  We introduce a quantum interferometric scheme that uses states that are sharp
in frequency and delocalized in position. The states are frequency modes of a
quantum field that is trapped at all times in a finite volume potential, such
as a small box potential. This allows for significant miniaturization of
interferometric devices. Since the modes are in contact at all times, it is
possible to estimate physical parameters of global multi-mode channels. As an
example, we introduce a three-mode scheme and calculate precision bounds in the
estimation of parameters of two-mode Gaussian channels. This scheme can be
implemented in several systems, including superconducting circuits, cavity-QED
and cold atoms. We consider a concrete implementation using the ground state
and two phononic modes of a trapped Bose-Einstein condensate. We apply this to
show that frequency interferometry can improve the sensitivity of phononic
gravitational waves detectors by several orders of magnitude, even in the case
that squeezing is much smaller than assumed previously and that the system
suffers from short phononic lifetimes. Other applications range from
magnetometry, gravimetry and gradiometry to dark matter/energy searches.
