Japan launching quantum computer prototype likely based on quantum dot and photonics

Japan has unveiled its first quantum computer prototype, amid a global race to build ever-more powerful machines with faster speeds and larger brute force that are key towards realizing the full potential of artificial intelligence.

Japan’s machine can theoretically make complex calculations 100 times faster than even a conventional supercomputer, but use just 1 kilowatt of power – about what is required by a large microwave oven – for every 10,000 kilowatts consumed by a supercomputer.

Above – Universal logic gates for quantum-dot electron-spin qubits using trapped quantum-well exciton polaritons
Author: Shruti Puri, Peter L. McMahon, and Yoshihisa Yamamoto Publication: Physical Review B Publisher: American Physical Society

Launched on Monday, the creators – the National Institute of Informatics, telecom giant NTT and the University of Tokyo – said they are building a cloud system to house their “quantum neural network” technology.

The quantum cloud will be available at https://qnncloud.com/ starting next Monday.

Stanford University Professor Emeritus Yoshihisa Yamamoto is heading the project.

They are targeting commercialization by March 2020. They will be targeting large optimization problems with urban traffic congestion and smartphones optimization and discovery of new drugs and chemicals.

Japan’s prototype taps into a 1km-long optical fibre cable packed with photons, and exploits the properties of light to make super-quick calculations.

Yoshihisa Yamamoto published a Physics Review B article early in 2017 – Universal logic gates for quantum-dot electron-spin qubits using trapped quantum-well exciton polaritons

The US devotes US$200 million (S$271 million) yearly for quantum computing research, while China is building a US$10 billion research centre for quantum applications. Japan has set aside 30 billion yen (S$361 million) for quantum computing over a decade starting in April.


In this paper we introduce and analyze a system design for quantum-dot-based qubits that simultaneously supports scalable one-qubit and two-qubit gates, and single-shot qubit measurement. All three key processes (one-qubit gates, two-qubit gates, and qubit measurement) rely on the interaction between the electron in each quantum dot and exciton polaritons formed in a quantum well situated near the quantum dots. A key feature of our proposed system is the use of polariton traps, which we show enhances the quantum-dot–quantum-well interaction by a factor of 10 and consequently results in
100× faster two-qubit gates. We also introduce a one-qubit gate that is based on a combination of optical and microwave control, which is supported in the same device and system configuration as the other operations, in contrast to the conventional one-qubit gate that is based on all-optical control.


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