  Nontrivial symmetry of order parameters is crucial in some of the most
interesting quantum many-body states of ultracold atoms and condensed matter
systems. Examples in cold atoms include p-wave Feshbach molecules and d-wave
paired states of fermions that could be realized in optical lattices in the
Hubbard regime. Identifying these states in experiments requires measurements
of the relative phase of different components of the entangled pair
wavefunction.
  We propose and discuss two schemes for such phase sensitive measurements,
based on two-particle interference revealed in atom-atom or atomic density
correlations. Our schemes can also be used for relative phase measurements for
non-trivial particle-hole order parameters, such as d-density wave order.
