diff --git a/exercises/Exercise5.ipynb b/exercises/Exercise5.ipynb new file mode 100644 index 0000000..779e2b3 --- /dev/null +++ b/exercises/Exercise5.ipynb @@ -0,0 +1,87 @@ +{ + "cells": [ + { + "cell_type": "markdown", + "metadata": {}, + "source": [ + "# Exercise 5\n", + "\n", + "\n", + "## 1. Clifford Gates and Paulis\n", + "\n", + "\n", + "(a) For $n$ qubits, there are $4^n$ possible tensor products of Paulis (one of which is the $n$-qubit identity). Show that (up to a phase) these can be expressed as a product of $2n$ $n$-qubit Paulis.\n", + "\n", + "(b) If $U$ is a Clifford gate, the following property holds\n", + "\n", + "$$\n", + "U P U^\\dagger \\sim P' \\,\\,\\,\\,\\, \\forall P,\n", + "$$\n", + "\n", + "where $P$ and $P'$ are Paulis and $\\sim$ denotes equality up to a factor of $\\pm 1$ or $\\pm i$. If this relation holds for the $2n$ Pauli generators of part (a), show that it also holds for all $n$-qubit Paulis.\n", + "\n", + "\n", + "\n", + "## 2. Single-Qubit Clifford Gates\n", + "\n", + "\n", + "(a) Show that the Paulis are Cliffords themselves.\n", + "\n", + "(b) Show that $H$, $S$ and $S^\\dagger$ are Clifford gates.\n", + "\n", + "(c) Show that $T=S^{1/2}$ is not a Clifford gate.\n", + "\n", + "\n", + "## 3. Two-Qubit Clifford Gates\n", + "\n", + "For more than one qubit, Clifford gates map between tensor products of Pauli operators.\n", + "\n", + "For two qubits\n", + "\n", + "$$\n", + "U \\,( P \\otimes Q )\\, U^\\dagger \\sim P' \\otimes Q' \\,\\,\\,\\,\\, \\forall P,Q\n", + "$$\n", + "\n", + "where $P$, $Q$, $P'$ and $Q'$ are all Paulis and $\\sim$ denotes equality up to a factor of $\\pm 1$ or $\\pm i$.\n", + "\n", + "(a) Show that the controlled-NOT is a Clifford gate.\n", + "\n", + "(b) Show that the controlled-Hadamard is not a Clifford gate.\n", + "\n", + "## 4. Three-Qubit Clifford Gates\n", + "\n", + "(a) Provide an example of a three-qubit Clifford gate, and show that it is indeed a Clifford. This should be a truly three qubit gate, and therefore not one that can be expressed purely as a tensor product of single- and two-qubit gates.\n", + "\n", + "(b) Show that the Toffoli gate is not Clifford." + ] + }, + { + "cell_type": "code", + "execution_count": null, + "metadata": {}, + "outputs": [], + "source": [] + } + ], + "metadata": { + "kernelspec": { + "display_name": "Python 3", + "language": "python", + "name": "python3" + }, + "language_info": { + "codemirror_mode": { + "name": "ipython", + "version": 3 + }, + "file_extension": ".py", + "mimetype": "text/x-python", + "name": "python", + "nbconvert_exporter": "python", + "pygments_lexer": "ipython3", + "version": "3.9.1" + } + }, + "nbformat": 4, + "nbformat_minor": 4 +}