A laboratory testbed (10 km fiber spool) demonstrated a raw detection rate of 45 Mcps and an effective secret‑key rate of 7.8 Gbps after error correction and privacy amplification. The measured QBER was 1.9 %, confirming the predicted tolerance margin. Crucially, the adaptive LDPC module reduced the number of required decoding iterations from a worst‑case 30 to an average of 7, cutting latency to < 2 µs per block.
Classical error‑correction in QKD must reconcile discrepancies without revealing key material. Standard LDPC codes are fixed; if the channel conditions drift, efficiency plummets. JUQ‑565 incorporates an adaptive LDPC framework: during the sifting phase, the parties estimate the instantaneous QBER, then select a pre‑computed code from a repository spanning rates (R = 0.5)–(0.9). The chosen code’s parity‑check matrix is communicated over an authenticated classical channel, and belief‑propagation decoding proceeds. Simulations demonstrate a reconciliation efficiency (\beta) > 0.96 for QBERs up to 3 %. JUQ-565
JUQ‑565 was conceived to address these shortcomings. It combines three core innovations: A laboratory testbed (10 km fiber spool) demonstrated
In a d‑dimensional Hilbert space, a maximally entangled state can be written as if the channel conditions drift