NTT: Implementation of a modular quantum light source for fault-tolerant large-scale universal optical quantum computers – QNT Press Release


NTT Corporation (NTT, President and CEO: Jun Sawada, Chiyoda-ku, Tokyo) (TYO:9432) In cooperation with the University of Tokyo (President: Fujii Teruo, Bunkyo-ku, Tokyo) and the Institute of Physics and Chemistry (President: Hiroshi Matsumoto, Wako City, Saitama Prefecture) developed a fiber-coupled quantum light source (squeeze light source) (*1), which is a large-scale fault-tolerant The key technology of universal optical quantum computer.

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Figure 1: Generation of large-scale quantum entangled states through time-domain multiplexing technology (Graphic: Business Wire)

Quantum computers are being researched and developed around the world because they can use unique phenomena of quantum mechanics (such as quantum superposition states and quantum entangled states) for parallel computing processing. Although various methods are being considered, the optical quantum computer using photons has many advantages. For example, it does not require low temperature and vacuum equipment required by other methods, making it compact. In addition, by creating time-domain multiplexed quantum entangled states, the number of qubits can be easily increased without the need for micro-integrated circuits or device parallelization. In addition, due to the broadband characteristics of light, high-speed calculation processing becomes possible. In addition, quantum error correction has been theoretically proven to be achieved by using continuous variables of light using the parity of photons, rather than by using discrete variables using the presence or absence of photons. This method has high compatibility with optical communication technologies such as low-loss optical fibers and high-function optical devices, and has made great progress for the construction of general-purpose large-scale fault-tolerant optical quantum computers.

To realize a light quantum computer, one of the most important components is a quantum light source that generates compressed light, which is the origin of quantum properties in light quantum computers. In particular, a fiber-coupled quantum light source is highly needed. Squeezed light is a non-classical light with an even number of photons and squeezed quantum noise, which is used to generate quantum entanglement. In addition, compressed light plays an extremely important role in quantum error correction, because the parity check of the photon number makes quantum error correction possible. In order to realize a large-scale general-purpose fault-tolerant optical quantum computer, we need a fiber-coupled compressed light source that has highly compressed quantum noise and a fiber-coupled compressed light source that can maintain the parity of photon numbers even in high photon number components. For example, a compression level of more than 65% is required to generate multiple quantum entanglement in the time domain (two-dimensional cluster state) that can be used for large-scale quantum computing (*2). However, since it is difficult to produce high-quality compressed light, such equipment has never been developed.

In this research, we have developed a new fiber-coupled quantum light source that can work at the wavelength of optical communication. By combining it with fiber optic components, we successfully generated continuous wave compressed light for the first time, with a compressed quantum noise of more than 75% and a sideband frequency of more than 6 THz, even in a closed fiber optic system. This means that the key components of the optical quantum computer have been implemented in the form of compatible optical fibers, while maintaining the broadband characteristics of light. This will help develop optical quantum computers in stable and maintenance-free systems that use optical fibers and optical communication equipment. This will greatly promote the development of rack-mounted large-scale optical quantum computers.

The results of this study will be published in the American scientific journal Applied Physics Letters on December 22, 2021 (US time). This paper was also selected as the “Editor’s Pick” paper. Part of this research is supported by…

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