  In their seminal paper, Caves and Schumaker presented a new formalism for
quantum optics, intended to serve as a building block for describing two-photon
processes, in terms of new, generalized qudratures. The important,
revolutionary concept in their formalism was that it was fundamentally
two-mode, i.e. the related observables could not be attributed to any single
one of the comprising modes, but rather to a generalized complex quadrature
that could only be attributed to both of them. Here, we propose a subtle, but
fundamentally meaningful modification to their important work. Unlike the above
proposal, we deliberately choose a frequency-agnostic definition of the
two-mode quadrature, that we motivate on physical grounds. This simple
modification has far-reaching implications to the formalism -- the real and
imaginary parts of the quadratures now coincide with the famous EPR variables,
and our two-mode operators transform trivially under two-mode and single-mode
squeezing operations. Their quadratic forms, which we call the "quadrature
power" are shown to succinctly generate the $SU(1,1)$ algebra of squeezing
Hamiltonians, and correspond directly to important, broadband physical
observables, that have been directly measured in experiment and are explicitly
related to properties like squeezing and entanglement. This new point of view
gives a fresh perspective on two-mode processes that is completely agnostic to
the bandwidth, and reveals intriguing new ways for understanding and measuring
broadband two-mode squeezing.
