QANTIS: Hardware-Calibrated Sequential POMDP Belief Updates on IBM Heron
This work provides an operating envelope for using current quantum hardware as a belief-update primitive in partially observable autonomous systems, but it is an incremental hardware case study without end-to-end speedup claims.
QANTIS demonstrates that a quantum processor can serve as a calibrated belief-update service for sequential POMDP planning, preserving posterior accuracy across up to 32 steps on IBM Heron hardware. In all reported decision checks, the hardware posterior selects the same action as the exact Bayes posterior.
Autonomous systems under partial observability act on beliefs, not raw sensor events. QANTIS treats the quantum processor as a calibrated belief-update service in that loop: it receives a prior and an observation model, estimates the rare-event evidence term, and returns an ordinary posterior to a classical planner. This paper asks whether that service can be reused across a sequential Tiger POMDP horizon on present IBM Heron hardware without corrupting the planner-facing posterior. We answer with a controlled hardware case study rather than an end-to-end autonomy or wall-clock speedup claim. The study compares no amplification, guarded Grover amplification, and all-step fixed-point amplification on the same trajectory, then checks whether the returned posterior would change the downstream action. All-step FPAA preserves the Tiger posterior across the reported 8-step and 12-step primary runs, and the 20-step and 32-step controls remain inside the same operating band. In every reported decision check, the hardware posterior and the exact Bayes posterior select the same immediate action. Boundary-aware BIQAE stabilizes amplitude estimation near zero and near one, while a rare-event sweep maps the logical sample-complexity envelope for one-in-a-million evidence. The result is an operating envelope for a hardware-calibrated belief-update primitive, not a standalone hardware-advantage claim.