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Questions tagged [postselection]

In quantum computing theory post-selection refers to giving a quantum computer the power to choose the outcomes of certain measurements, which greatly increases its computational power. In this case the, perhaps exponentially many, extra runs required to obtain the output are ignored. The important point is that an interference pattern is not produced immediately. (https://physics.stackexchange.com/a/38938)

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Plotting Fisher Information using PennyLane

I made 2-qubit based circuit with post-selection method. Post-selection method is, Let $$ K = \begin{bmatrix} \sqrt{1-\gamma} & 0 \\ 0 & 1 \end{bmatrix}\,. $$ Then, $$ \rho_{\text{post-...
Donguk kim's user avatar
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We take the reciprocal $\lambda^{-1}$ of eigenvalues in HHL - but what's stopping us from raising them to a positive exponent $\lambda^m$?

The HHL algorithm generally can be thought of as diagonalizing our matrix $A$ with the quantum phase estimation algorithm, and applying a specific function $f(\lambda)=\lambda^{-1}$ to the eigenvalues ...
Mark Spinelli's user avatar
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How to perform a multi Pauli rotation with arbitary angle?

Recently, I was trying to find some methods to perform a multi Pauli rotation gate with arbitary angle. I want to use the method proposed in the paper arXiv:1808.02892v3, and the circuit is shown as ...
Zehong Fan's user avatar
1 vote
1 answer
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Is this generalized 2D cluster state still a universal resource?

Let $G = (V,E)$ be a graph that defines the graph state $$ |G\rangle = \prod_{(i,j)\in E} CZ_{i,j}|+\rangle^{\otimes |V|}. $$ Alternatively, we can write $$ | G \rangle = \sum_{x \in \{0,1\}^{|V|}} ...
trillianhaze's user avatar
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An improved search algorithm based on weak value amplification?

I am having difficulties understanding this paper (arXiv:1910.12390), so asking this question. As far as what I see from mathematics of this paper, all improvements over Grover's search disappear when ...
Zimmermann's user avatar
2 votes
1 answer
285 views

How to select the statevetor of a qubit in a multiqubit circuit in qiskit?

I need to use and plot the state of the first qubit in my multiqubit circuit, but the issue is that I need to use post selection - I want only the results of which the other qubits in the circuit are ...
Shiran's user avatar
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Efficient simulation of linearly assembled Quantum States

In this paper section 4.2 the author describes how to efficiently simulate linearly assembled quantum states. When describing the procedure to do so the author shows the following circuit: The ...
Bertrand Einstein IV's user avatar
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Post-selection applied to quantum teleportation

In this answer, it is stated that applying post-selection to quantum teleportation results in Alice communicating to Bob backwards in time. Could someone explain how this works? I am particularly ...
Owen's user avatar
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3 votes
1 answer
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On the probability of preparing of a uniform superposition by performing a controlled-multiplication and post-selecting $0$

I take as a starting point Watrous's celebrated paper defining the Quantum Merlin-Arthur (QMA) class. He provides a protocol for Arthur to test whether an element $h$ is not in a group $\mathcal{H}$ ...
Mark Spinelli's user avatar
3 votes
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Does strong error reduction for PostQMA exist?

$\mathsf{PostQMA}$ can be defined as the following (see Morimae-Nishimura and Usher-Hoban-Browne): A promise problem $\mathcal{L}=(\mathcal{L_{yes},L_{no}})$ is in $\mathsf{PostQMA(c,s)}$ if there ...
Yupan Liu's user avatar
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How is postselection used in quantum tomography?

I refer to this paper but reproduce a simplified version of their argument. Apologies if I have misrepresented the argument of the paper! Alice has a classical description of a quantum state $\rho$. ...
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HHL algorithm -- problem with the outcome of postselection

See edit at the end of the question All the references in this question refer to Quantum algorithm for solving linear systems of equations (Harrow, Hassidim & Lloyd, 2009). HHL algorithm ...
Adrien Suau's user avatar
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What is postselection in quantum computing?

A quantum computer can efficiently solve problems lying in the complexity class BQP. I have seen a claim that one can (potentially, because we don't know whether BQP is a proper subset or equal to PP) ...
Sir Cornflakes's user avatar