We provide a group theory approach to coherent states describing quantum space-time and its properties. This provides a relativistic framework for the metric of a Riemmanian space with bosonic and fermionic coordinates, its continuum and discrete states, and a kind of { \it"quantum optics"} for the space-time. { \bf New} results of this paper are: (i) The space-time is described as a physical coherent state of the complete covering of the SL(2C) group, eg the Metaplectic group Mp(n). (ii) (The discrete structure arises from its two irreducible: $\textit{ even}$ $(2n)$ and $\textit{ odd}$ $(2n\;+\;1)\;$ representations, ($n = 1,\, 2, \,3\,...$ ), spanning the complete Hilbert space $\mathcal{ H} = \mathcal{ H}_{ odd}\oplus \mathcal{ H}_{ even}$. Such a global or { \it complete} covering guarantees the CPT symmetry and unitarity. Large $n$ yields the classical and continuum manifold, as it must be. (iii) The coherent and squeezed states and Wigner functions of quantum-space-time for black holes and de Sitter, and (iv) for the quantum space-imaginary time (instantons), black holes in particular. They encompass the semiclassical space-time behaviour plus high quantum phase oscillations, and notably account for the classical-quantum gravity duality and trans-Planckian domain. The Planck scale consistently corresponds to the coherent state eigenvalue $\alpha = 0$ (and to the $n = 0$ level in the discrete representation). It is remarkable the power of coherent states in describing both continuum and discrete space-time. The quantum space-time description is { \it regular}, there is no any space-time singularity here, as it must be.
Categories: gr-qc hep-th quant-ph