They’re clearly pretty serious about it (why build a gigantic dilution refrigerator, otherwise?) but they’re definitely going to need to wring a factor of two out of the precision of their device fabrication process. Specifically, the laser annealing process for their Josephson junctions currently leaves their qubits with about a 14 MHz frequency spread. The IBM approach to this requires that the qubits are fabricated very precisely in three well-separated frequency bands. I’m pretty sure any frequency “collisions” between qubits in different frequency bands make them useless. Right now they’d have about an 8% chance of fabricating a 127 qubit chip with no collisions. To get the same chance to yield a 1000 qubit chip, they need qubit frequency spreads between 9-10%. The main constraint on this is currently the difficulty of predicting qubit frequencies (measured at milliKelvin temperatures) from resistance measurements conducted at room temperature.I’m hoping they’ll publish when they figure it out, because I’m really curious about how they’re gonna crack this one.
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