Silicon nitride quantum gate, 81% computational reliability
First domestic implementation of quantum entanglement light source and device A domestic research team has developed a technology that allows existing quantum processors, which only operate at very low temperatures, to operate at room temperature.
The Electronics and Telecommunications Research Institute (ETRI) announced on the 29th that it has successfully developed the light source elements and optical integrated circuits necessary for implementing a quantum internet using silicon (Si) and silicon nitride (Si₃N₄; silicon nitride), and implemented a quantum gate (CNOT) using these.
▲ Silicon photonic integrated circuit using nano-alignment packaging equipment
Aligning chips and input/output optical fibers [Photo = ETRI]
Quantum Internet is an Internet technology that transmits quantum data by utilizing quantum mechanical phenomena such as quantum superposition and quantum entanglement of photons. It is considered a next-generation information and communication infrastructure technology because it has higher data transmission security and computational power than the existing Internet.
Quantum information communication can be implemented in various ways, such as ion traps, superconductors, and quantum optics. The two methods above only operate smoothly at extremely low temperatures, such as -272.9℃, which is very close to absolute zero. In addition, the experimental environment must be set up to minimize external influences such as magnetic fields and currents, which requires a lot of cost.
The research team chose the quantum optical method to secure the technological lead. This is because it is less affected by the surrounding environment, can operate at room temperature, and is easy to integrate into a small size, making it advantageous for commercialization. This achievement is significant as it is the first case of implementing optical integrated circuit quantum gate technology in Korea.
Classical information performs calculations using bits that have a definite state of 0 or 1, and logic gates such as OR and AND. On the other hand, quantum information performs calculations using qubits (quantum bits; qubits) whose state of 0 or 1 is not definite, and quantum gates such as CNOT.
To this end, the research team developed a quantum light source device that uses the degenerate four-wave mixing process in silicon to create a “photon pair,” in which two photons, the smallest unit of light, exist in a “quantum entanglement” state. They have developed a “laser gun” that creates photons, which are light grains that serve as qubits and the smallest unit of light to transmit quantum data, one by one.
▲ Input/output multichannel optical fibers on silicon photonic integrated circuit chips
Combined and installed [Photo = ETRI]
The quantum light source device can generate photon pairs in an entangled state at a ratio of 1:700. In addition, ETRI created an optical integrated circuit using optical waveguides made of silicon and silicon nitride, which have good optical transmission loss characteristics. When a single photon pair created by the quantum light source device is input into this circuit, the quantum state of the photon can be controlled through the quantum interference phenomenon.
Using optical integrated circuits, it is possible to implement CNOT quantum gates, one of the quantum information processing operations. In particular, this is the world's first case of implementing CNOT quantum gates using an optical integrated circuit utilizing silicon nitride optical waveguides. The circuit developed by the research team resulted in a fidelity of up to 81% when operating the gate.
In the future, the research team plans to conduct follow-up research to improve the photon pair generation rate of the quantum light source device, reduce the propagation loss rate of the optical waveguide, and increase the gate reliability to more than 99%.
