1 vote
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### Measurement of any qubit state in Y-basis [duplicate]

how can I measure any qubit state in Y-basis in qiskit. there is this solution here How to measure in another basis but it gives the qubit's position on bloch sphere in z-axis where as I think it ...
4k views

### Qiskit - Z expectation value from counts?

For a given state $|\psi\rangle$, how would I work out $\langle\psi|Z|\psi\rangle$ ? If I run a quantum circuit and get the counts dictionary on qiskit, I get observables in the Z basis. For n=1 ...
2k views

### Given a state $|\phi\rangle=\frac{1}{\sqrt{2}}(|0\rangle+e^{i\theta}|1\rangle)$, how do I know the angle $\theta$?

Question1. If there is a state $|\phi\rangle=\frac{1}{\sqrt{2}}(|0\rangle+e^{i\theta}|1\rangle)$, and I want to know the angle $\theta$. What kind of measurement should I do? Could somebody give me ...
542 views

### How is it possible to guess what state the qubit was in by measuring it?

Let's say that the qubit is in the state $\psi = \alpha|0\rangle+\beta|1\rangle$. We want to find out the values $\alpha$ and $\beta$. If we measure it in, say, the standard basis, then the outcome we ...
798 views

### Computing variance under the action of a unitary operator

I wish to calculate the expectation and variance for an observable on a particular qubit of a multi qubit quantum state. I'm using a quantum computing simulation library which allows me to apply ...
577 views

### What is the state of a qubit after measuring some a Pauli operator?

I'm confused about the state of a system after a measurement. Say we have a particle $v$ in the state: $|\psi\rangle= \sqrt{1/4} \ |0\rangle + \sqrt{3/4} \ |1\rangle$. From my understanding, if one ...
428 views

### Measuring in rotated basis for mult-qubit circuits

In a previous question (and others), someone asked about measuring on a basis other than the computational one, but for one qubit circuit. Here it was asked for a specific basis. Suppose I have a two-...
328 views

### Calculating bipartite state from joint probability distribution

We can calculate single qubit state by measuring it in pauli observables {$\sigma_{x},\sigma_{y},\sigma_{z}$} and then looking at its probability distribution. How to do this when we are having joint ...