We observe that a weak guided light field transmitted through an ensemble of
atoms coupled to an optical nanofiber exhibits quadrature squeezing. From the
measured squeezing spectrum we gain direct access to the phase and amplitude of
the energy-time entangled part of the two-photon wavefunction which arises from
the strongly correlated transport of photons through the ensemble. For small
atomic ensembles we observe a spectrum close to the lineshape of the atomic
transition, while sidebands are observed for sufficiently large ensembles, in
agreement with our theoretical predictions. Furthermore, we vary the detuning
of the probe light with respect to the atomic resonance and infer the phase of
the entangled two-photon wavefunction. From the amplitude and the phase of the
spectrum, we reconstruct the real- and imaginary part of the time-domain
wavefunction. Our characterization of the entangled two-photon component
constitutes a diagnostic tool for quantum optics devices
