Experimentally feasible protocol for semiquantum key distribution

Quantum key distribution (QKD) protocols make it possible for two quantum parties to generate a secret shared key. Semiquantum key distribution (SQKD) protocols, such as “QKD with classical Bob” and “QKD with classical Alice” (that have both been proven robust), achieve this goal even if one of the parties is classical. However, existing SQKD protocols are not experimentally feasible with current technology. Here we suggest a protocol, “Classical Alice with a controllable mirror,” that can be experimentally implemented with current technology (using four-level systems instead of qubits), and we prove it to be robust.