  The future of quantum photonic technology depends on the realization of
efficient sources of single photons, the ideal carriers of quantum information.
Parametric downconversion (PDC) is a promising route to create highly coherent,
spectrally pure single photons for quantum photonics using versatile
group-velocity matching (GVM) and tailored nonlinearities. However, the
functionality to actively control the poling period of nonlinear crystals used
in PDC is currently missing, yet would enable to dynamically modify the
wavelength of single photons produced in the PDC process. Here a detailed GVM
study is presented for functional PMN-0.38PT material which can be dynamically
repolled at ambient conditions with fields as low as 0.4 kV/mm. Our study
reveals phase-matching conditions for spectrally pure single photon creation at
5-6 microns. Further, a practical approach is proposed for on-flight wavelength
switching of the created single photons. The reported reconfigurable
functionality benefits a wide range of emerging quantum-enhanced applications
in the mid-IR spectral region where the choice of single photon sources is
currently limited.
