Security of Quantum Cryptographic Protocols Under Minimal Assumptions on the Hardware

Many quantum technologies rely on preparing, characterising, and reliably measuring entangled states. A central practical issue is how much we need to assume about the behaviour of the hardware used in a protocol. In this talk, I will begin with the notion of “security’’ for a quantum cryptographic protocol and outline the theoretical quantities that govern it. Examples include conditional Rényi entropies, sandwiched Rényi divergences, and extractability, which play key roles across tasks such as QKD, randomness generation, entanglement certification, and quantum state certification. I will then focus on how, for certain well-designed protocols, these quantities can be obtained directly from experimental data under minimal assumptions on the devices. This leads to device independent and semi–device independent approaches. As examples, I will discuss the security of our recent device independent state certification protocol, as well as our new device independent randomness expansion protocols, with an emphasis on how to compute the required bounds on entropic quantities and extractability in a fully device independent manner.