Experimental Quantum Key Distribution in an Indefinite Causal Order
This work experimentally implemented a BB84-like quantum cryptography protocol using a photonic quantum SWITCH to detect eavesdroppers. Instead of comparing key material, it detects eavesdropping by measuring control qubit measurements within the SWITCH. The method achieves an average detection probability of 0.15 per shared qubit, proving that indefinite causal order can be used for eavesdropper detection without sacrificing key bits.