International Journal of Quantum Information

The quantum nonlocal correlation between an atom and coherent field is described quantitatively in terms of multi-photon and phase damping processes. Especially, considering a two-level atom interacts with a single-mode quantized field in a coherent state inside a phase-damped cavity, and taking into account the number of multi-photon transitions and phase damping effect, the entanglement is investigated during the time evolution as a function of involved' parameters in the system. The results show that the enhancement of the transitions are very useful in generating a high amount of entanglement. Due to the significance of how a system is quantum correlated with its environment in the construction of a scalable quantum computer, the entanglement dynamics between the bipartite system with its environment is evaluated and investigated during the dissipative process. Finally, the physical interpretation of the correlation behaviors between the subsystems is explained through the statistical properties of the field.

Using the Calderbank–Shor–Steane (CSS) construction, pure q-ary asymmetric quantum error-correcting codes attaining the quantum Singleton bound are constructed. Such codes are called pure CSS asymmetric quantum maximum distance separable (AQMDS) codes. Assuming the validity of the classical maximum distance separable (MDS) Conjecture, pure CSS AQMDS codes of all possible parameters are accounted for.

Symmetric Dicke states are a generalization of W-states that display interesting properties. These properties enable one to generate arbitrarily large symmetric Dicke states using operations on finite (2k) number of qubits. This paper formulates explicitly some basic results needed for this purpose. These results are synthesized into a generic Scalable Entangling Protocol. Examples are provided to illustrate the approach generality. A concomitant graphical representation allows fast comprehension of the protocol inputs, operations and outcomes.

We study the quantum correlations between source and target pairs in different protocols of entanglement distillation of one kind of entangled states. We find that there does not exist any quantum correlation in the standard recurrence distillation protocol, while quantum discord and even quantum entanglement are always present in the other two cases of the improved distillation protocols. In the three cases, the distillation efficiency improved with the quantum correlations enhanced.

Recently, Yin et al. (Int. J. Quantum Inform. 10 (2012) 1250041) proposed a quantum proxy group signature scheme with χ-type entangled states. The scheme combines the properties of group signature and proxy signature. The study points out that the semi-honest Trent can give the forged signature under the assumption of this scheme. And, we find that even if the three parties honestly perform the scheme, the signature still cannot be realized with high efficiency.

A scheme is proposed to directly implement the optical swap gate and quantum Fredkin gate based on the Mach–Zehnder interferometer (MZI). The distinct advantage of the present scheme is that ancilla single-photons are not needed. The optical swap gate is deterministic and does not need the photon number resolving detectors. The total success probability of the present Fredkin gate can reach 1/16 by using basic linear-optics elements.

Generalized behavior of a nondeterministic CNOT gate based on physical implementation is subject of this work. We define an abstract probabilistic model of the CNOT gate and describe a general proposition of realizability assessment based on experimental features. Theoretical results are directly confronted to experimental realization. Two CNOT models are brought out for this purpose.

We investigate the effect of Kerr nonlinearity and optomechanical couplings on cavity field spectra in an optomechanical system driven by a pump field. In the mean-field approximation, the system exhibits optical bistability for a wide range of parameters. The spectra are numerically calculated for different initial states, which show that a single peak in the spectrum splits because of the presence of the optomechanical coupling and the increase of the number of phonon. In addition, the peak position in the cavity field spectra changes due to the Kerr nonlinearity, while the cavity detuning is modified. The strength of spectra determines the size of the photon-phonon conversion capabilities. These results provides a theoretical basis for optical communication.

We analyze theoretically the performance of four-state quantum key distribution protocols implemented with a realistic heralded single-photon source. The analysis assumes a noisy model for the detector heralding generation of individual photons via spontaneous parametric down-conversion, including dark counts and imperfect photon number resolution. We identify characteristics of the heralding detector that defines the attainable cryptographic key rate and the maximum secure distance. Approximate analytical formulas are applied to multiplexed detection and compared with results of numerical calculations.

The possibility of generating entangled network via Dzyaloshinskii–Moriya interaction is investigated. The entanglement between the different nodes is quantified. This entangled network is employed to send information between different users who are members on this network. The effect of the field strength and the magnetic field parameters on the degree of entanglement of the network and the average fidelity is discussed. We show that by controlling these parameters one can maximize the average fidelity of the teleported state.