Within the ALLEGRO project, we are exploring how Quantum Digital Twin (QDT) concepts can enhance Quantum Key Distribution (QKD) systems.

Our work starts by detailing the quantum channel (qCh) components — their functionalities and imperfections — and identifying how DARIUS can leverage these aspects to improve QKD performance. Finally, we introduce three DARIUS use cases that address real-world challenges.

📡 System Overview (see Figure 32):

  • QTx (Quantum Transmitter):
    • Single Photon Emitter (SPE) generates photons.
    • Wave Plate modifies the photons’ State of Polarization (SOP) based on the transmitted qubit.
  • SMF (Single Mode Fiber): Connects QTx to QRx, but can distort SOP and introduce photon loss due to environmental factors.
  • QRx (Quantum Receiver):
    • Balanced Beam Splitter (BS) randomly selects measurement basis (R or D) but may also cause photon loss.
    • Electronic Polarization Controllers (EPCs) compensate SOP distortions via tunable retardation/orientation.
    • Polarizing Beam Splitter (PBS) separates photons into H and V polarization states, introducing minor losses.
    • Wave Plate in the D basis enables measurement of D or A polarized photons.
    • Single Photon Detectors (SPDs) count photons — though affected by dark counts, i.e., false detections.

💡 Why this matters:
Understanding and modeling these imperfections is crucial for designing robust QKD systems. By integrating them into a QDT framework, DARIUS can:

  1. Enhance QKD resilience against channel distortions.
  2. Optimize SOP compensation strategies.
  3. Predict and mitigate photon loss impacts in real time.

Stay tuned as we share more about the three DARIUS use cases and how they bring us closer to next-generation secure quantum communication.

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