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arxiv: 2602.18156 · v2 · pith:AG4KMLZTnew · submitted 2026-02-20 · 🪐 quant-ph

Dispersive Hong-Ou-Mandel Interference with Finite Coincidence Windows

T.J. Walstra , A.J. Hasenack , D.J. de Ruiter , P.W.H. Pinkse , T.D. Bradley , B. Skoric This is my paper

Pith reviewed 2026-05-22 10:35 UTC · model grok-4.3

classification 🪐 quant-ph
keywords Hong-Ou-Mandel interferencegroup velocity dispersioncoincidence windowtype-II SPDCtime-tagging modulesquantum opticsfiber transmissionphoton indistinguishability
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The pith

Finite coincidence windows break dispersion cancellation in Hong-Ou-Mandel interference and restore sensitivity to symmetric group velocity dispersion.

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

The paper investigates the effect of realistic detector timing on Hong-Ou-Mandel interference when photon pairs travel through dispersive fiber. In standard treatments, symmetric group velocity dispersion cancels for type-II SPDC pairs, but the rectangular coincidence window of time-tagging modules acts as a temporal filter that breaks this cancellation. The authors derive an analytical model that predicts oscillations in the coincidence rate and broadening of the HOM dip. They test the model by sending photon pairs from a ppKTP source through fibers up to 29 km long and find quantitative agreement, from which the dispersion parameter can be extracted. The result shows that finite detection windows must be included when predicting visibility in dispersive quantum links.

Core claim

The rectangular coincidence window inherent to modern time-tagging modules breaks the standard dispersion cancellation condition and restores sensitivity to symmetric group velocity dispersion, leading to characteristic oscillations and dip broadening in the HOM interference. The analytical model for type-II SPDC processes accounts for this temporal filter and matches experimental data collected with fibers of lengths up to 29 km.

What carries the argument

Rectangular temporal filter imposed by the finite coincidence window in the coincidence probability integral for dispersed type-II SPDC photon pairs.

If this is right

  • The visibility and shape of the HOM dip become sensitive to symmetric dispersion once the finite window is included.
  • Fiber dispersion parameters can be extracted directly from the oscillation period in the measured dip.
  • Quantum communication links using dispersive fiber must incorporate detector timing resolution when calculating expected interference visibility.
  • The model applies to any two-photon interference setup that uses rectangular coincidence gating after dispersion.

Where Pith is reading between the lines

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

  • The same window-induced oscillations could appear in other two-photon experiments such as Franson interferometry over fiber.
  • In multi-node quantum networks the effect may accumulate and reduce visibility beyond what dispersion alone predicts.
  • Replacing the rectangular window with a Gaussian or other smooth filter shape would likely suppress the oscillations and restore partial cancellation.
  • The oscillations provide a new observable for calibrating timing resolution in situ during quantum channel characterization.

Load-bearing premise

The model assumes an ideal rectangular coincidence window with sharp edges and no additional detector timing jitter or higher-order dispersion.

What would settle it

An experiment that records the HOM dip shape after fiber transmission and finds no oscillations whose period scales with the product of dispersion and window duration would contradict the central claim.

Figures

Figures reproduced from arXiv: 2602.18156 by A.J. Hasenack, B. Skoric, D.J. de Ruiter, P.W.H. Pinkse, T.D. Bradley, T.J. Walstra.

Figure 1
Figure 1. Figure 1: FIG. 1. Orthogonally polarized photons from a filtered pp [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. FWHM of the model (solid lines) and data (points) [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. Example fits showing predicted oscillations for differ [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. Average scaled residuals of a subset of the data with [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗
read the original abstract

Hong-Ou-Mandel (HOM) interference is a fundamental tool for assessing photon indistinguishability in quantum information processing. While the effect of chromatic dispersion on HOM interference has been widely studied, the interplay between dispersion and the finite detection window of realistic measurement devices remains under-explored. In this work, we demonstrate that the rectangular coincidence window inherent to modern time-tagging modules, which effectively acts as a temporal filter, breaks the standard dispersion cancellation condition and restores sensitivity to symmetric group velocity dispersion. We derive an analytical model for type-II SPDC processes that predicts a modification of the HOM dip shape, specifically the emergence of characteristic oscillations and dip broadening. We experimentally validate this theoretical framework using a ppKTP source and transmission through optical fibers of lengths up to 29 km. The experimental data show excellent agreement with the model, confirming the presence of window-induced oscillations and allowing for the precise extraction of the fiber dispersion parameter. These findings underscore the importance of accounting for finite timing resolution in the design and characterization of dispersive quantum communication links.

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

1 major / 1 minor

Summary. The paper claims that the rectangular coincidence window of modern time-tagging modules acts as a temporal filter that breaks the standard dispersion cancellation condition in Hong-Ou-Mandel interference for type-II SPDC. This restores sensitivity to symmetric group-velocity dispersion, producing characteristic oscillations and dip broadening. An analytical model is derived from first-principles quantum optics and validated experimentally with a ppKTP source and fiber transmission up to 29 km, yielding excellent agreement and enabling precise extraction of the fiber dispersion parameter.

Significance. If the central result holds, the work is significant for the characterization and design of dispersive quantum communication links, where finite timing resolution must be accounted for in HOM-based indistinguishability tests. The combination of an analytical derivation for type-II SPDC with direct experimental validation over long fibers provides a practical tool for dispersion extraction and highlights a previously under-explored device-level effect. The experimental agreement supplies external grounding that mitigates concerns about model assumptions.

major comments (1)
  1. The analytical model (as summarized in the abstract and derived for type-II SPDC) assumes an ideal rectangular coincidence window with sharp cutoffs. While the experimental data up to 29 km show excellent agreement and visible oscillations, the derivation does not include a convolution with realistic detector jitter (~10-50 ps) or finite rise-time response, nor does it bound the jitter tolerance required to preserve the predicted oscillations. Because oscillation frequency scales with dispersion-induced temporal walk-off, this omission leaves open whether the reported effect would remain observable under typical time-tagger non-idealities; a quantitative estimate or additional simulation would strengthen the claim that the rectangular-window effect dominates.
minor comments (1)
  1. Clarify in the methods or figure captions whether the coincidence window width Tw was fixed or optimized per fiber length, and report the extracted dispersion value with uncertainty to allow direct comparison with standard fiber specifications.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their thorough review and constructive feedback on our manuscript. We are pleased that the referee recognizes the significance of our findings regarding the impact of finite coincidence windows on dispersive HOM interference. Below, we address the major comment point by point.

read point-by-point responses

  1. Referee: The analytical model (as summarized in the abstract and derived for type-II SPDC) assumes an ideal rectangular coincidence window with sharp cutoffs. While the experimental data up to 29 km show excellent agreement and visible oscillations, the derivation does not include a convolution with realistic detector jitter (~10-50 ps) or finite rise-time response, nor does it bound the jitter tolerance required to preserve the predicted oscillations. Because oscillation frequency scales with dispersion-induced temporal walk-off, this omission leaves open whether the reported effect would remain observable under typical time-tagger non-idealities; a quantitative estimate or additional simulation would strengthen the claim that the rectangular-window effect dominates.

    Authors: We thank the referee for highlighting this important consideration. Our derivation intentionally models an ideal rectangular window to analytically capture the breaking of dispersion cancellation due to the finite coincidence window, which is the central contribution of the work. The experimental results, obtained with a commercial time-tagging module, exhibit the predicted oscillations and dip broadening with excellent quantitative agreement to the ideal model, even over 29 km of fiber where the temporal walk-off is substantial. This agreement indicates that the detector jitter in our setup (typically < 20 ps for modern modules) does not significantly degrade the visibility of the oscillations. To further strengthen the manuscript, we will add a paragraph in the discussion section providing a quantitative estimate of the jitter tolerance. Specifically, we will show that the oscillation amplitude remains observable provided the jitter standard deviation is less than approximately 10% of the coincidence window width. We will also include a supplementary simulation demonstrating the effect of convolving the ideal coincidence probability with a Gaussian jitter distribution of 30 ps FWHM, confirming that the key features persist under realistic conditions. revision: partial

Circularity Check

0 steps flagged

No significant circularity in the derivation chain

full rationale

The paper derives an analytical model from first-principles quantum optics for type-II SPDC processes that incorporates the rectangular coincidence window as a temporal filter. This leads to explicit predictions of oscillations and dip broadening that break standard dispersion cancellation. The model is then validated against independent experimental data from a ppKTP source transmitted through fibers up to 29 km, allowing extraction of dispersion parameters. No load-bearing steps reduce by construction to self-definition, fitted inputs renamed as predictions, or self-citation chains; the central claim remains externally grounded in the experimental benchmarks rather than tautological.

Axiom & Free-Parameter Ledger

1 free parameters · 2 axioms · 0 invented entities

The model relies on standard assumptions from quantum optics for SPDC and detector response; one fitted parameter (fiber dispersion) is extracted from data rather than predicted a priori.

free parameters (1)
  • fiber dispersion parameter
    Extracted by fitting the modified HOM dip shape to experimental data from fiber transmission.
axioms (2)
  • domain assumption Type-II SPDC produces orthogonally polarized photon pairs with the stated joint spectral amplitude
    Invoked as the source model in the analytical derivation for the interference pattern.
  • domain assumption Coincidence window is perfectly rectangular with no timing jitter beyond the stated filter
    Central to breaking the dispersion cancellation condition in the model.

pith-pipeline@v0.9.0 · 5735 in / 1380 out tokens · 44100 ms · 2026-05-22T10:35:31.778172+00:00 · methodology

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Reference graph

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