# Tag Info

## Hot answers tagged circuit-construction

Accepted

### Does the Quantum Fourier Transform require universality?

Yes, the QFT requires universality. No, there isn't a non-universal gate set that implements the QFT. Just having the QFT as an operation is already computationally universal, because it can generate ...
• 37.1k

### How are quantum algorithms devised?

Many people having given a lot of thought about these kinds of questions - I really like Aharanov's discussion in a Qiskit article here. Recalling some history, we may have: Feynman took a guess that ...
Accepted

• 10.1k
Accepted

### Calculating the classical OR gate in a 3 qubit (+1 ancillary qubit) circuit

There are two errors in your code: You only initialize the first two bits, the last bit of the input is unused. Thus, you should replace: ...
• 6,162

### How to convert a simple matrix into circuit?

In qiskit, you can run the following code: ...
• 47

### Map $n$ qubit state with complex amplitudes to $n+1$ qubit state with real amplitudes

This will violate unitarity of the transformation $U$. Consider states $$\begin{bmatrix}\frac1{\sqrt2} \\ \frac1{\sqrt2}\end{bmatrix} (b=d=0)$$ and \begin{bmatrix}i\frac1{\sqrt2} \\ i\frac1{\sqrt2}\...
• 9,050

### Encoding circuit for $[\![6, 4, 2]\!]$ code

We can obtain an encoding circuit for the $[\![m,m-2,2]\!]$ code for any even $m$ by generalizing the circuit displayed in the question. More precisely, for every new qubit we prepend a CNOT gate with ...
• 22.5k