Alice & Bob Boson 4
Alice & Bob Boson 4
Register profile — the machine's variant of its architecture
qubit type: dissipatively stabilised cat qubit
gate mechanism: bosonic Z gate
connectivity: single qubit
control: room-temperature control
control placement: room-temp
readout: dispersive
gate evidence: no published figure
codes: two-legged-cat
flags: phase-flip time unpublished
Technologies by layer — the machine's cell per layer
| 1 Qubit carrier | Bosonic cavity mode · primary ▣ §I and Fig. 2A–C (memory mode at 1.1 GHz, buffer at 7.9 GHz, ATS); abstract (22 s bit-flip time); the paper Alice & Bob's Boson 4 page links as Boson 4 ✅ dissipatively stabilised cat qubit on a transmon-free chip: a lumped-element memory mode (1.1 GHz) coupled through an ATS to a 7.9 GHz buffer; bit-flip time 22 s for the squeezed cat at n̄ = 4.1 in the paper, up to 430 s (over 7 min) quoted by Alice & Bob for the cloud chip |
| 2 Encoding | Cat-code encoding (biased noise) · primary ▣ §I (dissipation engineering for squeezed-like cat qubits); Fig. 3 (bit-flip protection by squeezing) ✅ two-legged cat stabilised by two-photon dissipation; the paper adds a squeezed (moon-cat) deformation: bit-flip time 22 s at n̄ = 4.1, 160× a standard cat |
| 3 Gate mechanism | Ancilla-mediated bosonic gates (cat CX, dual-rail CZ, beamsplitter) · primary ▣ §III (Zeno gates); Fig. 4 (Z-gate fidelity with squeezing) ✅ bosonic Z gate on a single cat qubit: a Zeno gate, a resonant memory drive orthogonal to the cat axis rolls the fringes while two-photon dissipation pins the basis states |
| 4 Connectivity / transport | |
| 5 Control | Room-temperature electronics + per-qubit coax/flex · primary ▣ App. A2 (room-temperature setup); Fig. A1 (wiring diagram) ✅ room-temperature control: buffer, memory, longitudinal and reset drives up-converted from IQ signals of a Quantum Machines controller |
| 6 Readout | Dispersive microwave readout (+TWPA, Purcell) · primary ▣ §II ('Measuring Z is done by a memory displacement followed by a photon number measurement'); App. C1 and Fig. C1 (longitudinal photon-number readout calibration) ✅ readout through the buffer: a longitudinal pump displaces the buffer conditioned on the memory photon number, and Z is measured by a memory displacement followed by that photon-number measurement — the protocol developed on Boson 3 (Réglade et al., Nature 629, 778, 2024) |
| 7 Code | Bosonic concatenation (repetition-cat, LDPC-cat, GKP+qLDPC) · primary ▥ Boson 4 milestone ✅ single dissipative cat qubit; bit-flip time above 7 minutes (sweep 7 Oct 2026, source read) |
| 8 Decoder | |
| 9 Interconnect | |
| 10 Manufacturing | Superconducting-qubit lithography (Al/AlOx/Al junctions, Nb wiring, 300 mm) · primary ▤ Fig. 2B (optical micrograph: fractal capacitor, 29-junction chain, ATS, quarter-wavelength coplanar filter); App. A1 (tantalum patterning on sapphire; Dolan-bridge Al junctions) ✅ planar superconducting circuit patterned in a tantalum film sputtered on sapphire, aluminium junctions by the Dolan-bridge technique: a lumped-element memory (fractal capacitor and a 29-junction chain) with a quarter-wavelength coplanar-waveguide filter; no machined 3-D cavity (Boson 3's memory was a quarter-wave coplanar resonator: Réglade et al., Nature 629, 778, 2024) |
Standard records
T1 relaxation → 430 s · best-2024 (Boson 4, transmon-free)
May 2024 · source
evidence: ✅ 7 / 10
Pictures
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