3

I am a computer engineer and have recently started understanding quantum computers.

I am still struggling to wrap my head around some concepts.

One such query is the following - It is said that during the computation the qubits exist in the multiple states with some probability until it is measured. Once the act of measurement is done all the probabilities collapse and one answer is the output.

Now, what I am not able to get my head around is, how are we sure that this collapsed answer is the right answer? Since the superposition states are probabilistic in nature, there is a probability (though slim) of a wrong answer being output too.

Also since we cannot see or measure the intermediate superposition states we do not know which state has the highest probability. So how do we make quantum computer output the right answer?

I would highly appreciate someone to guide me through this.

4The computation is

choreographedin such a way that there's a high probability of getting the right answer. That's exactly why the probabilistic quantum algorithms have to be run several times. Anyway, you won't really be able to understand this concept unless you actually thumb through the math of some basic quantum algorithms. Better pick up a good textbook! – Sanchayan Dutta – 2019-11-01T16:25:48.5072Sanchayan's comment is just the correct answer and I recommend that it be repeated as a stated answer to the question. The only thing I would change is to replace "have to be run several times" with "may have to be run more than once". The answer is indeed statistical and the algorithm may have to be repeated. But if it has a 99.99% chance of being correct, "several" is an overstatement. – Greg Kuperberg – 2019-11-01T16:38:00.290

@SanchayanDutta: can you suggest me some good resources to understand the math behind the Quantum Algorithms since as you rightly guessed I am struggling to understand it, even the supposed hello world algorithm of Deutsch-Jozsa algorithm – dhiraj suvarna – 2019-11-01T17:19:55.233

@dhirajsuvarna Are there any organised resources available from where I can begin my quantum computing studies?

– Sanchayan Dutta – 2019-11-01T17:51:55.217@SanchayanDutta: Thank You for the link. Its good. – dhiraj suvarna – 2019-11-02T16:33:03.173