Expressibility of variational quantum circuits
The expressibility of a parametrized quantum circuit describes how good (in case of high expressibility) or how bad it covers the space of quantum states.
Let's check out some examples to see what the expressibility of a circuit really means.
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Use the little triangles to change the gates used in the circuit. $R_x(\theta)$ , $R_y(\theta)$ , and $R_z(\theta)$ describe a parametrized rotation around the x, y, or z axis. H is the Hadamdard gate. Uniformly random single-qubit unitaries are applied if U is chosen.
Explore how different parametrized circuits allow you to explore the states of a qubit.
This applet is inspired by a paper by Sukin Sim, Peter D. Johnson, Alan Aspuru-Guzik, where they explore the expressibility and entangling capability for different Ansätze.
The animation is a derivate of a project from Roope Salmi (MIT licensed) (MIT licensed).