Transjunction coupling. ON vs OFF

Matched ablation on a T03 cluster slice: 3×26Q = 78Q, same seeds and 1024 shots, coupled transjunctions enabled vs disabled. Primary metric: raw localized inter-context correlation (ICC) on ring-linked qubit pairs. Readout mitigation is a diagnostic channel.

Plain English

What this test is: A matched ON vs OFF experiment: same 78Q circuit, transjunction coupling enabled vs disabled. Only the bridge wiring changes.
Why we did it: ICC asks whether coupling matters. This ablation isolates transjunctions on designated bridge qubit pairs.
What QPC computed: Localized ICC on ring-linked pairs · 1024 shots · T03 cluster slice · IBM Heron r2 · ibm_fez and ibm_marrakesh.
Headline result: Both Heron r2 backends pass on raw: |Δ localized ICC| > 0.05. Fez +0.056 · Marrakesh +0.061 on bridge pairs.
What this page reports: Turning transjunctions ON raises localized ICC on bridged pairs. Full-width ICC across all 26 indices sits near zero: most pairs were never bridged.

Verdict

Both IBM Heron r2 backends pass |Δ localized ICC| > 0.05 on raw counts (June 2026). Mitigated values are diagnostic.

Coupled runs show higher localized ICC than decoupled, consistent with transjunction imprint on designated coupling pairs.

Full-width ICC (all 26 aligned qubit indices) stays near zero (~0.003 Δ). Most pairs were never bridged. This page reports designated coupling pairs only.

Results by backend

Backend	Coupled ICC (raw)	Decoupled ICC (raw)	Δ ICC (raw)	Δ localized ZZ (raw)	Coupled job	Decoupled job
IBM Heron r2 · ibm_fez	0.063	0.007	+0.056	+0.108	`d8fh39ralsvc7391oe30`	`d8fh3ro7jphs739m98n0`
IBM Heron r2 · ibm_marrakesh	0.084	0.024	+0.061	+0.141	`d8fi333alsvc7391pvag`	`d8fi34jalsvc7391pve0`

Verify jobs in the IBM Quantum console. Diagnostic (readout-mitigated) Δ ICC: Fez +0.064 · Marrakesh +0.069. Architecture pass is on raw.

Proof figure. Marrakesh (primary, raw)

Mean localized ICC on raw counts: coupled vs decoupled

Coupled ON

0.084

Coupled OFF

0.024

Δ raw = +0.061 · threshold 0.05. Mitigated Δ = +0.069 (diagnostic).

Method (short)

Layout: 3 contexts × 26Q morphogrammatic encoding (depth 8, seeds 7000–7002).
ON: coupled transjunctions (proprietary bridge wiring).
OFF: identical context circuits, bridges removed.
Observable: Bridge-local ICC on transjunction-linked qubit pairs (indices not published).
Noise layer: QPC readout mitigation on the bridge subset is a diagnostic recompute of ICC/ZZ. Primary architecture numbers are raw.

Developer notes (MD) Noise Reducer report

Scope

This is a controlled coupling ablation. Domain prediction ablation lives on the QQ pilot page.
Ring wrap pair (ctx2↔ctx0) can show weaker ICC than adjacent pairs. See per-pair JSON.
Complements open-instance scale evidence (T01–T05) on the same Heron r2 fleet.