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1500 questions
6
votes
1 answer
Implementation of Grover's Algorithm (minimum spanning tree)
I am trying to solve a minimum spanning tree problem using Grover's Algorithm. To accomplish this I would need to search a list for the minimum weight or edge for each point, for example:
Given the following list:
How would one use Grover's…
Maxwellsequations
- 75
- 3
6
votes
3 answers
Can't draw figures with Qiskit in Visual Studio
I'm using Qiskit in Visual Studio 2019. I want to draw quantum circuits, but it only shows their sizes with text instead of figures. The output on the interactive window is like this.
>>> from qiskit import QuantumRegister, ClassicalRegister,…
Lemonade
- 61
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6
votes
1 answer
Clarification of a procedure to compute the product of the exponential of two matrices
In trying to understand a method outlined here (arXiv), page 3, subroutine 1. Consider
$$R_3 =
\begin{bmatrix} 0 & 0 & 1 \\
0 & 0 & 0 \\
0 & 0 & 0
\end{bmatrix} .$$
Let $A$ be a complex square matrix. Define $X_3(A) = R_3 \otimes A + R_3^{\dagger}…
IntegrateThis
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6
votes
1 answer
IBM Q devices scheduling of gates with different durations
I was trying to figure out how scheduling works in IBM devices.
The thing that's bugging me is that in the quantum computer implementations I had seen before, the cycle concept is used. Say, for example, a cycle = 20ns. And all operations take that…
Kelthar
- 149
- 5
6
votes
1 answer
How to decompose a controlled unitary $C(U)$ operation where $U$ is a 2-qubit gate?
In the vein of this question, say I have a 2-qubit unitary gate $U$ which can be represented as a finite sequence of (say) single qubit gates, CNOTs, SWAPs, cXs, cYs and cZs. Now I need to implement a controlled-$U$ gate and hence need its…
Sanchayan Dutta
- 17,945
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- 112
6
votes
1 answer
Defining qubit operator from scratch
I'm a beginner with Qiskit and the Python language at all.
Here is my question:
One of the VQE function arguments is qubit operator (qubitOp).
I saw some examples where the qubitOp object was produced by some already existing Qiskit module.
For…
Alex Tarantul
- 61
- 2
6
votes
3 answers
Why is the application of an oracle function not a measurement?
Why is the application of an oracle function not a measurement, causing the collapse of the system? How can you know the state of the system (the input of the oracle function) without measurement?
michiel perdeck
- 93
- 3
6
votes
1 answer
Physical qubit of optical quantum computer
I was researching how optical quantum computers work and discovered a KLM protocol that allows for building quantum gates using linear optics elements like mirrors, beam splitters, and phase shifters. However, I was wondering how would we get the…
Aleksandar Kostovic
- 347
- 1
- 5
6
votes
1 answer
Why do we use complex-conjugate instead of complex-conjugate-transpose when calculating the concurrence?
When we use the formula to calculate two-qubit entanglement, like these:
$$
C(\rho)=\max \left\{\sqrt{e_{1}}-\sqrt{e_{2}}-\sqrt{e_{3}}-\sqrt{e_{4}}, 0\right\}\tag{18}
$$
with the quantities $e_{i}\left(e_{1} \geq e_{2} \geq e_{3} \geq e_{4}\right)$…
karry
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6
votes
1 answer
What is the HOG test and how would it help proving quantum supremacy?
Proposed experiments in achieving quantum supremacy, such as with BosonSampling or using random circuits, have been described as using a (not necessarily Turing complete) quantum computer to perform some sampling problem.
An example would be to…
Mark Spinelli
- 15,378
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- 83
6
votes
3 answers
Phase estimation error analysis
This question is about Lemma $7.1.2$ in Kaye, Laflamme, and Mosca's textbook:
Let $\omega = \frac{x}{2^n} = 0.x_1x_2\ldots x_n$ be some fixed number. The phase estimation algorithm applied to the input state $|\psi\rangle =…
NNN
- 403
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6
votes
1 answer
How is a physical qubit measured and how is the result interpreted?
To my understanding, most of the qubits we use today are just Josephson junctions coupled to a resonator that is triggering the qubits to go to different states by using microwave pulses. The same resonators are also used to read the information…
Aleksandar Kostovic
- 347
- 1
- 5
6
votes
1 answer
Direct derivation of the Kraus representation from the natural representation, using SVD
$\newcommand{\Y}{\mathcal{Y}}\newcommand{\X}{\mathcal{X}}\newcommand{\rmL}{\mathrm{L}}$As explained for example in Watrous' book (chapter 2, p. 79), given an arbitrary linear map $\Phi\in\rmL(\rmL(
\X),\rmL(\Y))$, for every linear operator…
glS
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6
votes
1 answer
What's the standard definition of a CNOT gate for qutrits?
I am actually working on quantum computing with qutrits. I am trying to define standard qubit gates for qutrits. The CNOT gate for qubits is defined as follows: $$|x,y\rangle \to |x,y+x \bmod 2\rangle.$$
So the matrix is $$\mathrm{UCN} =…
Marco Falso
- 63
- 5
6
votes
2 answers
Why is the boundary of the set of states in the generalised Bloch representation comprised of singular matrices?
Consider an arbitrary qudit state $\rho$ over $d$ modes.
Any such state can be represented as a point in $\mathbb R^{d^2-1}$ via the standard Bloch representation:
$$\rho=\frac{1}{d}\left(\mathbb I +\sum_k c_k\sigma_k\right)$$
with $\sigma_k$…
glS
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