Linked Questions
10 questions linked to/from Why can I apply $HS^\dagger$ and then measure in the computational basis to measure $Y$?
1
vote
0
answers
161
views
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 ...
11
votes
2
answers
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 ...
- 111
5
votes
2
answers
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 ...
- 85
3
votes
3
answers
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 ...
- 2,177
5
votes
2
answers
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 ...
- 151
3
votes
2
answers
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 $.
From my understanding, if one ...
- 155
3
votes
3
answers
428
views
Measuring in rotated basis for mult-qubit circuits
In a previous question (and others), someone asked about measuring on a basis other than the computational one, but for one qubit circuit. Here it was asked for a specific basis.
Suppose I have a two-...
- 131
3
votes
2
answers
328
views
Calculating bipartite state from joint probability distribution
We can calculate single qubit state by measuring it in pauli observables {$\sigma_{x},\sigma_{y},\sigma_{z}$} and then looking at its probability distribution. How to do this when we are having joint ...
- 331
2
votes
1
answer
210
views
In Variational Quantum Eigensolvers, what does "grouping Pauli operators into tensor products requiring the same post-rotations" mean?
In this paper (nature version), the authors state
We group the Pauli operators into tensor product basis sets that require the same post-rotations.
As a result, they have the table S2 in the suppl. ...
- 920
3
votes
1
answer
122
views
When defining the state vector of a qubit in qiskit, what difference does putting "j" make?
I'm following the Qiskit textbook. I'm currently here: https://quantum-computing.ibm.com/jupyter/user/qiskit-textbook/content/ch-states/representing-qubit-states.ipynb
Here's an example of my ...
