Effects of phase decoherence on the entanglement of a two-qubit anisotropic Heisenberg XYZ chain with an in-plane magnetic field

We investigate the phase decoherence effects on the entanglement of a two-qubit anisotropic Heisenberg model with a nonuniform magnetic field in the x–z-plane. As a measure of the entanglement, the concurrence of the system is calculated. It is shown that when the magnetic field is along the z-axis, the nonuniform and uniform components of the field have no influence on the entanglement for the cases of and , respectively. But when the magnetic field is not along the z-axis, both the uniform and the nonuniform components of the field will introduce the decoherence effects. It is found that the effects of the Heisenberg chain's anisotropy in the Z-direction on the entanglement are dependent on the direction of the field. Moreover, the larger the initial concurrence is, the higher value it will exhibit during the time evolution of the system for a proper set of the parameters ν, Δ, θ, γ , B and b.     

Universal fermi gas with two- and three-body resonances

We consider a Fermi gas with two components of different masses, with the s-wave two-body interaction tuned to unitarity. In the range of mass ratio 8.62相似文献   

Fermi-Bose Systems, Macroscopic Quantum Superposition States and Entanglement

We study the entanglement of states of a simple Fermi-Bose system. The Hilbert space is C ² l₂ (N). An explicit expression is given for the entanglement. We consider number states, coherent states and macroscopic quantum superposition states in the product system. Explicit formulas for the entanglement are also given in each of these cases.     

Entanglement in Bipartite Generalized Coherent States

Entanglement of formation in a class of bipartite generalized coherent states is discussed. It is shown that a positive parameter can be associated with these bipartite states so that the states with equal value for the parameter are of equal entanglement. For the class of states considered, the maximum possible entanglement of one ebit is attained if the value of the positive parameter is . It is shown that the entanglement of formation is one ebit when the relative phase between the composing states is π in the class of bipartite generalized coherent states considered.     

Entanglement generation in trapped atoms

The two atoms in the ion trap are entangled by the interaction with an external excited atom. The evolution of the entanglement is analytically derived without the decoherence. Considering the spontaneous decay from the environment, the evolution of the entanglement is similar to the damping Rabi oscillation. The generation of entanglement is induced by the dipole-dipole type interaction of atoms. It is found that the entanglement of two trapped atoms is robust with the uniform interaction with the external atom. The collective spontaneous emission from the coupling between the atoms may enhance the entanglement.     

Stability of the two-dimensional Fermi polaron

A system composed of an ideal gas of N fermions interacting with an impurity particle in two space dimensions is considered. The interaction between impurity and fermions is given in terms of two-body point interactions whose strength is determined by the two-body binding energy, which is a free parameter of the model. If the mass of the impurity is 1.225 times larger than the mass of a fermion, it is shown that the energy is bounded below uniformly in the number N of fermions. This result improves previous, N-dependent lower bounds, and it complements a recent, similar bound for the Fermi polaron in three space dimensions.     

Global entanglement and coherent states in an {\sf N}-partite system

We consider a quantum system consisting of N parts, each of which is a “quKit” described by a K dimensional Hilbert space. We prove that in the symmetric subspace, , a pure state is not globally entangled, if and only if it is a coherent state. It is also shown that in the orthogonal complement all states are globally entangled.     

On the critical temperature in a Boson-Fermion mixture with attraction between the components

The dependence of the critical temperature shift in the Bose component of a degenerate Bose-Fermi gas mixture in a harmonic trap on the number of bosons and fermions has been obtained on the basis of the effective Hamiltonian of the Bose subsystem. The presence of the Fermi component leads to a qualitatively new behavior of the shift, as compared to the case of a single interacting Bose gas in the trap. Namely, the T _c(N) dependence has a different curvature in the presence of the Fermi component.     

Entanglement entropy of fermions in any dimension and the Widom conjecture

We show that entanglement entropy of free fermions scales faster than area law, as opposed to the scaling L(d-1) for the harmonic lattice, for example. We also suggest and provide evidence in support of an explicit formula for the entanglement entropy of free fermions in any dimension d, S approximately c(deltagamma, deltaomega)L(d-1) logL as the size of a subsystem L-->infinity, where deltagamma is the Fermi surface and is the boundary of the region in real space. The expression for the constant c(deltagamma, deltaomega) is based on a conjecture due to Widom. We prove that a similar expression holds for the particle number fluctuations and use it to prove a two sided estimate on the entropy S.     

Measurement of M-shell X-ray production cross sections for the element 73 \leqslant Z \leqslant 83 using 5.96 keV photons

Total M-shell X-ray production cross sections (M XRF) of the some elements in the atomic number range were measured at 5.96 keV incident photon energy using a Si(Li) detector. The results are compared with the experimental and theoretical values in the literature.     

Transport of a quantum degenerate heteronuclear Bose-Fermi mixture in a harmonic trap

We report on the simultaneous transport of mixed quantum degenerate gases of bosonic ⁸⁷Rb and fermionic ⁴⁰ K in a harmonic potential. The samples are transported over a distance of to the geometric center of a Ioffe-Pritchard type magnetic trap. This transport mechanism was implemented by modification of the QUIC trap and is free of losses and heating. It significantly extends the capabilities of this trap design. We demonstrate a launching mechanism for quantum degenerate samples and show that highly homogeneous magnetic fields can be created in the center of the QUIC trap. The transport mechanism may also be cascaded to cover even larger distances for interferometric experiments with quantum degenerate samples.     

Study of spectator tagging in the reaction np → ppπwith a deuteron beam

The reaction has been studied in a kinematically complete experiment at a single beam momentum GeV/c (T = 759MeV). All four ejectiles have been detected in the large-acceptance time-of-flight spectrometer COSY-TOF. We analyzed the data along the lines of the spectator model as a means to isolate the quasi-free reaction. The spectator proton was identified by its momentum and flight direction thus yielding access to the associated Fermi motion of the bound neutron. A comparison is carried out with Monte Carlo simulations based on two different parameterizations of the deuteron wave function. Up to a Fermi momentum of roughly 150MeV/c no significant deviations between experimental and simulated data of various observables were found from which we conclude that the deuteron can indeed be taken as a valid substitute for the neutron.     

First production of ultracold neutrons with a solid deuterium source at the pulsed reactor TRIGA Mainz⋆

The production rates of ultracold neutrons (UCN) with a solid deuterium converter have been measured at the pulsed reactor TRIGA Mainz. Exposed to a thermal neutron fluence of n·cm^-2·pulse^-1, the number of detected very cold and ultracold neutrons ranges up to 200 000 at 7mol of solid deuterium (sD₂) in combination with a pre-moderator (mesitylene). About 50% of the measured neutrons can be assigned to UCN with energies E of where V _F(sD ₂) = 105 neV and V _F(guide) = 190 neV are the Fermi potentials of the sD₂ converter and our stainless steel neutron guides, respectively. Thermal cycling of solid deuterium, which was frozen out from the gas phase, considerably improved the UCN yield, in particular at higher amounts of sD₂.     

Two qubit entanglement preservation through the addition of qubits

An entanglement preservation scheme is proposed by considering the exact evolution of an N$N$-qubit interacting system in a common reservoir. We find that the steady-state concurrence is dependent only on the number of qubits, the qubit–reservoir coupling strength and the initial conditions of the system. Furthermore, we show that as N→∞$N\to \infty$, the initial entanglement between the two qubits is preserved.     

Budding and fission of a multiphase vesicle

We present a model of bi-phasic vesicles in the limit of large surface tension. In this regime, the vesicle is completely stretched and well described by two spherical caps with a fold, which concentrates the membrane stress. The conservation laws and geometric constraints restrict the space of possible shapes to a pair of solutions labeled by a parameter given by line tension/pressure. For a given value of , the two solutions differ by the length of the interface between domains. For a critical value, , the two vesicle shapes become identical and no connected solution exists above this critical value. This model sheds new light on two proposed mechanisms (osmotic shocks and molecule absorption) to explain the budding and the fission in recent experiments.     

Entanglement in the second quantization formalism

We study properties of entangled systems in the (mainly non-relativistic) second quantization formalism. This is then applied to interacting and non-interacting bosons and fermions and the differences between the two are discussed. We present a general formalism to show how entanglement changes with the change of modes of the system. This is illustrated with examples such as the Bose condensation and the Unruh effect. It is then shown that a non-interacting collection of fermions at zero temperature can be entangled in spin, providing that their distances do not exceed the inverse Fermi wavenumber. Beyond this distance all bipartite entanglement vanishes, although classical correlations still persist. We compute the entanglement of formation as well as the mutual information for two spin-correlated electrons as a function of their distance. The analogous, non-interacting collection of bosons displays no entanglement in the internal degrees of freedom. We show how to generalize our analysis of the entanglement in the internal degrees of freedom to an arbitrary number of particles.     

Tails of the dynamical structure factor of 1D spinless fermions beyond the Tomonaga approximation

We consider one-dimensional (1D) interacting spinless fermions with a non-linear spectrum in a clean quantum wire (non-linear bosonization). We compute diagrammatically the 1D dynamical structure factor, S(ω,q), beyond the Tomonaga approximation focusing on it's tails, |ω| ≫vq, i.e. the 2-pair excitation continuum due to forward scattering. Our methodology reveals three classes of diagrams: two “chiral” classes which bring divergent contributions in the limits ω→±vq, i.e. near the single-pair excitation continuum, and a “mixed” class (so-called Aslamasov-Larkin or Altshuler-Shklovskii type diagrams) which is crucial for the f-sum rule to be satisfied. We relate our approach to the T=0 ones present in the literature. We also consider the case and show that the 2-pair excitation continuum dominates the single-pair one in the range: |q|T/k_F ≪ω±vq ≪T (substantial for q ≪k_F). As applications we first derive the small-momentum optical conductivity due to forward scattering: σ∼1/ω for T ≪ω and σ∼T/ω² for T ≫ω. Next, within the 2-pair excitation continuum, we show that the attenuation rate of a coherent mode of dispersion Ω_q crosses over from , e.g. γ_q ∼|q|³ for an acoustic mode, to , independent of Ω_q, as temperature increases. Finally, we show that the 2-pair excitation continuum yields subleading curvature corrections to the electron-electron scattering rate: , where V is the dimensionless strength of the interaction.     

Dilepton-tagged $Q\overline{Q}+\mathrm{jet}$ events at the LHC

We propose a new method for identifying and isolating events through semileptonic decays of the pair. Employing these decay dileptons to tag the jet in a specific kinematic region provides a clean signature of jets associated with heavy-quark production. The measurement, in both pp and heavy-ion collisions, is essential for addressing heavy-quark fragmentation in vacuum and in a dense medium. We present next-to-leading order calculations of production (leading order in production) in TeV pp collisions at the LHC and discuss the feasibility of the measurement in heavy-ion collisions at TeV.