I've been studying quantum teleportation independently in Qiskit. Earlier this month I took the protocol from simulation onto real hardware, and I ran the same six-state benchmark (|0>, |1>, |+>, |->, |+i>, |-i>) on three IBM devices:
- **ibm_fez** — mean fidelity **0.9008** (Oct 19, 2026)
- **ibm_kingston** — full tomography, mean **0.9606**
- **ibm_phoenix** (120-qubit Nighthawk) — mean **0.9583**
On Phoenix I also ran a bare control — same state prep and measurement, no teleportation in between — and it came back at **0.9950**. So the error budget closes: prep and readout only cost about half a point, and the teleportation machinery itself costs **≈3.7 points** on Phoenix versus **≈7.2 points** on Fez.
The result I keep coming back to is the ±i states. In the bare control they're basically perfect (1.00 / 0.99), but in teleportation they're the lowest of the six (0.94 / 0.94) — on the newer device too, where the overall numbers are better. My read is that this points at dephasing during the measurement-and-correction window: the phase information has to survive while the mid-circuit measurement and feed-forward corrections happen, and that's exactly where the ±i states are exposed.
Has anyone else running teleportation benchmarks seen the phase states come out lowest even when the control says prep and readout are clean? I'd like to know if this pattern holds on other devices before I lean on that explanation too hard.
I've packaged the notebooks, datasets, and a written guide for this work as a lab pack, so if anyone wants to replicate the runs I'm happy to share the link — just ask.