  We investigate how the temporal coherence interference properties of light in
a Michelson-Morley interferometer (MMI), using only a single-photon detector,
can be understood in a quantum-optics framework in a straightforward and
pedagogical manner. For this purpose we make use of elementary quantum field
theory and Glaubers theory for photon detection in order to calculate the
expected interference pattern in the MMI. If a thermal reference source is used
in the MMI local oscillator port in combination with a thermal source in the
signal port, the interference pattern revealed by such an intensity measurement
shows a distinctive dependence on the differences in the temperature of the two
sources. The MMI can therefore be used in order to perform temperature
measurements. A related method was actually used to carry out high precision
measurements of the cosmic micro-wave background radiation on board of the COBE
satellite. The theoretical framework allows us to consider any initial quantum
state. The interference of single photons as a tool to determine the angular
peak-frequency of a one-photon pulse interfering with a single-photon reference
pulse is, e.g., considered. A similar consideration for coherent laser pulses
leads to a different response in the detector. The MMI experimental setup is
therefore in a sense an example of an optical device where one can exhibit the
difference between classical and quantum-mechanical light using only intensity
measurements.
