Researchers have developed a way to create high-visibility quantum interference between two independent semiconductor quantum dots which can enable quantum communication.
A quantum network is an important element of the quantum computer and quantum communication systems. It facilitates the transmission of information in the form of quantum bits, also called qubits, between physically separated quantum processors. Therefore, a high-performance quantum network requires not only ultra-low-loss quantum channels and quantum memory, but also high-performance quantum light sources. There has been exciting recent progress in satellite-based quantum communications and quantum repeaters, but a lack of suitable single-photon sources has hampered further advances.
The photon source should emit only one photon for quantum application. It also needs to attain brightness, the single-photon sources should have high system efficiency and a high repetition rate. Now to be used in applications like quantum teleportation which demands interfering with independent photons, the single photons should be indistinguishable. Additional requirements include a scalable platform, tunable and narrowband linewidth (favorable for temporal synchronization), and interconnectivity with matter qubits.
Quantum dots (QDs) have been recognized as a promising source for such applications. However, in the past two decades, the visibility of quantum interference between independent QDs has rarely exceeded the classical limit of 50% and distances have been limited to around a few meters or kilometers.
An international team of researchers has achieved high-visibility quantum interference between two independent QDs linked with ~300 km optical fibers. They report efficient and indistinguishable single-photon sources with ultra-low-noise, tunable single-photon frequency conversion, and low-dispersion long fiber transmission. The single photons are generated from resonantly driven single QDs deterministically coupled to microcavities. Quantum frequency conversions are used to eliminate the QD inhomogeneity and shift the emission wavelength to the telecommunications band. The observed interference visibility is up to 93%. According to senior author Chao-Yang Lu, professor at the University of Science and Technology of China (USTC), “Feasible improvements can further extend the distance to ~600 km.”
Reference: “Quantum interference with independent single-photon sources over 300 km fiber.” DOI: 10.1117/1.AP.4.6.066003