QuMod: Parallel Quantum Job Scheduling on Modular QPUs using Circuit Cutting

Vinooth Kulkarni, Aaron Orenstein, Xinpeng Li, Shuai Xu, Daniel Blankenberg, Vipin Chaudhary

#550 of 2593 · Quantum Physics
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Tournament Score
1470±28
10501750
60%
Win Rate
26
Wins
17
Losses
43
Matches
Rating
3.8/ 10
Significance
Rigor
Novelty
Clarity

Abstract

The quantum computing community is increasingly positioning quantum processors as accelerators within classical HPC workflows, analogous to GPUs and TPUs. However, many real-world applications require scaling to hundreds or thousands of physical qubits to realize logical qubits via error correction. To reach these scales, hardware vendors employing diverse technologies -- such as trapped ions, photonics, neutral atoms, and superconducting circuits -- are moving beyond single, monolithic QPUs toward modular architectures connected via interconnects. For example, IonQ has proposed photonic links for scaling, while IBM has demonstrated a modular QPU architecture by classically linking two 127-qubit devices. Using dynamic circuits, Bell-pair-based teleportation, and circuit cutting, they have shown how to execute a large quantum circuit that cannot fit on a single QPU. As interest in quantum computing grows, cloud providers must ensure fair and efficient resource allocation for multiple users sharing such modular systems. Classical interconnection of QPUs introduces new scheduling challenges, particularly when multiple jobs execute in parallel. In this work, we develop a multi-programmable scheduler for modular quantum systems that jointly considers qubit mapping, parallel circuit execution, measurement synchronization across subcircuits, and teleportation operations between QPUs using dynamic circuits.

AI Impact Assessments

(3 models)

Scientific Impact Assessment: QuMod: Parallel Quantum Job Scheduling on Modular QPUs using Circuit Cutting

1. Core Contribution

QuMod proposes a parallel quantum job scheduler for modular quantum processing unit (QPU) architectures that integrates circuit cutting with two operational modes: Local Operations (LO) and Local Operations with Classical Communication (LOCC). The scheduler jointly handles qubit mapping, parallel circuit execution, measurement synchronization across subcircuits, and teleportation operations between QPUs. The key novelty lies in combining multi-programming scheduling (running multiple quantum jobs in parallel) with adaptive circuit cutting decisions on modular, classically-interconnected QPU systems. The scheduler dynamically decides whether and how to cut circuits, grouping upstream and downstream subcircuits while respecting causal ordering constraints imposed by LOCC's feed-forward requirements.

2. Methodological Rigor

The paper presents algorithms for scheduling (Algorithm 1), circuit cutting mode selection (Algorithm 2), and grouping with LO/LOCC constraints (Algorithm 3). The formalization of feasibility constraints (Equation 4), cost functions (Equations 5-7), and slot computation (Equation 8) provides a reasonable mathematical framework.

However, the evaluation has significant limitations:

  • Simulation-only evaluation: The entire evaluation uses a SimPy-based discrete-event simulator parameterized with IBM calibration data, not actual quantum hardware. While understandable given the nascent state of modular QPU architectures, this limits the credibility of fidelity claims.
  • Limited workload diversity: Only three workload scenarios are tested (small MQT-QUEKO circuits, large >127-qubit circuits, and a random heterogeneous mix of 158 circuits). The 50-job scheduling window is relatively small.
  • Incomplete baselines: The paper compares only QuMod LO vs. QuMod LOCC. There is no comparison against other scheduling approaches (e.g., FIFO, fair-share, or the prior work from references [11]-[16] that the paper builds upon). Without external baselines, it is difficult to assess relative improvement.
  • Fidelity metric concerns: LPST is used as a "fidelity-like reliability proxy," but the actual fidelity impact of circuit cutting (the additional variance from quasi-probability reconstruction) is not rigorously quantified. The noise model appears simplified.
  • Missing statistical analysis: Results in Table I are presented as single numbers without confidence intervals, error bars, or repeated trials, making it difficult to assess statistical significance.
  • 3. Potential Impact

    The problem addressed—scheduling quantum jobs on modular QPU architectures—is genuinely important for the future of quantum cloud computing. As vendors like IBM, IonQ, and others move toward modular designs, schedulers that understand circuit cutting tradeoffs will become essential infrastructure.

    However, the immediate practical impact is limited because:

  • Modular QPU architectures with classical interconnects are still extremely rare (essentially IBM's demonstration with two Eagle processors).
  • The sampling overhead of circuit cutting (even at 4^k for LOCC) remains a major practical barrier that limits the utility of cutting beyond a small number of cuts.
  • The paper does not address quantum error correction workloads, which would be the primary driver for modular architectures at scale.
  • 4. Timeliness & Relevance

    The paper is timely in the sense that modular quantum computing is an active research direction, and IBM's 2024 Nature demonstration of classically-linked QPUs validates the general premise. The quantum cloud scheduling problem will indeed become more important as quantum computing matures.

    However, the paper arrives at an awkward time—modular architectures are still too early-stage for the scheduling problem to be practically pressing, yet the theoretical framework presented is not deep enough to provide lasting algorithmic insights.

    5. Strengths & Limitations

    Strengths:

  • Addresses a real and emerging problem at the intersection of quantum computing and systems research
  • Clean algorithmic presentation with well-defined constraints and cost functions
  • Distinguishes between LO and LOCC modes with clear analysis of their scheduling implications (Section II.C is well-written)
  • Uses the qiskit-addon-cutting library, grounding the work in practical tooling
  • The grouping algorithm (Algorithm 3) with upstream/downstream conflict detection is a reasonable and novel contribution
  • Limitations:

  • No comparison to prior work: The paper builds on QGroup [12] and QuFlex [13] (by some of the same authors) but never directly compares against them. This makes incremental improvement hard to assess.
  • Scalability unclear: The evaluation uses at most 158 circuits and 11 simulated backends. How the approach scales to larger job queues and more diverse modular topologies is unknown.
  • Oversimplified communication model: The classical communication delay (Equation 3) is a simple linear model. Real classical interconnects have more complex latency characteristics.
  • No analysis of cut placement quality: The paper relies on qiskit-addon-cutting for determining where to cut, without analyzing whether different cut placements would yield better scheduling outcomes.
  • Writing quality: The paper reads more like a workshop or short paper than a full conference contribution. The evaluation section is thin, and the related work is scattered throughout rather than consolidated.
  • Incremental over authors' prior work: QuMod appears to be a relatively straightforward extension of QGroup and QuFlex to the modular setting, adding LOCC-awareness and upstream/downstream grouping constraints.
  • Reproducibility: While the simulator is described, no code or data is released.
  • Overall Assessment

    QuMod addresses a valid problem in quantum systems research and presents a reasonable first-cut solution for scheduling on modular QPU architectures. However, the evaluation is too limited to convincingly demonstrate the approach's benefits, the lack of baselines beyond self-comparison (LO vs. LOCC) weakens the contribution, and the work appears incremental over the authors' prior scheduling papers. The paper would benefit substantially from hardware validation (even on IBM's two-QPU system), stronger baselines, and deeper analysis of the scheduling quality-fidelity tradeoff.

    Rating:3.8/ 10
    Significance 4.5Rigor 3Novelty 4Clarity 5

    Generated Apr 14, 2026

    Comparison History (43)

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    Paper 1 addresses a critical systemic bottleneck in quantum computing scalability: managing and scheduling resources across modular Quantum Processing Units (QPUs). As hardware vendors pivot to modular architectures to scale towards fault tolerance, effective job scheduling, circuit cutting, and interconnect management become essential. This systems-level contribution has broad implications for integrating quantum accelerators into classical HPC workflows. Paper 2 offers a practical but narrower data-processing optimization specifically for near-term quantum machine learning, limiting its overall infrastructural impact compared to Paper 1.

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    Paper 2 introduces a simple, broadly applicable technique (split-ensemble training) that improves near-term quantum machine learning without additional hardware cost. Its practical applicability across existing quantum hardware and algorithmic generality give it immediate impact. Paper 1 addresses an important but narrower scheduling problem for modular QPUs—a relevant engineering contribution, but its impact is constrained to a specific architectural paradigm still under development. Paper 2's low barrier to adoption, hardware validation, and relevance to the large near-term quantum computing community give it higher potential impact.

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