Chat with John Preskill

Richard P. Feynman Professor of Theoretical Physics at Caltech

About John Preskill

In 1998, he coined the term 'quantum supremacy', not as hype, but as a precise, experimentally falsifiable threshold: the point where a quantum device performs a task infeasible for any classical computer, even in principle. That phrase reshaped the field’s ambition and accountability, anchoring decades of hardware development to a concrete theoretical benchmark. Preskill didn’t just theorize about qubits, he built conceptual scaffolding for quantum error correction, proving that fault-tolerant computation could survive noise if redundancy scaled correctly, a result that turned skepticism into roadmap. His lectures at Caltech don’t rehearse textbook derivations; they dissect the epistemic boundaries of quantum mechanics itself, asking not just how quantum computers work, but what their existence implies about information, time, and the nature of physical law. He writes with uncommon clarity about deep uncertainty: not ignorance, but the kind that arises when gravity, entanglement, and black hole thermodynamics collide.

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Conversation Starters

Not sure where to begin? Try asking John Preskill:

  • “What specific calculation would convince you quantum supremacy has truly been achieved?”
  • “How does your 2012 'quantum decoherence firewall' argument reshape black hole information recovery?”
  • “Why did you shift focus from quantum field theory to quantum error correction in the late 1990s?”
  • “What experimental signature would most strongly support your ER=EPR conjecture?”

Frequently Asked Questions

Did Preskill ever collaborate directly with Feynman on quantum computing?
No, Feynman died in 1988, before Preskill’s foundational work on quantum error correction began. However, Preskill deeply engaged with Feynman’s 1982 lecture 'Simulating Physics with Computers,' extending its vision by confronting the practical obstacle Feynman acknowledged but didn’t solve: decoherence. Preskill’s 1996 paper on quantum error-correcting codes provided the first rigorous framework to protect quantum information, transforming Feynman’s speculative proposal into an engineering discipline.
What is Preskill’s stance on near-term NISQ devices?
He coined the term 'NISQ' (Noisy Intermediate-Scale Quantum) in 2018 to describe today’s imperfect devices, not as endpoints, but as probes. He argues they’re valuable only if used to test quantum many-body physics or generate classically intractable data for verification, not for commercial speedups. His skepticism centers on whether variational algorithms can overcome barren plateaus without quantum advantage in sampling fidelity.
Has Preskill revised his view on black hole firewalls since the 2012 AMPS paradox?
Yes, he co-authored the 2013 'ER=EPR' conjecture with Maldacena, proposing that entangled particles are connected by microscopic wormholes. This reframed the firewall debate: instead of choosing between unitarity and locality, the geometry of spacetime itself encodes entanglement. He now treats firewalls as artifacts of applying semiclassical reasoning beyond its domain, not fundamental features.
Why does Preskill emphasize 'quantum literacy' over quantum literacy for policymakers?
Because quantum technologies increasingly influence encryption policy, AI safety frameworks, and national security strategy, but decisions are being made by people trained in classical probability and linear algebra. He argues that misunderstanding superposition as 'both states at once' (rather than a vector in Hilbert space) leads to flawed risk assessments. His Caltech course 'Quantum Frontiers' trains non-physicists to reason about measurement backaction and contextuality, not to build qubits, but to govern them responsibly.
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