244 research outputs found
Finite temperature fidelity susceptibility for one-dimensional quantum systems
We calculate the fidelity susceptibility chi_f for the Luttinger model and
show that there is a universal contribution linear in temperature T (or inverse
length 1/L). Furthermore, we develop an algorithm - based on a lattice path
integral approach - to calculate the fidelity F(T) in the thermodynamic limit
for one-dimensional quantum systems. We check the Luttinger model predictions
by calculating chi_f(T) analytically for free spinless fermions and numerically
for the XXZ chain. Finally, we study chi_f at the two phase transitions in this
model.Comment: typo in Eq. (9) corrected, published versio
Spin diffusion and the anisotropic spin-1/2 Heisenberg chain
Measurements of the spin-lattice relaxation rate 1/T_1 by nuclear magnetic
resonance for the one-dimensional Heisenberg antiferromagnet Sr_2CuO_3 have
provided evidence for a diffusion-like contribution at finite temperature and
small wave-vector. By analyzing real-time data for the auto- and
nearest-neighbor spin-spin correlation functions obtained by the density-matrix
renormalization group I show that such a contribution indeed exists for
temperatures T>J, where J is the coupling constant, but that it becomes
exponentially suppressed for T << J. I present evidence that the
frequency-dependence of 1/T_1 in the Heisenberg case is smoothly connected to
that in the free fermion case where the exponential suppression of the
diffusion-like contribution is easily understood.Comment: 9 pages, 7 figure
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