Although scientists have successfully demonstrated Linear Optical Quantum Computing, a scalable quantum computing approach that uses all-optical architecture with qubits represented by photons and controlled by mirrors and beam splitters, they have only done so on a very small scale.
Now, a new study has developed a way to integrate single-photon sources into optical circuits, leading to the creation of integrated quantum circuits that could help researchers scale up this method to larger numbers of photons.
One of the biggest challenges when creating a Linear Optical Quantum Computing system is the integration of the following incompatible components: single-photon sources, routing devices, photon manipulation devices and single-photon detectors.
In the new study, the team successfully embeds single-photon-generating quantum dots inside of nanowires, which were then subsequently encapsulated in a waveguide. They accomplished this by using a "nanomanipulator" in order to transfer and align the components. After being embedding inside the waveguide, the team was able to select and route single photons to different regions of the optical circuit.
"We proposed and demonstrated a hybrid solution for integrated quantum optics that exploits the advantages of high-quality single-photon sources with well-developed silicon-based photonics," said Iman Zadeh, co-author of the study. "Additionally, this method, unlike previous works, is fully deterministic, i.e., only quantum sources with the selected properties are integrated in photonic circuits."
The new setup possesses a promising coupling efficiency, which is one of the most important metrics for Linear Optical Quantum Computing as it determines the amount of photon loss and, in turn, the computer's reliability. The study revealed the setup to have a coupling efficiency of 24 percent, and the team estimates that further optimization could push this number to 92 percent.
Future research will ideally increase coupling efficiency, as well as achieve on-chip entanglement and increase the complexity of the photonic circuits and single-photon detectors.
"Ultimately, the goal is to realize a fully integrated quantum network on-chip," said Ali Elshaari, another co-author of the study. "At this moment there are a lot of opportunities, and the field is not well explored, but on-chip tuning of sources and generation of indistinguishable photons are among the challenges to be overcome."
The findings were published in the March 8 issue of Nano Letters.
