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Chinese Physics B

A low-noise and high-stability DC source for superconducting quantum circuits

Daxiong 大雄 Sun 孙, Jiawei Zhang, Peisheng 培生 Huang 黄, Yubin Zhang, Ziqing Guo, Tingjin Chen, Rui Wang, Xuandong Sun, Jiajian Zhang, Wenhui Huang, Jiawei Qiu, Ji Chu, Ziyu Tao, Weijie Guo, Xiayu Linpeng, Ji Jiang, Jingjing Niu, Youpeng Zhong, Dapeng Yu

Published Jun 6, 2025• 1 citation
Publisher

Abstract

Abstract With the rapid scaling of superconducting quantum processors, electronic control systems relying on commercial off-the-shelf instruments face critical bottlenecks in signal density, power consumption, and crosstalk mitigation. Here we present a custom dual-channel direct current (DC) source module (QPower) dedicated to large-scale superconducting quantum processors. The module delivers a voltage range of ±7 V with 200 mA maximum current per channel, while achieving the following key performance benchmarks: noise spectral density of 20 nV/ Hz at 10 kHz, output ripple <500 μVpp within 20 MHz bandwidth, and long-term voltage drift <5 μVpp over 12 hours. Integrated into the control electronics of a 66-qubit quantum processor, QPower enables qubit coherence time of T 1 = 87.6 μs and Ramsey dephasing time of T 2 = 5.1 μs, with qubit resonance frequency drift constrained to ±40 kHz during 12-hour operation. This modular design is compact in size and efficient in energy consumption, providing a scalable DC source solution for intermediate-scale quantum processors with stringent noise and stability requirements, with potential extensions to other quantum hardware platforms and precision measurement systems.

DOI
10.1088/1674-1056/ade1c5

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Abstract With the rapid scaling of superconducting quantum processors, electronic control systems relying on commercial off-the-shelf instruments face critical bottlenecks in signal density, power consumption, and crosstalk mitigation. Here we present a custom dual-channel direct current (DC) source module (QPower) dedicated to large-scale superconducting quantum processors. The module delivers a voltage range of ±7 V with 200 mA maximum current per channel, while achieving the following key performance benchmarks: noise spectral density of 20 nV/ Hz at 10 kHz, output ripple <500 μVpp within 20 MHz bandwidth, and long-term voltage drift <5 μVpp over 12 hours. Integrated into the control electronics of a 66-qubit quantum processor, QPower enables qubit coherence time of T 1 = 87.6 μs and Ramsey dephasing time of T 2 = 5.1 μs, with qubit resonance frequency drift constrained to ±40 kHz during 12-hour operation. This modular design is compact in size and efficient in energy consumption, providing a scalable DC source solution for intermediate-scale quantum processors with stringent noise and stability requirements, with potential extensions to other quantum hardware platforms and precision measurement systems.
Abstract Scaling superconducting quantum processors increasingly relies on custom control electronics that can simultaneously satisfy spectral purity, multi-channel isolation, and long-term stability within a compact and integrated platform. Here we present Quantum microwave source (QMW), a classical three-channel broadband low-noise microwave source that consolidates qubit XY drive, readout excitation, and Josephson parametric amplifier (JPA) pump generation onto a single hardware module operating from 4 to 14 GHz with an output power range of -20 to +10 dBm. Electronic characterization yields a spurious-free dynamic range greater than 55 dB, equivalently a largest spur below -55 dBc, a phase noise as low as -110 dBc/Hz at 10 kHz offset for a 5 GHz carrier and below -103 dBc/Hz at the same offset across the full band, and output power stability within 0.1 dB over 24 hours. Integrated into the control chain of a 36-qubit superconducting processor, QMW pumps a JPA to 19.2 dB gain to enable high-SNR single-shot readout, while sustaining qubit coherence times of T 1 = 60.1 ± 0.8 μs, T 2,Ramsey = 24.2 ± 1.5 μs, and T 2,echo = 58.6 ± 2.1 μs, and an average single-qubit gate fidelity of 99.95 ± 0.05% measured by randomized benchmarking. The compact and modular nature of QMW provides a scalable microwave generation solution for largescale superconducting quantum processors, with potential extensions to other quantum hardware platforms and precision measurement applications.
The Superconducting Quantum Computing (SQC) is one of the most promising quantum computing techniques. The SQC requires precise control and acquisition to operate the superconducting qubits. The ultra-precision DC source is used to provide a DC bias for the qubit to work at its operation point. With the development of the multi-qubit processor, to use the commercial precise DC source device is impossible for its large volume occupation. We present our ultra-precision DC source which is designed for SQC experiments in this paper. The DC source contains 12 channels in 1U 19~inch crate. The performances of our DC source strongly beat the commercial devices. The output rang is -7~V to +7~V with 20~mA maximum output current. The Vpp of the output noise is 3~uV, and the standard deviation is 0.497~uV. The temperature coefficient is less than 1~ppm/∘^{\circ}∘C in 14~V range. The primary results show that the total drift of the output within 48h at an A/C room temperature environment is 40~uV which equal to 2.9~ppm/48h. We are still trying to optimize the channel density and long-term drift / stability.
We describe a dual current source designed to provide static flux biases for a superconducting qubit and for the Superconducting QUantum Interference Device (SQUID) which measures the qubit state. The source combines digitally programmable potentiometers with a stabilized voltage source. Each channel has a maximum output of ±1 mA, and can be adjusted with an accuracy of about ±1 nA. Both current supplies are fully computer controlled and designed not to inject digital noise into the quantum bit and SQUID during manipulation and measurement of the flux. For a 275 μA setting, the measured noise current is 2.6 parts per million (ppm) rms, in a bandwidth of 0.0017–10 Hz, from which we estimate dephasing times of hundreds of nanoseconds in the particular case of our own qubit design. By resetting the current every 10 min, we are able to reduce the drift to no more than 5 ppm at a current of 750 μA over a period of 3 days. The current source has been implemented without thermal regulation inside a radiofrequency-shielding room, and is used routinely in our quantum coherence experiments.
Abstract As superconducting quantum computing continues to advance at an unprecedented pace, there is a compelling demand for the innovation of specialized electronic instruments that act as crucial conduits between quantum processors and host computers. Here, we introduce a microwave measurement and control system (M2CS) dedicated to large-scale superconducting quantum processors. M2CS features a compact modular design that balances overall performance, scalability and flexibility. Electronic tests of M2CS show key metrics comparable to commercial instruments. Benchmark tests on transmon superconducting qubits further show qubit coherence and gate fidelities comparable to state-of-the-art results, confirming M2CS’s capability to meet the stringent requirements of quantum experiments running on intermediate-scale quantum processors. The compact and scalable nature of our design holds the potential to support over 1000 qubits after upgrade in stability and integration. The M2CS architecture may also be adopted to a wider range of scenarios, including other quantum computing platforms such as trapped ions and silicon quantum dots, as well as more traditional applications like microwave kinetic inductance detectors and phased array radar systems.
Control electronics for superconducting quantum processors have strict requirements for accurate command of the sensitive quantum states of their qubits. Hinging on the purity of ultra-phase-stable oscillators to upconvert very-low-noise baseband pulses, conventional control systems can become prohibitively complex and expensive when scaling to larger quantum devices, especially as high sampling rates become desirable for fine-grained pulse shaping. Few-gigahertz radio-frequency (RF) digital-to-analog converters (DACs) present a more economical avenue for high-fidelity control while simultaneously providing greater command over the spectrum of the synthesized signal. Modern RF DACs with extra-wide bandwidths are able to directly synthesize tones above their sampling rates, thereby keeping the system clock rate at a level compatible with modern digital logic systems while still being able to generate high-frequency pulses with arbitrary profiles. We have incorporated custom superconducting qubit control logic into off-the-shelf hardware capable of low-noise pulse synthesis up to 7.5 GHz using an RF DAC clocked at 5 GHz. Our approach enables highly linear and stable microwave synthesis over a wide bandwidth, giving rise to high-resolution control and a reduced number of required signal sources per qubit. We characterize the performance of the hardware using a five-transmon superconducting device and demonstrate consistently reduced two-qubit gate error (as low as 1.8%), which we show results from superior control chain linearity compared to traditional configurations. The exceptional flexibility and stability further establish a foundation for scalable quantum control beyond intermediate-scale devices.
The technological development of hardware heading toward universal fault-tolerant quantum computation requires a large-scale processing unit with high performance. While fluxonium qubits are promising with high coherence and large anharmonicity, their scalability has not been systematically explored. In this work, we propose a superconducting quantum information processor based on compact high-coherence fluxoniums with suppressed crosstalk, reduced design complexity, improved operational efficiency, high-fidelity gates, and resistance to parameter fluctuations. In this architecture, the qubits are readout dispersively using individual resonators connected to a common bus and manipulated via combined on-chip RF and DC control lines, both of which can be designed to have low crosstalk. A multi-path coupling approach enables exchange interactions between the high-coherence computational states and at the same time suppresses the spurious static ZZ rate, leading to fast and high-fidelity entangling gates. We numerically investigate the cross resonance controlled-NOT and the differential AC-Stark controlled-Z operations, revealing low gate error for qubit-qubit detuning bandwidth of up to 1 GHz. Our study on frequency crowding indicates high fabrication yield for quantum processors consisting of over thousands of qubits. In addition, we estimate low resource overhead to suppress logical error rate using the XZZX surface code. These results promise a scalable quantum architecture with high performance for the pursuit of universal quantum computation.