  We show a new remarkable connection between the symmetric form of a quantum
stochastic differential equation (QSDE) and the strong resolvent limit of
Schr\"odinger equations in Fock space: the strong resolvent limit is unitary
equivalent to QSDE in the adapted (or Ito) form, and the weak limit is unitary
equivalent to the symmetric (or Stratonovich) form of QSDE.
  We prove that QSDE is unitary equivalent to a symmetric boundary value
problem for the Schr\"odinger equation in Fock space. The boundary condition
describes standard jumps of the phase and amplitude of components of Fock
vectors belonging to the range of the resolvent. The corresponding Markov
evolution equation (the Lindblad or Markov master equation) is derived from the
boundary value problem for the Schr\"odinger equation.}
