# Questions tagged [superposition]

Quantum superposition is a fundamental principle of quantum mechanics. It states that, much like waves in classical physics, any two (or more) quantum states can be added together ("superposed") and the result will be another valid quantum state; and conversely, that every quantum state can be represented as a sum of two or more other distinct states. Mathematically, it refers to a property of solutions to the Schrödinger equation. (Wikipedia)

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### How does Grover's operator work - specifically applying the H gate in the operator

I am following this video (https://www.youtube.com/watch?v=0RPFWZj7Jm0) and the professor applies an H gate at the start of the reflection operator (one H gate was applied at the beginning of the main ...
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### The heart of all of quantum physics is superposition

I am going to teach an introductory course on quantum information and I thought about this statement that I want to give at the very beginning. Would you agree on that? From my perspective, every ...
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### Quantum Computer Basics [closed]

I am a newbie to Quantum Computing world. My collage professor asked me to do presentation on quantum computing. I have read many articles online but still I think I am not satisfied with what I found....
1 vote
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### Does Rx(θ) applied on pure states create superposition?

I'm struggling to find if $\text{Rx}(\theta)$ gate would convert a pure state qubit $|0\rangle$ to a superposition $\cos( \theta) |0\rangle + \sin(\theta) |1\rangle$. A definitive answer with ...
1 vote
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### Are entanglement and superposition necessary and sufficient for quantum universality?

A set of quantum gates is universal when it can approximate any unitary operation with arbitrary precision. These unitary operations are used in quantum algorithms, in a general sense, manipulating ...
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### Quantum adder of two states that are themselves superpositions

I have two states $|a\rangle = \frac{1}{\sqrt N}\sum_{i=0}^{N-1}|i\rangle|a_i\rangle$ and $|b\rangle = \frac{1}{\sqrt N}\sum_{j=0}^ {N-1} |j\rangle|b_j\rangle$, with $i,j,a_i,b_j \in \mathbb{N}$. I ...
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### CNOT entangling a third qubit and how measurement impacts entanglement

I'm trying to understand entanglement, superposition and the effects of measurement on entangled qubits a bit better. About entanglement: I know that the circuit below will entangle the two qubits: ...
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### Why doesn't reading the ancilla qubit in Quantum Error Correction kill entanglement?

In Quantum Error Correction we have ancilla qubits (in gray) that will be entangled with the pair of bits we want to check. Because we don't want to directly measure the "main" qubits (in ...
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1 vote
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### QiskitError: 'Sum of amplitudes-squared does not equal one.'

I'm coding a 429 element length string to compare to other same length strings, but I keep getting that error. I used ljust to fill the string to a 512 element ...
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1 vote
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### Multiple Hadamard gates Transformation on N qbits

I am newbie to quantum computing and having a bit confusion regarding the action of Hadamard gate on multiple qbits which are already in superposed state (I well understand how it works for qbits ...
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### How does a Hadamard gate impact the initial/previous values of a Qubit? [closed]

I've been studying Quantum Computing and one thing that intrigued me is: given a qubit q1 with an initial value x, when I apply a Hadamard gate on it, then it goes to superposition, so the probability ...
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### Mark a state if it is part of another register

I am wondering something, especially about Grover algorithm: imagine I have a quantum register $a$ and a quantum register $b$ of equal length. Then, suppose I apply some algorithms on $a$ s.t. it is ...
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Given an arbitrary $|\psi\rangle=\sum_{i=0}^n\alpha_i|i\rangle$, $K=\{i\mid \alpha_i\not=0\}$, and $k=\vert K\vert$, is it possible to generate the state $\frac{1}{\sqrt k}\sum_{i\in K}|i\rangle$? I ...