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I refer to A DIY Guide to Building a Quantum Computer and Researchers advance noise cancelling for quantum computers.

With my friends, I would like to build our simplified quantum computer.

We are also keen to reduce the noise, so my question: is there some quick and easy way to reduce noise?

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    $\begingroup$ Welcome to Quantum Computer SE! This is, in principle, possible (depending on a number of factors), although a 'quick and easy way to reduce noise' depends very much on the type of quantum computer you're looking at (and is definitely an open problem), so would you be able to add more detail into this so we know where best to help? One of the first questions you'd need to ask yourself would be what you're going to use for a qubit $\endgroup$ – Mithrandir24601 Jan 12 '20 at 18:20
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    $\begingroup$ Does this answer your question? How to build a quantum computer in your house? $\endgroup$ – peterh Jun 5 '20 at 12:34
  • $\begingroup$ it does for sure. I believe this will make quantum computers accessible $\endgroup$ – Nathan Aw Jun 6 '20 at 10:42
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I read the article and it seems too rudimentary to provide a manual how to build a quantum computer home. It also contain some "half-truth" about quantum computers, e.g.:

Quantum computers take advantage of strange properties from quantum mechanics to filter through possible solutions much more quickly than conventional computers. When someone asks about the many ways a drug can impact a cancer cell...

and

A quantum computer, on the other hand, has a unique way of sorting through possible solutions and can have an answer in a matter of minutes!

This is true for some tasks but not for all. There are some problems that quantum computer cannot solve faster than classical computer.

Regarding the noise:

One way to reduce noise is to make the quantum system cold. Very cold. As close as possible to the coldest temperature that can be physically reached

and

Next, you will have to limit other types of energy that create noise, such as external magnetic or electric fields ... (Finding clever ways of reducing noise is an ongoing problem and is a big barrier for scientists developing these computers.)

From these quotes, it is obvious that to build quantum computer at home is impossible. Firstly, how to reach temperature close to absolute zero? Reducing vibration is also very difficult and expensive. So, there is no easy way how to do so at your own.

Quotes from the second article:

While the MIT experiment to validate the protocol won't immediately make large-scale quantum computers practically viable, it is a major step toward making them more precise.

According to the research team, there are still years of additional work required in order to perfect the detection and cancellation of noise in quantum systems. In particular, future research will move from a single-sensor system to a two-sensor system, enabling the characterization of noise correlations across different qubits.

You can see that even for scientists with the state-of-art equipment, it is difficult to apply the knowledge about the noise to reduce it and to build a big quantum computer which can be widely used.

Please consider the first articles as and introduction (with some inaccuracies) for laymen how a quatum computers work. Overall, it seems impossible to build a quantum computer in easy and cheap way at home. But please do not feel discouradged and continue to study quantum computing.

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    $\begingroup$ Worth remembering that, although the most successful quantum computer to date might be superconducting (and near absolute zero), there is no fundamental principle of quantum computing that states a quantum computer must be run below room temperature. Indeed, we do have qubits at room temperature $\endgroup$ – Mithrandir24601 Jan 13 '20 at 20:35
  • $\begingroup$ @Mithrandir24601: Thanks for pointing this out. I reacted purely on the article in question. $\endgroup$ – Martin Vesely Jan 13 '20 at 21:52
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The source of noise in your system, and how to reduce it, is really dependent on the quantum computing architecture you're pursuing.

As stated above the most successful quantum computers at the moment are of the superconducting qubit flavor. And as the articles suggest, the way to reduce noise is low temperature and low vibrations, and perhaps chip design(layout of the resonators, and microwave feeds) all of any other easy things have already been Incorporated.

The superconducting qubits however aren't exactly accessible to the amateur, unless you have hundreds of thousands of dollars to throw at it. A dilution refrigerator will run you upwards of $100,000, AWG's for each qubit can run quite a bit too. Then there is the chip fabrication, which is completely out of my range of knowledge.

However there do exist other architectures which are more easily amateur accessible, though they all have their drawback(hence no real commercial adoption)

Nitrogen Vacancy centers in diamond provide you a fairly easy to manipulate and read out qubit. For a basic setup see: Little bits of diamond: Optically detected magnetic resonance of nitrogen-vacancy centers. They suffer from a scaleability problem. And the inherent challenge is that to scale them up, you naturally introduce magnetic noise. Though you could in principle utilize the electron spin as a bus and interface and nuclear spins in the diamond as your qubits.

Another accessible option is NMR computing. Nuclear spins are your qubits, and you readout and manipulate they through RF. They too suffer from scaleability, and a readout. So you end up needing to work with ensembles (Which provide you with your statistics in one shot) however you can't really initialize the system properly. A nice review: Quantum Computing with NMR

I'm sure there are some other easily accessible architectures, but I'm not so familiar with them.

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