Scientists Develop First Single Photon Router

According to the report of the American Physicists Organization Network on August 22, Swedish and Spanish scientists jointly developed the first router to work at the single-photon level, which was made of an "artificial atom". They also successfully demonstrated the embedded in a transmission line. How this router in the medium transports a single photon from one input port to one of the two output ports. Scientists say that this kind of single-photon router can serve as a quantum node in the quantum information network in the future and provide basic data processing and routing.

Researchers led by physicists Persson Dickinson and Chris Wilson of Chalmers University of Technology in Sweden completed the study in collaboration with scientists from the National Research Council of Spain. The results were published in the journal Physical Review Letters. .

Compared to electrons, controlling and guiding photons is more difficult. This is mainly because photons do not have strong interactions like electrons. Therefore, current routers mostly use electrons. However, an important requirement of quantum tunneling is that particles can distribute data over long distances. Photons are “natural” able to travel farther than other quantum systems such as atoms. Therefore, using photons as information carriers in quantum information networks is better. .

To build this single-photon router, scientists use a superconducting qubit (the smallest unit of information in a quantum computer) as an "artificial atom" (although this qubit actually consists of several atoms, but it has a discrete energy state, Like real single atom). The scientists then coupled this qubit to a one-dimensional transmission line, where microwave photons can travel along this transmission line. Later, the scientists continued to apply a weak photon probe on it, sometimes supplementing a more intense control pulse. Without this intense control pulse, artificial atoms reflect incident photons and incident photons travel to output port 1. When this intense control pulse occurs, it causes electromagnetically induced transparency (EIT), which causes the atom to become transparent to this faint probe beam, causing the photon to travel to output port 2. In this way, scientists can direct incident photons to one of two output ports.

Dai Xin said that this is the first router to work at the single-photon level, and its extinction efficiency can reach 99.6%, which shows that photons can be effectively coupled to the router and be well controlled. Moreover, its switching time (the time it takes for an incident photon to switch from one port to another) is only a few nanoseconds. In addition, this kind of router can be easily extended so that it has more output ports, which is essential for its use as a quantum dot.

Dyson pointed out that in addition to the quantum computer networks that are mainly used in the future, such routers are also very useful for research. For example, they can be used to distribute single photon source photons to several experiments on the same chip, allowing scientists to use the same Beam light for more experiments.