An 8-photon qubit chip for quantum computation
Researchers at ETRI have announced the demonstration of a silicon photonics chip that can control 8 photons and enable 6-qubit entanglement, and they plan to scale to 16-qubit PICs in the near future
Researchers at the Electronics and Telecommunications Research Institute (ETRI) in South Korea have announced that they have developed a system capable of controlling eight photons using a PIC. With this system, the team say they can explore various quantum phenomena, such as multipartite entanglement resulting from the interaction of the photons.
According to ETRI, its extensive research on silicon photonics quantum circuits has led to the demonstration of 2-qubit and 4-qubit quantum entanglement, achieving the best performance from a 4-qubit silicon photonics chip. These achievements resulted from their collaborative effort with KAIST and the University of Trento in Italy and were published in the scientific journals Photonics Research and APL Photonics.
Recently, ETRI announced the demonstration of 6-qubit entanglement using a chip designed to control 8 photonic qubits, representing a record-breaking achievement in quantum states based on a silicon photonics chip.
Quantum circuits based on photonic qubits are among the most promising technologies currently under active research for building a universal quantum computer. Several photonic qubits can be integrated into a tiny silicon chip as small as a fingernail, and a large number of these tiny chips can be connected via optical fibres to form a vast network of qubits, enabling the realisation of a universal quantum computer. Photonic quantum computers offer advantages in terms of scalability through optical networking, room-temperature operation, and low energy consumption.
A photonic qubit can be encoded using a pair of propagation paths of a photon, with one path assigned as 0 and the other as 1. For a 4-qubit circuit, 8 propagation paths are required, and for 8 qubits, 16 paths are needed. Quantum states can be manipulated on a photonic chip, which includes photon sources, optical filters and linear-optic switches, and are finally measured using highly sensitive single-photon detectors.
The 8-qubit chip includes 8 photonic sources and approximately 40 optical switches that control the propagation paths of the photons. About half of these 40 switches are specifically used as linear-optic quantum gates. The setup provides the fundamental framework for a quantum computer by measuring the final quantum states using single-photon detectors.
According to ETRI, the research team measured the Hong-Ou-Mandel effect, a quantum phenomenon in which two different photons entering from different directions can interfere and travel together along the same path. The researchers also say they demonstrated a 4-qubit entangled state on a 4-qubit integrated circuit (5mm x 5mm). Recently, they have expanded their research to 8-photon experiments using an 8-qubit integrated circuit (10mm x 5mm). The researchers plan to fabricate 16-qubit chips within this year, followed by scaling up to 32 qubits as part of their ongoing research towards quantum computation.
Yoon Chun-Ju, assistant vice president of the Quantum Research Division of ETRI, said: “We plan to advance our quantum hardware technology for a cloud-based quantum computing service. Our main goal is to develop a lab-scale system to strengthen our research capabilities in quantum computation.”
Lee Jong-Moo with ETRI's Quantum Computing Research Section, who led this work, stated: “Research for the practical implementation of quantum computers is highly active worldwide. However, extensive long-term research is still needed to realise practical quantum computation, especially to overcome computational errors caused by noise in the quantum processes.”
