<p>Discretizing the <i>λϕ</i>⁴ scalar field theory on a lattice yields a system of coupled anharmonic oscillators with quadratic and quartic potentials. We begin by analyzing the two coupled oscillators in the second quantization method to derive several analytic relations to the second-order perturbation, which are then employed to numerically calculate the thermal out-of-time-order correlator (OTOC), <i>C</i>_<i>T</i> (<i>t</i>). We find that the function <i>C</i>_<i>T</i> (<i>t</i>) exhibits exponential growth over a long time window in the early stages, with Lyapunov exponent <i>λ</i> ~ <i>T</i> ^1/4, which diagnoses quantum chaos. We furthermore investigate the quantum chaos properties in a closed chain of N coupled anharmonic oscillators, which relates to the 1+1 dimensional interacting quantum scalar field theory. The results reveal an interesting property that the signatures of quantum chaos appear at low perturbative orders in the OTOC.</p>