Fig. 1: Schematic set-up of our twin-field quantum key distribution protocols.
From: Optimized protocol for twin-field quantum key distribution
In each trial, Alice and Bob randomly choose code mode and test mode and send their quantum states to the untrusted receiver Eve. If a code mode is selected, Alice (Bob) prepares coherent state chosen from \(\{|\alpha {e}^{i{k}_{a(b)}\pi }\rangle ,|\alpha {e}^{i({k}_{a(b)}+\frac{1}{M})\pi }\rangle ,\ldots ,|\alpha {e}^{i({k}_{a(b)}+\frac{M-1}{M})\pi }\rangle \}\). If a test mode is selected, Alice (Bob) prepares coherent state chosen from \(\{\left|{\beta }_{0}{e}^{i{\phi }_{0}}\right\rangle ,\left|{\beta }_{1}{e}^{i{\phi }_{1}}\right\rangle ,\ldots ,\left|{\beta }_{k}{e}^{i{\phi }_{k}}\right\rangle \}\). After interference at beam splitter (BS) and detector click on Eve’s side, she announces the outcome. More detailed explanation can be found in protocol descriptions.
