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36
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5 answers
How to derive the CNOT matrix for a 3-qubit system where the control & target qubits are not adjacent?
In a three-qubit system, it's easy to derive the CNOT operator when the control & target qubits are adjacent in significance - you just tensor the 2-bit CNOT operator with the identity matrix in the untouched qubit's position of…
ahelwer
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36
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Introductory material for quantum machine learning
In the past few days, I have been trying to collect material (mostly research papers) related to Quantum machine learning and its applications, for a summer project. Here are a few which I found interesting (from a superficial…
Sanchayan Dutta
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35
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2 answers
What exactly is an oracle?
What exactly is an "oracle"? Wikipedia says that an oracle is a "blackbox", but I'm not sure what that means.
For example, in the Deutsch–Jozsa algorithm,$\hspace{85px}$,is the oracle just the box labeled $`` U_f " ,$ or is it everything between the…
Marco Fellous-Asiani
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34
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Effects of quantum computing on parallel universes
I have heard a few times that one way of describing quantum computers is that they essentially use the computing power of their counterparts in alternate realities that they access through superposition. My first question is, of course,
is this…
Snowshard
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How do I build a gate from a matrix on Qiskit?
I'm creating a gate for a project and need to test if it has the same results as the original circuit in a simulator, how do I build this gate on Qiskit? It's a 3 qubit gate, 8x8 matrix:
$$
\frac{1}{2}
\begin{bmatrix}
1 & 0 & 1 & 0 & 0 & 1 & 0 & -1…
Nillmer
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34
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1 answer
What exactly is "Random Circuit Sampling"?
Many people have suggested using "Random Circuit Sampling" to demonstrate quantum supremacy. But what is the precise definition of the "Random Circuit Sampling" problem? I've seen statements like "the task
is to take a random (efficient) quantum…
grok
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33
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2 answers
Has there been any truly ground breaking advance in quantum algorithms since Grover and Shor?
(Sorry for a somewhat amateurish question)
I studied quantum computing from 2004 to 2007, but I've lost track of the field since then. At the time there was a lot of hype and talk of QC potentially solving all sorts of problems by outperforming…
Alex Kinman
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What are magic states?
I wonder what are magic states, and a magic state gadget. While I'm reading a paper, these terms frequently appear.
김동민
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32
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What is the difference between a relative phase and a global phase? In particular, what is a phase?
I know that $re^{i\theta} = x + iy$ for any complex number $x + iy$ by Euler's formula. How do you calculate relative and global phase?
LeWoody
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What's the point of Grover's algorithm if we have to search the list of elements to build the oracle?
Grover's algorithm is used, among other things, to search an item $\mathbf{y}$ in an unordered list of items $[\mathbf{x}_0, \mathbf{x}_1, ..., \mathbf{x}_{n-1}]$ of length $n$. Even though there are plenty of questions here regarding this topic, I…
incud
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What's the difference between a pure and mixed quantum state?
As per my limited understanding, a pure state is the quantum state where we have exact information about the quantum system. And the mixed state is the combination of probabilities of the information about the quantum state of the quantum system.…
Koder101
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31
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2 answers
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) increase the efficiency of a quantum computer by…
Sir Cornflakes
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31
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5 answers
Can the Bloch sphere be generalized to two qubits?
The Bloch sphere is a nice visualization of single qubit states. Mathematically, it can be generalized to any number of qubits by means of a high-dimensional hypersphere. But such things are not easy to visualize.
What attempts have been made to…
James Wootton
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31
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What could be the possible future applications for HHL algorithm?
Note on the vocabulary: the word "hamiltonian" is used in this question to speak about hermitian matrices.
The HHL algorithm seems to be an active subject of research in the field of quantum computing, mostly because it solve a very important…
Adrien Suau
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31
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What precisely is quantum annealing?
Many people are interested in the subject of quantum annealing, as an application of quantum technologies, not least because of D-WAVE's work on the subject. The Wikipedia article on quantum annealing implies that if one performs the 'annealing'…
Niel de Beaudrap
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