Quantum cryptography generates unbreakable cryptographic codes by encoding information using single photons, which until now have relied on highly attenuated lasers as sources^{1, 2}. But these sources can create pulses that contain more than one photon, making them vulnerable to eavesdropping by photon splitting^{3, 4}. Here we present an experimental demonstration of quantum cryptography that uses a photon turnstile device, which is more reliable for delivering photons one at a time. This device allows completely secure communication in circumstances under which this would be impossible with an attenuated laser.

1. Quantum Entanglement Project, ICORP, JST, MURI, UCLA, E. L. Ginzton Labs, Stanford University, Stanford, California 94305, USA
2. NTT Basic Research Laboratories, Atsugi, Kanagawa 243-0198, Japan
3. Solid State Photonics Laboratory, Stanford University, Stanford, California 94305, USA

Correspondence to: Edo Waks¹ e-mail: Email: edo@stanford.edu