Per IBM's documentation for quantum circuits, the general unitary operator is defined as: $\hat{U}=\begin{bmatrix}cos(\frac{\theta}{2})&-e^{i\phi}sin(\frac{\theta}{2})\\e^{i\phi}sin(\frac{\theta}{2})&e^{i\phi+i\lambda}cos(\frac{\theta}{2})\end{bmatrix}$ For a better understanding I was working ...

when I perform 2 H gates on a single qubit, why is that the probability of getting 0 as the outcome is 100%? Why is it not 50% 0 and 50% 1 ? why is the second H gate not putting the input from first H gate into superposition state?

I am trying to solve a system of linear equation using HHL algorithm in Qiskit. I have a problem with understanding the purpose of the following function. state_fidelity() To understand this I have followed their official documentation. But it is not clear to me yet. They used this function...

The diamond distance between two operations is the maximum trace distance between their outputs for any input: $$\text{Diamond}(U, V) = \max_{a} \;\; \text{Trace}(U(a), V(a))$$ Note that the diamond distance is not subadditive, since $R_Z(\epsilon) \cdot R_Z(\epsilon)$ has a diamond distance fr...

Since the entropy of the universe always increases, does it mean that the information content (the number of bits) keeps increasing with time?