Academy of Sciences Institute of Physics 43 quantum bits processor Zhuangzi revealed
New on November 11, a one-dimensional superconducting quantum processor named "Zhuangzi" (a philosopher of the Warring States period) has been developed by a research team led by Fan Jiao, director of the Laboratory of Solid-State Quantum Information and Computing, Institute of Physics, Chinese Academy of Sciences.
In today's paper [1], "Observing topological zero modes on a 41-qubit superconducting processor," Fan demonstrates the "Zhuangzi" superconducting quantum processor with 43 quantum bits. "Superconducting quantum processors with 43 quantum bits.
The focus of this paper is to simulate the Aubry-Andre´-Harper (AAH) model with a processor in order to observe the so-called topological zero mode. Readers interested in this field can read the paper, and we focus here on this superconducting quantum processor.
Link to the paper：
https://arxiv.org/abs/2211.05341
As shown in the figure below, the "Zhuangzi" superconducting quantum processor has 43 quantum bits, all arranged on a diagonal, which is the so-called one-dimensional layout, including control lines and resonators on both sides of the diagonal. The middle of the device like a cross is the superconducting quantum bits, you can count whether 43.
The 43-qubit "Shoko" sample used in this work was made on a 430-micron-thick sapphire chip using standard wafer cleaning. Specifically, a 100 nm aluminum layer was first deposited on a 15 × 15 mm2 sapphire substrate and patterned by photolithography using 0.70 µm of positive SPR955 resist. Then, wet etching is used to fabricate large structures such as microwave coplanar waveguide resonators, transmission lines, control lines, and capacitors for transmon quantum bits. Finally, to suppress parasitic modes, many air bridges are constructed on the chip.
In addition, they optimized the end of the XY/Z control line (near the quantum bits) by moving the end away from the quantum bits and then grounding it to reduce crosstalk to other quantum bits due to microwave signals and flux bias. Normally, the control line is grounded directly at the end, but the microwave signal does not disappear instantaneously and continues to propagate along the metal. If the spatial distance between the quantum bits is not far enough, it can easily lead to the propagation of microwave signals to adjacent quantum bits, generating crosstalk. By extending the ends of the control lines to ensure that their ground ports are far away from the quantum bits, the leaking microwave signals can be kept away from the quantum bits, thus reducing microwave crosstalk. Also, for DC bias, extended control lines can generate currents in the opposite direction of the input current, producing mutually canceling fluxes and effectively reducing flux crosstalk.
Crosstalk case. The size of each dot indicates the absolute value of the Z crosstalk matrix element from its corresponding starting quantum bit to the target quantum bit. All crosstalk coefficients are less than 2.26%, except for Q42 to Q43, where the crosstalk is 3.13%
They then placed the superconducting quantum chip in a BlueFors dilution chiller with a mixing chamber (MC) at a temperature of about 20 milliKelvin (-273.13 degrees Celsius). Typical wiring for the control electronics and cryogenic equipment is shown in the figure below.
There are five readout transmission lines, each equipped with a superconducting Josephson parametric amplifier (JPA), a low-temperature low-noise amplifier (LNA), and a room-temperature radio frequency amplifier (RFA). The readout pulses on these transmission lines are first generated by a microwave arbitrary waveform generator (AWG) consisting of two digital-to-analog converter (DAC) channels and a local oscillator (LO), then interacted with the chip and amplified by the amplifier at different temperatures, and finally modulated by an analog-to-digital converter (ADC).
Schematic diagram of the experimental system and wiring information. Here, MC denotes hybrid chamber, RFA denotes room temperature RF amplifier, LNA denotes low noise amplifier, and JPA denotes Josephson parametric amplifier
To reduce the number of low-temperature control lines in the RFA, they combined the high-frequency microwave excitation signal and low-frequency bias signal at room temperature using a directional coupler, and combined the XY and Z control lines of quantum bits into one at low temperature. They set a microwave switch controlled by an experimental trigger signal at each LO port to suppress the thermal excitation from the continuous microwave signal. Zero calibration is performed for each AWG to reduce intrinsic leakage and mirror leakage.
Their superconducting quantum processor uses a one-dimensional layout consisting of 43 transmon quantum bits (Q1-Q43) arranged in a row. Generally speaking, it is much less difficult experimentally to use a one-dimensional layout compared to a two-dimensional layout. However, this topology requires a significant overhead to reorganize (shuffling) the quantum bits, and thus the fault tolerance threshold is much lower than that of two-dimensional [2].
When it comes to superconducting quantum processors, we are most familiar with Google's "Humboldt" and CSU's "Zuchongzhi", both of which have two-dimensional layouts, 6×9 for Humboldt and 6×11 for Zuchongzhi, as shown in the figure below.
Zuchongzhi's superconducting quantum processor has a two-dimensional layout
Why does the "Zhuangzi" at the Institute of Physics of the Chinese Academy of Sciences have a one-dimensional layout? Because the processor is specifically designed to capture the substantial topological features of a one-dimensional quantum many-body system from a complex energy band structure. The paper mentions that "using a superconducting quantum processor assisted by highly controllable Floquet engineering, our results establish a general hybrid simulation approach to explore quantum topological many-body systems in the NISQ era."
About Fan Jo
Fan Jiao, Research Fellow, Institute of Physics, Chinese Academy of Sciences, Director of Solid State Quantum Information and Computing Laboratory, Leader of Q03 Group. 2005 November, joined Institute of Physics, Chinese Academy of Sciences, Researcher/PhD Supervisor. National High-level Talents Special Support Program for Science and Technology Innovation Leaders; Head of Innovation Team in Key Areas of the Ministry of Science and Technology, Team Name: "Solid State Quantum Computing and Quantum Information Innovation Team"; Received Special Allowance from the State Council Government; Received Zhou Peiyuan Physics Award in 2021; Head of Innovation Group of National Natural Science Foundation of China. Received the Silver Award from the University of Chinese Academy of Sciences in 2021; received the Tang Lixin Teaching Master Award from the University of Chinese Academy of Sciences in 2022.
He has visited and conducted collaborative research at Stanford University, IBM Research Center, Oxford University, University of Hong Kong, Chinese University of Hong Kong, and National University of Singapore.
His main research interests include: theoretical and experimental research on quantum computing and quantum simulation. Recently, he has focused on: (i) superconducting quantum computing theory and experiments; (ii) experimental collaboration with Diamond NV Center; (iii) quantum phenomena simulation, quantum virtual machine.
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Reference：
[1]https://arxiv.org/abs/2211.05341
[2]https://www.nature.com/articles/s41534-018-0074-2
