We investigate the contact process in one dimension by a quantity K(L, t) to measure the spatial correlation length. K(L,t)=Lσ2/⟨ρ⟩2\documentclass[12pt]{minimal}
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\begin{document}$$K(L,t) = L\sigma ^2 / \langle \rho \rangle ^2$$\end{document} is defined as a function of time, where L, ρ\documentclass[12pt]{minimal}
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\begin{document}$$\rho $$\end{document}, σ2\documentclass[12pt]{minimal}
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\begin{document}$$\sigma ^2$$\end{document}, and ⟨⋯⟩\documentclass[12pt]{minimal}
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\begin{document}$$\langle \cdots \rangle $$\end{document} are the system size, the particle density, the variance of ρ\documentclass[12pt]{minimal}
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\begin{document}$$\rho $$\end{document}, and the ensemble average, respectively. At the critical point, K(t) follows a power law of K(t)∼t1/z\documentclass[12pt]{minimal}
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\begin{document}$$K(t) \sim t^{1/z}$$\end{document} with z=1.5821(16)\documentclass[12pt]{minimal}
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\begin{document}$$z=1.5821(16)$$\end{document}. We estimate the correlation length exponent ν⊥=1.1014(33)\documentclass[12pt]{minimal}
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\begin{document}$$\nu _\perp = 1.1014(33)$$\end{document} using the relation Kstat(p)∼(pc-p)-ν⊥\documentclass[12pt]{minimal}
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\begin{document}$$K_\mathrm {stat}(p) \sim (p_c - p)^{-\nu _\perp }$$\end{document} in the subcritical regime, where Kstat\documentclass[12pt]{minimal}
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\begin{document}$$K_\mathrm {stat}$$\end{document} is the stationary value of K. K(t) is proportional to the correlation length therefore we could obtain the information of the correlation length directly using K(t).
