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(GQR46/AFC4) Geometry–Coherence Admissibility Architecture and Control Envelope Expansion in Cavity-Enhanced Rare-Earth Atomic Frequency Comb Memories.

JAMES SUTTON

Published Feb 18, 2026• 0 citations
Publisher

Abstract

Cavity-enhanced rare-earth atomic frequency comb (AFC) memories exhibitoperational limits arising from both spectral ridge instability and finite optical coherence time.While geometric ridge-drift tolerance and coherence-time constraints have previously beenanalysed separately, practical device robustness requires a unified control-oriented framework.Here we introduce a geometry–coherence admissibility architecture that treats spectralpreparation as a constrained engineering problem. We define a dimensionless geometric toleranceratio and combine it with an exponential coherence survival metric to obtain a joint admissibilitycondition governing reliable operation.Monte Carlo yield simulations reveal a bounded admissible region in strain–coherenceparameter space and identify a recoverable collapse regime in which baseline preparation failsbut active spectral control restores admissibility. The controller acts to displace the operationalboundary by modifying effective dephasing coupling, thereby expanding the usable designenvelope.The resulting geometry–coherence phase diagram provides a quantitative tolerance map forintegrated rare-earth photonic quantum memory systems and establishes a general methodologyfor admissibility-constrained spectral preparation in coherence-limited platforms. Full 70 article programme https://github.com/jamessutton600613-png/GQR/blob/main/Programme_Index.md The programme contains both standalone and self referencing articles. These can all be read as notes in proof of GQR1.

DOI
10.5281/zenodo.18686192

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Cavity-enhanced atomic frequency comb (AFC) quantum memories are typicallyanalyzed in terms of spectral preparation and cavity efficiency. However, geometric toleranceand optical coherence jointly determine quantum admissibility. We introduce a coupledgeometry–coherence admissibility framework in which strain-induced inhomogeneity reduceseffective coherence time 𝑇2,eff , while cavity-induced ridge drift defines a geometric toleranceratio 𝜌. We show that quantum operation requires simultaneous satisfaction of geometric andcoherence constraints, yielding a dominance decomposition and collapse boundary in strainspace. The framework clarifies how cavity design and material coherence budgets jointly boundachievable storage times. Full 70 article programme https://github.com/jamessutton600613-png/GQR/blob/main/Programme_Index.md The programme contains both standalone and self referencing articles. These can all be read as notes in proof of GQR1.
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Abstract: We present a regime-resolved modelling study of cavity-enhanced Eu3+:Y2SiO5atomic frequency comb (AFC) quantum memories that quantifies bandwidth robustness acrosscontrast and comb-bandwidth parameter space. Using Kramers–Kronig–consistent susceptibilityreconstruction and frequency-domain cavity transfer modelling with representative integrated-device parameters, we construct contrast–bandwidth response atlases for wide- and narrow-cavityregimes. While first-order dispersion cancellation between spectral pit and AFC structures canbe achieved, robustness is shown to be governed by higher-order susceptibility curvature undercavity phase feedback. For representative configurations, cavity narrowing reduces admissibleoperating volume by approximately 35–40%, despite comparable peak echo amplitude. Theatlas methodology provides a quantitative tolerance-analysis framework for integrated rare-earthphotonic memories. Full 70 article programme https://github.com/jamessutton600613-png/GQR/blob/main/Programme_Index.md The programme contains both standalone and self referencing articles. These can all be read as notes in proof of GQR1.
Abstract: Atomic frequency comb (AFC) memories employ periodic spectral absorptionstructures that produce delayed photon echoes through collective rephasing of atomic excitations.Recent modelling studies have examined robustness limits of cavity-enhanced rare-earth AFCsystems from a geometric tolerance perspective, identifying dimensionless stability criteria foradmissible operating regions. Here we present a complementary dynamical framework that linksthe spectral comb structure directly to the temporal impulse response of the medium.Starting from a frequency-domain description of the comb absorption profile, we reconstructthe complex transfer function and show that periodic spectral geometry generates a temporallyrecurrent impulse response with peaks separated by 1/Δ, where Δ is the comb spacing. Convolu-tion with arbitrary input pulses reproduces the characteristic AFC echo dynamics and enablesdirect evaluation of retrieval efficiency. Numerical simulations recover three key AFC properties:deterministic echo timing 𝑡echo = 1/Δ, efficiency scaling governed by comb finesse 𝐹 = Δ/𝛾,and the influence of cavity bandwidth on retrieval efficiency.The results provide a unified description connecting spectral comb geometry, impulse responserecurrence, and echo formation in AFC memories. This perspective complements previoustolerance analyses by revealing the dynamical origin of echo recurrence and offers a compactframework for analysing and designing comb-based quantum memories. Full programme https://github.com/jamessutton600613-png/GQR/blob/main/Programme_Index.md The programme contains both standalone and self referencing articles. These can all be read as notes in proof of GQR1.
Atomic frequency comb (AFC) systems provide robust temporal recurrence but do not, in their symmetricform, ensure preservation of directional equivalence. As a result, signal amplitude may be maintained whilesignal identity remains ambiguous.In this work, we examine the structure of the AFC response across three stages. First, baseline measure-ments reveal persistent forward–backward asymmetry despite low disturbance. Second, direct mode-resolvedanalysis shows only weak trends with high variability, indicating that the accessible spectral space does notadmit a stable interpretation. Third, the introduction of selective filtering (“fuzz removal”) produces a quali-tative transition: sharply defined band structure emerges immediately, with spectral weight concentrating intoa restricted set of modes.These results demonstrate that the relevant operation is not the construction of structure, but its revelationthrough suppression of non-persistent components. AFC systems therefore act as recurrence substrates, whilereliable memory behaviour requires a selection layer that enforces persistence under constraint.This establishes a clear distinction between accessibility and stability, and provides a pathway for engi-neering AFC-based memory systems in which structure is controlled through constraint-driven selection ratherthan amplitude preservation alone. Full 70 article programme https://github.com/jamessutton600613-png/GQR/blob/main/Programme_Index.md The programme contains both standalone and self referencing articles. These can all be read as notes in proof of GQR1.
High signal integrity in quantum memory systems is often assumed to be recoverable throughdownstream optimisation. Here, using a model of atomic frequency comb (AFC) dynamics, weshow that signal integrity is instead determined at formation. Across a broad parameter space,the system exhibits a transient regime in which signal amplitude remains close to a clean referencewhile directional asymmetry emerges between forward and backward evolution (AB̸ = BA). Thisdefines an echological regime, characterised by low signal disturbance and loss of path equivalence.Time-resolved analysis reveals a universal transition from an early structured regime to a noise-dominated state, with the transition time largely independent of comb parameters. Apparent late-time stability is shown to arise from loss of accessible structure rather than recovery of the originalsignal. Comparison of observables further demonstrates that convergence in raw intensity canmask divergence in more sensitive representations, indicating that stability is strongly observable-dependent.These results imply that AFC systems, in their symmetric form, act as recurrence substratesrather than complete memory devices. Reliable memory requires an additional selection or filter-ing layer capable of suppressing ambiguous components and restoring directional asymmetry in acontrolled manner. More generally, the findings establish that signal integrity is not produced bycorrection, but emerges when system parameters are aligned with a constrained operating regimeat formation. Full 70 article programme https://github.com/jamessutton600613-png/GQR/blob/main/Programme_Index.md The programme contains both standalone and self referencing articles. These can all be read as notes in proof of GQR1.