Abstract: Continuous-variable QKD offers an economically compelling path toward urban quantum cryptography by utilizing standard coherent telecommunications transceivers. This paper evaluates local oscillator distribution, phase noise compensation, and high-rate reconciliation algorithms.
Transmitting the local oscillator alongside quantum signals opens side-channel attack vectors. We implement a True Local Local Oscillator (LLO) architecture where an independent laser at the receiver tracks optical phase drift using pilot reference tones, entirely eliminating co-propagating optical power vulnerabilities.
At low signal-to-noise ratios, error reconciliation limits secret key rates. Using multi-edge low-density parity-check (MET-LDPC) codes accelerated on graphics processing clusters, we demonstrate reconciliation efficiencies exceeding 95.6% at SNR levels down to 0.02.
Coexistence tests with 16 active 100G classical DWDM channels show that CV-QKD signals placed in the 1550 nm C-Band sustain 1.8 Mbps secret key throughput over 25 km of urban dark fiber, proving CV-QKD to be the most cost-effective solution for data center interconnection.