QUANTUM ENTANGLEMENT AND SQUEEZING IN COUPLED HARMONIC AND ANHARMONIC OSCILLATOR SYSTEMS

We investigate the fundamental connection between quadrature squeezing and continuous variable entanglement within a general class of two-coupled oscillator systems. We determine the quantitative relationship between them through the squeezing parameter and the entanglement entropy of the lowest energy eigenstate of the coupled oscillator systems numerically. Unlike the relation between entanglement and uncertainty product, we found that this relationship is, by no means, the same for the whole class of coupled oscillator systems: to a large extent it depends on the order and strength of the anharmonic potential, which implies that knowledge of the anharmonic potential of the coupled oscillator system is required before one can characterize the degree of entanglement through the squeezing parameter. Our results reveal that a more effective approach to enhance squeezing is to adjust the anharmonicity of the system potential, instead of increasing the quantum correlations between the oscillators. In addition, by probing into a quantum catastrophe model, we uncover transitions in the entanglement entropy and squeezing relation as the potential changes from a single well to a triple well, and then a double-well structure. The transitions appear through distinct entropy-squeezing relation, with a multi-well structure displaying a larger change in the antisqueezing behavior of the position quadrature than the single-well structure, for the same change in the entanglement entropy.