Ground state entanglement in quantum spin chains
Quantum Information & Computation
Entanglement distillation from quasifree fermions
Quantum Information & Computation
Classical simulation of dissipative fermionic linear optics
Quantum Information & Computation
The rational approximations of the unitary groups
Quantum Information Processing
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Notions of a Gaussian state and a Gaussian linear map are generalized to the case of anticommuting (Grassmann) variables. Conditions under which a Gaussian map is trace preserving and (or) completely positive are formulated. For any Gaussian map an explicit formula relating correlation matrices of input and output states is presented. This formalism allows to develop the Lagrangian representation for fermionic linear optics (FLO). It covers both unitary operations and the single-mode projectors associated with FLO measurements. Using the Lagrangian representation we reduce a classical simulation of FLO to a computation of Gaussian integrals over Grassmann variables. Explicit formulas describing evolution of a quantum state under FLO operations are put forward.