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1500 questions
11
votes
2 answers
Transpilation into custom gate set in qiskit
In qiskit, I can transpile a given circuit into a some predefined gate set as follows (just an example)
from qiskit import QuantumCircuit
from qiskit.compiler import transpile
from qiskit.circuit.random import random_circuit
basis_gates = ['id',…
Nikita Nemkov
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votes
1 answer
What's the role of mixer in QAOA?
In QAOA algorithm, two terms are being discussed; 1) clause or cost (C) Hamiltonian and 2) mixer consisting of pauli X gates.
What is the role of this mixer? Not clear why it comes after the C. Doesn't it cause the state to flip after evaluating…
John Parker
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11
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3 answers
Why are diagonal Hamiltonians considered classical?
I've been following UT QML course (http://localhost:8888/tree/UNI/PHD/UT-QML) and during their lecture on the Ising hamiltonian, they point out that the hamiltonian of an Ising model without a transverse field commutes
$$ H=-\sum_{} J_{ij}…
César Leonardo Clemente López
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What is the complexity of estimating the expectation value of an observable?
The average value of an operator $O$ in the state $\left.|\psi\right>$ is
$$\overline{O}=\left<\psi|O|\psi\right>$$
Now for simplicity let $\left.|\psi\right>=\left.|0\right>^n$ and assume we have a circuit that prepares $O$. How many times one has…
Nikita Nemkov
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11
votes
1 answer
Empirical Algorithmics for Near-Term Quantum Computing
In Empirical Algorithmics, researchers aim to understand the performance of algorithms through analyzing their empirical performance. This is quite common in machine learning and optimization. Right now, we would like to know something about the…
hopefully coherent
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votes
1 answer
Is there any general statement about what kinds of problems can be approximated more efficiently using a quantum computer?
As the name already suggests, this question is a follow-up of this other. I was delighted with the quality of the answers, but I felt it would be immensely interesting if insights regarding optimization and approximation techniques were added, but…
fr_andres
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11
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5 answers
What is quantum entanglement, and what role does it play in quantum error correction?
I want to understand what quantum entanglement is and what role does it play in quantum error correction.
NOTE:
As per the suggestions of @JamesWootton and @NielDeBeaudrap, I have asked a separate question for the classical analogy here.
Chinni
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What is stopping FACTORING from being BQP-complete?
Classical complexity theory makes much of the study of so-called intermediate problems - that is, problems that are in $\mathsf{NP}$ but are nonetheless not known to be in $\mathsf{P}$ and further not expected to be $\mathsf{NP}$-complete.
Commonly…
Mark Spinelli
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11
votes
2 answers
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 take measurements in an intermediate step?
John Wong
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11
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2 answers
In shadow tomography, how is the state reconstructed from its shadows?
I'm reading Huang et al. (2020) (nature physics), where the authors present a version of Aaronson's shadow tomography scheme as follows (see page 11 in the arXiv version):
We want to estimate a state $\rho$. We apply a number of random unitary…
glS
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2 answers
Is qsphere an actual term representing 5 qubits?
I'm a total beginner, I've been brought here by the featured stackoverflow blog post so I started studying.
Watching this youtube video (A Beginner’s Guide To Quantum Computing (3:58), I saw this slide where it talks about superposition:
At first I…
Adelin
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11
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Rigorous security proof for Wiesner's quantum money
In his celebrated paper "Conjugate Coding", Wiesner proposed a scheme for quantum money that is unconditionally impossible to counterfeit, assuming that the issuing bank has access to a giant table of random numbers and that banknotes can be brought…
Didix
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votes
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Quantum memory assisting classical memory
Consider a classical computer, one making, say, a calculation involving a large amount of data. Would quantum memory allow it to store that information (in the short term) more efficiently, or better handle that quantity of data?
My thought would be…
auden
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11
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2 answers
What can we learn from 'quantum bogosort'?
Recently, I've read about 'quantum bogosort' on some wiki. The basic idea is, that like bogosort, we just shuffle our array and hope it gets sorted 'by accident' and retry on failure.
The difference is that now, we have 'magic quantum', so we can…
Discrete lizard
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3 answers
Is the tensor product of two states commutative?
I'm reading "Quantum Computing Expained" by David McMahon, and encountered a confusing concept.
At the beginning of Chapter 4, the author described the tensor product as below:
To construct a basis for the larger Hilbert space, we simply form…
akawarren
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