Observation of feedback-directed quantum dynamics in large-scale quantum processors
Pith reviewed 2026-05-10 15:51 UTC · model grok-4.3
The pith
Feedback-directed measurements steer random quantum dynamics to produce intrinsic asymmetry on large-scale processors.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Feedback-directed circuit architectures integrate spatially structured mid-circuit measurements with real-time conditional operations to steer the evolution of random dynamics, thereby generating directional information flow and intrinsic asymmetry that is observed in a robust and noise-resilient manner on IBM quantum processors and is distinct from the non-Hermitian skin effect.
What carries the argument
Feedback-directed monitored circuits in which measurement outcomes serve as active control signals to direct non-unitary evolution and create asymmetry.
Load-bearing premise
The quantum hardware executes the intended mid-circuit measurements and conditional operations faithfully enough that the observed asymmetry originates from the feedback design rather than from noise or calibration artifacts.
What would settle it
Running the same circuits on the processor but with the conditional feedback operations disabled while retaining the mid-circuit measurements, and checking whether the reported asymmetry signature disappears.
Figures
read the original abstract
Programmable quantum hardware provides an emerging platform for exploring and controlling non-unitary quantum dynamics through measurement-based operations. In this work, we introduce feedback-directed circuit architectures that integrate spatially structured mid-circuit measurements with real-time conditional operations to steer the evolution of random dynamics, and perform their large-scale simulations (up to 100 qubits) on programmable digital quantum processors. By promoting measurement from a passive readout to an active control signal, these adaptive monitored circuits enable directional information flow and generate intrinsic asymmetry in random circuit simulations. We implement this framework on IBM superconducting quantum processors and observe robust, noise-resilient signatures of feedback-induced asymmetry distinct from the more well-known non-Hermitian skin effect. Our results establish feedback as a programmable resource for non-unitary control, opening new avenues for engineering measurement-based dynamics, non-equilibrium phenomena, and tunable open-system behavior on large-scale quantum hardware.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript introduces feedback-directed circuit architectures that integrate spatially structured mid-circuit measurements with real-time conditional operations to steer the evolution of random quantum dynamics. Large-scale simulations (up to 100 qubits) are performed classically, and the framework is implemented on IBM superconducting quantum processors, where the authors report observing robust, noise-resilient signatures of feedback-induced asymmetry that are claimed to be distinct from the non-Hermitian skin effect.
Significance. If the experimental results hold and the observed asymmetry can be rigorously attributed to the feedback mechanism rather than hardware artifacts, this would constitute a meaningful contribution to the study of measurement-based non-unitary dynamics. It positions feedback as a programmable control resource on current quantum hardware, with potential implications for engineering open-system behavior and non-equilibrium phenomena. The classical simulations up to 100 qubits provide a useful benchmark for the ideal case.
major comments (1)
- The central experimental claim (abstract and hardware implementation section) that mid-circuit measurements plus real-time conditionals produce directional asymmetry distinct from the non-Hermitian skin effect rests on the unverified assumption that IBM hardware faithfully realizes the intended architecture. The manuscript must include quantitative control experiments (e.g., delayed feedback, randomized conditionals) and comparisons against realistic noise models to demonstrate that latency, readout errors, and calibration artifacts do not dominate or mimic the reported signatures; without these, the robustness and distinction claims cannot be assessed.
minor comments (1)
- The abstract would benefit from explicit numerical metrics (e.g., asymmetry measures, error bars, or statistical significance) for the 'robust, noise-resilient signatures' to allow immediate evaluation of the observation strength.
Simulated Author's Rebuttal
We thank the referee for the constructive review and for highlighting the importance of rigorously validating the experimental implementation against hardware artifacts. We address the major comment below and will strengthen the manuscript accordingly.
read point-by-point responses
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Referee: The central experimental claim (abstract and hardware implementation section) that mid-circuit measurements plus real-time conditionals produce directional asymmetry distinct from the non-Hermitian skin effect rests on the unverified assumption that IBM hardware faithfully realizes the intended architecture. The manuscript must include quantitative control experiments (e.g., delayed feedback, randomized conditionals) and comparisons against realistic noise models to demonstrate that latency, readout errors, and calibration artifacts do not dominate or mimic the reported signatures; without these, the robustness and distinction claims cannot be assessed.
Authors: We agree that additional quantitative controls are required to substantiate that the observed asymmetry arises from the feedback mechanism rather than hardware-specific effects. The current manuscript compares experimental data to ideal classical simulations up to 100 qubits and notes qualitative differences from the non-Hermitian skin effect, but does not include the specific controls suggested. In the revised manuscript we will add a dedicated subsection presenting: (i) delayed-feedback control runs in which the conditional operations are intentionally postponed by several circuit layers, (ii) randomized-conditional runs that replace the structured feedback with random bit flips of equal probability, and (iii) direct comparisons of the measured asymmetry against noise models constructed from IBM’s reported readout and gate-error calibrations for the same device. These additions will allow readers to assess whether the reported signatures survive when the intended feedback architecture is disrupted or when realistic noise is applied. revision: yes
Circularity Check
No significant circularity in experimental observation and simulation
full rationale
The paper introduces feedback-directed circuit architectures and reports their implementation on IBM superconducting quantum processors along with classical simulations up to 100 qubits. The central claims consist of direct experimental observations of feedback-induced asymmetry, presented as hardware results rather than any mathematical derivation or prediction that reduces to fitted parameters, self-citations, or ansatzes by construction. No load-bearing step equates an output to its own inputs via definition or prior author work; the architecture is defined and executed explicitly, with asymmetry signatures distinguished from the non-Hermitian skin effect through comparison of observed data. This is self-contained experimental work with independent content from hardware execution and simulation.
Axiom & Free-Parameter Ledger
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Reference graph
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1(a), which serves to ef- fect information scrambling [61, 70, 71]
Unitary random circuit without measurements and feedback As the most basic example, we consider the random quantum-circuit ansatz in Fig. 1(a), which serves to ef- fect information scrambling [61, 70, 71]. Its architecture 3 Random circuit + single-qubit conditional X operators If 0 Measurement with conditional SWAP Classical register = SWAP R Random R ga...
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1(b)) after each random unitary layer (blue) at every iteration i
Random circuit with pure mid-circuit measurements To generate non-unitary, measurement-induced dy- namics, the most direct approach is to stochastically ap- ply mid-circuit measurements (red boxes in Fig. 1(b)) after each random unitary layer (blue) at every iteration i. One layer of evolution is then described by the quan- tum channel ρ7→M Pure meas(ρscr...
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We first consider the single-qubit feedback protocol of Eq
Random circuit with conditional single-qubit X operators To implement asymmetrically directed feedback, we now attach conditional operations to the mid-circuit mea- surements. We first consider the single-qubit feedback protocol of Eq. 3, illustrated by the purple boxes in Fig. 1(c). In this protocol, if qubitjis measured and the outcome is 0, a condition...
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Random circuit with conditional 2-qubit SWAP operators To realize asymmetrically directed feedback, we next consider a more sophisticated protocol based on two- qubit conditional-SWAP operations, as described by Eq. 4 and illustrated in Fig. 1(d). In this architecture, each green block denotes a measurement-conditioned op- eration applied with fixed proba...
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Effective stochastic model for feedback-directed dynamics To further understand the measurement feedback dy- namics, we provide a complementary approximate de- scription of it from a stochastic perspective. In our measurement-based circuits, the dynamics between mea- surement events are largely governed by the unitary scrambling layers. Mid-circuit measur...
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Quantitative characterization of the extent of dynamical feedback We next quantitatively characterize the measured dy- namical evolution in the 100-qubit chain subject to con- ditional spin flips. To isolate initial boundary effects, we 8 consider the net center-of-mass shift at iteration (time)i δN c(i) =L(⟨N c(i)⟩ − ⟨N c(1)⟩),(24) whereLis the system si...
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Measurements of robust transport signatures The above results demonstrate that mid-circuit mea- surements combined with conditional operations can gen- erate a robust directional flow that remains observable up to system sizes of 100 qubits. For larger systems, how- ever, the dynamics naturally spread over an extended bulk region, so the feedback-induced ...
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is described by the local quantum channel Ex,x+1(ρ) =K 0ρK † 0 +K 1ρK † 1 +K idρK † id,(26) with Kraus operatorsK 0 =p pSWAPSWAPx,x+1Px[0], K1 = p pSWAP Px[1], Kid =p 1−p SWAP I.HereP x[0] =|0⟩ ⟨0|andP x[1] =|1⟩ ⟨1| project onto the measured outcomes at qubitx. Thus, with probabilityp SWAP, qubitxis measured; if the outcome is 0, a SWAP is applied between...
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