Why quantum needs fault tolerant?

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1

Hi, I heard about fault tolerant for QC. Can you help me know why?

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2

Hi, @therealsqueezingpand
Welcome to the forum!

A fault-tolerant quantum computer is one that can properly work despite errors occurring. Those errors can happen for a variety of reasons given that there are many pieces of hardware involved. Unfortunately, any real world implementation will have errors.

For example, consider a situation where you were trying to implement a quantum circuit with several gates and qubits and an error happened (maybe a one of your basis states switch from 1 to 0), that error will propagate and render an incorrect computation :frowning: We need a way to correct these errors as the computation goes along! And luckily for us :partying_face:, there is a whole field dedicated to Quantum error correction to achieve this fault-tolerance.

If you want to explore these subjects, there is a set of interactive modules in the Pennylane codebook dedicated to Quantum fault tolerance.

Let me know if this helped and/or you have any other questions.

3

Thank u @dangulom :smile: so you’re saying if I have a bug in my code the fault tolerant quantum computer wlil fix it for me? Sounds amazing!! How does it know I made a mistake?

4

Not quite! that’s not what I meant :no_mouth: sorry for not being clear enough. A fault-tolerant quantum computer doesn’t fix programming bugs or logic errors in your code. It handles errors caused by quantum hardware imperfections.

I was saying that a quantum computer is a physical device, it is made up of many small pieces of hardware (for instance, waveguides of silicon). All of those parts, not completely isolated from the environment, have to work perfectly in order to perform computations to give correct and reliable results. But they rarely do so, they are very delicate, and even tiny interactions with their environment can introduce errors. For example, an operation performed into a qubit could affect other qubits by mistake or it can simply result in a slightly different operation than the intended one.

To detect and correct such errors, Quantum error correction codes perform “syndrome” measurements (see this module for an example). These measurements work like a diagnostic tool: they reveal information about the error without disturbing the encoded quantum information. For example, if a qubit flips unintentionally, syndrome measurements identify the flip so it can be corrected.

II hope this clears things up! Let me know if you have more questions :smile:

5

I see, thank u @dangulom for the nice answer! This is a very interesting topic, i will have to read more :sunglasses:

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