Programming Quantum Computers - Part 1

Overview

• Introduction to programming quantum computers.
• Comparison with classical computer programming.
• Explanation of compilers, machine code, and logic gates in classical and quantum computing.
• Detailed discussion on quantum mechanics principles: superposition and entanglement.
• Introduction to quantum logic gates and Quantum Computing algorithms.

Classical Computers

How Coding Works

• Programming languages (Python, C++, Java, etc.) allow interaction with computers using near-human language commands.
• Example: Code to count to 10 written by ChatGPT.

Compilers

• Special programs that convert high-level programming language into machine language.
• Different languages have specific compilers acting as translators.
• Compilers as black boxes: take human-written code (input) → output machine code (sequence of 1s and 0s).

Machine Code

• Set of instructions telling computer about specific bits to operate on.
• Contains 1s and 0s interpreted as direct instructions for electrical signal flow.

Logic Gates

• Fundamental building blocks of classical computers (e.g., AND, OR gates).
• Physical circuits made up of bits.
• Perform mathematical operations and transfer information between bits.

Quantum Computers

High-Level Programming

• Quantum computers are coded using high-level programming languages like IBM’s Qiskit.
• These languages run on classical computers, compiled, and then executed on Quantum Hardware.

Principles of Quantum Mechanics

Superposition

• A Quantum system can be in multiple states at the same time.
• System's state only collapses to a definite state upon measurement.
• Probability of collapse given by square of the state's coefficient.

Entanglement

• Measurement of one entangled particle’s state informs the other’s state immediately.
• Example: Bell State
• Entangled state probabilities (e.g., 50% chance of 00 and 50% of 11).

Quantum Logic Gates

• Operations changing a qubit’s state in a known, repeatable way.
• Single- and multi-qubit gates (analogous to classical NOT and AND gates).
• Implemented differently across quantum hardware (e.g., neutral atoms, superconducting qubits).

Implementing Algorithms

• Quantum gates strung together to form algorithms (quantum circuits).
• Classical programming abstractions applied (e.g., coding in Qiskit).
• Use of classical computers to write/compile quantum code.

Example Algorithm: Deutsch-Jozsa

• Problem: Determine if a function is constant or balanced.
• Classical Solution: Requires 3 evaluations.
• Quantum Solution: Requires only 1 evaluation.
• Steps:
  1. Prepare qubits (0 and 1 respectively) and apply Hadamard gate.
  2. Evaluate the function on qubits.
  3. Measure results and analyze if constant or balanced.

Summary

• Classical and quantum algorithms differ but follow some underlying principles.
• Quantum Computing offers significant advantages for certain types of problems.
• Next part: Implementation of Deutsch-Jozsa algorithm using Qiskit on a real quantum computer.