Use of single photons as carriers for quantum bits could enable reliable security during quantum data transmission. Researchers have found that an existing material could be used to build a system for the reliable generation of single photons under ambient conditions. A research team from Moscow Institute of Physics and Technology (MIPT) showed how a single-photon emitting diode based on silicon carbide (SiC), a semiconductor material used in optoelectronics, could be used to emit up to several billion photons per second. Researchers further showed that the electroluminescence of color centers in SiC could be used to increase the data transfer rate in unconditionally secure quantum communication lines to more than 1 Gb/s. Electrical excitation causes a point defect in the crystal lattice of silicon carbide (SiC) to emit single photons, which are of use to quantum cryptography. Courtesy of Elena Khavina, MIPT Press Office. Quantum cryptography, unlike classical encryption algorithms, relies on the laws of physics. One cannot copy an unknown quantum state without altering the original message. This means that a quantum communication line cannot be compromised without the knowledge of the sender and the receiver. Single photon generation is necessary for secure quantum transmission; otherwise, an eavesdropping party might intercept one of the transmitted photons and thus get a copy of the message. The MIPT team focused on SiC’s color center — a point defect in the lattice structure of SiC that can emit or absorb a photon at a wavelength to which the material is transparent in the absence of defects. The team investigated the physics behind the process of single-photon emission from color centers of SiC under electrical pumping. Researchers showed that color centers in SiC could be superior to any other quantum light emitter under electrical control at room temperature. Using a theoretical approach and numerical simulations, researchers demonstrated that at room temperature, the photon emission rate from a PIN SiC single-photon emitting diode could exceed 5 Gcounts per second, which is higher than what can be achieved with electrically driven color centers in diamond or epitaxial quantum dots. According to researchers, these findings could lay the foundation for the development of practical photonic quantum devices, which could be produced in a well-developed CMOS compatible process flow. Researchers point out that new materials are likely to be found that will rival SiC in terms of brightness of single-photon emission. However, unlike SiC, the new materials will require new technological processes to be used in mass production of devices. By contrast, SiC-based single-photon sources are compatible with CMOS technology, which is a standard for manufacturing electronic integrated circuits. This makes SiC a promising material for building ultrawide-bandwidth, unconditionally secure data communication lines for quantum communications. The research was published in npj Quantum Information (doi:10.1038/s41534-018-0066-2).