Entanglement in Excited States

Willi-Hans Steeb, Yorick Hardy

Zhou Dong-Lin, Kuang Le-Man

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.

Lan Xu, Le‐Man Kuang

We introduce a new kind of continuous-variable-type entangled pure states, called single-mode excited entangled coherent states (SMEECSs), which are obtained through actions of a creation operator of a single-mode optical field on the ECSs. We study the mathematical properties and entanglement characteristics of the SMEECSs, and investigate the influence of photon excitations on quantum entanglement. It is shown that the SMEECSs form a type of cyclic representation of the Heisenberg–Weyl algebra. It is found that the photon excitations seriously affect the entanglement character of the SMEECSs. We also show how such states can be produced by using cavity QED and quantum measurements.

Juanfernando Angel-Ramelli

Abstract In this work we calculate the entanglement entropy of certain excited states of the quantum Lifshitz model (QLM). The QLM is a 2 + 1-dimensional bosonic quantum field theory with an anisotropic scaling symmetry between space and time that belongs to the universality class of the quantum dimer model and its generalizations. The states we consider are constructed by exciting the eigenmodes of the Laplace–Beltrami operator on the spatial manifold of the model. We perform a replica calculation and find that, whenever a simple assumption is satisfied, the bipartite entanglement entropy of any such excited state can be evaluated analytically. We show that the assumption is satisfied for all excited states on the rectangle and for almost all excited states on the sphere and provide explicit examples in both geometries. We find that the excited state entanglement entropy obeys an area law and is related to the entanglement entropy of the ground state by two universal constants. We observe a logarithmic dependence on the excitation number when all excitations are put onto the same eigenmode.