Quantum Digital Signatures (2D Phase Space)

Quantum digital signatures let a sender authenticate a classical message so that a forger — even one with unlimited computing power — cannot alter it undetected, using non-orthogonal coherent states in place of a trusted mathematical hardness assumption. This simulator plots the two public-key phase-space clouds |α⟩ and |−α⟩ directly on the physical in-phase/quadrature (I/Q) plane, sized by real quantum shot noise, runs unambiguous state discrimination on simulated verification copies, and tracks how the state overlap s = e^(−2|α|²) and copy count L combine into an exponential forgery bound s^L — watch an honest verification settle near the overlap rate while a forger's attempt collapses as L grows, and drag/zoom the plot to explore the decision boundary up close.