Grover's algorithm

John Preskill traces quantum computing from Feynman’s proposal to simulate nature with quantum systems through quantum error correction and today’s hardware approaches. He explains entanglement, interference, and Grover’s search algorithm, emphasizing that quantum computers do not simply perform many readable calculations at once. He discusses likely applications in materials and chemistry, the risks to current public-key cryptography, and quantum communication and sensing. He also describes open challenges in scaling hardware, the uncertain prospects of competing technologies, and how quantum information may inform basic physics and education.