Subvacuum effects in Quantum Critical Theories from Holographic Approach

Subvacuum phenomena on a massive particle induced by a squeezed vacuum state of strongly coupled critical fields with a dynamical scaling $z$ are studied by employing the holographic approach. The corresponding dual description is the string moving in the 4+1-dimensional Lifshitz geometry. The squeezed vacuum state is constructed from the Bogoliubov transformations of the creation and annihilation operators of the pure vacuum state as a result from the perturbed geometry. Then the influence on particle's velocity dispersion from the squeezed vacuum is studied. With appropriate choices of squeezing parameters, the velocity dispersion is found smaller than the value caused by the normal vacuum fluctuations. This leads to a subvacuum effect. We find that the reduction in the velocity dispersion is suppressed by a large coupling constant of quantum critical fields, but is in principle observable. We then investigate the effect of the squeezed vacuum to the decoherence dynamics of a quantum particle. It is found possible for this decoherence to be below the level from the pure vacuum, rendering another subvacuum phenomenon of recoherence. We make some estimates of the degree of recoherence, and show that, in contrary to the velocity dispersion, the recoherence effect is proportional to the large coupling constant, and can potentially be observed. Finally we make a comparison with the effect on the particle influenced by a relativistic free field with the dynamical scaling $z=1$.