quantum mechanics , as an important branch of modern physics, mainly explores the movement rules of tiny particles, and uses quantum superposition state to intuitively display the microscopic atom and molecular world, so that people can understand two completely different particle states present in the same physical system from different angles.
Figure | Quantum Mechanics (Source: Pixabay)
quantum computer can use the physical characteristics in quantum mechanics to perform calculations that are almost impossible for traditional computers. This theoretical application has attracted widespread attention from industry insiders in recent years and can greatly improve the production efficiency of electronic products.
Improve the precision regulation of quantum systems is the focus of the development of quantum computers. It is reported that quantum computing has two basic operations, namely, single quantum and double qubit gate operations. Quantum computers use qubits in quantum superpositions of 0 and 1 to perform calculations. In order to achieve high-performance, superimposed quantum computing goals in quantum computers, fast and accurate quantum bitgate operations are required.
In larger circuits, the superconducting circuit method can more efficiently complete the superposition state of of quantum . Moreover, it is easier to realize strong coupling between quantum bits, thereby performing dual qubit gate operations more quickly and efficiently.
In the process of executing the superconducting circuit method, the coupling between qubits needs to be completed with coupler . Therefore, in terms of high-level superconducting quantum computers, couplers are currently important components related to their performance.
In July this year, Toshiba (Toshiba) stated in a paper that residual coupling can be eliminated through the electromagnetic wave irradiation coupler. However, this method fails to achieve the purpose of quickly and with high precision to realize the dual qubit gate.
Recently, Toshiba researchers have made new breakthroughs in quantum computer frameworks and parts optimization, and have developed a tunable coupler that can operate dual qubit gates at high speed, namely dual cross-frequency coupler, which is expected to greatly improve the speed and accuracy of quantum computing.
(Source: Physical Review Applied)
related paper was published on the Physical Review Applied on September 15 under the title "Double-Transmon Coupler: Fast Two-Qubit Gate with No Residual Coupling for Highly Detuned Superconducting Qubits".
Figure | Superconducting quantum computer schematic diagram (Source: Toshiba)
According to the superconducting quantum computer schematic diagram, the tunable coupler connects two qubits and performs accurate quantum operations by operating the coupling between the qubits.
At present, the latest technology applied in quantum computers can close the coupling of cross-frequency qubits and close frequency. However, when other qubits are irradiated with electromagnetic waves, crosstalk between bands is easily generated, resulting in erroneous calculation results.
In addition to this, another drawback of the current technology is that it cannot make the qubits completely closed, resulting in significantly different frequencies, resulting in residual coupling, and thus lead to errors.
And the latest dual-span coupler manufactured by Toshiba can be applied on cross-frequency qubits at fixed frequency, with higher stability and easy design.
paper mentioned that the dual-span frequency coupler successfully realizes coupling between fixed frequency qubits with significantly different frequencies, and can fully switch and control the dual-qubit gate at high speed and precision.
Figure | Superconducting qubit tunable coupler dual-span coupler circuit diagram (Source: Toshiba)
dual-span coupler includes two fixed-frequency transfrequency qubits, as shown in Cross-frequency 3 and 4 in the figure, and two other fixed-frequency transfrequency qubits for calculation, such as Cross-frequency 1 and Cross-frequency 2 in the figure.
Figure | Flux relationship of coupling strength of double-span coupler (Source: Toshiba)
The paper also mentioned that the double-span subcoupler has a ring, and the three x on the ring represents two span sub-span superconducting tunnel junctions and an additional superconducting tunnel junctions. The magnetic flux Φex in the loop can be tuned by an external magnetic field, so that the coupling strength between the qubits on both sides reaches zero accuracy, thereby completely blocking the coupling in the loop.
In addition, by increasing the magnetic flux, the coupling strength can also be increased to several tens of megahertz, thereby achieving the purpose of quickly operating the dual qubit gate.
results show that the operating accuracy of the double-span coupler can reach 99.99%, and the running time is shortened to 24 nanoseconds. Therefore, dual-span couplers are expected to make significant contributions to the development of higher performance quantum computers.
It should be noted that it is best to use a cross-frequency qubit gate in actual operation, because the frequency is significantly different, it can reduce crosstalk errors and correct the qubit frequency design value deviation in time, so that the manufactured double-span sub-coupler is highly stable, has a simple structure and is easy to manufacture, thereby saving the time required to manufacture the device and improving the manufacturing output of the device.
In the future, the dual-span coupler technology is expected to promote further updates and iterations of high-sex energy subcomputers, but also makes great contributions to different fields such as realizing " carbon neutral " and new drug research and development.
According to reports, Toshiba plans to start making templates for dual-cross frequency couplers this year and perform demonstrations. The company's goal is to further utilize the advantages of dual-span couplers in the future, so that the speed and accuracy of quantum computers and other related electronic products can reach the highest level of world-class speed and accuracy.
Reference:
1.https://arxiv.org/abs/2203.11451
2.https://www.global.toshiba/ww/technology/corporate/rdc/rd/topics/22/2209-01.html
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