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
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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 ...
1 vote
0 answers
21 views

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 ...
7 votes
1 answer
2k views

What is a proof for the principle of deferred measurement?

Does anyone know of a proof for the 'principle of deferred measurement'?
-1 votes
1 answer
121 views

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 (...
3 votes
1 answer
205 views

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 ...
3 votes
2 answers
268 views

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 ...
2 votes
1 answer
570 views

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} + |...
10 votes
2 answers
949 views

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 ...
4 votes
1 answer
386 views

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 ...