IBM Quantum Flamingo (l-coupler proof of concept)

Raveh Neeman

doi:10.5281/zenodo.22674814

IBM · superconducting circuits · DEMONSTRATED (proof of concept, Nov 2024; the production Flamingo-based system promised for end-2025 was not delivered under that name) (Nov 2024) · qubits not published · access: lab-only

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

Register profile — the machine's variant of its architecture

qubit type: fixed-frequency transmon

gate mechanism: tunable couplers on each Heron R2 chip; CNOT across chips through l-couplers (235 ns)

connectivity: heavy-hex on each chip; four chip-to-chip l-couplers (cables up to 1 m)

control: room-temperature RF

control placement: room-temp

readout: dispersive

gate evidence: no published figure

flags: a component, not a machine, schedule risk

Technologies by layer — the machine's cell per layer

1 Qubit carrier	Transmon · primary ▥ 🔎 two 156-qubit Heron R2 chips; transmon qubits as in the Heron line
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 ▥ Heron R2 paragraph ('preserves the tunable coupler architecture'); 'L-couplers allow us to implement CNOT gates across distant chips' ✅ Heron R2's tunable-coupler architecture on each chip; CNOT across chips through l-couplers (best 3.5% error at 235 ns, test devices)
4 Connectivity / transport	Static nearest-neighbour lattice · primary ▥ Heron R2 paragraph ('156 qubits in a heavy-hex layout') ✅ heavy-hex layout on each 156-qubit Heron R2 chip
5 Control	Room-temperature electronics + per-qubit coax/flex · primary ◌ 🔎 room-temperature RF control (Heron line)
6 Readout	Dispersive microwave readout (+TWPA, Purcell) · primary ◌ 🔎 dispersive readout (Heron line)
7 Code	— none — nothing in this layer ▥ 🔎 no QEC; interconnect proof of concept
8 Decoder	— none — nothing in this layer ◌ 🔎 no decoder
9 Interconnect	Multi-chip modules / l-couplers (same cryostat) · primary ▥ coupler taxonomy ('L-couplers, which connect chips with cables'); Flamingo sentence ✅ four l-couplers — cables up to 1 m — join two Heron R2 chips; best cross-chip CNOT 3.5% error at 235 ns (test devices, Nov 2024)
10 Manufacturing	Superconducting-qubit lithography (Al/AlOx/Al junctions, Nb wiring, 300 mm) · primary ◌ 🔎 superconducting-qubit lithography (IBM); no Flamingo-specific fab source

evidence: ✅ 3 / 10