The spectral and dynamical properties of dissipative quantum systems, as modeled by a damped oscillator in the Fock space, are investigated from a topological point of view. Unlike a physical lattice system that is naturally under the open boundary condition, the bounded-from-below nature of the Fock space offers a unique setting for understanding and verifying non-Hermitian skin modes under semi-infinity boundary conditions that are elusive in actual physical lattices. A topological characterization based on the complex spectra of the Liouvillian superoperator is proposed and the associated complete set of topologically protected skin modes can be identified, thus reflecting the complete bulk-boundary correspondence of point-gap topology generally absent in realistic materials. Moreover, we discover anomalous skin modes with exponential amplification even though the quantum system is purely dissipative. Our results indicate that current studies of non-Hermitian topological matter can greatly benefit research on quantum open systems and vice versa.
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