Quantum Fisher Information of a 3-Qubit State

We investigate the properties of quantum Fisher information in a general superposition of a 3-qubit GHZ state and two W states. Numerical calculation for quantum Fisher information of the 3-qubit state is given. It is shown that the mean spin direction, the length of mean spin and quantum Fisher information are determined by the coefficients of superposition and the relative phase between the GHZ state and the W states.     

Quantum Fisher Information and the Heisenberg Limit in Superpositions of Two W States and Symmetric State

We investigate the quantum Fisher information and the Heisenberg limit in superposition of a four-qubit symmetric state and two W states. Numerical and analytical calculations for quantum Fisher information and the Heisenberg limit of the four-qubit state are driven. It is shown that quantum Fisher information of the four-qubit state depends on the superposition coefficients and the relative phase. It is also shown that under certain conditions, the maximal quantum Fisher information occurred; which leads to the estimation sensitivity beats the Heisenberg limit.     

Quantum Fisher Information of Superposition of Many-Body GHZ-Class State and <Emphasis Type="Italic">W</Emphasis> State

We investigate the properties of quantum Fisher information in a general superposition of many-body GHZ-class state and W state. It is shown that mean spin direction is determined by the superposed coefficients and the relative phase between the GHZ-class state and the W state and it is independent of the relative phase between the GHZ-class state; while mean spin length and quantum Fisher information are only determined by the superposed coefficients.     

Quantum Fisher Information and Heisenberg Limit in Multi-qubit State

We investigate the quantum Fisher information and Heisenberg limit in multi-qubit pure state superposed by a GHZ state and two W states with a relative phase. Analytical expressions of quantum Fisher information and phase estimation sensitivity are derived. It is shown that the maximal quantum Fisher information occurs and the phase estimation is enhanced to the Heisenberg limit when the number of qubits is large.     

Single-Particle Coherence and the Reciprocal of the Mean Quantum Fisher Information in Three-Particle Phase State

We investigate the relation between the single-particle coherence and the reciprocal of the mean quantum Fisher information (RMQFI) in three-particle phase state. It is shown that the phase state is a entangled state that it is useful for sub-shot-noise phase estimation sensitivity. The single-particle coherence and RMQFI have the similar behaviors.     

The Reciprocal of the Mean Quantum Fisher Information per Particle in Generalized Two-Axis Twisting Model

We investigate the reciprocal of the mean quantum Fisher information per particle (RMQFI) in generalized two-axis twisting model; which generalizes the two-axis twisting model including a linear interaction controlled by an external field. In particular, we are interested in the dependence of RMQFI on the external field. By adopting frozen-spin approximation, we obtain the theoretical and numerical results for RMQFI, which is a periodical function. Except certain special conditions, the state is always entangled and the stronger external field induces to stronger entanglement and larger period of oscillation of RMQFI.     

Controlling Entanglement in Multi-Qubit System with an External Field

We investigate entanglement dynamics with the reciprocal of mean quantum Fisher information per particle (RMQFI) in multi-qubit system governed by generalized two-axis twisting Hamiltonian; which generalizes the two-axis twisting model including a linear interaction controlled by an external field. In particular, we are interested in the dependence of RMQFI on the external field. By adopting frozen-spin approximation, we derive the theoretical and numerical results for RMQFI. Except certain special conditions, the system is always entangled and the smaller external field induces to better entanglement.     

Spin Squeezing and Quantum Fisher Information in One-Axis Twisting Model with Decay

We investigate spin squeezing and the reciprocal of the mean quantum Fisher information per particle (RMQFI) of a collective spin governed by a one-axis twisting Hamiltonian with decay. In particular, we are interesting in the dependence of spin squeezing and RMQFI on the decay rate. The larger decay rate induces to stronger squeezing in certain regime and the larger period of RMQFI.     

Single-Particle Coherence and RMQFI in Two-Species BECs

We investigate the relation between the single-particle coherence and the reciprocal of the mean quantum Fisher information per particle (RMQFI) in Bose-Einstein condensates (BECs) in the presence of interatomic interaction and interspecies interaction. The single-particle coherence and RMQFI depend on the interatomic interaction. It is shown that the larger interatomic interaction more rapidly induces entanglement.     

Controlling Many-Body Entanglement with an External Field

We investigate how an appropriate choice of the external field allows one to control many-body entanglement characterized by spin squeezing and the reciprocal of mean quantum Fisher information per particle (RMQFI). By adopting frozen-spin approximation, we succussed in obtaining analytical expressions of the spin squeezing parameter and RMQFI. The stronger external field induces stronger squeezing, the smaller value of RMQFI and the larger period.     

Quantum Fisher Information of Superpositions with 3-Qubit Ghz-Class State and W State

We investigate the quantum Fisher information in a general superposition of a GHZ-class state and a W state. It is shown that the mean spin direction is determined by the four coefficients of superposition and the relative phase between the GHZ-class state and the W state and it is independent of the relative phase between the GHZ-class state; while the length of mean spin is only determined by the four superposition coefficients. It is also shown that the quantum Fisher information of the superposition state is determined by the four superposition coefficients and the two relative phases.     

Dynamical Properties of Some Statistical Quantities for a Quantum System in Generalized Negative Binomial States

We estimate the quantum state of a qubit and a quantized radiation field yielding a generalized negative binomial distribution (GNBD). We give an explicit form for various generalized negative binomial states associated to superposition, even, odd, and q-deformed states. We investigate the dynamical properties of the Mandel parameter as a quantifier of the statistical properties for the radiation field corresponding to its dynamics. We obtain the quantum Fisher information based on the estimation of the atomic state and compare it with the Mandel parameter for different instances of the GNBD. The link between the statistical quantities for different parameters of the GNBD is explored.     

Quantum Fisher Information of Several Qubitsin the Superposition of A GHZ and two W Stateswith Arbitrary Relative Phase

We study the quantum Fisher information (QFI) of a system of several particles which is in a superposition of a GHZ and two W states with arbitrary relative phase. We show that as the number of particles increases from 3 to 4, the behavior of QFI drastically changes. We also show how the dependence of QFI on the relative phase weakens as the number of particles increases. We also analyze the QFI for the state for several instances of N due to the change of the relative phases.     

Phase damping destroys quantum Fisher information of W states

We study the quantum Fisher information (QFI) of W states in the basic decoherence channels. We show that, as decoherence starts and increases, under i) depolarizing, QFI smoothly decays; ii) amplitude damping, QFI first exhibits a sudden drop to the shot noise level, then decreases to zero and finally increases back to the shot noise level; iii) phase damping, QFI is zero for all non-zero decoherence. We also find that on the contrary to GHZ states, QFI of W states in x and y directions are equal to each other and zero in z direction.     

Phase Sensitivity in Yurke-Like State

We investigate we investigate the quantum Fisher information and phase sensitivity in Yurke-like state superposed by two special multi-particle states and a symmetric state with relative phase. By studying the influences of superposition coefficients and relative phase on the maximal quantum Fisher information and phase sensitivity, we reveal some entanglement properties of Yurke-like state.     

Fisher Information of Free-Electron Landau States

An electron in a constant magnetic field has energy levels, known as the Landau levels. One can obtain the corresponding radial wavefunction of free-electron Landau states in cylindrical polar coordinates. However, this system has not been explored so far in terms of an information-theoretical viewpoint. Here, we focus on Fisher information associated with these Landau states specified by the two quantum numbers. Fisher information provides a useful measure of the electronic structure in quantum systems, such as hydrogen-like atoms and under some potentials. By numerically evaluating the generalized Laguerre polynomials in the radial densities, we report that Fisher information increases linearly with the principal quantum number that specifies energy levels, but decreases monotonically with the azimuthal quantum number m. We also present relative Fisher information of the Landau states against the reference density with m=0, which is proportional to the principal quantum number. We compare it with the case when the lowest Landau level state is set as the reference.     

Enlarged omnidirectional photonic gap in one dimensional ternary plasma photonic crystals that contain metamaterials

We study the dynamics of multipartite quantum correlations measured by the lower bound of concurrence and quantum discord in a three-qubit system coupled to an XY spin chain. For the initial pure GHZ and W state, we find the lower bound of entanglement is more robust than the quantum discord against the decoherence induced by the spin environment. But for the Werner state, the sudden death of discord is not observed even in the presence of entanglement sudden death. By comparing the evolutions for the GHZ and W states, we show that the W state preserves more quantum correlations than the GHZ state. In addition, we put research emphasis on the relation between the dynamics of multipartite quantum correlations and the quantum phase transition of the spin environment.     

Remote preparation of the N-particle GHZ state using quantum statistics

We present a remote preparation of the N-particle GHZ state protocol in which only the effects of quantum statistics of indistinguishable particles are used. The N-particle GHZ state can be successfully prepared in the limit of N → ∞.     

Correlation Effects in the Moshinsky Model

We investigate quantum correlations in the ground state of the Moshinsky model formed by N harmonically interacting particles confined in a harmonic potential. The model is solvable which allows an exact determination of entanglement between the subset of p particles and the remaining N ? p particles. We study linear entropies and von Neumann entropies of the bipartitions and compare their behavior with that of the relative correlation energy and of the statistical Kutzelnigg coefficient.     

Quantum state engineering in ion-traps via adiabatic passage

We propose two relatively robust schemes to generate entangled W states of three (or generally N) ions in ion trap systems by using adiabatic passage technique and appropriately designed ion-field couplings in a single step. In the first scheme, we apply the N-pod fractional stimulated Raman adiabatic passage (F-STIRAP) technique to generate W state of N ions using two Gaussian laser pulses. We also show that the W state of N ? 1 ions can be created via a simple N-pod standard STIRAP by two laser pulses. In the second scheme, we generate the entangled state of N ions via ??-pulse technique by a single laser pulse. We also study the population transfer of the system by numerical solutions of the master equation, considering the effect of decoherence channels due to laser intensity fluctuations and dissipation in the phonon modes.