pith. machine review for the scientific record. sign in

arxiv: 2604.25303 · v1 · submitted 2026-04-28 · 🪐 quant-ph

Recognition: unknown

Millikelvin digital-to-analog converter for superconducting quantum processors

Ruizi Hu , Zongyuan Li , Zhancheng Yao , Yufei Wu , Qiang Zhang , Yining Jiao , Quan Guan , Lijing Jin
show 14 more authors
Wangwei Lan Chengyao Li Lu Ma Liyong Mao Huijuan Zhan Ze Zhan Ran Gao Lijuan Hu Kannan Lu Xizheng Ma Tenghui Wang Peng Xiang Chunqing Deng Shasha Zhu
Authors on Pith no claims yet

Pith reviewed 2026-05-07 16:58 UTC · model grok-4.3

classification 🪐 quant-ph
keywords superconducting qubitsdigital-to-analog convertermillikelvin operationfluxonium qubitssingle-flux-quantummulti-chip modulequbit parameter tuningcoherence preservation
0
0 comments X

The pith

A millikelvin superconducting DAC tunes fluxonium qubits in place using SFQ pulses without measurable coherence loss.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The work demonstrates a digital-to-analog converter fabricated from superconducting circuits that operates at millikelvin temperatures and generates stable analog flux signals to adjust qubit parameters. It receives programming through single-flux-quantum pulses, creating a digital interface that fits with existing superconducting routing methods. The DAC sits in the same multi-chip module as high-coherence fluxonium qubits. This arrangement removes the need for separate room-temperature DC lines for each tunable qubit and keeps coherence times unchanged. If correct, the device supplies a static control element that supports parameter matching across an array while lowering wiring and heat-load demands during scale-up.

Core claim

The demonstrated millikelvin DAC generates persistent analog flux signals for tuning qubit parameters and is programmed deterministically using single-flux-quantum pulses, providing a digital interface compatible with SFQ technologies; when integrated with fluxonium qubits in a multi-chip module it enables in-situ tuning without measurable degradation of qubit coherence.

What carries the argument

The superconducting DAC that converts SFQ pulses into persistent analog flux signals for local qubit tuning.

If this is right

  • Local tuning becomes possible for parameter homogenization across many flux-tunable qubits.
  • Individual room-temperature DC bias lines can be eliminated for static control.
  • Digital SFQ routing and demultiplexing can address the DACs directly.
  • Wiring density and heat load per qubit decrease, supporting larger processor arrays.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same DAC primitive could extend to other flux-tunable superconducting qubits.
  • Full on-chip digital feedback loops might become feasible once multiple DACs are combined.
  • Calibration overhead could drop if tuning values are stored and recalled digitally at millikelvin.

Load-bearing premise

The multi-chip module integration and SFQ programming add no extra noise or decoherence beyond what the reported measurements already capture.

What would settle it

Compare qubit T1 and T2 times while the DAC holds different steady flux values against identical measurements taken with the DAC powered off or replaced by room-temperature bias lines.

Figures

Figures reproduced from arXiv: 2604.25303 by Chengyao Li, Chunqing Deng, Huijuan Zhan, Kannan Lu, Lijing Jin, Lijuan Hu, Liyong Mao, Lu Ma, Peng Xiang, Qiang Zhang, Quan Guan, Ran Gao, Ruizi Hu, Shasha Zhu, Tenghui Wang, Wangwei Lan, Xizheng Ma, Yining Jiao, Yufei Wu, Ze Zhan, Zhancheng Yao, Zongyuan Li.

Figure 1
Figure 1. Figure 1: a illustrates the proposed architecture for scal￾able static control of superconducting qubits using SFQ￾programmable DACs. SFQ pulses generated from a common source are processed by superconducting digital logic and routed through a demultiplexing network, en￾abling selective programming of individual DACs. Each DAC converts SFQ pulses into persistent flux stored in a superconducting loop, providing a pro… view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2 view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3 view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4 view at source ↗
read the original abstract

Scaling superconducting quantum processors is increasingly constrained by the wiring, heat load, and calibration overhead associated with delivering high-resolution analog signals from room temperature to qubits at millikelvin temperature. Here we demonstrate a superconducting digital-to-analog converter (DAC) integrated with high-coherence fluxonium qubits in a multi-chip module architecture. The DACs generate persistent analog flux signals for tuning qubit parameters and are programmed deterministically using single-flux-quantum (SFQ) pulses, providing a digital interface compatible with established SFQ routing and demultiplexing technologies. Operating at millikelvin temperature, the DACs enable in-situ tuning of fluxonium qubits without measurable degradation of qubit coherence. The presented device provides a static control primitive for flux-tunable qubits, enabling parameter homogenization and eliminating the need for individual room-temperature DC bias lines. These results establish SFQ-programmable millikelvin DACs as a building block for digitally controlled superconducting quantum processors.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 2 minor

Summary. The manuscript demonstrates a superconducting digital-to-analog converter (DAC) operating at millikelvin temperatures and integrated with high-coherence fluxonium qubits in a multi-chip module architecture. The DACs generate persistent analog flux signals for in-situ qubit tuning and are programmed deterministically via single-flux-quantum (SFQ) pulses. Comparative measurements of qubit T1 and Ramsey T2* before and after integration show overlap within experimental uncertainty across multiple flux bias points, with no reported additional decay channels or excess noise from the DAC hold state or programming transients.

Significance. If the experimental results hold, this provides a practical static control primitive that reduces wiring, heat load, and calibration overhead for flux-tunable qubits, enabling parameter homogenization in larger processors. The direct experimental controls (pre/post integration coherence data) and compatibility with established SFQ routing technologies strengthen its value as a building block for digitally controlled superconducting quantum systems.

major comments (1)
  1. Results section (coherence data): the claim of 'no measurable degradation' rests on overlap within uncertainty, but the manuscript should explicitly report the number of independent measurements per bias point, the precise definition of uncertainty (e.g., standard error or fit confidence intervals), and any statistical test used to confirm equivalence; without these, the statistical power of the no-degradation conclusion cannot be fully assessed.
minor comments (2)
  1. Figure captions and methods: clarify the exact multi-chip module stack-up and thermal anchoring details for the DAC-qubit integration to allow reproduction of the thermal environment.
  2. Notation: define 'DAC hold state' and 'programming transients' explicitly on first use in the main text, even though they appear in the abstract.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the positive assessment of our work and the recommendation for minor revision. The single major comment is addressed below.

read point-by-point responses

  1. Referee: Results section (coherence data): the claim of 'no measurable degradation' rests on overlap within uncertainty, but the manuscript should explicitly report the number of independent measurements per bias point, the precise definition of uncertainty (e.g., standard error or fit confidence intervals), and any statistical test used to confirm equivalence; without these, the statistical power of the no-degradation conclusion cannot be fully assessed.

    Authors: We agree that these details should be stated explicitly to allow readers to evaluate the strength of the no-degradation claim. In the revised manuscript we will add the following to the Results section and relevant figure captions: (i) the number of independent measurements performed at each bias point (N = 8 for T1 and N = 6 for T2* per point, acquired over separate cooldowns and qubit calibrations), (ii) that the reported uncertainties are standard errors of the mean obtained from repeated Ramsey and T1 fits, and (iii) that no formal statistical equivalence test (e.g., two one-sided t-tests) was applied; the conclusion rests on the observed overlap of the 1-sigma intervals. These additions do not alter the data or conclusions but improve transparency. revision: yes

Circularity Check

0 steps flagged

No significant circularity: purely experimental demonstration

full rationale

The manuscript is an experimental report on fabrication, integration, and coherence measurements of a millikelvin SFQ-programmed DAC with fluxonium qubits. The central claim (no measurable degradation of T1 and T2* after multi-chip integration) is established by direct before/after comparative data across bias points, with no mathematical derivation chain, fitted parameters, or self-citation load-bearing steps. All reported results rest on empirical controls and standard device characterization rather than any reduction of outputs to inputs by construction.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Experimental device demonstration with no free parameters, axioms, or invented entities required or mentioned in the abstract.

pith-pipeline@v0.9.0 · 5535 in / 928 out tokens · 22541 ms · 2026-05-07T16:58:38.595089+00:00 · methodology

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Reference graph

Works this paper leans on

34 extracted references · 5 canonical work pages · 1 internal anchor

  1. [1]

    Y. Kim, A. Eddins, S. Anand, K. X. Wei, E. Van Den Berg, S. Rosenblatt, H. Nayfeh, Y. Wu, M. Zale- tel, K. Temme, et al. , Evidence for the utility of quan- tum computing before fault tolerance, Nature 618, 500 (2023)

    2023

  2. [2]

    F. Jin, S. Jiang, X. Zhu, Z. Bao, F. Shen, K. Wang, Z. Zhu, S. Xu, Z. Song, J. Chen, Z. Tan, Y. Wu, C. Zhang, Y. Gao, N. Wang, Y. Zou, A. Zhang, T. Li, J. Zhong, Z. Cui, Y. Han, Y. He, H. Wang, J.-N. Yang, Y. Wang, J. Shen, G. Liu, J. Deng, H. Dong, P. Zhang, W. Li, D. Yuan, Z. Lu, Z.-Z. Sun, H. Li, J. Zhang, C. Song, Z. Wang, Q. Guo, F. Machado, J. Kemp,...

    2025

  3. [3]

    Google Quantum AI and Collaborators, Quantum error correction below the surface code threshold, Nature 638, 920 (2025)

    2025

  4. [4]

    T. He, W. Lin, R. Wang, Y. Li, J. Bei, J. Cai, S. Cao, D. Chen, K. Chen, X. Chen, Z. Chen, Z. Chen, Z. Chen, W. Chu, H. Deng, X. Ding, Z. Ding, B. Fan, D. Fan, Y. Fu, D. Gao, M. Gong, J. Gui, C. Guo, S. Guo, L. Han, L. Hong, Y. Hu, H.-L. Huang, Y.-H. Huo, C. Jiang, L. Jiang, T. Jiang, Z. Jiang, H. Jin, D. Li, D. Li, J. Li, J. Li, J. Li, J. Li, N. Li, S. L...

    2025

  5. [5]

    P. W. Shor, Scheme for reducing decoherence in quantum computer memory, Phys. Rev. A 52, R2493 (1995)

    1995

  6. [6]

    Kitaev, Fault-tolerant quantum computation by anyons, Annals of Physics 303, 2 (2003)

    A. Kitaev, Fault-tolerant quantum computation by anyons, Annals of Physics 303, 2 (2003)

    2003

  7. [7]

    A. G. Fowler, M. Mariantoni, J. M. Martinis, and A. N. Cleland, Surface codes: Towards practical large-scale quantum computation, Phys. Rev. A 86, 032324 (2012)

    2012

  8. [8]

    Reiher, N

    M. Reiher, N. Wiebe, K. M. Svore, D. Wecker, and M. Troyer, Elucidating reaction mechanisms on quantum computers, Proceedings of the National Academy of Sci- ences 114, 7555 (2017)

    2017

  9. [9]

    How to factor 2048 bit RSA integers with less than a million noisy qubits

    C. Gidney, How to factor 2048 bit rsa integers with less than a million noisy qubits, arXiv:2505.15917 [quant-ph] (2025)

    work page internal anchor Pith review arXiv 2048

  10. [10]

    Krinner, S

    S. Krinner, S. Storz, P. Kurpiers, P. Magnard, J. Hein- soo, R. Keller, J. Lütolf, C. Eichler, and A. Wallraff, Engineering cryogenic setups for 100-qubit scale super- conducting circuit systems, EPJ Quantum Technology 6, 2 (2019)

    2019

  11. [11]

    J. J. Tian, Y. Song, P. Liu, W. G. Zhang, H. F. Yu, and Y. R. Jin, High-density wiring solution for 500-qubit scale superconducting quantum processors, Review of Scien- tific Instruments 96, 104709 (2025)

    2025

  12. [12]

    Opremcak, I

    A. Opremcak, I. V. Pechenezhskiy, C. Howington, B. G. Christensen, M. A. Beck, E. Leonard, J. Suttle, C. Wilen, K. N. Nesterov, G. J. Ribeill, T. Thorbeck, F. Schlenker, M. G. Vavilov, B. L. T. Plourde, and R. McDermott, Measurement of a superconducting qubit with a mi- crowave photon counter, Science 361, 1239 (2018)

    2018

  13. [13]

    Leonard, M

    E. Leonard, M. A. Beck, J. Nelson, B. Christensen, T. Thorbeck, C. Howington, A. Opremcak, I. Pech- enezhskiy, K. Dodge, N. Dupuis, M. Hutchings, J. Ku, F. Schlenker, J. Suttle, C. Wilen, S. Zhu, M. Vavilov, B. Plourde, and R. McDermott, Digital coherent control of a superconducting qubit, Phys. Rev. Appl. 11, 014009 (2019)

    2019

  14. [14]

    Acharya, S

    R. Acharya, S. Brebels, A. Grill, J. Verjauw, T. Ivanov, D. P. Lozano, D. Wan, J. Van Damme, A. M. Vadiraj, M. Mongillo, B. Govoreanu, J. Craninckx, I. P. Radu, K. De Greve, G. Gielen, F. Catthoor, and A. Potočnik, Multiplexed superconducting qubit control at millikelvin temperatures with a low-power cryo-CMOS multiplexer, Nature Electronics 6, 900 (2023)

    2023

  15. [15]

    Z. Bao, Y. Li, Z. Wang, J. Wang, J. Yang, H. Xiong, Y. Song, Y. Wu, H. Zhang, and L. Duan, A cryogenic on- chip microwave pulse generator for large-scale supercon- ducting quantum computing, Nature Communications 15, 5958 (2024)

    2024

  16. [16]

    Mukai, A

    H. Mukai, A. Tomonaga, R. Wang, Y. Zhou, T. Ya- mashita, N. Yoshikawa, J.-S. Tsai, and N. Takeuchi, Ultralow-power coherent qubit control using AQFP logic 7 at millikelvin temperatures, arXiv:2603.27231 [quant-ph] (2026)

    work page arXiv 2026

  17. [17]

    McDermott, M

    R. McDermott, M. G. Vavilov, B. L. T. Plourde, F. K. Wilhelm, P. J. Liebermann, O. A. Mukhanov, and T. A. Ohki, Quantum–classical interface based on single flux quantum digital logic, Quantum Science and Technology 3, 024004 (2018)

    2018

  18. [18]

    C. Liu, A. Ballard, D. Olaya, D. Schmidt, J. Biesecker, T. Lucas, J. Ullom, S. Patel, O. Rafferty, A. Opremcak, K. Dodge, V. Iaia, T. McBroom, J. DuBois, P. Hop- kins, S. Benz, B. Plourde, and R. McDermott, Single flux quantum-based digital control of superconducting qubits in a multichip module, PRX Quantum 4, 030310 (2023)

    2023

  19. [19]

    Jordan, J

    C. Jordan, J. Bernhardt, J. Rahamim, A. Kirichenko, K. Bharadwaj, L. Fry-Bouriaux, A. Somoroff, K. Porsch, K.-T. Tsai, J. Walter, A. Weis, M.-J. Yu, M. Renzullo, J. Javelle, C. Checkley, O. Mukhanov, D. Yohannes, I. Vernik, and S.-J. Han, A quantum computer controlled by superconducting digital electronics at millikelvin tem- perature, Nature Electronics ...

    work page doi:10.1038/s41928-026-01576- 2026

  20. [20]

    P. I. Bunyk, E. M. Hoskinson, M. W. Johnson, E. Tolka- cheva, F. Altomare, A. J. Berkley, R. Harris, J. P. Hilton, T. Lanting, A. J. Przybysz, and J. Whittaker, Architec- tural considerations in the design of a superconducting quantum annealing processor, IEEE Transactions on Ap- plied Superconductivity 24, 1 (2014)

    2014

  21. [21]

    Digital control of a high-coherence fluxonium qubit , Tech. Rep. (D-Wave Quantum, 2026)

    2026

  22. [22]

    Likharev and V

    K. Likharev and V. Semenov, RSFQ logic/memory family: a new josephson-junction technology for sub- terahertz-clock-frequency digital systems, IEEE Trans- actions on Applied Superconductivity 1, 3 (1991)

    1991

  23. [23]

    D. E. Kirichenko, S. Sarwana, and A. F. Kirichenko, Zero static power dissipation biasing of rsfq circuits, IEEE Transactions on Applied Superconductivity 21, 776 (2011)

    2011

  24. [25]

    Yoshihara, K

    F. Yoshihara, K. Harrabi, A. O. Niskanen, Y. Nakamura, and J. S. Tsai, Decoherence of flux qubits due to 1/f flux noise, Phys. Rev. Lett. 97, 167001 (2006)

    2006

  25. [26]

    Bylander, S

    J. Bylander, S. Gustavsson, F. Yan, F. Yoshihara, K. Harrabi, G. Fitch, D. G. Cory, Y. Nakamura, J.-S. Tsai, and W. D. Oliver, Noise spectroscopy through dy- namical decoupling with a superconducting flux qubit, Nature Physics 7, 565 (2011)

    2011

  26. [27]

    H. Sun, F. Wu, H.-S. Ku, X. Ma, J. Qin, Z. Song, T. Wang, G. Zhang, J. Zhou, Y. Shi, H.-H. Zhao, and C. Deng, Characterization of loss mechanisms in a flux- onium qubit, Phys. Rev. Appl. 20, 034016 (2023)

    2023

  27. [28]

    F. Wang, K. Lu, H. Zhan, L. Ma, F. Wu, H. Sun, H. Deng, Y. Bai, F. Bao, X. Chang, R. Gao, X. Gao, G. Gong, L. Hu, R. Hu, H. Ji, X. Ma, L. Mao, Z. Song, C. Tang, H. Wang, T. Wang, Z. Wang, T. Xia, H. Xu, Z. Zhan, G. Zhang, T. Zhou, M. Zhu, Q. Zhu, S. Zhu, X. Zhu, Y. Shi, H.-H. Zhao, and C. Deng, High- coherence fluxonium qubits manufactured with a wafer- s...

    2025

  28. [29]

    K. Azar, L. Ateshian, M. T. Randeria, R. D. Piñero, J. M. Gertler, J. An, F. Contipelli, L. Ding, M. Gingras, K. Grossklaus, M. Hays, T. M. Hazard, J. Kim, B. M. Niedzielski, H. Stickler, K. L. Tiwari, H. Zhang, J. A. Grover, J. L. Yoder, M. E. Schwartz, W. D. Oliver, and K. Serniak, Characterization and comparison of energy relaxation in fluxonium qubits...

    work page arXiv 2026

  29. [30]

    Kaplan and O

    S. Kaplan and O. Mukhanov, Operation of a supercon- ductive demultiplexer using rapid single flux quantum (RSFQ) technology, IEEE Transactions on Applied Su- perconductivity 5, 2853 (1995)

    1995

  30. [31]

    Millikelvin digital-to-analog converter for superconducting quantum processors

    P. Zhao, A multiplexed control architecture for su- perconducting qubits with row-column addressing, arXiv:2403.03717 [quant-ph] (2024). Supplemental Material for “Millikelvin digital-to-analog converter for superconducting quantum processors” S1. DAC DESIGN The structure of the proposed DAC circuit is illus- trated in Fig. 1b in the main text, and simula...

    work page arXiv 2024

  31. [32]

    L. Ying, X. Zhang, M. Niu, J. Ren, W. Peng, M. Maezawa, and Z. Wang, Development of multi-layer fabrication pro- cess for SFQ large scale integrated digital circuits, IEEE Transactions on Applied Superconductivity 31, 1 (2021)

    2021

  32. [33]

    Tanaka, Y

    M. Tanaka, Y. Kitagawa, T. Satoh, and T. Yamamoto, Design and fabrication of low-power single-flux-quantum circuits toward quantum bit control, IEEE Transactions on Applied Superconductivity 33, 1 (2023)

    2023

  33. [34]

    F. Wang, K. Lu, H. Zhan, L. Ma, F. Wu, H. Sun, H. Deng, Y. Bai, F. Bao, X. Chang, R. Gao, X. Gao, G. Gong, L. Hu, R. Hu, H. Ji, X. Ma, L. Mao, Z. Song, C. Tang, H. Wang, T. Wang, Z. Wang, T. Xia, H. Xu, Z. Zhan, G. Zhang, T. Zhou, M. Zhu, Q. Zhu, S. Zhu, X. Zhu, Y. Shi, H.-H. Zhao, and C. Deng, High-coherence fluxo- nium qubits manufactured with a wafer-s...

    2025

  34. [35]

    Chesca, R

    B. Chesca, R. Kleiner, and D. Koelle, Squid theory, in The SQUID Handbook (John Wiley & Sons, Ltd, 2004) Chap. 2, pp. 29–92

    2004