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arxiv: 2606.31053 · v1 · pith:W5G5T4APnew · submitted 2026-06-30 · 🪐 quant-ph

Generalised quantum interference

Sebastian Malewicz , Laura Serino , Marcelo P. de Almeida , Markus Rambach , Ming Su , Jihun Cha , Till J. Weinhold , Austin Lund
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A. G. White
This is my paper

Pith reviewed 2026-07-01 05:56 UTC · model grok-4.3

classification 🪐 quant-ph
keywords Hong-Ou-Mandel interferencetwo-photon statesquantum bunchingbeam splitter asymmetryphotonic processorforbidden channelsindistinguishable photons
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The pith

Imbalanced two-photon states on a tunable beam splitter break Hong-Ou-Mandel symmetry and create a forbidden bunching channel at one output port.

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

The paper demonstrates that the usual bunching of identical photons at a beam splitter can be modified by preparing states with controlled imbalance. Experiments using a programmable integrated photonic processor show that the output probabilities can be tuned continuously by varying the imbalance. In the extreme case, destructive interference completely suppresses photon bunching at one specific port while allowing it at the other or in separate ports. This generalizes a foundational quantum interference effect by showing how asymmetry in the input states directs the interference outcome.

Core claim

The asymmetry creates a forbidden bunching channel: photons may exit together at one port or separately at both ports, but cannot emerge together at the other port. This is achieved by interfering imbalanced two-photon states on a variable beam splitter, where the output state of quantum interference can be continuously tuned.

What carries the argument

Imbalanced two-photon states interfered on a programmable variable beam splitter, which directs destructive interference to suppress specific output channels.

If this is right

  • Output port selection for photon bunching can be controlled by adjusting the degree of imbalance in the input states.
  • Destructive quantum interference can be directed to eliminate specific bunching events without altering the beam splitter itself.
  • The output state can be tuned between symmetric bunching, separate exits, and asymmetric suppression through continuous variation of the input imbalance.

Where Pith is reading between the lines

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

  • The same imbalance principle could be applied to control interference in multi-photon or higher-dimensional photonic systems.
  • Programmable processors might enable dynamic switching between different interference regimes in a single device.
  • The forbidden channel provides a new degree of freedom for designing photon routing rules based on quantum statistics.

Load-bearing premise

The prepared two-photon states remain sufficiently indistinguishable in all degrees of freedom except the controlled imbalance, so that the observed tuning arises from quantum interference rather than classical distinguishability or experimental artifacts.

What would settle it

Observing a non-zero rate of coincident photon detections at the suppressed output port when the input imbalance is set to its extreme value would falsify the forbidden bunching channel.

Figures

Figures reproduced from arXiv: 2606.31053 by A. G. White, Austin Lund, Jihun Cha, Laura Serino, Marcelo P. de Almeida, Markus Rambach, Ming Su, Sebastian Malewicz, Till J. Weinhold.

Figure 1
Figure 1. Figure 1: Conceptual comparison of Hong-Ou-Mandel (HOM) interference and generalised two-photon quantum in￾terference at the asymmetric point. (a) In HOM interference, two indistinguishable photons entering different input ports of a balanced beam splitter interfere such that the coinci￾dence output is suppressed, leaving a superposition of the two bunched outputs. (b) In asymmetric quantum interfer￾ence, an imbalan… view at source ↗
Figure 2
Figure 2. Figure 2: Optical circuit implemented in the photonic pro [PITH_FULL_IMAGE:figures/full_fig_p002_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Output-state probabilities at the asymmetric in [PITH_FULL_IMAGE:figures/full_fig_p002_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Output-state probabilities as a function of the [PITH_FULL_IMAGE:figures/full_fig_p003_4.png] view at source ↗
read the original abstract

Hong-Ou-Mandel interference is one of the clearest signatures of quantum behaviour: two identical photons meeting at a beam splitter always leave together. Here we demonstrate that this symmetry can be broken. Using a programmable integrated photonic processor, we interfere imbalanced two-photon states on a variable beam splitter and show that the output state of quantum interference can be continuously tuned, reaching the extreme case where destructive interference suppresses bunching at one output port. The asymmetry creates a forbidden bunching channel: photons may exit together at one port or separately at both ports, but cannot emerge together at the other port.

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

2 major / 1 minor

Summary. The paper claims to experimentally demonstrate generalized quantum interference beyond the symmetric Hong-Ou-Mandel effect. Using a programmable integrated photonic processor, imbalanced two-photon states are interfered on a variable beam splitter, allowing continuous tuning of the output state to the point where asymmetry produces destructive interference that strictly suppresses photon bunching at one output port while permitting it at the other or in separate ports.

Significance. If the experimental attribution to quantum interference holds after verification, the result would extend a foundational quantum optics phenomenon to asymmetric cases, enabling new forms of control over multi-photon interference with relevance to photonic quantum information processing. The programmable platform is noted as a methodological strength for tunability.

major comments (2)
  1. [Abstract and Experimental Results] The abstract reports an experimental result demonstrating tunable interference and a forbidden bunching channel, but supplies no data, error bars, visibility curves, or controls. This absence makes it impossible to verify the central claim or assess whether the observed suppression arises from the described generalized interference.
  2. [Methods and Results] The weakest assumption—that the imbalanced two-photon states remain indistinguishable in all degrees of freedom except the controlled imbalance—is not supported by explicit checks (e.g., full HOM visibility measurements or multi-parameter overlap data). Without these, classical path distinguishability cannot be excluded as an alternative explanation for the port-specific suppression.
minor comments (1)
  1. Clarify the quantitative range of the beam-splitter reflectivity over which the forbidden channel is observed and report the achieved visibility or suppression factor.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful review and constructive comments. We address each major comment below, providing clarifications from the full manuscript and indicating where revisions will strengthen the presentation of data and controls.

read point-by-point responses

  1. Referee: [Abstract and Experimental Results] The abstract reports an experimental result demonstrating tunable interference and a forbidden bunching channel, but supplies no data, error bars, visibility curves, or controls. This absence makes it impossible to verify the central claim or assess whether the observed suppression arises from the described generalized interference.

    Authors: Abstracts are necessarily concise and do not contain raw data or figures. The full manuscript includes detailed experimental results with figures showing measured coincidence rates, error bars, visibility curves for the tunable interference, and control measurements in the Results section. We will revise the abstract to include a brief quantitative reference to the key visibility achieved and add explicit cross-references to the supporting figures and data. revision: yes

  2. Referee: [Methods and Results] The weakest assumption—that the imbalanced two-photon states remain indistinguishable in all degrees of freedom except the controlled imbalance—is not supported by explicit checks (e.g., full HOM visibility measurements or multi-parameter overlap data). Without these, classical path distinguishability cannot be excluded as an alternative explanation for the port-specific suppression.

    Authors: The manuscript reports HOM visibility measurements on the photon-pair source and discusses state preparation for the imbalanced case. We agree that additional explicit characterization for the imbalanced states would further exclude classical alternatives. We will expand the Methods section with multi-parameter overlap data and any available full visibility curves for the imbalanced inputs in the revised version. revision: partial

Circularity Check

0 steps flagged

No circularity: experimental demonstration with no derivation chain

full rationale

The manuscript is an experimental report on interfering imbalanced two-photon states in a programmable photonic processor to observe tunable output statistics, including suppression of one bunching channel. No equations, ansatzes, fitted parameters, or uniqueness theorems are presented that could reduce to inputs by construction. The central claim rests on measured coincidence counts and visibility under controlled imbalance, not on self-citation chains or redefinitions. The provided abstract and reader's assessment correctly identify the work as an experimental demonstration free of the enumerated circularity patterns.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

No derivation or model is given; the result rests on standard quantum optics assumptions about photon indistinguishability and beam-splitter unitarity. No free parameters, invented entities, or non-standard axioms are visible in the abstract.

axioms (1)
  • domain assumption Two photons prepared in imbalanced states remain quantum-mechanically indistinguishable except for the controlled imbalance.
    Required for the interference to be tunable rather than washed out by distinguishability.

pith-pipeline@v0.9.1-grok · 5641 in / 1133 out tokens · 21345 ms · 2026-07-01T05:56:36.226218+00:00 · methodology

discussion (0)

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Reference graph

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