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RIKEN: Making “qubits” from silicon semiconductors:
-Superconducting rivals have emerged-
RIKEN
The international research team announced on January 20th in the English scientific journal Nature.
We made a “qubit” from a silicon semiconductor and succeeded in operating it with applicable accuracy.
Quantum computers using silicon are suitable for large scale.
This is a step toward the realization of quantum computers.
Quantum computer calculation error:
Quantum computer
It has the potential to perform calculations at ultra-high speed, but the problem is that calculation errors are likely to occur.
99% accuracy by operating the element:
For practical use, it is necessary to have an accuracy of 99% or more for each operation of the element.
Conventionally, with silicon qubits,
The accuracy of the operation of interlocking the two elements was only 98%.
RIKEN Center for Emerging Physical Characteristics
Seigo Tarucha, Deputy Director
The international team
We created a qubit that uses the magnetic properties of electrons by confining two electrons in a minute space inside silicon.
With a unique method that combines permanent magnets and microwaves,
By manipulating this, an accuracy of 99.5% was achieved.
Actually, two types of calculations for quantum computers were carried out.
It is said that it was confirmed that the correct answer was given with a high probability.
3 methods such as “superconductivity”:
So far, qubits of the same level have been produced by three methods such as “superconductivity”.
Strengths of silicon semiconductors:
Silicon semiconductors have various strengths such as already developed processing technology.
We aim to increase the scale from now on.
National Institute of Advanced Industrial Science and Technology
New Principles Research Center
Until now, the superconducting method has been the only winner.
However, a strong rival called a silicon semiconductor has emerged.
It raises expectations for large-scale quantum computers.
Science / IT: Yomiuri Shimbun Online
https://www.yomiuri.co.jp/science/20220119-OYT1T50275/
Scientists achieve key elements for fault-tolerant quantum computation in silicon spin qubits
To do the current work, published in Nature, the group decided to experiment with a quantum dot structure
that was fabricated by nanofabrication on a strained silicon/silicon germanium quantum well substrate, using a controlled-NOT (CNOT) gate.
In previous experiments,
the gate fidelity was limited due to slow gate speed.
To improve the gate speed,
they carefully designed the device and tuned the device operation condition
by voltages applied to gate electrodes to combine established fast single-spin rotation technique using micromagnets and a large two-qubit coupling.
This allows them
to enhance the gate speed by a factor of 10 compared to the previous works.
Interestingly,
it was previously believed the increasing gate speed would always lead to better fidelity,
but they found that there was a limit, and that beyond that the increasing speed actually made the fidelity worse.
Through the work, they discovered that
a property called the Rabi frequency—a marker of how the qubits change states in response to an oscillating field—
is key to the performance of the system, and they found a range of frequencies
for which the single-qubit gate fidelity was 99.8 percent and the two-qubit gate fidelity was 99.5 percent, clearing the required threshold.
To test the capability of the new system, the researchers implemented
a two-qubit Deutsch-Jozsa algorithm and the Grover search algorithm.
On both algorithms output correct results with a high fidelity of 96-97%,
demonstrating that silicon quantum computers can perform quantum calculations with high accuracy.
RIKEN
https://www.riken.jp/en/news_pubs/research_news/pr/2022/20220120_1/index.html
Fast universal quantum gate above the fault-tolerance threshold in silicon | Nature