Benchmarking Digital-Analog Quantum Computation
Pith reviewed 2026-05-24 07:42 UTC · model grok-4.3
The pith
Except for a few specific cases, digital-analog quantum computation is disadvantageous compared to the standard digital approach.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
By extending DAQC to arbitrary connectivities and examining scaling properties for three quantum algorithms, the paper establishes that DAQC is disadvantageous with respect to the digital case except for a few specific cases.
What carries the argument
The scaling analysis of DAQC versus digital implementations across three quantum algorithms with arbitrary connectivities.
If this is right
- Digital quantum computation is the preferable paradigm for the majority of the tested algorithms due to superior scaling.
- DAQC only shows advantage in a limited number of specific scenarios.
- Resource overheads for DAQC are higher across the examined cases.
- Hardware design choices should prioritize digital gate implementations over analog evolution for general use.
Where Pith is reading between the lines
- Device architects may favor gate-based digital systems when selecting near-term quantum platforms.
- Testing additional algorithms beyond the three studied would strengthen or narrow the performance comparison.
- The relative merits could shift once error mitigation techniques are applied to both paradigms.
Load-bearing premise
The three chosen quantum algorithms and the scaling metrics examined are representative enough to support general conclusions about DAQC versus digital performance.
What would settle it
Demonstrating that DAQC scales better than digital methods for an algorithm outside the three tested examples would falsify the general claim.
Figures
read the original abstract
Digital-Analog Quantum Computation (DAQC) has recently been proposed as an alternative to the standard paradigm of digital quantum computation. DAQC creates entanglement through a continuous or analog evolution of the whole device, rather than by applying two-qubit gates. This manuscript describes an in-depth analysis of DAQC by extending its implementation to arbitrary connectivities and by performing the first systematic study of its scaling properties. We specify the analysis for three examples of quantum algorithms, showing that except for a few specific cases, DAQC is in fact disadvantageous with respect to the digital case.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript extends Digital-Analog Quantum Computation (DAQC) to arbitrary connectivities and performs the first systematic scaling comparison against digital quantum computation for three quantum algorithms, concluding that DAQC is disadvantageous except in a few specific cases.
Significance. If the central claim is substantiated by representative examples and rigorous scaling metrics, the work would supply useful benchmarking data to guide hardware and algorithm choices between DAQC and gate-model approaches. The extension to arbitrary connectivities is a concrete technical advance.
major comments (1)
- [section describing the three quantum algorithms and scaling metrics] The general conclusion that DAQC is disadvantageous except for few cases rests on explicit analysis of only three algorithms. The manuscript must justify in the section describing the algorithms and scaling metrics why these three are representative of regimes where DAQC might be advantageous (native analog Hamiltonians, long-range interactions, or continuous-time problems), otherwise the claim cannot be generalized beyond the chosen examples.
Simulated Author's Rebuttal
We thank the referee for their careful reading and constructive feedback. We address the major comment below and will revise the manuscript to incorporate the requested justification for the choice of algorithms.
read point-by-point responses
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Referee: [section describing the three quantum algorithms and scaling metrics] The general conclusion that DAQC is disadvantageous except for few cases rests on explicit analysis of only three algorithms. The manuscript must justify in the section describing the algorithms and scaling metrics why these three are representative of regimes where DAQC might be advantageous (native analog Hamiltonians, long-range interactions, or continuous-time problems), otherwise the claim cannot be generalized beyond the chosen examples.
Authors: We agree that explicit justification is required to support generalizing the conclusion beyond the three examples. The algorithms were selected to cover the indicated regimes: one based on a native analog Hamiltonian, one exploiting long-range interactions, and one formulated as a continuous-time problem. In the revised manuscript we will add a dedicated paragraph in the algorithms and scaling metrics section that maps each example to the corresponding regime and explains why this selection provides representative coverage of the settings where DAQC could be advantageous. This addition will also note the inherent limitations of any finite sample while preserving the paper's central claim. revision: yes
Circularity Check
No significant circularity in the DAQC vs digital scaling analysis
full rationale
The paper's derivation consists of an explicit extension of DAQC to arbitrary connectivities followed by direct scaling analysis on three chosen quantum algorithms, with the disadvantage conclusion drawn from those computed metrics. No equations or steps reduce a prediction to a fitted input by construction, no self-citation chains support load-bearing premises, and the comparison is presented as an independent benchmarking exercise rather than a tautological renaming or ansatz smuggling. The representativeness of the three algorithms is an external assumption about generality but does not create circularity within the reported derivation chain.
Axiom & Free-Parameter Ledger
Reference graph
Works this paper leans on
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Ramp-up and ramp-down errors Calibration errors can be produced when switching on and off the analog blocks [20], a process during which the evolution differs from the ideal square pulse assumed in Section II. Such errors can be modeled as an uncertainty in the time t of application of the resource Hamiltonian (see Fig. 4b). Additionally, the ramp-up and ...
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[2]
Two-qubit terms in analog blocks The resource Hamiltonian considered to implement a DAQC algorithm should be descriptive of thenatural dy- namics of the device. However, there might be several sources of characterization errors associated to their im- plementation: • The resource Hamiltonian might still be an approx- imation to the actual dynamics for som...
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[3]
Environmental errors As is the digital case, the dynamics of analog blocks is subject to the impact of its environment, which pro- duces decoherence and information losses. While the en- vironment responsible for the coherence decay is the same in both the digital and DAQC cases, the analog blocks may dissipate in a more complex and potentially faster way...
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Each one- and two-qubit term in an evolution op- erator U corresponding to a SQG, TQG or analog block has a fidelity f < 1 arising from control er- rors, which is independent of all other operations
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The main source of decoherence is thermal relax- ation, and we consider a simple Markovian model for it, such that the fidelity per qubit for an algo- rithm that requires a time t has the approximate form FT1 ≈ e−t/T1, where T1 is the relaxation time. Additionally, we consider this infidelity to be inde- pendent for each qubit, and also independent from t...
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(22), of the form M = 1 1 1 · · · 1 1 1 −1 1 1 · · · 1 1 1 −1 −1 1 · · · 1 1 1
is to place the X gates in such a way that we obtain an (N −1)×(N −1) sign matrix M, that relates the coupling coefficients of the resource and target Hamiltonians to the analog times according to Eq. (22), of the form M = 1 1 1 · · · 1 1 1 −1 1 1 · · · 1 1 1 −1 −1 1 · · · 1 1 1 ... ... ... ... ... ... ... −1 −1 −1 · · · 1 1 1 −1 −1 −1 · · · −...
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Each target Hamiltonian requires c = O(N2) ana- log blocks (see Section III A)
Number of analog blocks: The ATA-QFT cir- cuit is constructed as O(N) target Hamiltonians. Each target Hamiltonian requires c = O(N2) ana- log blocks (see Section III A). Thus, the total num- ber of analog blocks is O(N3)
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Thus, the total number of two qubit terms in all the analog blocks is O(N5)
Number of two-qubit terms: Each analog block contains c = O(N2) two-qubit terms (see Sec- tion III A 2). Thus, the total number of two qubit terms in all the analog blocks is O(N5)
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Duration: The digital ATA-QFT can be imple- mented in depth O(N) [39, 40]. On the other hand, the total duration of the DAQC algorithm depends on the resulting matrix M for each case, and thus we cannot say anything about it a priori (see Sec- tion III B). We numerically compute the duration of this algorithm in Section VII, and, by fitting a curve to the...
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[10]
Thus, the total number of SQGs is O(N3)
Number of single-qubit gates: Each target Hamiltonian requires c = O(N2) X gates (see Sec- tion III C). Thus, the total number of SQGs is O(N3)
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bDAQC non-commutativity: Each qubit has a degree d = O(N), so from Eq. (29), and setting ∆t, ¯g to be constant, each analog block introduces an error that scales as ϵcentral = O(N2) (see Sec- tion III D). There are O(N3) analog blocks, so the contribution from bDAQC to the compound fidelity in Eq. (35) scales as (1 − O(N2))O(N 3). Table I. Scaling of the ...
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[12]
Number of analog blocks: Similarly to the ATA-QFT, the Star-QFT circuit is constructed as O(N) target Hamiltonians. However, in this case, each target Hamiltonian requires c = O(N) analog blocks, because the other analog blocks get can- celled. On the other hand, in total, the need for O(N) SWAP gates introduces O(N) analog blocks. Thus, the total number ...
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[13]
Therefore, the total number of two-qubit terms in all the analog blocks is O(N3)
Number of two-qubit terms: Each analog block contains c = O(N) two-qubit terms. Therefore, the total number of two-qubit terms in all the analog blocks is O(N3)
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[14]
Duration: The digital Star-QFT can be imple- mented in depth O(N2). In the digital-analog cir- cuit, the n-th target Hamiltonian has n null cou- pling coefficients (meaning that gjk = 0), which eliminates n − 1 analog blocks (recalling the dis- cussion of Eq. (39)). In addition, the difference between one coupling coefficient and the next de- creases expo...
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[15]
Thus, the total number of SQGs is O(N2)
Number of single-qubit gates: Each target Hamiltonian requires O(N) X gates. Thus, the total number of SQGs is O(N2)
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[16]
bDAQC non-commutativity: Each external qubit, on which X gates are applied, has one cou- pling, so from Eq. (29), each analog block intro- duces an infidelity that scales as O(1), when ∆ t, ¯g are set to be constant. There are O(N2) analog blocks, so the contribution to the compound fi- delity (see Eq. (35)) introduced by bDAQC scales as (1 − O(1))O(N 2)....
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All-to-all Quantum Fourier Transform As can be seen from Fig. 8a, the fidelities of QFT in both DAQC paradigms are below the fidelity in DQC over the entire range of the number of qubits N studied. One reason is that, even though each two-qubit term in analog blocks is more error-robust, the number of two- qubit terms is much smaller in DQC. For example, ...
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Star Quantum Fourier Transform From Fig. 8b, one can see that the fidelities for DAQC are also below the DQC fidelity for the whole range of N studied in this case. However, the fidelities of DAQC are higher with respect to the ATA case, as was expected from the analysis of the error scaling in Section V B. Thus, we see explicitly the dependence of the pe...
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Star GHZ state preparation In Fig. 8c, we can see that the fidelities for sDAQC are better than those of DQC, because the number of two- qubit terms is the same and the analog evolution is more resilient to the control errors. Additionally, and as expected, the time of the digital- analog algorithm is constant whereas that of the digital algorithm scales ...
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