Summary
Non‐Gaussian operations have been studied intensively in recent years due to their ability to increase the secret key rate for certain CV‐QKD protocols. However, most previous studies on such protocols are carried out in a single‐mode setting, even though in reality any quantum state contains multimode components in frequency space. In this work, we investigate the use of non‐Gaussian operations in a multimode CV‐QKD system. Our main finding is that, contrary to single‐mode CV‐QKD systems, in generic multimode CV‐QKD systems, it is possible to use non‐Gaussian operations to increase the optimized secret key rate. More specifically, we find that at losses of order 30dB, which represents a distance of order 160km and the effective maximum distance for CV‐QKD, the key rate for multimode non‐Gaussian operations can be orders of magnitude higher than single‐mode operations. Our results are important for real‐world CV‐QKD systems, especially those dependent on quantum error correction—a process that requires non‐Gaussian effects.