  Field-trials are of key importance for novel technologies seeking
commercialization and wide-spread adoption. This is certainly also the case for
Quantum Key Distribution (QKD), which allows distant parties to distill a
secret key with unconditional security. Typically, QKD demonstrations over
urban infrastructures require complex stabilization and synchronization systems
to maintain a low Quantum Bit Error (QBER) and high secret key rates over time.
Here we present a field-trial which exploits a low-complexity self-stabilized
hardware and a novel synchronization technique, to perform QKD over optical
fibers deployed in the city center of Padua, Italy. In particular, two
techniques recently introduced by our research group are evaluated in a
real-world environment: the iPOGNAC polarization encoder was used for the
preparation of the quantum states, while the temporal synchronization was
performed using the Qubit4Sync algorithm. The results here presented
demonstrate the validity and robustness of our resource-effective QKD system,
that can be easily and rapidly installed in an existing telecommunication
infrastructure, thus representing an important step towards mature, efficient
and low-cost QKD systems.
