Wavelength-shifting attack on a chip-based continuous-variable quantum key distribution system

Integrated continuous-variable quantum key distribution (CV-QKD) systems based on photonic chips offer a promising avenue for establishing large-scale and low-cost global quantum networks. In such systems, the grating coupler (GC) serves as an interface for optical coupling, but its strongly wavelength-dependent efficiency creates a severe security loophole in practice. In this paper, we propose a wavelength-shifting attack targeting the wavelength-dependent GC in chip-based CV-QKD systems. By intercepting Alice's quantum states and resending forged quantum states together with a local oscillator (LO), both at a shifted wavelength, this attack manipulates the receiver's excess-noise estimation, effectively masking the excess noise introduced by Eve. Numerical simulations show that the attack can keep Bob's estimated excess noise below the security threshold, leading Alice and Bob to infer a positive secret key rate while the actual secure key rate is zero. This research reveals how the integrated components can be exploited to mount side-channel attacks. To mitigate this vulnerability, we propose practical defenses, including on-chip wavelength monitoring and randomized shot-noise calibration. These findings provide important guidance for the secure development of next-generation integrated quantum communication systems.