Qubit clock in quantum cosmology

We investigate the emergent time scenario in quantum cosmology based on the Page-Wotters approach. Using a quantum cosmological model with a qubit clock, it is demonstrated how the entanglement between the qubit clock and the geometry derives emergence of a time parameter which defines evolution of the timeless quantum state of the universe. We show the universe wave function conditioned by a qubit clock obeys the standard Schr\"{o}dinger equation and the Fisher information for the clock state, which quantifies entanglement between the universe and the clock, contributes as a negative energy density.