NEC
Successful demonstration of principle of qubit-controlled
superconducting circuit for large-scale quantum computers
Proposes circuit technology that increases the density of microwave transmission paths by 1,000 times for quantum bit control
……
point
・ Proposed and successfully demonstrated the principle of a
superconducting circuit that can control over 1,000 quantum bits with a single microwave cable
・ The number of cables between room temperature and cryogenic temperature can be significantly reduced.
・Accelerate development toward practical application of large-scale quantum computers
[Image 1: https://prtimes.jp/i/78149/602/resize/d78149-602-2c911229bac89b30ebef-0.jpg&s3=78149-602-3fea5063bea0793bc30fb15f65a3d9bc-3000×1176.jpg] Comparison overview of the quantum bit control method used in this research and the conventional technology
Naoki Takeuchi, Principal Researcher, Global Research Center for Quantum and AI Fusion Technology Business Development, National Institute of Advanced Industrial Science and Technology (hereinafter referred to as “AIST”), is working with the National University Corporation Yokohama to accelerate the development of large-scale superconducting quantum computers. In collaboration with Professor Nobuyuki Yoshikawa of National University, Assistant Professor Daiki Yamaei (at the time of the research), Professor Taro Yamashita of Tohoku University, and Chief Researcher Tsuyoshi Yamamoto of NEC Corporation, we developed a super We proposed a conduction circuit and successfully demonstrated the principle of circuit operation. To realize a practical quantum computer, it is necessary to control the state of a large number of qubits operating at extremely low temperatures, and the number of qubits required is said to be as high as 1 million. In existing quantum computers, each microwave signal generated at room temperature is transmitted via different cables to the quantum bits at extremely low temperatures. This requires a large number of cables connecting room temperature and cryogenic
temperatures, which limits the maximum number of controllable qubits to around 1,000.
This time, we have proposed a superconducting circuit that can control multiple qubits with a single cable by multiplexing microwaves, and successfully demonstrated its principle in liquid helium (absolute temperature 4.2 K). If this technology is put into practical use, it will be possible to increase the density of microwave transmission paths by approximately 1,000 times compared to conventional methods, making it possible to dramatically increase the number of qubits that can be controlled at extremely low temperatures. . This is expected to accelerate the development of large-scale quantum computers. Details of this research result will be published in “NPJ Quantum Information” on June 3, 2024 (London time).
[Glossary] Social background of reference development Quantum computers have the potential to solve specific problems faster than existing computers. For this reason, research institutes around the world are conducting research and development toward the realization of quantum computers. Among several methods, the development of quantum computers using superconducting elements, which are compatible with integrated circuit processes, is actively underway. However, in order to realize a practical level
superconducting quantum computer, it is necessary to integrate a huge number of qubits at extremely low temperatures in a refrigerator, and the number is said to be one million.
One of the important issues toward realizing large-scale
superconducting quantum computers is how to control qubits. In the existing control method, microwave signals generated outside the refrigerator at room temperature are irradiated to each quantum bit at an extremely low temperature inside the refrigerator. Therefore, the number of cables between room temperature and cryogenic temperature increases proportionally to the number of qubits. However, there is an upper limit to the number of cables that can be installed inside a refrigerator due to heat inflow and space considerations, so existing control methods limit the maximum number of qubits to around 1,000. Achieving a practical large-scale superconducting quantum computer requires circuit technology that increases the density of microwave transmission paths for qubit control. Background of the research AIST has been developing superconducting digital/analog integrated circuits to realize next-generation computers and detectors. This time, we focused on the excellent energy efficiency of superconducting integrated circuits and their high affinity with microwave technology, and worked to develop a quantum bit-controlled superconducting circuit.
This research and development is supported by the JST Emergent Research Support Project “Innovative quantum bit control technology using adiabatic superconducting circuits (2022-2028)” (JPMJFR212B), the JSPS Grant-in-Aid for Scientific Research/Fundamental Research (S) “Reversible “Creation of ultra-low energy integrated circuit technology that exceeds thermodynamic limits using quantum magnetic flux circuits (2019-2023)” (JP19H05614), JSPS Grant-in-Aid for Scientific Research/Fundamental Research (S) “Demonstrating quantum supremacy Supported by “Creation of superconducting spintronics large-scale quantum computing circuits (2019-2023)” (JP19H05615). Research content
Figure 1(a) shows a block diagram of the qubit-controlled
superconducting circuit proposed this time. This figure shows the case of irradiating three qubits with microwaves. This circuit, like the qubit, is placed at extremely low temperatures and consists of a superconducting resonator and a superconducting mixer (proposed in this research). A signal in which multiple microwaves (f1, f2, f3) are multiplexed (multiplexed microwave) and a baseband signal for pulse signal generation are input from room temperature. The multiplexed microwaves are separated by a superconducting resonator, and a superconducting mixer generates a pulsed microwave signal from each microwave and baseband signal. As a result, multiple qubit control microwave signals (microwaves 1 to 3) can be output from one microwave input (multiplexed microwave). In principle, there are only two cables that connect room temperature and cryogenic temperature, regardless of the number of qubits: the multiplexed microwave and the baseband signal, so the number of cables can be dramatically reduced. However, the number of microwaves that can be multiplexed is limited by the loss of the superconducting resonator, so the number of qubits that can be controlled with one cable is estimated to be several thousand at most.
Figure 1(b) shows the simulation waveform when two microwaves (4.5 GHz and 5 GHz) are multiplexed. Microwave 1 (4.5 GHz) and microwave 2 (5 GHz) are output from superconducting mixer 1 and superconducting mixer 2, respectively. Each microwave can be individually turned on/off by control signals 1 and 2, and any qubit can be irradiated with microwaves. Such flexible microwave manipulation is a key feature for implementing quantum algorithms. Additionally, simulations estimated the circuit’s power consumption and found it to be only 81.8 pW per qubit. Low-power operation is an important benefit, since even a small amount of heat inside the refrigerator can destroy the state of the qubit.
[Image 2: https://prtimes.jp/i/78149/602/resize/d78149-602-4b69209e3431390401c5-0.jpg&s3=78149-602-c842198035da2c37f3316f877bc7cffc-3156×1477.jpg] Figure 1 (a) Block diagram of the proposed quantum bit-controlled superconducting circuit, (b) simulation waveform.
*The figures in the original paper are quoted or modified. The proposed quantum bit-controlled superconducting circuit was fabricated using AIST’s superconducting integrated circuit process, and a proof-of-principle experiment was conducted in an extremely low temperature environment. Figure 2(a) shows a chip photo of the fabricated qubit-controlled superconducting circuit. This circuit consists of two sets of superconducting resonators and a
superconducting mixer. Using this chip, we demonstrated the basic microwave operations required for qubit control. Figure 2(b) shows an example of the measurement results. This diagram shows that the two multiplexed microwaves are separated into microwaves 1 and 2, and each can be controlled on and off individually.
[Image 3: https://prtimes.jp/i/78149/602/resize/d78149-602-9e08022a772631861cbf-0.jpg&s3=78149-602-a227f351f5c8355e9a614581fe89a49e-1679×661.jpg] Figure 2 (a) Chip photo of quantum bit-controlled superconducting circuit, (b) Microwave manipulation experiment.
*The figures in the original paper are quoted or modified. From the above, it has been shown that by using the proposed quantum bit-controlled superconducting circuit, it is possible to dramatically improve the density of microwave transmission paths for quantum bit control. It is hoped that this circuit will become a fundamental technology for realizing large-scale superconducting quantum computers.
Future plans
In the future, we will perform integration tests of the proposed quantum bit-controlled superconducting circuit and quantum bits, with the aim of demonstrating quantum bit control using this circuit. Additionally, we will further improve the functionality of this circuit so that it can execute all the quantum gates required for quantum calculations.
Paper information
Magazine: npj Quantum Information
Title: Microwave-multiplexed qubit controller using adiabatic superconductor logic
Author name: Naoki Takeuchi, Taiki Yamae, Taro Yamashita, Tsuyoshi Yamamoto, and Nobuyuki Yoshikawa
DOI: 10.1038/s41534-024-00849-2
Glossary
quantum bit
The smallest unit of information in quantum computation. This can be realized with various devices using superconductors, semiconductors, etc.
microwave
Electromagnetic waves with frequencies from 3 GHz to 30 GHz. Microwaves around 5 GHz are used to control the superconducting qubit. resonator
A circuit that oscillates at a specific frequency. Here, it is used to separate multiplexed microwaves.
mixer
A circuit that outputs a signal that is the product of two input signals. baseband signal
Unmodulated signal. Here, the signal that determines the shape of the microwave signal output from the qubit-controlled superconducting circuit.
pulsed microwave signal
In quantum bit control, microwaves are irradiated onto the quantum bit for a certain period of time. Therefore, the quantum bit control circuit needs to output a pulsed microwave signal. Institution information
National Institute of Advanced Industrial Science and Technology (AIST) https://www.aist.go.jp/
Branding and Public Relations Department News Room hodo-ml@aist.go.jp National University Corporation Yokohama National University https://www.ynu.ac.jp
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National University Corporation Tohoku University
https://www.tohoku.ac.jp/
Graduate School of Engineering Information and Public Relations Office eng-pr@grp.tohoku.ac.jp
NEC
https://jpn.nec.com/
Global Innovation Strategy Department
https://jpn.nec.com/cgi-bin/cs/2005sep/opinion_form4.cgi
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