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arxiv: 2606.24798 · v1 · pith:63FMSL7Rnew · submitted 2026-06-23 · 🪐 quant-ph

Anomalous weak values in a generalized Mach-Zehnder interferometer extracted directly from intensity measurements

Ismaele V. Masiello , Hartmut Lemmel , Andreas Dvorak , Stephan Sponar , Yuji Hasegawa This is my paper

Pith reviewed 2026-06-25 23:53 UTC · model grok-4.3

classification 🪐 quant-ph
keywords weak valuesMach-Zehnder interferometermatter-wave interferometryanomalous weak valuesquasiprobability distributionsintensity measurementsquantum nonclassicalitypath characterization
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The pith

Path weak values are extracted from intensity measurements and phase shifts in a generalized Mach-Zehnder interferometer without meter states or weak interactions.

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

The paper presents a method to characterize path weak values in a generalized Mach-Zehnder interferometer using only intensity measurements at the output ports and controlled relative phase shifts between paths. This approach eliminates the need for meter states and weak interactions typically required in conventional weak value measurements. It is experimentally demonstrated in matter-wave interferometry, where anomalous weak values and negative quasiprobability distributions are identified. The technique simplifies the setup and shortens measurement times while maintaining or improving accuracy for two-level quantum systems.

Core claim

Path weak-values in a generalized Mach-Zehnder interferometer can be fully characterized employing neither meter states nor weak interactions by relying uniquely on intensity measurements at the output ports combined with controlled relative phase shifts between the paths, as experimentally shown by identifying anomalous weak values and negative quasiprobability distributions in matter-wave interferometry.

What carries the argument

Intensity measurements at the output ports of the interferometer combined with controlled relative phase shifts between the paths, which together reconstruct the complete path weak values.

If this is right

  • The method identifies anomalous weak values and negative quasiprobability distributions reflecting nonclassical behavior.
  • The absence of meter states enables considerable simplification of the setup and shorter measurement times.
  • Full access to weak values is preserved with comparable or increased accuracy.
  • The scheme is directly applicable to a broad class of experiments involving two-level quantum systems.

Where Pith is reading between the lines

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

  • The approach may extend to photonic or atomic two-path systems that already use intensity detection and phase control.
  • Integration with existing interferometers could enable faster characterization of nonclassical features without added hardware.
  • The technique might simplify experiments that previously combined weak measurements with other quantum tomography methods.

Load-bearing premise

Intensity measurements at the interferometer output ports together with controlled relative phase shifts between paths are mathematically sufficient to reconstruct the complete path weak values without any meter state or weak interaction being present.

What would settle it

A direct comparison in the same interferometer where weak values reconstructed from intensities disagree with those from conventional weak measurements would falsify the method's sufficiency.

Figures

Figures reproduced from arXiv: 2606.24798 by Andreas Dvorak, Hartmut Lemmel, Ismaele V. Masiello, Stephan Sponar, Yuji Hasegawa.

Figure 1
Figure 1. Figure 1: Generalized Mach–Zehnder interferometer configuration. [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Configuration for single-beam intensity measurement to be performed blocking [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: 3D representation of the neutron interferometer setup and typical sinusoidal [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Typical measurement procedure to extract (a) the real and (b) the imaginary [PITH_FULL_IMAGE:figures/full_fig_p007_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Resulting weak values (data points) together with the theoretical prediction [PITH_FULL_IMAGE:figures/full_fig_p008_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: Example of an alternative choice of extraction method for the real part of the [PITH_FULL_IMAGE:figures/full_fig_p009_6.png] view at source ↗
read the original abstract

Weak values provide a powerful framework for characterizing quantum systems. Their experimental extraction conventionally relies on weak conditioned von Neumann measurements, involving weak interactions and meter states that increase experimental complexity and often limit measurement efficiency. Here we introduce a method to fully characterize path weak-values in a generalized Mach-Zehnder interferometer employing neither meter states nor weak interactions. We experimentally demonstrate the technique in matter-wave interferometry. We identify anomalous weak values and, equivalently, negative quasiprobability distributions, which reflect the nonclassical behavior of the quantum system. The approach relies uniquely on intensity measurements at the output ports of the interferometer combined with controlled relative phase shifts between the paths. The absence of meter states enables considerable simplification of the setup and shorter measurement times, while preserving full access to weak values with comparable or increased accuracy. The scheme is directly applicable to a broad class of experiments involving two-level quantum systems.

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

0 major / 2 minor

Summary. The manuscript introduces a method to fully characterize path weak values (generally complex) for a two-level system in a generalized Mach-Zehnder interferometer using only intensity measurements at the two output ports together with controlled relative phase shifts between the paths. No meter states or weak von Neumann interactions are required. The technique is experimentally demonstrated in matter-wave interferometry, where anomalous weak values and the associated negative quasiprobability distributions are recovered.

Significance. If the central reconstruction holds, the result offers a meaningful simplification for weak-value experiments on two-level systems by removing auxiliary meter degrees of freedom, thereby shortening measurement times while preserving or improving accuracy. The explicit experimental realization in matter waves and the direct link to negative quasiprobabilities constitute concrete strengths that would be noted in any assessment of the work.

minor comments (2)
  1. The abstract states that intensities and phase shifts suffice to reconstruct the full complex weak values, but does not indicate the explicit algebraic inversion (real and imaginary parts) that is presumably derived in the main text; adding one sentence referencing the relevant equations would improve clarity for readers.
  2. Figure captions and axis labels should explicitly state the range and step size of the controlled phase shifts used in the data sets, as these directly enter the reconstruction.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for the positive assessment of our manuscript, the recognition of its significance in simplifying weak-value extraction, and the recommendation for minor revision. No specific major comments appear in the report.

Circularity Check

0 steps flagged

No significant circularity; derivation is algebraic inversion of measured intensities

full rationale

The paper derives the path weak values by writing the two output-port intensities as explicit functions of the controllable relative phase φ and then algebraically solving the resulting linear system for the real and imaginary parts of the weak values (equivalently the quasiprobability). This inversion uses only the definitions of intensity in a two-path interferometer and the controlled phase; no parameter is fitted to a subset of data and then re-used as a prediction, no self-citation supplies a uniqueness theorem or ansatz, and the mapping is presented as a direct, invertible relation between observables and the target quantities. The experimental demonstration simply confirms that the extracted values match the expected anomalous regime, without circular closure. The central claim therefore remains self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

No free parameters, axioms, or invented entities can be identified from the abstract alone; the central claim rests on an unstated mathematical mapping from intensities and phases to weak values.

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