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arxiv: 2604.19115 · v1 · submitted 2026-04-21 · 🪐 quant-ph

Wave--particle transition and quantum Zeno effect in which-way experiments with a superconducting quantum processor

Shiyu Wang , Zhiguang Yan , Clemens Gneiting , Rui Li , Franco Nori , Yasunobu Nakamura This is my paper

Pith reviewed 2026-05-10 03:05 UTC · model grok-4.3

classification 🪐 quant-ph
keywords wave-particle dualityquantum Zeno effectwhich-way experimentMach-Zehnder interferometersuperconducting quantum processorquantum complementarityinformation leakagefringe visibility
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The pith

Precise control of which-way measurement strength in a superconducting Mach-Zehnder interferometer demonstrates the wave-to-particle transition of a photon and the quantum Zeno effect under continuous monitoring.

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

The paper implements a Mach-Zehnder interferometer on a two-dimensional superconducting quantum processor to study wave-particle duality through tunable which-way measurements. Varying the measurement strength on one path shows the photon shifting from producing interference fringes to revealing which-path information. State tomography on the path qubits confirms that stronger measurements destroy entanglement and coherence while leaking information to the environment, which the authors quantify through derived relations linking entropy to fringe visibility. Applying the measurement continuously during evolution reveals the quantum Zeno effect, where the path is partially obstructed and purity along with von Neumann entropy display nonmonotonic behavior. These results connect complementarity to quantum information measures in a hardware platform with high controllability.

Core claim

In which-way experiments on a two-dimensional superconducting quantum processor, varying the measurement strength on one path of a Mach-Zehnder interferometer causes a photon to transition from exhibiting wave-like interference to particle-like which-path knowledge. Quantum state tomography on the two path qubits shows that stronger measurements break the entanglement and coherence, leading to information leakage quantified by complementarity relations between entropy and fringe visibility. Continuous application of the which-way measurement during evolution induces the quantum Zeno effect, resulting in nonmonotonic changes in purity and von Neumann entropy as the path is partially blocked.

What carries the argument

The tunable-strength which-way measurement applied to one arm of the Mach-Zehnder interferometer realized with superconducting qubits, which tunes the trade-off between path distinguishability and interference visibility while enabling continuous monitoring for Zeno dynamics.

If this is right

  • Increasing which-way measurement strength reduces interference visibility while increasing path distinguishability according to complementarity.
  • Which-way measurements destroy entanglement between the two paths and cause measurable information leakage to the environment.
  • Continuous which-way monitoring partially obstructs the interferometer path and produces nonmonotonic evolution of purity and von Neumann entropy.
  • The derived entropy-visibility relations quantify how measurement strength controls the wave-particle transition in the tomographic data.

Where Pith is reading between the lines

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

  • The platform's controllability over measurement strength could allow systematic tests of other complementarity scenarios, such as delayed-choice variants, without changing hardware.
  • The observed link between which-way information and entropy leakage suggests using similar qubit readouts to engineer controlled decoherence in quantum information protocols.
  • Nonmonotonic entropy under continuous monitoring points to potential uses in measurement-based state protection schemes where partial obstruction stabilizes certain dynamics.

Load-bearing premise

The superconducting qubits and readout faithfully implement ideal photon paths and which-way detectors without dominant uncontrolled decoherence, calibration errors, or tomography inaccuracies that would mimic the reported transitions and Zeno dynamics.

What would settle it

If the measured fringe visibility fails to decrease monotonically with increasing which-way measurement strength in agreement with the tomographic entropy values, or if continuous monitoring does not produce the predicted nonmonotonic purity and entropy curves, the claimed wave-particle transition and Zeno obstruction would not hold.

Figures

Figures reproduced from arXiv: 2604.19115 by Clemens Gneiting, Franco Nori, Rui Li, Shiyu Wang, Yasunobu Nakamura, Zhiguang Yan.

Figure 1
Figure 1. Figure 1: Experimental setup and quantum circuits. a, False-colored optical image of the 16-qubit superconducting chip. The 16-qubit chip has a 4×4 qubit array composed of four units; each unit contains four frequency-tunable transmons (orange). Each qubit is coupled to an individual λ/4 readout resonator (brown), and the four readout resonators within the same unit are coupled to a common Purcell filter (pink). Nei… view at source ↗
Figure 2
Figure 2. Figure 2: Evolution and interference pattern of the 4-qubit MZ interferometer. a, Evolution of the population ⟨nˆi⟩ in Qi (i = 0, 1, 2) from t = 0 ns to t = 80 ns. The photon initially generated at Q0 propagates to Q1 and Q2. For the subsequent which-way measurement experiments, we decouple the qubits when the population of Q0 reaches its minimum. b, Numerical simulation of the population evolution under the same co… view at source ↗
Figure 3
Figure 3. Figure 3: Quantum Zeno effect in the 12-qubit MZ interferometer. a–d, Evolution of Qi’s population ⟨nˆi⟩ from t = 0 ns to t = 200 ns under the which-way measurement-induced dephasing rate Γm/2π = 0, 5.921, 11.195, and 18.134 MHz, respectively. Path 2 of the MZ interferometer is blocked by the quantum Zeno effect as the which-way measurement strength applied to Q2 increases. e–h, Numerical simulations of the populati… view at source ↗
Figure 4
Figure 4. Figure 4: Relations between quantum information, which-way measurement-induced dephasing rate, and visibility of the MZ interferometers. a–e refer to the 4-qubit MZ interferometer, while f–h correspond to the 12-qubit MZ interferometer. a, Concurrence CQ1Q2 of Q1 and Q2 vs. the average which-way measurement-induced dephasing rate Γm. b, Purity Ps in the single-excitation subspace vs. Γm. c, Von Neumann entropy Ss in… view at source ↗
read the original abstract

Wave--particle duality demonstrates the peculiar nature of quantum mechanics. In which-way experiments, depending on the measurement scheme, a particle exhibits either wave-like or particle-like properties, as summarized by Bohr's principle of complementarity. In this work, we implement Mach-Zehnder (MZ) interferometry on a two-dimensional (2D) superconducting quantum processor. With precise control of the which-way measurement strength, we demonstrate the transition of a photon from wave-like to particle-like behavior. Furthermore, by performing quantum state tomography on two qubits located in the two paths, we demonstrate that which-way measurements break the entanglement and coherence between the two paths and cause information leakage from the quantum system to the environment. To capture this behavior quantitatively, we derive complementarity relations between the entropy and the fringe visibility. By applying a continuous which-way measurement during the evolution, we also observe the quantum Zeno effect that partially obstructs the interferometer path, giving rise to nonmonotonic behavior of purity and von Neumann entropy. Our experiments provide a detailed characterization of the full interferometer dynamics, reveal the relation between wave--particle duality and quantum information, and demonstrate the potential of superconducting quantum processors for testing quantum foundations under high precision and controllability.

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

3 major / 2 minor

Summary. The manuscript reports an experimental implementation of Mach-Zehnder interferometry on a 2D superconducting quantum processor. By tuning the strength of which-way measurements, it demonstrates the transition from wave-like to particle-like photon behavior. Quantum state tomography on the two path qubits shows entanglement breaking and information leakage to the environment. Complementarity relations are derived between entropy and fringe visibility. Continuous which-way measurements are used to observe the quantum Zeno effect, manifested as nonmonotonic behavior in purity and von Neumann entropy.

Significance. If the central claims hold after addressing controls for device noise, the work offers a controlled superconducting-platform demonstration of wave-particle duality, Bohr complementarity, and the Zeno effect, with explicit connections to quantum-information quantities (entropy, entanglement). The ability to tune measurement strength and perform tomography provides a quantitative link between which-way information gain and loss of coherence, which is valuable for foundations experiments. The platform's controllability could enable extensions to more complex interferometric tests.

major comments (3)
  1. [Zeno-effect results] The reported nonmonotonic purity and von Neumann entropy under continuous which-way measurement (abstract and results on Zeno dynamics) lack error bars, statistical significance tests, or explicit comparison to zero-measurement-strength controls. Without these, it is unclear whether the nonmonotonicity exceeds fluctuations or uncontrolled decoherence.
  2. [Experimental implementation and tomography] No device-specific noise model (T1/T2 times, gate infidelities, readout crosstalk) or numerical simulation is presented showing that the observed visibility transition and entropy changes cannot be reproduced by hardware imperfections alone. This is load-bearing for the claim that the behaviors arise from intended which-way information gain and Zeno obstruction rather than artifacts.
  3. [Complementarity relations] The complementarity relations between entropy and fringe visibility are stated as derived post-experiment, but the manuscript does not show whether they are used to predict or fit the data or remain purely descriptive; this affects the strength of the quantitative link claimed between duality and quantum information.
minor comments (2)
  1. [Methods] The abstract and methods would benefit from explicit reporting of the number of experimental repetitions, tomography reconstruction method, and how measurement strength is calibrated and verified.
  2. [Figures] Figure captions should include error estimation procedures and any averaging over runs to improve reproducibility.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for their thorough review and constructive comments on our manuscript. We address each major point below and have revised the manuscript to incorporate the requested clarifications and additions.

read point-by-point responses

  1. Referee: [Zeno-effect results] The reported nonmonotonic purity and von Neumann entropy under continuous which-way measurement (abstract and results on Zeno dynamics) lack error bars, statistical significance tests, or explicit comparison to zero-measurement-strength controls. Without these, it is unclear whether the nonmonotonicity exceeds fluctuations or uncontrolled decoherence.

    Authors: We appreciate the referee highlighting the need for statistical rigor in the Zeno-effect section. The nonmonotonic behavior was observed experimentally, but error bars and formal tests were omitted from the initial submission. In the revised manuscript we will add error bars from repeated runs, include statistical significance tests (e.g., t-tests against a null hypothesis of monotonic decay), and present zero-measurement-strength control data to confirm that the observed nonmonotonicity in purity and entropy exceeds fluctuations and uncontrolled decoherence. revision: yes

  2. Referee: [Experimental implementation and tomography] No device-specific noise model (T1/T2 times, gate infidelities, readout crosstalk) or numerical simulation is presented showing that the observed visibility transition and entropy changes cannot be reproduced by hardware imperfections alone. This is load-bearing for the claim that the behaviors arise from intended which-way information gain and Zeno obstruction rather than artifacts.

    Authors: We agree that a quantitative noise model is essential to substantiate the claims. The original manuscript described the device but did not include a comprehensive noise characterization or simulations. The revision will add measured T1/T2 times, gate infidelities, and readout crosstalk values for the qubits involved, together with numerical simulations of the interferometer dynamics that incorporate these parameters. These simulations will demonstrate that the observed visibility transition, entanglement breaking, and Zeno dynamics cannot be reproduced by hardware noise alone. revision: yes

  3. Referee: [Complementarity relations] The complementarity relations between entropy and fringe visibility are stated as derived post-experiment, but the manuscript does not show whether they are used to predict or fit the data or remain purely descriptive; this affects the strength of the quantitative link claimed between duality and quantum information.

    Authors: The complementarity relations were derived from quantum-information principles before the experiments and subsequently applied to the data. To make this explicit, the revised manuscript will show the relations used to fit the measured visibility-versus-entropy data points and will include plots comparing the theoretical curves with experimental results, thereby demonstrating their predictive and quantitative role rather than a purely descriptive one. revision: yes

Circularity Check

0 steps flagged

No circularity: experimental data and tomography drive claims; derived relations are post-hoc and independent

full rationale

The paper reports direct implementation of MZ interferometry on a 2D superconducting processor, with tunable which-way measurement strength, quantum state tomography on path qubits, and continuous monitoring to observe Zeno-induced nonmonotonic purity/entropy. Complementarity relations between entropy and fringe visibility are derived to quantify observed behavior but are not inputs to data generation, fitting procedures, or predictions that reduce to the same measurements by construction. No self-definitional loops, fitted inputs renamed as predictions, load-bearing self-citations, uniqueness theorems imported from prior author work, or ansatz smuggling appear in the derivation chain. The central results rest on hardware-controlled experiments and tomography rather than tautological reductions, making the logic self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claims rest on standard quantum mechanics without new free parameters or invented entities; the measurement strength is an experimental control knob rather than a fitted constant.

axioms (1)
  • domain assumption Bohr complementarity and standard unitary evolution plus projective measurements apply to the superconducting circuit implementation.
    Invoked throughout the description of wave-particle transition and Zeno dynamics.

pith-pipeline@v0.9.0 · 5531 in / 1189 out tokens · 44373 ms · 2026-05-10T03:05:20.077060+00:00 · methodology

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Forward citations

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