Two-mode Entangled Coherent States Research Articles

The entanglement and nonclassical properties of multi-photon amplified added based two-mode entangled coherent states

We explore into the non-classical characteristics of a new entangled coherent state (CS), also known as a multi-photon addition amplified coherent state (MPAACS) gn̂â†m, which is produced by adding any quantity of photons to two-mode coherent states with various gain factor values. A superposition of photon-added amplified two-mode CSs (MPAACS) also exists in this novel entangled state. It is proven that the gain factor and Laguerre polynomials are related to the MPAACS normalization factor. Analytical discussion is also had regarding entanglement and quantum statistical properties. Regarding concurrence, our findings further suggest that by selecting suitable values for the gain factor g, photon added (m,n), and coherent amplitude, entanglement for the output state can occur. Specifically, the enhancement of the entanglement can be found at large g values at fixed (m,n) in comparison to (m,n) values at fixed g and small amplitude with ϕ=0 or pi. Besides that, the analyses of nonclassicality reveal that, when comparing the results for several values (m,n) at fixed g and with several values g at fixed (m,n), the low-order antibunching effect, the cross-correlation function, and the Wigner function all support the sub-Poissonian statistics. When analyses of the nonclassicality and the negative value of the WF for ϕ=0 are larger at fixed parameter (m,n), but larger at g fixed for ϕ=π, the TMAA-TMC states perform better.

Local quantum uncertainty and non-commutativity measure discord in two-mode photon-added entangled coherent states

Local quantum uncertainty and non-commutativity measure discord in two-mode photon-added entangled coherent states

Realization of Quantum Swap Gate and Generation of Entangled Coherent States

The cross fusion of quantum mechanics and information science forms quantum information science. Quantum logic gates and quantum entanglement are very important building blocks in quantum information processing. In this paper, we propose one-step schemes for realizing quantum swap gates and generating two-mode entangled coherent states via circuit QED. In our scheme, due to the adiabatic elimination of the excited state of the qutrit under the condition of large detuning, the decoherence of the spontaneous emission of the qutrit can be ignored. The fidelity of the quantum swap gate remains at a very high level. In addition, we also explore the nonclassical properties of two-mode entangled coherent states prepared in our scheme by addressing the second-order correlation function and intermodal squeezing. In particular, two classes of entangled coherent states demonstrate distinct entanglement and nonclassical behavior.

Quantum Teleportation via Entangled State of Light in Schwarzschild Black Hole

In this paper, we describe the properties of quantum entanglement and teleportation between Alice and Bob who is freely falling toward the Schwarzschild black hole. To this aim, in the flat Minkowski spacetime before a black hole is formed, Alice and Bob share a two-mode entangled coherent state (ECS) generated by Kerr medium and the beam splitter. We will show that the degree of entanglement decreases with increasing the radius of black hole r. Moreover, the fidelity of quantum teleportation via ECS, as a quantum channel, is also reduced because of the Hawking-Unruh effect.

Entanglement of a new type of two-mode photon-added entangled coherent state

ABSTRACTWe introduce a new entangled state, which is composed of two photon-added coherent states. We discuss the entanglement of this state by using several sufficient entanglement criteria, such as higher-order entanglement criterion, EPR criterion, SU(1,1) algebra and Cauchy–Schwarz inequality. These criteria reflect some entanglement effects of this new state, but fail to find the degree of entanglement directly. Thus, we use the covariance to measure the entanglement in this state. Our findings show that the degree of entanglement decreases with the increasing of photon-number and the amplitude of the coherent states. One interesting result is that the new entangled state becomes a maximally entangled state when the photon-added number is 1 and the amplitude of the coherent states is zero, which is just one of the four Bell states.

One-Mode Wigner Quasi-Probability Distribution Function for Entangled Coherent States Generated by Beam Splitter and Cavity QED

In this paper, we use the displacement operator together with parity operation to construct the superposition of two coherent states. By transmitting this superposition from 50–50 beam splitter the two-mode qubit-like entangled coherent state (ECS) is generated. Moreover, we introduce a controllable method for producing qutrit-like ECS using atom–field interaction in cavity QED and beam splitter. We will show that the distances of peaks of Wigner functions for reduced density matrices of two-mode ECS's are entanglement sensitive and can be witnesses of entanglement. To confirm the results we use concurrence measure to compare bipartite entanglement of ECS's with the behaviour of peaks of Wigner functions. Moreover, we investigate decoherence effects on Wigner function, arising from transmitting ECS's through noisy channels.

Quantum Discord for Information Transmission Using Coherent States

We suggest theoretically the possibility to transmit information through a decohering quantum channel employing Glauber’s coherent states. In fact, we study the dynamics of quantum correlations of two-mode entangled bipartite coherent states in the presence of the amplitude damping effect. In addition, we examine the quantum correlations based on quantum discord, which is a powerful key source in quantum information processing.

Quantum properties of two-mode entangled coherent states

Coherent states are the quantum states, which give the closest description to classical states. Since their superpositions show quantum properties, research on these states has been of great interest. In addition, having nonclassical properties is necessary for quantum correlations. In this paper, we focus on two-mode entangled coherent states which are out of phase, and study the nonclassical properties such as squeezing of quadrature operators, antibunching and oscillatory photon statistics. Then we discuss about their entanglement, which is a quantum correlation in different conditions and compare the results.

Preparation and non-classical characteristics of two-mode entangled coherent state

We propose a scheme to generate two-mode entangled coherent states using a Λ-type rf-SQUID qubit to induce the interaction between two transmission line resonators (TLRs). The proposed scheme takes advantage of the easy integration of solid quantum circuit. Through investigating the dynamical evolution, we find the relationship between the initial quantum state of the superconducting qubit and the quantum entanglement of the field modes. We analyze as well the influence of decoherence effect on the non-classical characteristics of the optical field by means of the density operator, fidelity and Mandel Q. The investigation results indicate that one should first optimize the preparation of the initial quantum state of qubit so as to prepare two-mode entangled state with high entanglement degree and obvious non-classical characteristics. The qubit initially prepared in (|0〉+|1〉)/2 does not get entangled with the two modes of field. Inversely, the qubit can effectively improve the degree of entanglement between field modes and obviously promote the anti-bunching effect and squeezing effect if it is initially prepared in ground state |0〉.

Production of the Superposition of Nonlinear Coherent States and Entangled Nonlinear Coherent States

In this paper, by using the parity operator as well as the nonlinear displacement-type operator, we define new operators which by the action of them on the vacuum state of the radiation field, superposition of two nonlinear coherent states and two-mode entangled nonlinear coherent states are generated. Also, we show that via the generalization of the presented method, the superposition of more than two nonlinear coherent states and n-mode entangled nonlinear coherent states can be generated.

Bell-inequality tests using asymmetric entangled coherent states in asymmetric lossy environments

We study an asymmetric form of two-mode entangled coherent state (ECS), where the two local amplitudes have different values, for testing the Bell-Clauser-Horne-Shimony-Holt (Bell-CHSH) inequality. We find that the asymmetric ECSs have obvious advantages over the symmetric form of ECSs in testing the Bell-CHSH inequality. We further study an asymmetric strategy in distributing an ECS over a lossy environment and find that such a scheme can significantly increase violation of the inequality.

Controllable preparation of two-mode entangled coherent states in circuit QED

Although the multi-level structure of superconducting qubits may result in calculation errors, it can be rationally used to effectively improve the speed of gate operations. Utilizing a current-biased Josephson junction (λ-type rf-SQUID) as a tunable coupler for superconducting transmission line resonators (TLRs), under the large detuning condition, we demonstrate the controllable generation of entangled coherent states in circuit quantum electrodynamics (circuit QED). The coupling between the TLRs and the qubit can be effectively regulated by an external bias current or coupling capacitor. Further investigations indicate that the maximum entangled state can be obtained through measuring the excited state of the superconducting qubits. Then, the influence of the TLR decay on the prepared entangled states is analyzed.

Nonclassical properties and generation of excited entangled coherent states of motion of a trapped ion

We studied the two-mode squeezing of excited entangled coherent states and found that the deeper the two-mode squeezing, the larger the excitation number. In the end, we proposed a new method for preparing two-mode excited entangled coherent states of vibrational motion of a trapped ion by applying the interaction of a single two-mode trapped ion with many traveling wave light fields with different frequencies.

Teleportation of a two-mode entangled coherent state encoded with two-qubit information

We propose a scheme to teleport a two-mode entangled coherent state encoded with two-qubit information, which is better than the two schemes recently proposed by Liao and Kuang (2007 J. Phys. B: At. Mol. Opt. Phys. 40 1183) and by Phien and Nguyen (2008 Phys. Lett. A 372 2825) in that our scheme gives higher value of minimum assured fidelity and minimum average fidelity without using any nonlinear interactions. For involved coherent states | ± α⟩, minimum average fidelity in our case is ⩾0.99 for |α| ⩾ 1.6 (i.e. |α|2 ⩾ 2.6), while previously proposed schemes referred above report the same for |α| ⩾ 5 (i.e. |α|2 ⩾ 25). Since it is very challenging to produce superposed coherent states of high coherent amplitude (|α|), our teleportation scheme is at the reach of modern technology.

Creation and Destruction of Entanglement via Fourier Multiport Devices

We study entangling and disentangling functions of optical Fourier multiport devices in which input-output relation for the creation and annihilation operators is given by a finite Fourier transform. It is shown that these Fourier multiport devices can act as entanglement converters which can not only create entanglement from an unentangled state at the input but also destroy entanglement in an entangled state at the input. Creation and destruction of two-mode and three-mode entangled coherent states (ECSs) are investigated in detail. The creation and destruction of Bell-type two-mode ECS, GHZ-type and W-type three-mode ECSs are indicated explicitly through using Fourier four-port and six-port devices, respectively.

Coherent control of atom dipole squeezing and violation of Cauchy-Schwarz inequality

By studying the interaction of isolated two-level atom with two-mode entangled coherent state optical field, the time evolution of dipole squeezing quantum effect in the system is investigated in detail. The results show that the properties of interaction coherent mode determine the degree of atom dipole squeezing. Parameter ΔV of violation of Cauchy-Schwarz inequality of the interaction system is defined. Time evolution of parameter ΔVis studied, and it can be seen evidently from the results that the degree of violation of Cauchy-Schwarz inequality accords with the nonclassical property of interaction system. Through tuning the parameter of the coherent field, we can easily perform the remote control of the noncommercial properties.

Generation of two-mode entangled coherent states via a cavity QED system

A scheme is presented for the generation of entangled coherent states in a single-atom cavity-QED system. In the scheme, a three-level V-type atom interacts dispersively with a two-mode cavity and is driven by a classical field. We show that under large detuning conditions the cavity field can evolve into maximally entangled coherent states when one cavity mode is initially prepared in an odd coherent state. The effect of the cavity losses on the entanglement is also studied.

Two-mode excited entangled coherent states and their entanglement properties

This paper introduces two types of two-mode excited entangled coherent states (TMEECSs) |Ψ±(α, m, n)⟩, studies their entanglement characteristics, and investigates the influence of photon excitations on quantum entanglement. It shows that for the state |Ψ+(α, m, m)⟩ the two-mode photon excitations affect seriously entanglement character while the state |Ψ-(α, m, m)⟩ is always a maximally entangled state, and shows how such states can be produced by using cavity quantum electrodynamics and quantum measurements. It finds that the entanglement amount of the TMEECSs is larger than that of the single-mode excited entangled coherent states with the same photon excitation number.

Entanglement generation in a two-mode single-atom laser

We present a method of generating two-mode single atom laser based on the nonresonant interaction of a three-level Λ type atom in a two-mode cavity with three strong classical driving fields. An analytical solution for this effective dynamics under the presence of the cavity losses is obtained, which allow us to analyze the entanglement properties and the photon statistics of the two cavity modes exactly. It is also shown that the possible generation of the two-mode entangled coherent states in the transient regime after the atomic measurement.

Optical Generation of Single- or Two-Mode Excited Entangled Coherent States

With nonlinear Mach-Zehnder interferometer (NLMZI) and a type-I beta-barium borate (BBO) crystal, we optically generate single-mode excited entangled coherent states. This scheme can be easily generalized to generate two-mode excited entangled coherent states. We simply analyse different influences of single- and two-mode photon excitations on entangled coherent states.