Stark localization near Aubry-André criticality

Abstract: In this work, we investigate the Stark localization near the Aubry-Andr\'{e} (AA) critical point. We perform careful studies for reporting system-dependent parameters, such as localization length, inverse participation ratio (IPR), and energy gap between the ground and first excited state, for characterizing the localization-delocalization transition. We show that the scaling exponents possessed by these key descriptors of localization are quite different from that of a pure AA model or Stark model. Near the critical point of the AA model, in the presence of Stark field of strength $h$, the localization length $\zeta$ scales as $\zeta\propto h^{-\nu}$ with $\nu\approx0.29$ which is different than both the pure AA model ($\nu=1$) and Stark model ($\nu\approx0.33$). The IPR in this case scales as IPR $\propto h^{s}$ with $s\approx0.096$ which is again significantly different than both the pure AA model ($s\approx0.33$) and Stark model ($s\approx0.33$). The energy gap, $\Delta$, scales as $E\propto h^{\nu z}$, where $z\approx2.37$ which is however same as the pure AA model. Finally, we discuss how invoking a criticality inducing additional control parameter may help in designing better many-body quantum sensors. Quantum critical sensors exploit the venerability of the wavefunction near the quantum critical point against small parameter shifts. By incorporating a control parameter in the form of the quasi-periodic field, i.e., the AA potential, we show a significant advantage can be drawn in estimating an unknown parameter, which is considered here to be the Stark weak field strength, with high precision.