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Questions tagged [deferred-measurement]

The "principle of deferred measurement" refers to the idea that in almost all cases measurement may be performed as a last step in a quantum computation. This tag is dedicated to questions that explore the concept and/or potential exceptions to the concept.

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3 votes
1 answer

Can I postpone a Pauli gate $X$ over a conditioned measurement $Y$ or $X$?

The above circuit shows a first measurement, which is $\langle X \rangle$ or $\langle Y \rangle$, depending on the outcome of a second measurement. Assuming now that a third measurement decides ...
Daniele Cuomo's user avatar
1 vote
0 answers

Can transformations of qubits in quantum computing be carried out instead by transformations of the measurement instrument?

As far as I understand, transforming and maintaining states of qubit devices in quantum computers is associated with all sort of problems such as transformation errors and decoherence. At the same ...
QC student's user avatar
-1 votes
1 answer

What is the mathematical intuition behind deferred measurement? [duplicate]

Please give a complete proof of the principle of Deferred Measurement Principle, including careful notation (preferably explaining the meaning of each symbol) and rigorous mathematical reasoning (...
Ren-Xin Zhao's user avatar
3 votes
2 answers

what does it mean to "measure a qubit" if measurement is defined on operators

As far as I know "measurement" depends on the two variables : state and operator. So what exactly does measuring a qubit mean? is it implied that the operator is the $Z$ operator on that ...
unknown's user avatar
  • 2,148
2 votes
1 answer

Show that the effect of a Controlled Unitary on qubits followed by a measurement is unchanged depending on when measurement is taken

I understand that a Controlled Unitary is just a generalization of a control gate, such as CNOT etc, and that it is given in state representation as $$\hat C_U = |0\rangle\langle0|\otimes\mathbb{I} + |...
Dwye's user avatar
  • 121
7 votes
1 answer

What is a proof for the principle of deferred measurement?

Does anyone know of a proof for the 'principle of deferred measurement'?
Quantum Guy 123's user avatar
4 votes
1 answer

Using principle of deferred measurement to replace gates conditional on classical bits (c_if)

I am trying to implement the Iterative Phase Estimation algorithm on one of Qiskit's labs. I can do it for a 'nice' phase, such as 1/4 : But if I want to implement the algo generally (as a subroutine ...
Mykolas Sveistrys's user avatar
10 votes
2 answers

Are there any algorithms that take measurements in an intermediate step?

As a beginner in quantum computation, I noticed that all quantum algorithms take various gates followed by measuring the qubits in the last step. Is it always the case? Are there any algorithms that ...
John Wong's user avatar
  • 291
3 votes
1 answer

Does principle of deferred measurement imply information can travel faster than light?

I have been reading the book by Michael A Nielsen and Isaac Chuang and came across the principle of deferred measurement. They showed using this principle how the circuit for quantum teleportation can ...
Rishabh Kothary's user avatar