Witnessing Macroscopic Entanglement in a Staggered Magnetic Field
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We investigate macroscopic entanglement in an infinite XX spin-1/2 chain with staggered magnetic field, B_l=B+e^{-iπl}b. Using single-site entropy and by constructing an entanglement witness, we search for the existence of entanglement when the system is at absolute zero, as well as in thermal equilibrium. Although the role of the alternating magnetic field b is, in general, to suppress entanglement as do B and T, we find that when T=0, introducing b allows the existence of entanglement even when the uniform magnetic field B is arbitrarily large. We find that the region and the amount of entanglement in the spin chain can be enhanced by a staggered magnetic field.
Accepted for publication in Physical Review A, minor changes from previous version. 5 pages, 3 figures
Accepted for publication in Physical Review A, minor changes from previous version. 5 pages, 3 figures