# Richard Feynman > 1918–1988 · Physicist > > **Recorded contribution:** Proposed quantum computing (1981); quantum electrodynamics; Feynman diagrams ## How to use this dossier Read for a causal chain, not a hero story: inherited problem → contribution → mechanism → downstream capability → limit. Then close the page and complete the reconstruction exercise from memory. ## 1. Historical orientation Richard Feynman (1918–1988), better known for quantum electrodynamics, helped crystallize quantum computation as a scientific problem. In a 1981 lecture and a 1982 paper, he argued that generic classical simulation of quantum physics appears to require explosive resources and proposed computers whose components obey quantum mechanics. He did not supply today's universal circuit model, fault tolerance, or famous algorithms; those emerged through work by Paul Benioff, David Deutsch, Peter Shor, and many others. Feynman's first-principles contribution was to invert the simulation problem: if nature is quantum, use controllable quantum systems to reproduce its state evolution. ## 2. The problem inherited A classical simulator tracks amplitudes for a quantum system whose state space grows exponentially with particle count, making direct simulation infeasible even when the physical system evolves naturally. ## 3. The central contribution Feynman articulated why a universal classical probabilistic machine is not an evidently efficient simulator of quantum physics and proposed quantum-mechanical computing elements as the appropriate substrate. ## 4. Reconstruct the mechanism 1. Encode a physical system in qubits whose joint state contains complex amplitudes over many classical basis configurations. 2. Prepare an initial quantum state corresponding to the system and quantities of interest. 3. Apply controlled interactions whose unitary evolution approximates the target Hamiltonian through local operations and time steps. 4. Measure selected observables repeatedly to estimate outcome distributions rather than attempting to read every amplitude. ## 5. What changed downstream - Quantum simulation became a central proposed application of quantum computers. - The argument motivated formal models of universal quantum computation and later complexity theory. - It reframed hardware design around exploiting, rather than suppressing, superposition and interference. ## 6. Attribution, limits, and uncertainty - Benioff had already described quantum-mechanical models of computation, and Deutsch later formalized a universal quantum computer. - Feynman's proposal did not solve state preparation, error correction, decoherence, or measurement-cost problems. - A quantum representation can be exponentially large without allowing arbitrary amplitudes to be efficiently extracted. ## 7. Reconstruction lab Simulate one and two qubits with complex vectors. Apply a Hadamard gate followed by a controlled-NOT, sample the Bell state 1,000 times, and contrast the four stored amplitudes with the number needed for thirty qubits. Explain why measurement does not reveal the entire vector. ## 8. Evidence trail - [Simulating Physics with Computers](https://doi.org/10.1007/BF02650179) — International Journal of Theoretical Physics - [Richard P. Feynman – Biographical](https://www.nobelprize.org/prizes/physics/1965/feynman/biographical/) — Nobel Prize Outreach --- *Research checked 2026-08-09. Dates, roles, and claims about living people are historical snapshots. Linked sources remain the authority; this dossier is original instructional synthesis.*