Waveguide mode coding successfully "intervenes" in quantum computing, multi-degree-of-freedom optical quantum chip is about to come out
These different electric field lateral distribution characteristics are called different waveguide modes, and the larger the waveguide size, the more waveguide modes are supported.
These different waveguide modes are named according to the electric field distribution characteristics and are usually written as TE0, TM0, TE1, TM1, etc.
Ren Xifeng
Professor of University of Science and Technology of China
Not long ago, the internationally renowned academic journal "Physical Review Letters" published the important progress made by Academician Guo Guangcan's team from the University of Science and Technology of China in the research of photonic quantum chips: the team's Ren Xifeng's research group cooperated with Dai Daozin's team of Zhejiang University to achieve the first international achievement. Two-bit quantum logic gate operation for on-chip waveguide mode encoding.
The realization of this research result not only lays the foundation for the realization of multi-degree-of-freedom optical quantum chips, but also means that all the basic operations required for universal quantum computing with waveguide mode encoding can be realized.
What does such an "unintelligible" scientific research result mean?
The waveguide mode has attracted a lot of attention from the scientific community and the industry
"The waveguide mode encoding can be encoded from 0 to infinity, so it can be used for high-dimensional encoding processes." Ren Xifeng, a professor at the University of Science and Technology of China, told reporters that waveguides are usually used to directionally guide electromagnetic waves.
In a photonic chip, the light field is confined in an optical waveguide and transmitted with a specific lateral electric field distribution, or energy distribution.
Light will have different lateral electric field distributions depending on factors such as waveguide size, material properties, wavelength of light waves, etc.
"We call these different electric field lateral distribution characteristics as different waveguide modes." Ren Xifeng said that the larger the waveguide size, the more waveguide modes it supports.
These different waveguide modes are named according to the electric field distribution characteristics and are usually written as TE0, TM0, TE1, TM1, etc.
"When a waveguide supports two or more waveguide modes, we call it a multimode waveguide."
"If we encode information on these different waveguide modes, for example, TE0 encodes information bit 0 and TE1 encodes information bit 1, this method is called waveguide mode encoding." Ren Xifeng told reporters that because the waveguide mode can theoretically have There are many, so the coded information dimension exceeds the two-dimensional coding method of 0 and 1, which can be coded from 0 to infinity, so it can be used in the high-dimensional coding process.
It is precisely because the waveguide mode can be used to encode high-dimensional information and improve the channel capacity of communication that it has attracted more and more attention from the scientific community and the industry in the classical on-chip optical communication.
Waveguide mode encoding for quantum information processing for the first time
"Our collaborator, Professor Dai Daozin and his team have done a lot of influential work in this regard." Ren Xifeng said that in the first work they cooperated with, it was the first time in the world to use waveguide mode coding with For quantum information processing, the coherent conversion between waveguide mode, polarization and path-encoded entangled states is realized, which proves that the waveguide mode encoding method is also feasible for quantum signals.
Their work was published in Nature Communications.
"Because the carrier we use to carry quantum signals is photons, it is our second work to prepare a quantum light source encoded in a waveguide mode." Ren Xifeng said that in this work, they successfully created a silicon photonic chip. A quantum entanglement source for waveguide mode encoding was prepared on
The research results were also published in npj Quantum Information.
"It is precisely because of the technical accumulation and reserves of the previous work that our third work is about logic gates, and this work is also very innovative and challenging." Ren Xifeng told reporters that in order to realize the full on-chip waveguide mode To encode optical quantum information, they need to implement a two-bit quantum controlled NOT gate operation, which is the most important two-bit quantum operation and an indispensable logic gate for quantum computing.
"We first experimentally realized the quantum controlled NOT gate in a relatively mature path encoding method, accumulated technology, and explored experience." Ren Xifeng said that in this third work, they constructed the world's smallest size Optical quantum controlled NOT gates are also a great boost to the process of path encoding quantum information.
The results of this work were also published in the prestigious "Physical Review Letters".
Paving the way for waveguide mode-encoded quantum operations
Ren Xifeng told reporters that to realize the waveguide mode-encoded quantum logic gate, some special operations for independent regulation of the waveguide mode are required.
There are mainly two types here, one is to achieve different coupling intensities of the optical fields of different waveguide modes between two waveguides; the other is to achieve different energy attenuation ratios of the optical fields of different waveguide modes.
"These devices are not available before. We cooperated with Professor Dai Daozin's team and took the lead in proposing and successfully developing these two novel photonic devices." Ren Xifeng said that they independently designed and developed a waveguide mode coupler (TMDDC), Mode attenuator (MMA) two new multimode photonic devices can be used as basic devices for other multimode optical information processing.
"The waveguide mode-encoded quantum controlled NOT gates we demonstrate, coupled with single-bit rotation, can be cascaded to realize various quantum operations, providing the most basic tools for corresponding research fields."
As a high-dimensional information encoding technology, waveguide mode has attracted more and more attention because its high-dimensional information process can bring greater channel capacity, higher fidelity quantum operations, and more robust quantum information transmission.
"We have performed on-chip single-bit spin and two-bit quantum-controlled NOT gate operations for waveguide mode-encoded qubits, that is, all basic operations required for universal quantum computing. In theory, through this With the large-scale cascading of the two basic operations, we can realize quantum computing encoded by the waveguide mode." Ren Xifeng also admitted that there is still a long way to go.
"In addition, we also proved that this encoding method does not conflict with the original path encoding and polarization encoding, and can be coherently converted arbitrarily, so it also lays the foundation for the realization of multi-degree-of-freedom optical quantum chips." Ren Xifeng said.