New answers tagged measurement
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How can measure coherence of a coherent stare?
There are too many! Look up Mandel Q parameter, degree of coherence $g(2)$, negativity of the Glauber $P$ function, negativity of the Wigner function... I've probably even invented some myself.
For ...
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Nonsensical projection of initialized qubits in Qiskit
It seems the Aer backend is not compatible with initializing using integers in this version, here's a small change to make it work: You can use a string to tell the circuit to initialize in the $|1\...
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Why is there always a $k$-outcome experiment associated to operators such that $\sum_{i=1}^k M_i^* M_i=I$?
Imagine you want to make a measurement on a state $|\psi\rangle$ (and we will make the solution work for all possible $|\psi\rangle$). We introduce an ancilla system (Hilbert space dimension at least ...
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What is the probability of measuring in the following circuit?
Your computations are correct. If you look at the circuit you're creating, you can see the following:
In particular, note the 0 at the bottom of your measurements. ...
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What's the idea behind "pretty good measurements"?
I'll reproduce here a standard argument used to prove the fundamental bound for pretty good measurements (PGMs), the the most part taken from Watrous' book, with some minor changes in notation, ...
glS♦
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Is there a way to have multiple conditions in a `c_if` in Qiskit?
First of all, c_if is the old way for applying an operation conditioning on the value of a classical register. Instead, you should use ...
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Is a quantum state with coefficient 0 still there?
Do not confuse unitary operator and quantum operator in general.
Some quantum operators can transform a qubit state into $0$. For example, the Hamiltonian $\mathcal{H}$ is an operator, you can take ...
- 2,013
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Stabilizer States - Calculating measurement probabilities with the rank of the stabilizer table's X-block
The issue is that numpy.linalg.matrix_rank is assuming you want the rank over real numbers, when actually you want the rank over integers modulo 2.
For example, ...
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Is a quantum state with coefficient 0 still there?
The state after measuring 0 is $|0\rangle$ times an arbitrary nonzero complex number. In other words, it's the ray in Hilbert space that includes $|0\rangle$.
The number assigned to the measurement ...
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Why does the qubit give random results in the circuit with rearranged CNOTs for Steane's seven qubit code in Stim?
It doesn't work because you've rearrange your circuit as if the CNOT gates don't interact with each other, but they do.
Here is what you should do:
Add the missing three detectors to your circuit, ...
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Why does the qubit give random results in the circuit with rearranged CNOTs for Steane's seven qubit code in Stim?
I can't read your circuits, unfortunately. But if rearranging changes the outcome of your circuit, then the gates do not all commute.
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