelity. We find that if no photons are counted in both final outputs, the minimum assured fidelity (MAF), which is the minimum of the fidelity for any arbitrary information), is still nonzero except for the case when there is no decoherence and the information is in even coherent state. For non-zero photon counts, MAF decreases with increase in |α|2 for low noise but in the case of high noise, it increases, attains a maximum value and then decreases with |α|2. We discuss the variation of average fidelity with |α|2 and show that it depends appreciably on the information for low values of |α|2 only.
We consider the problem of teleporting superposed coherent state using nonmaximally entangled coherent state (NMECS) as quantum channel and study the effect of entanglement on the quality of teleportation. Based on the amount of entanglement shared between the sender and the receiver, we propose two unitary operation strategies to be adopted by the receiver to recover replica of information state with as large a fidelity as possible, and analyzed the behavior of minimum average fidelity (MAF) and mean fidelity (MF) with respect to entanglement. It is fascinatingly found that if the maximally entangled coherent state used in previously proposed schemes is replaced by a particular NMECS, MAF of quantum teleportation increases appreciably at small coherent amplitudes. For coherent amplitudes with |α|2≤0.5, MECS gives higher MF, while for |α|2≥0.5, NMECS gives higher MF.
In the present paper, we will review the methods to produce superposition of entangled coherent state using polarizing beam splitter and Kerr non linearity. These coherent states have many attractive features and can be used in various schemes. Entanglement, refers to the superposition of a multiparticle system and explains a new type of correlations between any two subsystems of the quantum system, which is not existing in the classical physics. The present paper deals with the use of these states in quantum teleportation, entanglement diversion and entanglement swapping schemes. Entanglement diversion and entanglement-swapping refers to a scheme which may entangle those particles which had never interacted before. In the swapping scheme, two pairs of entangled state are taken. One particle from each pair is subjected to a Bell-state-measurement. This would result in projection of the other two outgoing particles in an entangled pair. Quantum Teleportation of two mode and three modes states is also studied with perfect fidelity. Minimum assured fidelity which is defined as the minimum of the fidelity for any unknown quantum information of the states is also discussed. It is also shown how the success rate of teleportation of a superposition of odd and even coherent states can be increased from 50% to almost 100%. The scheme suggested by van Enk and Hirota was modified by Prakash, Chandra, Prakash and Shivani in 2007. We find that an almost teleportation, diversion and swapping is possible by simply separating vacuum state from the even state. The present paper also deals with study of effect of decoherence and noise on these states and the effect of noise on fidelity and minimum assured fidelity. It is also discussed that these schemes can also be applied to the process of entanglement diversion and entanglement swapping.
Quantum teleportation enables transferring quantum states by leveraging entanglement. The distribution of entangled states is challenged by decoherence, which degrades the teleportation performance. Continuous-variable teleportation with coherent-state qubits has gained particular interest because it can provide better performance than discrete-variable teleportation with polarization-encoded qubits and is more resilient to decoherence. However, most existing schemes employ a specific configuration of coherent-state qubits, namely Schrödinger cat states, and assume symmetric photon-loss channels. This work explores the teleportation of qubits based on coherent states through asymmetric quantum channels impaired by photon loss. First, we characterize the teleportation protocol for arbitrary coherent-state qubit configurations considering asymmetric and photon-loss channels. Then, we present case studies under both ideal entanglement distribution and lossy conditions. Results reveal a trade-off between state distinguishability and teleportation fidelity, providing insight into the optimal design of coherent-state qubits in practical teleportation protocols.
We study standard quantum teleportation of a one-qubit state for the situation in which the channel is subject to decoherence, and where the evolution of the channel state is ruled by a master equation in the Lindblad form. A detailed calculation reveals that the quality of teleportation is determined by both the entanglement and the purity of the channel state, and only the optimal matching of them ensures the highest fidelity of standard quantum teleportation. Also our results demonstrated that the decoherence induces distortion of the Bloch sphere for the output state with different rates in different directions, which implies that different input states will be teleported with different fidelities.