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Understanding (theoretical) computing power of quantum computers
I am very new to quantum computing and just try to understand things from a computer scientist's perspective.
In terms of computational power, what I have understood,
100 ideal qubits ... can equate to [$2^n$ pieces of information]
Now Rigetti…
J. Doe
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What limits scaling down the size of superconducting qubits?
There are multiple ways of building a qubit: Superconducting (transmons), NV-centers/spin-qubits, topological qubits, etc.
The superconducting qubits are the most well-known qubits and are also the easiest to build. The machines by IBM and Google,…
nippon
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9
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Qubits specification on IBMQ devices
As it is shown here, CNOT gates between different qubits have different error rates. I have the following questions:
1) While defining a circuit on QISkit, does q[0] always correspond to the same qubit on a device (e.g. the qubit labeled q0 on the…
Mathist
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Understanding the Group Leaders Optimization Algorithm
Context:
I have been trying to understand the genetic algorithm discussed in the paper Decomposition of unitary matrices for finding quantum circuits: Application to molecular Hamiltonians (Daskin & Kais, 2011) (PDF here) and Group Leaders…
Sanchayan Dutta
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9
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Efficiently performing controlled rotations in HHL
This question builds off of this question.
In the HHL algorithm, how do you efficiently do the $\tilde{\lambda}_k$-controlled rotations on the ancilla qubit? It seems to me that since you don't know the eigenvalues a priori, you would have to…
Paradox
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Simulation vs Construction of Fredkin gate with Toffoli gates
I'm working my way through the book "Quantum computation and quantum information" by Nielsen and Chuang. (EDIT: the 10th anniversary edition).
On chapter 3 (talking about reversibility of the computation) exercise 3.32, it is possible to see that…
Davide_sd
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9
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3 answers
$R_z$ gate representations
Why is the $R_z$ gate sometimes written as:
$$
R_{z}\left(\theta\right)=\begin{pmatrix}1 & 0\\
0 & e^{i\theta}
\end{pmatrix},
$$
while other times it is written as:
$$
R_{z}\left(\theta\right)=\begin{pmatrix}e^{-i\theta/2} & 0\\
0 &…
Bella
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Decomposition of arbitrary 2 qubit operator
As you know, universal quantum computing is the ability to construct a circuit from a finite set of operations that can approximate to arbitrary accuracy any unitary operation.
There also exist some results proving that exact decompositions of…
PDRX
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Can a stored programming model be applied to a Quantum Computer?
A stored programming computer model is that where a central memory is used to store both instructions and data that they operate on. Basically all the classical computers of today that follow the von Neumann architecture use the stored programming…
K Sarkar
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votes
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Generalization for $n$ quantum teleportations
In Breaking Down the Quantum Swap, it is stated:
Thanks to the CNOT, we can implement a xor-swap on a quantum computer. All we need to do is chain three CNOTs back and forth.
In a comment to a previous question, the author of the aforementioned…
user820789
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What good references would you recommend to understand the (continuous-variable) CV model of computation?
If you have good references about the CV model that are understandable from a computer science background, that would be great. If they include numerical examples, that would even be better.
cnada
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9
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What is quantum computing vs. what is not quantum computing
That is to say,
what are some common or popular misconceptions about what constitutes quantum computing?
and
how are those things misconceptions?
It could help in explaining to frame this while imagining as if you were explaining for a…
PowerLuser
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Is the Pauli norm of an observable minimized in its eigenbasis?
Consider an observable $O = \sum_i \lambda_i P_i$ decomposed into Paulistrings $P_i$ and a unitary $U$ each acting on $n$ qubits. The Pauli-norm of $O$ is defined as the 1-norm of the Pauli vector, i.e.
$$\|O\|_P = \sum_i |\lambda_i|.$$
I can write…
Refik Mansuroglu
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How to prove that this family of gates is in the Clifford Hierarchy?
Apologies. In the previous version of this question I drew the wrong circuit family. That circuit was order 6 and, therefore, by my own result (arxiv.org/2410.04711) the family was not in the Clifford Hierarchy. The description of the problem was…
Jonas Anderson
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Computational complexity of perturbed classical algorithms
Take a classical algorithm and compile it into quantum gates. For example, let's take the addition of two n-bit numbers. Obviously there is an efficient classical algorithm to determine the most likely bit string to arise as an output, because there…
James Wootton
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