  Partially spatially coherent qubits are more immune to turbulent atmospheric
conditions than coherent qubits, which makes them excellent candidates for
free-space quantum communication. In this article, we report the generation of
partially spatially coherent qubits in a spontaneous parametric down-conversion
(SPDC) process using a Gaussian Schell model (GSM) pump beam. For this
non-linear process, we demonstrate experimentally for the first time, the
transfer of spatial coherence features of the pump (classical) to the biphotons
(quantum) field. Also, the spatial profiles of partially coherent qubits
generated in type-I and type-II non-collinear SPDC process are experimentally
observed and multi-mode nature of partially coherent photons (qubit) is
ascertained. These investigations pave the way toward the efficient generation
of partially spatially coherent qubits with a tunable degree of spatial
coherence, which lead to wide range of applications in frontier areas such as
quantum cryptography, teleportation, imaging, and lithography.
