Three myths about quantum computing

In this series of posts I will discuss some misconceptions about quantum computing.

One often hears people saying that quantum physics is “strange” and that our classical intuition “breaks down” in the quantum world. I will try to argue that one should not brag about the weirdness of quantum mechanics without carefully investigating the corresponding phenomena in the classical world. In fact, many quantum phenomena no longer seem surprising once their lesser cousins in the classical probabilistic world are understood.

To illustrate my point, I will consider three basic properties of quantum information

  1. exponential state space
  2. no-cloning theorem
  3. quantum teleportation and superdense coding

and discuss how they translate to the classical case.

These topics are usually covered in the first class of an introductory quantum computing course, so none of what I discuss should come as a surprise to somebody who has taken such a course or read an introductory textbook on the topic. However, I have to admit that I was equally shocked both, when I learned these basic facts about quantum information in class, as when I later realized that they have a corresponding classical counterpart.

I would like to acknowledge all my “non-quantum” friends with whom I have had conversations about quantum physics. I would probably still believe in these misconceptions if I had not tried to explain you in simple terms why quantum physics is supposed to be so strange. Maybe it is not so strange after all…

p.s. For those of you who have never attempted to explain what you are doing to somebody who does not have a PhD degree in your area of expertise, consider the following three quotes by the founders of quantum mechanics:

Most of the fundamental ideas of science are essentially simple, and may, as a rule, be expressed in a language comprehensible to everyone.
—Albert Einstein

The physicist may be satisfied when he has the mathematical scheme and knows how to use it for the interpretation of the experiments. But he has to speak about his results also to non-physicists who will not be satisfied unless some explanation is given in plain language. Even for the physicist, the description in plain language will be the criterion of the degree of understanding that has been reached.
—Werner Heisenberg

If you cannot—in the long run—tell everyone what you have been doing, your doing has been worthless.
—Erwin Schrödinger

4 thoughts on “Three myths about quantum computing

  1. Pingback: Three myths about quantum computing — Part 2: No-cloning theorem | Mamuta memuāri

  2. Pingback: Three myths about quantum computing — Part 3: Teleportation and superdense coding | Mamuta memuāri

  3. Pingback: Three myths about quantum computing — Part 1: Exponential size state space | Mamuta memuāri

  4. Ah these were really interesting, specially the one about cloning. Of course, there is a limit to how far the parallelisms with classical probabilistic information can go (this follows from e.g. Bell’s Theorem), but determining where that limit is certainly interesting. I wonder in particular if there is any probabilistic equivalent of the Stern-Gerlach experiment…

    Re: the communication using natural language, it’s certainly worth trying for everyone involved – but my opinion is that for a really good understanding mathematics must be involved, in the same way that there is only so much you can learn about poetry without learning obscure facts about the language (and the culture) it is written in.

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