We analyze the relation between the entanglement and spin-squeezing parameter in the two-atom Dicke model and identify the source of the discrepancy recently reported by Banerjee and Zhou et al that one can observe entanglement without spin squeezing. Our calculations demonstrate that there are two criteria for entanglement, one associated with the two-photon coherences that create two-photon entangled states, and the other associated with populations of the collective states. We find that the spin-squeezing parameter correctly predicts entanglement in the two-atom Dicke system only if it is associated with two-photon entangled states, but fails to predict entanglement when it is associated with the entangled symmetric state. This explicitly identifies the source of the discrepancy and explains why the system can be entangled without spin-squeezing. We illustrate these findings in three examples of the interaction of the system with thermal, classical squeezed vacuum and quantum squeezed vacuum fields.We analyze the relation between the entanglement and spin-squeezing parameter in the two-atom Dicke model and identify the source of the discrepancy recently reported by Banerjee and Zhou et al that one can observe entanglement without spin squeezing. Our calculations demonstrate that there are two criteria for entanglement, one associated with the two-photon coherences that create two-photon entangled states, and the other associated with populations of the collective states. We find that the spin-squeezing parameter correctly predicts entanglement in the two-atom Dicke system only if it is associated with two-photon entangled states, but fails to predict entanglement when it is associated with the entangled symmetric state. This explicitly identifies the source of the discrepancy and explains why the system can be entangled without spin-squeezing. We illustrate these findings in three examples of the interaction of the system with thermal, classical squeezed vacuum and quantum squeezed vacuum fields.

Mar 17, 200315 citations

Spin squeezing as a measure of entanglement in a two-qubit system

Azeddine Messikh, Z. Ficek, Mohamed Ridza Wahiddin

We show that the two definitions of spin squeezing extensively used in the literature [M. Kitagawa and M. Ueda, Phys. Rev. A 47, 5138 (1993) and D.J. Wineland et al., Phys. Rev. A 50, 67 (1994)] give different predictions of entanglement in the two-atom Dicke system. We analyze differences between the definitions and show that the spin squeezing parameter of Kitagawa and Ueda is a better measure of entanglement than the commonly used spectroscopic spin squeezing parameter. We illustrate this relation by examining different examples of a driven two-atom Dicke system in which spin squeezing and entanglement arise dynamically. We give an explanation of the source of the difference using the negativity criterion for entanglement.We show that the two definitions of spin squeezing extensively used in the literature [M. Kitagawa and M. Ueda, Phys. Rev. A 47, 5138 (1993) and D.J. Wineland et al., Phys. Rev. A 50, 67 (1994)] give different predictions of entanglement in the two-atom Dicke system. We analyze differences between the definitions and show that the spin squeezing parameter of Kitagawa and Ueda is a better measure of entanglement than the commonly used spectroscopic spin squeezing parameter. We illustrate this relation by examining different examples of a driven two-atom Dicke system in which spin squeezing and entanglement arise dynamically. We give an explanation of the source of the difference using the negativity criterion for entanglement.

arXiv:quant-ph/0305166Physical Review ADec 5, 200325 citations

The effect of finite bandwidth squeezed light on entanglement creation in the Dicke model

Azeddine Messikh, Mohamed Ridza Wahiddin, Chin Hee Pah +1 more

We analyse the relation between local two-atom and total multi-atom entanglements in the Dicke system composed of a large number of atoms. We use concurrence as a measure of entanglement between two atoms in the multi-atom system, and the spin squeezing parameter as a measure of entanglement in the whole n -atom system. In addition, the influence of the squeezing phase and bandwidth on entanglement in the steady-state Dicke system is discussed. It is shown that the introduction of a squeezed field leads to a significant enhancement of entanglement between two atoms, and the entanglement increases with increasing degree of squeezing and bandwidth of the incident squeezed field. In the presence of a coherent field the entanglement exhibits a strong dependence on the relative phase between the squeezed and coherent fields, that can jump quite rapidly from unentangled to strongly entangled values when the phase changes from zero to π. We find that the jump of the degree of entanglement is due to a flip of the spin squeezing from one quadrature component of the atomic spin to the other component when the phase changes from zero to π. We also analyse the dependence of the entanglement on the number of atoms and find that, despite the reduction in the degree of entanglement between two atoms, a large entanglement is present in the whole n -atom system and the degree of entanglement increases as the number of atoms increases.We analyse the relation between local two-atom and total multi-atom entanglements in the Dicke system composed of a large number of atoms. We use concurrence as a measure of entanglement between two atoms in the multi-atom system, and the spin squeezing parameter as a measure of entanglement in the whole n -atom system. In addition, the influence of the squeezing phase and bandwidth on entanglement in the steady-state Dicke system is discussed. It is shown that the introduction of a squeezed field leads to a significant enhancement of entanglement between two atoms, and the entanglement increases with increasing degree of squeezing and bandwidth of the incident squeezed field. In the presence of a coherent field the entanglement exhibits a strong dependence on the relative phase between the squeezed and coherent fields, that can jump quite rapidly from unentangled to strongly entangled values when the phase changes from zero to π. We find that the jump of the degree of entanglement is due to a flip of the spin squeezing from one quadrature component of the atomic spin to the other component when the phase changes from zero to π. We also analyse the dependence of the entanglement on the number of atoms and find that, despite the reduction in the degree of entanglement between two atoms, a large entanglement is present in the whole n -atom system and the degree of entanglement increases as the number of atoms increases.

Journal of Optics B Quantum and Semiclassical OpticsApr 27, 20044 citations

Generalized spin-squeezing inequalities in N -qubit systems: Theory and experiment

Jarosław K. Korbicz, Otfried Gühne, Maciej Lewenstein +3 more

We present detailed derivations, various improvements and application to concrete experimental data of spin squeezing inequalities formulated recently by some of us [Phys. Rev. Lett. 95, 120502 (2005)]. These inequalities generalize the concept of the spin squeezing parameter and provide necessary and sufficient conditions for genuine two-, or three-qubit entanglement for symmetric states, and sufficient condition for general $N$ -qubit states. We apply our method to theoretical study of Dicke states, and, in particular, to $\mathrm{W}$ states of $N$ qubits. Then, we analyze the recently experimentally generated seven- and eight-ion $\mathrm{W}$ states [Nature 438, 643 (2005)]. we also present some details concerning this experiment. Finally, we improve criteria for detection of genuine tripartite entanglement based on entanglement witnesses.We present detailed derivations, various improvements and application to concrete experimental data of spin squeezing inequalities formulated recently by some of us [Phys. Rev. Lett. 95, 120502 (2005)]. These inequalities generalize the concept of the spin squeezing parameter and provide necessary and sufficient conditions for genuine two-, or three-qubit entanglement for symmetric states, and sufficient condition for general $N$-qubit states. We apply our method to theoretical study of Dicke states, and, in particular, to $\mathrm{W}$ states of $N$ qubits. Then, we analyze the recently experimentally generated seven- and eight-ion $\mathrm{W}$ states [Nature 438, 643 (2005)]. we also present some details concerning this experiment. Finally, we improve criteria for detection of genuine tripartite entanglement based on entanglement witnesses.

arXiv:quant-ph/0601038Physical Review ANov 14, 200696 citations

Stationary two-atom entanglement induced by nonclassical two-photon correlations

R Tana, Z. Ficek

A system of two two-level atoms interacting with a squeezed vacuum field can exhibit stationary entanglement associated with nonclassical two-photon correlations characteristic of the squeezed vacuum field. The amount of entanglement present in the system is quantified by the well known measure of entanglement called concurrence. We find analytical formulas describing the concurrence for two identical and nonidentical atoms and show that it is possible to obtain a large degree of steady-state entanglement in the system. Necessary conditions for the entanglement are nonclassical two-photon correlations and nonzero collective decay. It is shown that nonidentical atoms are a better source of stationary entanglement than identical atoms. We discuss the optimal physical conditions for creating entanglement in the system, in particular, it is shown that there is an optimal and rather small value of the mean photon number required for creating entanglement.A system of two two-level atoms interacting with a squeezed vacuum field can exhibit stationary entanglement associated with nonclassical two-photon correlations characteristic of the squeezed vacuum field. The amount of entanglement present in the system is quantified by the well known measure of entanglement called concurrence. We find analytical formulas describing the concurrence for two identical and nonidentical atoms and show that it is possible to obtain a large degree of steady-state entanglement in the system. Necessary conditions for the entanglement are nonclassical two-photon correlations and nonzero collective decay. It is shown that nonidentical atoms are a better source of stationary entanglement than identical atoms. We discuss the optimal physical conditions for creating entanglement in the system, in particular, it is shown that there is an optimal and rather small value of the mean photon number required for creating entanglement.

arXiv:quant-ph/0309195Journal of Optics B Quantum and Semiclassical OpticsMay 29, 200442 citations

Investigation of Quantum Spin Squeezing in Quantum Information Theory.

نسرین هاشمی دیجوجین, قادر نجارباشی, بهمن سیفی

Coherent and squeezed photon states have attracted a lot attetion in long time ago, since these states can generate in laboratory. These states are satisfying in minimum uncertainty relation. In recently, states have generates with electrons by Bose-Einstein condensations and particles oscillations. Also,this states are satisfying in minimum uncertainty relation, with this difference that parameters in this states are the first and second moments of soin operators instead of position and momentum operators.The similarity phenomenon about squeezing photon is exist for spin with that distance. The source of spin squeezing in multi-qubit states is entanglement. One applecations of spin squeezing is to detect quantum entanglement which plays a key role in both the foundations of quantum physics and quantum computation processing. In recent years, spin squeezing stsate parameters have close relation with entanglement measure, concurrence, that we can characterize entanglement for a class of many-body spin- states. In reality, spin squeezing parameters are witnesse for many bode entanglement. In this paper; we study relation betweenspin squeezed states and entanglement. Then; we stuy the squeezing spin for -mode and -mode entangled coherent states.Coherent and squeezed photon states have attracted a lot attetion in long time ago, since these states can generate in laboratory. These states are satisfying in minimum uncertainty relation. In recently, states have generates with electrons by Bose-Einstein condensations and particles oscillations. Also,this states are satisfying in minimum uncertainty relation, with this difference that parameters in this states are the first and second moments of soin operators instead of position and momentum operators.The similarity phenomenon about squeezing photon is exist for spin with that distance. The source of spin squeezing in multi-qubit states is entanglement. One applecations of spin squeezing is to detect quantum entanglement which plays a key role in both the foundations of quantum physics and quantum computation processing. In recent years, spin squeezing stsate parameters have close relation with entanglement measure, concurrence, that we can characterize entanglement for a class of many-body spin- states. In reality, spin squeezing parameters are witnesse for many bode entanglement. In this paper; we study relation betweenspin squeezed states and entanglement. Then; we stuy the squeezing spin for -mode and -mode entangled coherent states.

Jan 1, 20160 citations

N

-qubit states. We apply our method to theoretical study of Dicke states, and, in particular, to

\mathrm{W}

states of

N

qubits. Then, we analyze the recently experimentally generated seven- and eight-ion

\mathrm{W}

states [Nature 438, 643 (2005)]. we also present some details concerning this experiment. Finally, we improve criteria for detection of genuine tripartite entanglement based on entanglement witnesses.