Learn › reference · docs/phys.md

• Nothing is authored
• The model, and what it costs
• The technology file
• What a device becomes
• What it found
• The fab view
• Counted versus declared is a disclosure, not a verdict
• Integers, and one implementation
• Out of scope, deliberately
• Where these came from

qccd/phys/ — the electrodes a device implies#

The layer that turns a trap graph into metal with coordinates, and metal into an ion height. Before it, the only "electrodes" anywhere in this project were the authored integer control.wiring.electrodes_per_trap = 24 and a decorative pill tiling in the browser whose count came from drawn pixel length. Neither was falsifiable. Now rectangles exist, they have coordinates in nanometres, a fab tool opens them, and a field solver reads them.

qccd/phys/field.py     the gapless-plane RF pseudopotential, in closed form
qccd/phys/tech.py      the technology sidecar: every dimension in nm, with a source
qccd/phys/shapes.py    integer-nanometre polygons, cells, placements, design rules
qccd/phys/build.py     (Device, Technology) -> Layout.  Nothing is authored
qccd/phys/drc.py       design rules, plus disclosures that are deliberately not verdicts
qccd/phys/gds.py       a hand-written GDSII writer, and an independent reader
qccd/phys/svg.py       the same shape table, rendered for a person
qccd/analysis/field.py ANALYSES['field'] -- ion height, secular frequency, junction cost

The browser page can carry the metal as a backdrop -- qccd phys <device> --html -- but it is a view, not an editor: see the fab view for what it is deliberately not.

python -m qccd phys ring144_24v                    # the metal, and its DRC
python -m qccd phys chain --svg out/chain.svg
python -m qccd gds ring144_24v -o ring.gds         # 1372 polygons, database unit 1e-9 m
python -m qccd sweep field chain rf.w_rf_nm 60000,99500,140000 --set mass_u=137.905247

Nothing is authored#

build_layout(arch, tech) is a pure function. No field was added to Node or Segment, no section to .arch.json, no SCHEMA_VERSION bump, no architecture file changed, and the browser is untouched. The metal carries no information the pair does not already determine, so storing it would only create something to lose — Knowledge: d_technology_is_a_sidecar.

The model, and what it costs#

Planar electrodes in the z = 0 plane, ion above. Two assumptions, taken verbatim from the paper this layer is checked against:

1. that there is no gap between electrodes;
2. that the entire plane is covered by conducting electrodes.

— arXiv:2201.12579 ms.tex:200-208

Each electrode then contributes the solid angle it subtends, over 2π (Wesenberg, arXiv:0808.1623, eq. biotsavartpot; the companion analytic treatment is House, PRA 78 033402, which has no arXiv preprint and is recorded in Library/non_arxiv_ledger.csv). No mesh, no BEM, no external solver, no new dependency.

Every tolerance in this layer is quoted from one table, the same paper's measurement of its own model against FEM of the fabricated trap:

Wesenberg also states when the model may be used, and one condition drives a knob:

"necessary conditions … include that gaps between electrodes are much smaller than d, that the extent of the trap is much larger than d, and that the distance from ion to other conducting surfaces is much larger than d"

A finite rail violates the second in proportion to (h/L)². That is measured, not assumed: the truncation is monotone and second order, and rail_length_over_h exists because of it.

The technology file#

A sidecar, never part of the document. Dim has two fields and both are required — there is no Dim(41500). A source beginning declared: marks a number this project chose rather than read, and Technology.declared() lists them.

The one shipped preset has none. Every dimension of eth_junction_2201.12579.tech.json is either a page reference or a derivation checked against its inputs:

Two lattice scales, and why one is not enough#

nm_per_unit_x = 225000 nm: one axial trap pitch, which is three broadcast control electrodes. arXiv:2305.03828 states the conveyor belt supports "20 wells on each side (one for every three electrodes)"; 2201.12579 gives 75 µm segments. 3 × 75 = 225.

nm_per_unit_y = 355000 nm: one min_axis_pitch, the closest two parallel trap axes can be drawn, because each needs 175 µm of electrode stack on the facing side plus a gap.

These measure different things and they disagree. An isotropic 225 µm was tried first and shorts the north control column of every ring device against the opposite rail — the two rows physically do not fit.

What a device becomes#

Each axis-aligned segment gets two RF rails flanking its axis at w_g/2, one segmented centre control electrode between them, and two segmented control columns outboard at dc_setback. A non-axis-aligned segment is refused by id, never approximated. All 1,392 segments of all nine shipped devices are axis-aligned, and no lattice coordinate needs rounding — measured, not assumed.

Two things are interrupted, for the same reason:

• a control pad is dropped where a perpendicular rail crosses its column;
• a rail stops at a perpendicular trap's gap.

The second is not obvious and is not what the build plan said. Running both rail pairs straight through each other lays RF metal across both trap axes, and solving that finds no confined ion position anywhere near the junction — a 175 µm dead zone, because the ion would be directly over driven metal. Interrupting the rails leaves the four L-shaped quadrant electrodes of 2201.12579 fig. 7(a), which is the geometry that reproduces its numbers. Knowledge: fd_the_naive_crossing_must_keep_both_gaps_clear.

The junction is the paper's counterexample, on purpose#

A degree ≥ 3 node is drawn as the naive crossing and tagged role='naive_crossing', with the citation travelling in the layout notes. The optimized alternative in that paper is a cubic B-spline boundary fitted by Nelder–Mead; shipping it means shipping an optimizer. Drawing the counterexample costs nothing and yields a checkable number.

What it found#

Numbers this platform could not previously state. Each is pinned by a test and recorded in Knowledge/notes/accumulated.yaml.

The naive junction is as bad as the paper says. At 2201.12579's own conditions (⁴⁰Ca⁺, 40 V peak, 2π × 40 MHz), fed only the two published RF widths:

Nothing is fitted, and the assertions are written to the paper's bands and no tighter: the 84 µm is read off a figure. Far out along an arm the same geometry returns the linear-section closed form to 3.6e-4, approaching it monotonically, so agreement at the centre is not a coincidence of arm length. PLAN §0.5's prose about RF barriers is now two checked numbers.

No shipped device sits at its design height. A rail sized for 49.95 µm delivers it only in isolation.

Four of the nine are outside the model's own 5% band, so the shift is geometry rather than numerics. The null also moves off the trap axis, which is why height is solved in the transverse plane (transverse_null) and not in z alone — a search constrained to the axis reports no null at all for eight of the nine.

ring144_24v is not fabricable in this technology, and the threshold is exact:

along the rail    (w_g/2 + w_rf) + (dc_setback + dc_width) + gap = 300250 nm
across the rails  2 (dc_setback + dc_width + rail_end_extension + gap) = 460000 nm

The shipped scales are 225000 and 355000. One nanometre under either threshold and the violations return. The axial trap pitch the control electrodes imply is 225 µm and the axial requirement is 300 µm; they are incompatible. That is an independent geometric argument for PLAN §0.5's conclusion about the 24 verticals: they do not merely cost quanta, at these dimensions they do not fit.

The naive crossing also deletes control electrodes — 456 on ring144_24v, and all of them on grid9x9 and deck_unit_cell, which as drawn have nothing left to control them with. Unlike the confinement this is a count, not a simulation.

Four segments in cyclone_dual_loop run through nodes they are not incident to. EA35 goes from (35,0) to (35,3) straight through DT35 and DB35, both degree-2 nodes on the data loop. A planar trap has no overpass, so the graph and the plane disagree: if the crossing is real those nodes are degree 4, they are junctions, they are not being charged as junctions, and the router may send two ions through the same metal. ring144_24v has two more at degree 1 — its end-cap docks, which docs/adl.md already records. Reported, never repaired: arch/ is not this layer's to edit, and the two possible repairs say different things about the machine.

The fab view#

qccd phys <device> --html out/x.html renders the studio page with the derived electrodes underneath the schematic, in a gMetal group that sits first in the SVG and therefore below everything else.

It carries its own transform, and the page does no arithmetic to get it. The scale, the fit and even the scale bar's rectangle are computed in Python by qccd.phys.svg.metal_view_model and read verbatim. They have to be: the page's own px()/py() is anisotropic by up to K_ANISO = 12, and pushing a 99.5 µm by 16 mm rail through it would draw a shape no fab could make. A test strips the block's comments and strings and asserts it contains no *, /, Math., px( or py(.

The underlay does not register with the schematic, and the page says so. Registration would need the page's sx/sy to equal the technology's nm_per_unit_x / nm_per_unit_y; on chain72 those are 1.0 and 0.634, and no shipped device matches. One of the two views has to misstate a proportion and it is not the one with nanometres in it, so the metal is drawn true to scale with a scale bar — the one length on the page that means a physical distance — and a caption saying which view is which.

A page that did not ask for metal is unchanged. The payload is absent from the view model unless a technology was named, so every page emitted before this existed is byte-identical to the one emitted now. render.py never imports qccd.phys: the metal arrives as a dict, because a page is a property of a run and the metal is a property of (device, technology), and wiring one to the other in the renderer would make every page pay for a field solve it did not ask for.

What it is deliberately not: no engine.js edit, no parity bucket, no editing verb, no hit-testing, no palette tile. The mirrored half of this project is diffed at tolerance zero, and a fab view that computed anything would have to be diffed too.

Counted versus declared is a disclosure, not a verdict#

qccd/cost/hardware.py prices electrodes_per_trap = 24; this layer draws 5.89 per site on ring144_24v. Neither number is measured — the 24 is an authored integer that may count shim and compensation electrodes this layer does not draw, and the 5.89 follows from a dc_pitch and a lattice scale that are the technology's claims. So the report prints both, prints the axial trap pitch each implies (600 µm against 225 µm), and stops. Turning that into a pass/fail would be inventing a fact out of two conventions.

Nothing here is a verifier rule. RULE_STATEMENTS is still 23, BROWSER_SET still 17. Those are mirrored in engine.js and diffed at tolerance zero over every architecture file, so a Python-only rule firing there is an automatic red harness — and a design rule is a different kind of claim anyway, about a technology's fabrication limits, which the document does not declare and the browser cannot know.

Integers, and one implementation#

shapes.py and tech.py contain no float literal — checked by tokenising, so a comment saying "0.83h" is fine and 1e3 cannot sneak through. Coordinates are integer nanometres from the lattice to the GDSII file, whose database unit is 1e-9 m, so the round trip is == on lists of ints rather than a tolerance. Placement is quarter-turns through qccd/arch/component.py::translate_point; four of them compose to the identity by equality, not by approx.

The field kernel is Python only, forever. A transcendental solver cannot be differentialled at tolerance zero — atan2 is not required to agree to the ulp between CPython and V8 — so it is not written twice, and tests/test_field.py asserts that no symbol of it reaches engine.js, edit.js or editor.js.

Out of scope, deliberately#

No DC voltage solution, no waveform synthesis, no axial confinement, no gap modelling, no multi-layer solve (a non-zero z_offset refuses rather than approximating), no heating rate from geometry, no optimized junction geometry, and no trap depth — a 1-D bisection above the null returns a local maximum on one line, not the escape saddle, and depth is the quantity most sensitive to every declared hole. hardware_report.area_mm2 still reports 0.0; connecting it is a separate decision.

Where these came from#

python Knowledge/kg/query.py why            # phys/S0, S2 and S6 decisions, to their papers
python Knowledge/kg/query.py param h_ion    # every ion height on record, with its source

Findings: fd_gapless_model_error_is_published, fd_naive_crossing_is_quantified_under_our_own_model, fd_finite_rail_truncation_is_second_order, fd_naive_crossing_reproduced, fd_the_naive_crossing_must_keep_both_gaps_clear, fd_no_shipped_device_sits_at_its_design_height.

Library/ and Knowledge/ are gitignored, so the corpus and the notes above do not travel with a clone. The corpus is 1.1 GB and the graph database is past GitHub's per-file limit, which is why; but it also takes the ~200 KB of YAML notes with it. A !Knowledge/notes/ negation would keep the provenance and leave the bulk out.