  Photonic integrated circuits (PICs) are key in advancing quantum technologies
for secure communications. They offer inherent stability, low losses and
compactness compared to standard fiber-based and free-space systems.
  Our reasearch demonstrates PIC's effectivness in enhancing quantum
communications, implementing a three-state BB84 protocol with decoy-state
method. We employ an integrated receiver and superconducting nanowire single
photon detectors (SNSPDs) to achieve technological advancements.
  One of the most notable results is the extraction of a secret key over a
record-breaking 45 dB channel attenuation. Our results demonstrate a remarkable
220% boost in key rate compared to our prototype fiber-based receiver over a 10
dB channel attenuation. This improvement in the secret key rate (SKR) signifies
the potential of integrated photonics to advance the field of quantum
communication.
