Controlling the Photon Number Coherence of Solid-state Quantum Light Sources for Quantum Cryptography

Abstract

Quantum communication networks rely on quantum cryptographic protocols including quantum key distribution (QKD) using single photons. A critical element regarding the security of QKD protocols is the photon number coherence (PNC), i.e. the phase relation between the zero and one-photon Fock state, which critically depends on the excitation scheme. Thus, to obtain flying qubits with the desired properties, optimal pumping schemes for quantum emitters need to be selected. Semiconductor quantum dots generate on-demand single photons with high purity and indistinguishability. Exploiting two-photon excitation of a quantum dot combined with a stimulation pulse, we demonstrate the generation of high-quality single photons with a controllable degree of PNC. Our approach provides a viable route toward secure communication in quantum networks.

On-Demand Generation of Indistinguishable Photons in the Telecom C-Band Using Quantum Dot Devices

“…For most quantum communication protocols, the absence of photon number coherence (PNC) is required to avoid side-channel attacks and maintain security. As recently demonstrated for QD-generated photons at shorter wavelengths, standard TPE does not result in a significant degree of PNC in the emitted photon states, which can however be recovered and tuned by stimulating the XX-decay channel with a second laser pulse …”