Qusim.py – A toy multi-qubit quantum computer simulator written in Python
For the uninitiated - to simulate a basic quantum computer, all you need is the following:* A product state vector, which is a vector of size 2^n filled with complex numbers where n is the number of qbits you're using. You derive the product state from a series of individual qbits by taking their tensor product; this exponential term is why simulating quantum computers takes exponential space.* A set of common quantum logic gates, which are (2^n)x(2^n) matrices you multiply against the product state vector to derive the new product state vector; these matrices must be unitary (their conjugate-transpose is their inverse) (edited, see [0]) and therefore reversible (quantum computers are reversible computers). The full (2^n)x(2^n) matrices are derived by taking the tensor products of several 2x2 and 4x4 matrices.* The measurement logic, where you calculate how the product state collapses by taking the square of the absolute value of each entry in the product state (these entries are called amplitudes).This project is an implementation of those three things in Python. There is nothing special about the above mathematical constructs save that they match the observed semantics of a quantum system. This is good! Quantum computing is accessible to anyone who has taken a basic undergraduate course in linear algebra.[0] I previously believed all quantum operators were their own inverses (Unitary and Hermitian) but apparently that is not the case; see comments below.