Device-readiness audit: atom access and emitter coupling

Verdict

The repository contains a credible radiation-aware topology-discovery engine and one accepted controlled-grid full-vector step. It does not yet contain a validated atom–cavity device.

The one-wavelength protected opening is implemented correctly: the full strip |x| < 0.5 lambda0 is reset to air after every topology projection, and the retained full-vector checkpoint has exactly zero density there. For lambda0 = 780 nm, the modeled opening is 780 nm wide and the centered atom is 390 nm from either nominal dielectric boundary.

That geometric fact does not establish either of the two device goals:

1. a focused tweezer beam passes without unacceptable reflection, scattering, focus distortion, or trap displacement;
2. the atom emits predominantly into a useful cavity or guided output channel.

Neither observable has been calculated.

What the current checkpoint proves

• The 2.5D reduced optimizer passes analytic slab, DtN derivative, full directional-gradient, and independent richer-basis checks.
• The geometry-only 3D transfer reacquires the same selected vector branch at complex-field overlap 0.997021.
• The transferred design increases the directly sampled centered z-dipole response by 4.45--5.03% on the controlled grid.
• A later full-vector upper-branch linewidth step improves fitted Q from 967.292 to 968.652 and withheld-grid Q from 939.890 to 940.839; all 15 predeclared step gates pass.
• The retained Maxwell operator passes a fresh end-to-end boundary audit: complex-symmetry error 4.209e-14, Yee curl-gradient error 0.0, surface Dyson residual 1.093e-13, and two-period boundary-translation error 1.067e-11.

The operator is therefore not the immediate concern. Device calibration and convergence are.

Why the device is not ready

Resonance is not at the nominal emitter wavelength

With lambda0 = 780 nm, the retained full-vector resonance at normalized frequency 1.079456 corresponds to 722.59 nm. It is 7.95% above the target frequency, about 71 fitted full linewidths away from a 780 nm emitter. The lower transferred branch is at 726.83 nm. A 780 nm atom would not be resonant with either branch.

Uniformly scaling the structure would also scale the 780 nm protected opening, so resonance tuning should be treated as a constrained design task if the gap must remain one 780 nm wavelength wide.

The optimized observable is not the device observable

The 2.5D objective is primarily log(Q) with a frequency penalty. The current full-vector objective is the fitted linewidth Q of a centered-dipole response. The accepted linewidth step increases Q by 0.1406% while its centered response decreases from 166.551 to 166.132, a 0.251% reduction. Coupling is retained by a loose hard gate, not optimized.

The full-vector source is a centered z-oriented dipole, so the calculation is related to one component of the local Green response. However, the reported number is not normalized to vacuum, not evaluated for x/y dipoles, not mapped over the atomic wavepacket, and not decomposed into a desired guided port versus radiation and absorption. No Purcell factor, beta factor, QNM mode volume, g, kappa, gamma, or cooperativity is available.

The current grid is a development grid

The retained grid is 20 x 18 x 14 with spacings dx,dy,dz = 0.125,0.12,0.12 lambda0, or approximately 97.5,93.6,93.6 nm. The 0.32-lambda slab occupies only two z-centered voxels, representing 0.24 lambda of voxel thickness. The protected gap is represented exactly by eight x voxels.

The bundled fine profile is 40 x 26 x 22 with dx,dy,dz = 0.0625,0.08,0.08 lambda0; it has 68,640 vector unknowns, sixteen gap voxels, and four slab voxels representing the intended 0.32-lambda thickness. Its conservative memory estimate is 16.2 GB, so it fits on the 64 GB workstation. No retained fine-grid spectrum exists.

The absolute linewidth estimate already changes from 967.3 on the 12-point fit to 939.9 after adding interleaved samples, a 2.83% shift. That is much larger than the accepted 0.14% topology gain. The paired pole estimator also remains unaccepted because of a nearby two-mode cluster.

The density is not fabrication-ready

At projection beta 8, 43.75% of current design voxels lie between density 0.05 and 0.95; 75% lie between 0.01 and 0.99. There is no accepted binarization, erosion/dilation, minimum-line/space, thickness, sidewall-angle, roughness, material-dispersion, or absorption campaign.

The full-vector backend also assigns variables per 3D design voxel. The current two slab layers are tied by z symmetry, but the fine four-layer profile can vary inner and outer layer pairs independently. Before fine-grid optimization, the topology must be hard-tied through z if the intended fabrication is a single vertically extruded etch.

Tweezer transparency is untested

The model contains no incident Gaussian/Debye tweezer beam, no tweezer wavelength, NA, waist, propagation axis, polarization, or focal trajectory, and no chip/tether/substrate geometry. Zero density in the central strip only guarantees no direct geometric obstruction. A focused beam has finite tails that can illuminate the dielectric tips, and nearby dielectric can reflect or distort the trap even when the optical axis passes through air.

Required device qualification

Before another Q-only topology step, record the atom species and transition, dipole basis, tweezer wavelength/NA/polarization/access axis, actual material and thickness, desired photon output channel, and quantitative scattering and coupling targets.

Then implement and validate:

1. Emitter Green tensor: vacuum-normalized Im G(r,r;omega) for x/y/z dipoles, spatially averaged over the expected atomic wavepacket.
2. Useful-channel coupling: flux decomposition into the desired cavity or guided output and all competing radiation/material channels; report Purcell enhancement, beta, linewidth, and cooperativity for the chosen atomic transition.
3. Tweezer propagation: launch the actual focused vector beam at the tweezer wavelength and report transmitted fundamental-mode overlap, reflected/scattered power, focus intensity/phase displacement, and power scattered into the collection/imaging NA relative to a no-device reference.
4. Resonance targeting: constrain the relevant branch to the atomic frequency rather than allowing the Q objective to drift by several percent.
5. Grid/domain/PML convergence: transfer one fixed physical density to the current and fine grids without carrying spectral quantities; reacquire the modes and require stability of frequency, normalized LDOS, beta, linewidth, and complex fields. Repeat with displaced PML/domain boundaries.
6. Fabrication robustness: hard-tie z extrusion, binarize, then evaluate erosion/dilation, thickness, sidewall angle, index dispersion/loss, and minimum line/space.

Reasonable initial numerical gates are less than 0.5% resonance-frequency change and less than 10% change in linewidth, normalized LDOS/Purcell, and useful-channel beta between the two finest grids; complex-field overlap above 0.98; and less than 5% change under the accepted PML/domain sweep. Experimental tweezer-scattering and beta thresholds must come from the intended protocol.

Next computational campaign

Do not continue the current coarse upper-branch Q optimizer yet. The immediate campaign should be a fixed-geometry device qualification:

1. add vacuum-normalized centered Green-tensor and port-flux diagnostics on the current grid;
2. add the actual tweezer-beam scattering calculation;
3. make the fine-grid topology strictly extruded through z;
4. transfer the retained checkpoint to 40 x 26 x 22 and reacquire both nearby branches with the new observables;
5. decide whether either branch survives and meets the experiment-level targets;
6. only then resume optimization with a resonance-constrained coupling objective, using Q as one ingredient rather than the sole target.

The lower branch is the more natural first coupling candidate because its centered z-dipole response is larger and the geometry transfer already improved that response by about 5%. The two-mode cluster should be treated jointly or through direct Green-response/flux objectives rather than forced into a single ambiguous pole fit.

Campaign update: direct 780 nm optimization

The immediate objective/resolution changes requested after this audit are now implemented. The 2.5D optimizer directly differentiates the centered-emitter Green response at normalized frequency 1.0 (exactly 780 nm), rather than using Q as a proxy. On a 76 x 40 density grid with exactly 16 cells across the one-wavelength gap, one direct proposal improves the response by 0.41758% with driven-field overlap 0.99998168, inner/gap energy 0.79923 / 0.57180, zero protected-air density, and reflection error 1.110e-15.

This update does not change the device verdict. The result is a driven proposal, not an accepted 2.5D step, because strict nonlinear pole reacquisition did not return within the operational cutoff. Full-vector validation at 780 nm is also blocked by the inherited mirror's propagating lead. The full- vector topology has nevertheless been corrected to exact z extrusion, and a balanced refined grid now resolves the gap with 16 cells and the slab with four exact cells. See the 780 nm campaign record and the dated result note for the exact claim boundary.