What is quantum computing? Solutions to impossible problems

摘要： Quantum computing has great promise to solve problems that are too hard for classical computers to solve in reasonable amounts of time, but they are not yet practical

▲圖片標題(來源： Microsoft )

There’s no lack of hype in the computer industry, although even I have to admit that sometimes the technology does catch up to the promises. Machine learning is a good example. Machine learning has been hyped since the 1950s, and has finally become generally useful in the last decade.

Quantum computing was proposed in the 1980s, but still isn’t practical, although that hasn’t dampened the hype. There are experimental quantum computers at a small number of research labs, and a few commercial quantum computers and quantum simulators produced by IBM and others, but even the commercial quantum computers still have low numbers of qubits (which I’ll explain in the next section), high decay rates, and significant amounts of noise.

Quantum computing explained

The clearest explanation of quantum computing that I’ve found is in this video by Dr. Talia Gershon of IBM. In the video, Gershon explains quantum computing to a child, a teenager, a college student, and a graduate student, and then discusses quantum computing myths and challenges with Professor Steve Girvin from Yale University.

To the child, she makes the analogy between bits and pennies. Classical bits are binary, like pennies lying on the table, showing either heads or tails. Quantum bits (qubits) are like pennies spinning on the table, which could eventually collapse into states that are either heads or tails.

To the teenager, she uses the same analogy, but adds the word superposition to describe the states of a spinning penny. Superposition of states is a quantum property, commonly seen in elementary particles and in the electron clouds of atoms. In popular science, the usual analogy is the thought experiment of Schrödinger’s Cat, which exists in its box in a superposed quantum state of both alive and dead, until the box is open and it is observed to be one or the other.

Gershon goes on to discuss quantum entanglement with the teenager. This means that the states of two or more entangled quantum objects are linked, even if they are separated.

By the way, Einstein hated this idea, which he dismissed as “spooky action at a distance,” but the phenomenon is real and observable experimentally, and has recently even been photographed. Even better, light entangled with quantum information has been sent over a 50-kilometer optical fiber.

詳見全文Full Text： InfoWorld

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