I measured how GHZ entanglement fades with chain length on a free QPU — death line at ~12 qubits, but the "dead" GHZ-17 still shows the right pattern.

Hobbyist here, no physics background (30-year metalworker). I spent the weekend on Quantum Inspire's Tuna-17 measuring how GHZ fidelity decays as you add qubits to the chain. 1024 shots each, strict fidelity (% of shots that are all-0 or all-1). Plot attached. 4:84% 5:79% 6:72% 7:67% 8:65% 10:58% 13:46% 17:33% Crosses the 50% line between 10 and 13 — matches a simple ~7%/qubit rule (half-life ~10 links). What got me: even the "dead" GHZ-17 still has 000…0 and 111…1 as its top-2 outcomes out of 131,072 (207 and 127 counts, chance ~0.008 each). The wave fades but doesn't vanish. Also consistent at every length: all-zeros beats all-ones — I read that as T1 relaxation, excited states decaying toward ground during the circuit and readout. Sanity-checked with a readout calibration: reading a prepared |1> was only ~79% correct vs ~93% for |0>, so a big chunk of the asymmetry is readout, not decoherence. Not claiming anything new — just a fun, honest measurement anyone can reproduce for free. Questions and corrections very welcome; I only trust what I can measure. https://preview.redd.it/zpf23au2usch1.png?width=1350&format=png&auto=webp&s=56a60bb8400c17dd7e09068ec82261734abe3656 submitted by /u/Sufficient-Main-4101 [link] [comments]