Quantum Computing Explained Simply | Hacker News Reader

Quantum Computing Explained Simply

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67 pointsutkarshs1217 comments

This isn't a particularly good introduction to quantum computing. The fact that we can't scale down transistors into the quantum realm doesn't have much to do with the real motivation behind making quantum computers. The real motivation for making a quantum computer is that it allows us to perform algorithms that exploit the quantum behaviour of qubits.

To give a concrete example of this, there is a basic quantum logic gate called a Hadamard gate. This takes a qubit in the state |0> and transforms it into a qubit in the state (|0> + |1>)/sqrt(2). The resultant state is what is known as a superposition state - namely a superposition of both the |0> and |1> states. You can think of the |0> and |1> states as being analogous to the 0 and 1 states of a traditional bit. What this means is that when the qubit is measured (read queried) it will return a value of 0 or 1 with equal probability.

The point I'm making is that this is radically different to traditional computing and isn't simply just the next step along in 'valve transistor -> semiconductor -> ?'

Hi! I put this guide together and I'm really glad you brought this point up. When I thought of creating this guide, I wanted to make it really easy for beginners to graduate level by level up to quantum gates, which inspired me to instead break the information down in a series.

This Part-1 guide in the series is mean't to educate even complete noobs from how a basic computer works and how we have reached the limits of making them any more powerful. While you are accurate when you say Quantum algorithms can help us exploit the quantum behaviour of qubits, we are particularly interested and motivated to utilize them because we can exponentially increase our computing power.

I have another follow-up guide coming that would take the readers a few more levels up very soon.

> we are particularly interested and motivated to utilize [quantum computers] because we can exponentially increase our computing power.

On some problems.

Quantum computers are --- to the best of our knowledge --- exponentially faster at computing some things (e.g. discrete log and factoring), quadratically faster at others (e.g. NP-complete problems), and no better than classical computers at others.

(I assume you know this since you're writing an article on quantum computers, but want to clarify for others.)

Well, I kind of knew that people might associate the increment in computing power with that required in their daily computing needs like watching Youtube videos for example; for the same reason I made sure to explicitly mention in the Introduction, that - "it [Quantum Computers] promises tremendous computing power enough to help us solve some really tough mathematical problems that are holding back our progress in a number of fields."

It might be worth noting that this seems more to do with why different transistor types are being used (fin-fets, nano tubes, etc) since we really haven't reached the physical limit of "traditional" transistors yet. I'd also argue that the motivation behind quantum computers is very much unrelated to limitations on transistor sizes, and more about the algorithms that can potentially be much faster than on traditional logic, such as shor's factoring algorithm

> when the qubit is measured (read queried) it will return a value of 0 or 1 with equal probability

To clarify, qubits don't necessarily have equal probabilities of |0> and |1>. If the probabilities were always equal, we wouldn't be able to use quantum computers for anything besides generating coin flips! The "answer" from a quantum computer is encoded as output probabilities of the qubits, which are found by running the calculations a bunch of times and counting the frequency of each |0> and |1> state.

I think you've misread my comment as what you're saying is incorrect. When a qubit is in the state (|0> + |1>)/sqrt(2) it does have equal probabilities of being measured as either |0> or |1>. I think what you're trying to say is that (|0> + |1>)/sqrt(2) is not the only superposition state a qubit can be in. A qubit can be in any arbitrary position of the two possible states.

Your original comment is totally correct, but I thought it might mislead beginners - that's why I said "to clarify." I think there is a common confusion about whether a qubit can have probabilities besides 50:50. The Hadamard gate example explains superposition, but tends to increase this misconception, so I also wanted to emphasize the many other possible states and how an answer is extracted from them.

This is a bit misleading I think. There are a set of quantum algorithms with deterministic outcomes. The right answer will be measured with probability 1, or something very close...

If you are doing slides, then I'd strive to avoid scrolling. Either you scroll or your swipe, but doing both is kind of difficult. But I like the idea of small contained slides of content and graphs.

Thanks for letting me in on your experience. :) We totally believe that when information around a topic is broken down into bite-sized slide-like chapters its much less overwhelming to consume than everything dumped on a single page.

We are trying to give the authors an ability to contain the contents of a single slide within user view. Our editor is freshly released, so hopefully a future release soon enough would let educators do that and with some interaction features as well.

Is the slide software available online, e.g. github? I've been looking for something similar.

We built the editing tool for our users who would like to create Searchtrack guides to break down and express their knowledge. Unfortunately, it's not an open-source software. You can however request an invite to access it after signing up.

This was pretty short. But I thought people working on quantum computers were trying to understand the Wave function, and then see if they can make the Wave function do the calculations. In the case the world was a simulation, this is like accessing the computing power of the Simulation Computer of the world.

It was short because this article doesn't explain quantum computers. A better title is "Why we can make smaller transistors?" Quantum computers don't use transistors.

And quantum computers are not about understanding The Wave or hacking the word simulator. Another commenter post this link, that is a good initial introduction http://www.smbc-comics.com/comic/the-talk-3

(Anyway, to really understand what is quantum mechanics and quantum computers, you need a lot of algebra. Don't trust explanations without algebra.)

How is that no one has referenced "The Talk"?

http://www.smbc-comics.com/comic/the-talk-3

Wont't graphene transistors be the way forward? Does anyone have any info on this?

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