  Coherent multidimensional optical spectroscopy techniques are broadly applied
across the electromagnetic spectrum ranging from NMR to the UV. These reveal
properties of matter through correlation plots of signal fields generated in
response to sequences of short pulses with variable delays. Here we discuss a
new class of multidimensional techniques obtained by time-and-frequency
resolved photon coincidence counting measurements of N photons which
constitutes a 2N dimensional spectrum. A compact description of these signals
is developed based on time ordered superoperators rather than the normally
ordered ordinary operators used in Glauber's photon counting formalism.The
independent control of the time and frequency gate parameters reveals details
of matter dynamics not available otherwise. Application to an anharmonic
oscillator model with fluctuating energy and anharmonicity demonstrates the
power of these signals.
