IQM six-qubit star QPU (Deneb-class)

Raveh Neeman

doi:10.5281/zenodo.22674814

IQM Quantum Computers · superconducting circuits · DEMONSTRATED ([[4,2,2]] error detection, arXiv 17 Mar 2025); the paper does not name its QPU — IQM's six-qubit star architecture is Deneb (17 Mar 2025 (arXiv)) · 6 physical qubits · access: not stated in the paper (IQM Resonance has offered a Deneb backend)

architecture: Transmon lattice with tunable couplers · Open on the map

Register profile — the machine's variant of its architecture

qubit type: transmon (4.41–4.93 GHz) coupled to a central resonator (4.22 GHz)

gate mechanism: tunable couplers to a central computational resonator: MOVE (qubit-to-resonator state transfer) and CZ between qubits and the resonator

connectivity: star: effective local all-to-all through the central resonator

control: room-temperature RF

control placement: room-temp

readout: dispersive; readout fidelity 98.3–99.1% (Table III)

gate evidence: no published figure

codes: stab_4_2_2

flags: post-selection dominates the result

Technologies by layer — the machine's cell per layer

1 Qubit carrier	Transmon · primary ▤ §II (QPU description) ✅ six transmon qubits, each on a tunable coupler to the central resonator
2 Encoding	Bare physical qubit (no encoding) · primary ◌ 🔎 bare transmon two-level subspace; no encoding beyond the physical qubit
3 Gate mechanism	Tunable-coupler CZ / iSWAP · primary ▤ §II (MOVE and CZ operations) ✅ tunable couplers to the central resonator: MOVE transfers an ancilla state into the resonator; CZ between data qubits and the resonator
4 Connectivity / transport	— (Atlas gap: ∅G-bus) · primary ▤ Abstract ('six-qubit star lattice architecture … effective local all-to-all connectivity') ✅ star topology: all six qubits coupled only to the central computational resonator, effective local all-to-all
5 Control	Room-temperature electronics + per-qubit coax/flex · primary ◌ 🔎 room-temperature RF control
6 Readout	Dispersive microwave readout (+TWPA, Purcell) · primary ▤ App. G, Table III 🔎 readout fidelity 98.3–99.1% per qubit; mechanism not spelled out
7 Code	Error-detection codes ([[4,2,2]], d=2 surface, iceberg, spacetime) · primary ▤ Abstract ✅ [[4,2,2]]: two logical qubits on 4 data + 2 ancilla qubits; repeated error-detection cycles, logical error per cycle 0.25(2)–0.91(3)%
8 Decoder	— none — nothing in this layer ▤ §IV (post-selection conditioned on both stabilizer measurements) ✅ no decoder: runs are post-selected on both stabilizer results
9 Interconnect	— none — nothing in this layer ◌ 🔎 single six-qubit chip, no interconnect
10 Manufacturing	Superconducting-qubit lithography (Al/AlOx/Al junctions, Nb wiring, 300 mm) · primary ◌ 🔎 superconducting-qubit lithography (IQM); no machine-specific fab source

evidence: ✅ 5 / 10