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- Title
Spectrum of the density matrix of a large block of spins of the XY model in one dimension.
- Authors
Franchini, F.; Its, A.; Korepin, V.; Takhtajan, L.
- Abstract
We consider reduced density matrix of a large block of consecutive spins in the ground states of the XY spin chain on an infinite lattice. We derive the spectrum of the density matrix using expression of Rényi entropy in terms of modular functions. The eigenvalues λ form exact geometric sequence. For example, for strong magnetic field λ = C exp(− π τ n), here τ > 0 and C > 0 depend on anisotropy and magnetic field. Different eigenvalues are degenerated differently. The largest eigenvalue is unique, but degeneracy g increases sub-exponentially as eigenvalues diminish: $${g_{n}\sim \exp{(\pi \sqrt{n/3})}}$$. For weak magnetic field expressions are similar.
- Subjects
DENSITY matrices; ENERGY levels (Quantum mechanics); QUANTUM theory; MAGNETIC fields; ENTROPY; EIGENVALUES; MODULAR functions; SPECTRUM analysis
- Publication
Quantum Information Processing, 2011, Vol 10, Issue 3, p325
- ISSN
1570-0755
- Publication type
Article
- DOI
10.1007/s11128-010-0197-7