# Exploring Qubits and Multiple Qubit Systems

• Erwin
In summary: There's no real disadvantage to using multiple qubits as opposed to a single qubit, except that they take up more memory.In summary, multiple qubits help to speed up classical algorithms and are probabilistic in nature. There is no real disadvantage to using them, other than that they require more memory.
Erwin
At first, good evening.
I want you to know that Eng is not my first language, so you could find many errors while reading my posts.

I was reading something about qubit and multiple qubit systems, which combined can create a powerful processor for a new type of computer.

I'm not sure of how could the correlation between a pair of qubits would do it. Of sure, a single qubit contains a lot of information, it's like a complex number, but how can it be helpful?

Good evening to you as well! Your use of English is quite good for an alternative language. I believe I understand you well and share your curiosity.

I have an excellent understanding of "classical" computers and have investigated this same question myself recently. As well as I could verify, the value of a q-bit remains a simple bit represented in the quantum "spin" of an atom, for example up=1 or down=0. The difference is in how computations are performed and results are interpreted. From what I understand, the simple description would be that classical computers are deterministic while quantum computers are probabilistic. Where classical computers take a definite number of operations to complete a calculation, a quantum algorithm could find likely solutions with far less operations.

Erwin and Greg Bernhardt
What I found is that a qubit is not only a spin, because it has not only the 0 and 1 states, but also all the states between; for this reason, when we measure it we can, of sure, find only 0 or 1, following probabilistic's laws.
My question is a little bit deeper. I wish to know what happens when I combine two or more qubits: in this case there's more interesting consequence, that is the fundament for quantum computers.

It's a bit hard to explain what gives quantum computers an advantage, and especially hard to clarify the limitations of those advantage. The advantage is NOT that they are probabilistic.

Ultimately it comes down to the fact that operations are unitary matrices ( instead of permutation matrices or stochastic matrices like classical computers have ). That's why entanglement is a thing, that's why measuring half way through has different outcomes compared to measuring at the end, and that's why it's possible to represent a Fourier transform directly as an operation that can be factored into a short series of simple operations.

Strilanc said:
The advantage is NOT that they are probabilistic.
I actually took the probabilistic nature as a disadvantage. I don't know much but from what I read multiple q-bits are required to assure a sensible result for 1 bit of data, as opposed to the far more efficient checksum error detection method.

## 1. What is a qubit?

A qubit, short for quantum bit, is the basic unit of quantum information. It can exist in multiple states simultaneously, unlike a classical bit which can only have a value of 0 or 1.

## 2. How are multiple qubits used in quantum computing?

Multiple qubits can be used to store and process complex quantum information. They can also be entangled, meaning their states are correlated and can affect each other even when physically separated.

## 3. What is superposition and how does it relate to qubits?

Superposition is the ability of a qubit to exist in multiple states at the same time. This is a fundamental principle of quantum mechanics and allows for more efficient and powerful computation in quantum systems.

## 4. What is entanglement and why is it important in quantum computing?

Entanglement is a phenomenon where qubits become correlated and can affect each other even when separated by large distances. This allows for faster and more secure communication and can enhance the capabilities of quantum computers.

## 5. How are qubits physically implemented in quantum systems?

There are various physical systems that can be used to implement qubits, such as photons, atoms, and superconducting circuits. These systems are carefully controlled and manipulated to perform quantum operations and computations.

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