A significant improvement in the studies of quantum repeaters and quantum networks has been achieved recently by Professor Chuan-Feng Li’s research group in Key Laboratory of Quantum Information. Deterministic single photons emitted from a self-assembled quantum dot (QD) has been stored in a solid-state quantum memory in multi-temporal modes. This work demonstrates the first connection of two solid-state quantum systems, i.e., the QD and the solid-state quantum memory. These results will be useful in the construction of quantum repeaters and the quantum network based on all-solid devices. The paper is issued in Nature Communications on October 15.
Entanglement distribution plays an essential role in the construction of a quantum network. However, the distance of the distribution is limited to about 100 km using direct photon transmission, because of the photon loss in the quantum channels. In the longer-distance entanglement distribution, quantum repeaters are necessary, which are built on the storage of single photons and the two-photon Bell-state measurement. Up to now, the realized quantum repeaters are based on the storage of probabilistic photon sources (the generation rate is usually less than 1% and multi-photon terms exist), which makes the distribution time on the order of minutes.
Li’s group utilizes the self-assembled QD to generate the deterministic single photons (the generation rate could reach 100% in principle and only one photon exists each time), which are then sent to another optical table on which the quantum memory experiment is carried out, via a 10-m optical fiber. The QD and the quantum memory samples are separated by 5 m. They employ the local-heating technique to tune the wavelength of the QD to match the wavelength of the quantum memory, and then use the atomic frequency comb technique to store the single photons to a self-designed sandwich-like solid-state quantum memory [PRL 108, 190505; PRL 115, 113002]. The fidelity of the single-photon polarization state is 91.3%. They furthermore demonstrate the storage of the deterministic single photons with 100 temporal modes, which is the most temporal modes those have been stored in the single-photon level.
This work illustrates two critical points for the speedup of the entanglement distribution, which are the deterministic photon source and the multimode quantum memory. The former can increase the distribution rate exponentially, and the latter can increase this rate linearly. By combining these two factors, the distribution time in the long distance can be reduced to the order of a millisecond. This work is also the first demonstration of the connection of two solid-state quantum nodes, which provides the potential to construct an all-solid-state quantum network.
Sketch of quantum network. The balls represent the quantum nodes, and lines represent quantum channels. The nodes communicate with each other via the single photons which carry the quantum information. Balls with different colors represent different kinds of quantum systems. The inset shows the energy levels of the quantum dot and the solid-state quantum memory.
Link of the paper: http://www.nature.com/ncomms/2015/151015/ncomms9652/full/ncomms9652.html