Nord Quantique single-mode GKP
Nord Quantique single-mode GKP
Register profile — the machine's variant of its architecture
qubit type: GKP finite-energy grid state in a superconducting aluminium cavity; device envelope Delta = 0.38, n-bar ~ 2.96
gate mechanism: dispersive coupling to an auxiliary transmon; autonomous / measurement-based stabilisation; a claimed GKP-GKP 2Q gate has no paper
connectivity: single mode
control: room-temperature control
control placement: room-temp
readout: auxiliary-transmon readout, fidelity 0.95(1)
gate evidence: no published figure
codes: gkp
flags: post-selection dominates the result, unverifiable company claim
Technologies by layer — the machine's cell per layer
| 1 Qubit carrier | Bosonic cavity mode · primary ▣ Fig. 1a (device schematic: double-post cavity + auxiliary transmon); App. A.1 ✅ single-mode GKP grid state in a superconducting Al cavity + auxiliary transmon; Δ=0.38, n̄≈2.96; storage T1 360(10) µs, T2 640(40) µs (Jul 2026) |
| 2 Encoding | GKP grid encoding · primary ▣ Fig. 1b–d (char.-function tomography, Δ=0.38); §II.2 Grid-state encoding ✅ finite-energy GKP grid encoding in one microwave mode; SPAM 7(7)e-4 cardinal, 8(5)e-3 magic (survival 0.16), Jul 2026 |
| 3 Gate mechanism | Ancilla-mediated bosonic gates (cat CX, dual-rail CZ, beamsplitter) · primary ▣ Fig. 1e (sBs conditional displacements + aux rotations); App. A.2 Hamiltonian, A.5 ECD gate ✅ dispersive coupling to auxiliary transmon, 2χ/2π = −45.44 kHz; autonomous/measurement-based stabilisation; claimed GKP–GKP 2Q gate (2025) has no paper |
| 4 Connectivity / transport | Static nearest-neighbour lattice · primary ▣ Fig. 1a (single storage mode; no qubit–qubit coupling) ✅ single mode, one logical qubit; no qubit–qubit connectivity (degree 0) |
| 5 Control | |
| 6 Readout | Dispersive microwave readout (+TWPA, Purcell) · primary ▣ Fig. 1a (on-chip readout resonator + Purcell filter); Fig. 2b; App. A.3–A.4 ✅ auxiliary-transmon dispersive readout, fidelity 0.95(1); auxiliary T1 72(3) µs |
| 7 Code | Bosonic concatenation (repetition-cat, LDPC-cat, GKP+qLDPC) · primary ▤ abstract; results ✅ single-mode square-lattice GKP code with autonomous sBs correction in a 3D cavity (sweep 7 Oct 2026, source read) |
| 8 Decoder | — (Atlas gap: ∅G-auton) · primary ▤ §II.2.2 Autonomous implementation via auxiliary reset ✅ no classical decoder: autonomous, feed-forward-free stabilisation with analog closest-vector-problem decoding |
| 9 Interconnect | |
| 10 Manufacturing | 3D machined superconducting cavities · primary ▤ App. A.1 Experimental device 🔎 3-D superconducting aluminium cavity; no fab process published Superconducting-qubit lithography (Al/AlOx/Al junctions, Nb wiring, 300 mm) · alternate ◌ 🔎 Josephson-junction lithography for the auxiliary transmon; no fab process published |
Standard records
acceptance fraction → 0.24 · typical (cardinal states, 24-39%; 16% for magic states)
Jul 2026 · source
idle / memory error per round → 8.10e-3 · best-of-line (logical error per round, selection-free)
Jul 2026 · source
SPAM error → 7.00e-4 · best for any bosonic qubit (cardinal states)
Jul 2026 · source
T1 relaxation → 360 µs · best-of-line (storage mode)
Jul 2026 · source
T2 coherence (echo/DD) → 640 µs · best-of-line (storage mode)
Jul 2026 · source
evidence: ✅ 7 / 11