Mounir IDRASSI

I was invited to give this lecture/tutorial on Verifpal to undergraduate students just learning about cryptography. My thanks to the University of Edinburgh Informatics Department for this wonderful opportunity. It was great to meet so many students! youtube.com/watch?v=JYUo5gNc…

I spent the evening looking into quantum computing timelines as a non-expert in quantum computing. Here is what I’ve learned: We currently have machines with ~1,000–1,500 physical qubits at error rates around 10⁻³, and Google’s algorithm requires ~500,000 physical qubits operating coherently together with surface code error correction, yoked qubit storage, magic state cultivation producing ~500K T states per second, and reaction-limited execution at 10μs cycle times — none of which has been demonstrated beyond small-scale proof-of-concept experiments. Scaling from where we are to where this needs to be isn’t a matter of incremental improvement along a Moore’s Law curve; it requires solving qualitatively new engineering problems in qubit fabrication yield, correlated error suppression across a massive chip (or multi-chip interconnects that don’t exist yet), cryogenic wiring and control electronics for half a million qubits, real-time classical decoding at the required throughput, and sustained coherence of a “primed” quantum state across minutes of wall-clock time — any one of which could prove to be a multi-year bottleneck, and all of which must be solved simultaneously.​​​​​​​​​​​​​​​​ Given the above, I just don’t see how we’re going to get to a cryptographically relevant quantum computer by 2030, especially given that we need a ~350× increase in physical qubit count with simultaneously tighter error correlations, an entirely new cryogenic control and wiring architecture to address half a million qubits, real-time decoding infrastructure that doesn’t exist yet, magic state distillation factories operating at industrial throughput, and multi-minute coherent idle times for primed states — and historically, solving even one of these at scale has taken the field the better part of a decade.