  Standard one-way quantum computers (1WQC) combine time symmetric unitary
evolution, with asymmetric treatment of boundaries: state preparation allows to
enforce a chosen initial state, however, for the final state measurement
chooses a random value instead. As e.g. pull/push, negative/positive pressure,
stimulated emission/absorption causing deexcitation/excitation are CPT analogs,
and one can be used for state preparation, the second should allow for its CPT
analog, referred here as CPT(state preparation) - allowing for additional
chosen enforcement of the final state, its more active treatment than
measurement. It should act similarly to postselection, but through applied
physical constraints (instead of running multiple times). Like pumped to
$|1\rangle$ prepared state vs its "unpumped" $\langle 0|$ CPT analog, hopefully
allowing to construct two-way quantum computers (2WQC) e.g. hydrodynamical, and
hopefully photonic: seen as $\langle \Phi_{\textrm{final}}|U_{\textrm{quantum
gates}}|\Phi_{\textrm{initial}}\rangle$ like for scattering matrix, with
influenced both initial and final states. If possible, for example for an
instance of 3-SAT problem on $n$ variables, we could prepare ensemble of $2^n$
inputs with Hadamard gates, calculate 3-SAT alternatives for them, and use
CPT(state preparation) to enforce outcomes of all these alternatives to '1'.
This way hopefully restricting this ensemble to satisfying given 3-SAT problem:
$\sum_{a:\textrm{SAT}(a)} |a\rangle$, in theory allowing to attack NP problems
by simultaneously pushing and pulling information through the system for better
control.
