1/Quantum Computing System
In this R&D theme, we are developing a quantum computer using silicon electron spin qubits, and in particular, a large-scale silicon quantum computer utilizing silicon semiconductor integrated circuit technology.
In a large-scale integrated system, it is necessary to select a qubit to operate from among a large number of qubits. We have designated three challenges in this R&D theme. We will develop a "2D qubit array," which is the heart of a quantum computer, and a "High-precision qubit control and high-sensitive qubit readout circuit,” which is necessary to control the 2D qubit arrays.
In addition, in collaboration with other R&D themes, we are developing a "system architecture" to integrate the entire system and operate it as a computer, aiming to realize a large-scale system by taking advantage of silicon semiconductor integrated circuit technology, as well as its reproducibility, characteristic stability, and high temperature operation characteristics.
R&D Challenges
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1. 2D qubit array
We have designed and fabricated a chip (QCMOS) with a quantum dot array and the CMOS*1 peripheral circuits required for control and are confirming the operation of the prototype chip. By designing and optimizing the peripheral CMOS circuits for cryogenic operation, which is necessary for quantum computer operation, we have confirmed that the chip operates normally even at cryogenic temperatures (4.2K) and functions as a selector circuit to select and control quantum dots. As a result, the operation control of quantum dots by CMOS peripheral circuits, which is indispensable for large-scale production, has been realized, and it is now possible to obtain the variation characteristics of a large number of quantum dots. In fact, we have succeeded in acquiring the variation characteristics of 128 quantum dots in a prototype QCMOS and obtaining the basic data necessary for characteristic variation analysis. In this project, we plan to conduct detailed analysis and provide feedback to the circuit operation margin and control sequence, which are necessary for the design of high-precision control and high-sensitivity readout circuits for qubits.
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2. High-precision qubit control and high-sensitive qubit readout circuit
We are developing a control system which comprises high-precision control and high-sensitive qubit readout circuit for qubits in cryogenic temperature. To realize a viable Si-electron-spin based quantum computer, it is inevitably to develop a control system that enables effectively control the qubits of the Quantum bit array as well as to establish the large-scale quantum bit array technology. We aim to establish the control scheme in which the key components of the control system are integrated into the dilution refrigerator. To embed the system in to such an extreme condition of the dilution refrigerator, we must overcome the issues such as the limitations of circuit volume, number of wirings, and constraint of power consumption and noises, and then we must establish high-precision qubit control and high-sensitive qubit readout circuits. We now developing with Kobe University particularly (1) control circuits which is embedded at the 4K (Liquid helium temperature) stage in the refrigerator and (2) high-sensitive qubit readout circuits with CMOS & QCMOS technologies which is embedded near the qubits. We will continue to evaluate the performance of the developed circuits and combine them with prototype quantum dot arrays to demonstrate the operation of qubits.
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3. System architecture
We are promoting the development of this system to operate as a computer by overseeing the entire system in relation to other R&D themes. The components are distributed in different temperature ranges in the dilution refrigerator and in the room temperature section, and they work together to create a scalable architecture that can manage an increase in the number of qubits in the future. We are also developing a quantum operating system as a software environment for users to use devices based on this architecture. The quantum operating system has both functions for operating the device itself (operation environment) and for developing quantum programs to run on the quantum computer (development environment), enabling the execution of quantum programs that take advantage of the structure of silicon qubit arrays. The development of this quantum operating system is promoting in collaboration with the " Large-scale and high-coherence fault-tolerant quantum computer with dynamical atom arrays" by Project Manager Prof. Kenji Omori. Furthermore, we are constructing a cryogenic environment centered on a dilution refrigerator and a measurement environment to measure the characteristics of the control unit under low temperature conditions. Based on these results, we aim to realize integrated operation of the entire system in the future.
Principal Investigators
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Hitachi
Hiroyuki Mizuno