Thousands of scientists around the world are working hard to develop quantum computers—machines that can solve certain problems that are far beyond the reach of the world’s best supercomputers. Famous examples include code breaking and simulating complex molecules. Unlike ordinary computers, these machines exploit the laws of quantum mechanics. Like ordinary computers, the way a quantum computer works can be understood in terms of a few simple logic operations that act on bits of information. By combining many such operations together to form logic circuits, one can solve interesting problems. This document contains a detailed explanation of pictorial rules that can be used to design and analyze quantum logic circuits, along with a few practice problems to help students become familiar with the basic rules of quantum logic.
BEFORE the activity students should know:
AFTER the activity students should know:
For the purpose of this activity, we substituted math by using pictorial rules, where shapes and colors that will represent the different components of the computer, such as the bits and gates. We can represent programming a computer by stacking the many types of gates together to form a “logic circuit.” If we design this circuit in the right way, then we can perform useful computations where, for every input bit string we consider, the answer is given by the output bit string. In addition to representing classical information processing (like in today’s computers), we can also use these pictorial rules to describe quantum information processing. We called the quantum states “mists” (these mists are represented by a cloud outline). These misty states enable computations that are not feasible with classical computers. We can use gates for both classical and quantum circuits with the mist. However, the Hadamard gate is purely quantum and not possible on a classical computer. We can use the Hadamard gate with the mist creating a phenomenon known as quantum superposition (producing mist from non-mist in pictorial rules) and quantum entanglement (turn mists into non-mists in pictorial rules). We show using the visuals from this activity why in quantum mechanics, phase will always contain information behind events that lead to different outcomes.
In the student’s guide, students are asked to complete different challenges using the classical and quantum gates to see if they can arrive at the desired final state. The idea of this activity is that students start to form ideas about the difference between classical mechanics and quantum mechanics. Before letting students work on the challenges, go over the pictorial rules and work with them on the examples provided on the game instructions. Then let them do the initial challenge that only involves classic gates before introducing them into the H and S quantum gates.
Quantum Circuits Activity Video