Schrödinger Cat States in Giant Negative Magnetoresistance of 2D Electron Systems

We investigate the effect of giant negative magnetoresistance in ultrahigh mobility (\( \mu \gg 10^{7} cm^{2}V^{-1} s^{-1} \)) two-dimensional electron systems. These systems present a dramatic drop in the mangetoresistance at low magnetic fields (\( B < 0.1 \) T) and temperature (\( T \sim 0.1 \) K). This effect is reversed by increasing the temperature or the presence of an in-plane magnetic field. We explain this striking effect based on the description of these systems in terms of Schrödinger cat states (superposition of coherent states of the quantum harmonic oscillator). The increasing disorder in the sample due to the rising temperature or the in-plane magnetic field break up the Schrödinger cat states giving rise to mere coherent states which hold magnetoresistance in lower mobility samples.