Hannah Seabrook

Quantum key distribution (QKD) offers a theoretically secure method to share secret keys, yet practical implementations face challenges due to noise and loss over long-distance channels. Traditional QKD protocols require extensive noise compensation, hindering their industrial scalability and lowering the achievable key rates. Alternative protocols encode logical qubits in noise-resilient states, but at the cost of using many physical qubits, increasing susceptibility to loss and limiting transmission distance. In this talk, I will introduce a logical qubit encoding that uses antisymmetric Bell-states in the continuous photonic degrees of freedom, frequency and time. By leveraging the continuous space, I will show how we overcome this noise-loss robustness trade-off by minimising the number of photons per logical qubit, whilst optimising the encoding resilience over noise fluctuations. I will analyse the security of our encoding and demonstrate its robustness compared to existing state-of-the-art protocols. This approach provides a path towards scalable, efficient QKD implementations under realistic noise conditions.