Programming Quantum Computers - Part 1

Jul 2, 2024

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.