QITE on a superconducting processor: a microcontroller board holds a 144-qubit field for 280 ticks (QITE Hold), and the same equilibrium law runs inside one shot on 54 qubits (QITE In-Shot). Two registered experiments
Bernd Westrick
Two registered experiments with the QITE equilibrium law on the IBM Heron processor ibm_marrakesh, one day apart in nothing but the place where the law runs: outside the processor on a microcontroller board, and inside one shot in the processor's own feed-forward. Each experiment has its own registration, hashed before its first registered job, its own frozen scripts, complete raw data, verdict and write-up; the two archives in this record are independent of each other. QITE Hold (zenodo_qite_hold_20260923.zip, SHA-256 97853e20d86c146c16d6011191e9c038dddc743dfd5392476993187654f6e1d3; write-up custodia_paper_v1.pdf; working name Custodia). A microcontroller board (ESP32-C3) holds one pair of numbers per qubit for 144 qubits and turns each pair into a rotation angle. Every tick, one circuit of 144 single-qubit rotations is measured 4096 times; the fraction of ones per qubit goes to the board, the board updates its numbers by its fixed law and returns the angles of the next circuit; it never reads the processor's calibration. A registered programme of eight blocks ran over 280 ticks and 290 jobs: square waves, a hold, a staircase, a checkerboard of 18 zones up and 18 down, two state shocks written into the board, two disturbances written into the circuits, and a comparison with an open-loop reference of frozen angles. Of the seven binding lines, six were run and held; the seventh (drift against the open-loop reference) could not be run because the device did not drift by the registered minimum. The square waves came back with a gain of 0.231 of the commanded swing (the law: 0.25), the checkerboard put 98.5 % of (tick, zone) pairs on the commanded side, the disturbances were rejected to 0.557 and 0.539 of their open-loop size (the law: 4/7). A first registration (v1.0) ended at tick 130 through a design flaw of the host and is included in full. Registration SHA-256 1de82ab12a53c1da349196e8ef07851e6b2f176efc6bd1ca6ba14cacd1f7d54b. QITE In-Shot (zenodo_qite_inshot_20260923.zip, SHA-256 a087f88a95f17c6f8023d5ff40aff35901b5e3e87db531dcd76728511f7ae944; write-up qite_inshot_paper_v1.pdf). On each of 54 qubits, twenty rounds of a measurement followed by a rotation conditioned on that measurement, with angles that set the target level and the memory g; the records of a qubit form a two-state Markov chain whose second eigenvalue is 1 - g. The lines test that eigenvalue, not the level: the autocorrelations of the records for g = 0.3, 0.6 and 1.0 were +0.607, +0.366 and +0.046, the two memories in the ratio 1.657 (the law: 1.75); the relaxation from |0> came back at 0.690 and 0.446 per round (the law: 0.70 and 0.40, lowered by T1 during a round); a step of the target proceeded at 0.658 per round and, with g = 1, completed in one round; a kick of the state was followed by a return to within 0.012 of the unkicked hold; over the same twenty rounds an open-loop state lost 0.451 while the closed loop held within 0.006; 98 % of the qubits with a clean read-out showed their own rate within the registered band. All seven binding lines held; 17 jobs. The size is what the service's compiler accepted on the day (144, 72 and 64 qubits failed with an internal compiler error; every attempt is recorded with its job id). Registration SHA-256 51933de4196bfdd7998e6a5305f7576bb7d35ac137e8b6ce0109965372b4fe5c. Nothing here is a claim of quantum advantage: the observables are classical bits and the circuits contain no two-qubit gate. The claim of both experiments is one of control: a fixed law, registered in advance, holding a public quantum processor at commanded levels with the numbers the law says, once from a board over minutes and once inside the coherence time of the qubits. The board's firmware and the serial link layer are not part of the record; both are identified by their SHA-256 in the registration of QITE Hold. Licence: CC BY 4.0.
•Sep 23, 2026•0 citations