  We construct efficient deterministic dynamical decoupling schemes protecting
continuous variable degrees of freedom. Our schemes target decoherence induced
by quadratic system-bath interactions with analytic time-dependence. We show
how to suppress such interactions to $N$-th order using only $N$ pulses.
Furthermore, we show to homogenize a $2^m$-mode bosonic system using only
$(N+1)^{2m+1}$ pulses, yielding - up to $N$-th order - an effective evolution
described by non-interacting harmonic oscillators with identical frequencies.
The decoupled and homogenized system provides natural decoherence-free
subspaces for encoding quantum information. Our schemes only require pulses
which are tensor products of single-mode passive Gaussian unitaries and SWAP
gates between pairs of modes.
