Margolus–Levitin theorem

The Margolus–Levitin theorem, named for Norman Margolus and Lev B. Levitin, gives a fundamental limit on quantum computation (strictly speaking on all forms on computation). The processing rate cannot be higher than 6 × 10³³ operations per second per joule of energy. Or stating the bound for one bit:

A quantum system of energy E needs at least a time of h 4 E to go from one state to an orthogonal state, where h = 6.626 × 10⁻³⁴ J·s is Planck's constant and E is average energy.

The theorem is also of interest outside of quantum computation, e.g. it relates to the holographic principle, digital physics, simulated reality, the mathematical universe hypothesis and pancomputationalism.