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Looking for papers that are pessimistic about the feasibility of a quantum computer
I'm actually searching two types of documents (could be the same):
1) A synthesis about all the main gap/problems that make the physical realisation of a quantum computer actually infeasible.
2) Something more polemical that criticizes the point of…
Ievgeni
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Do the Kraus operators of a CPTP channel need to be orthogonal?
Let $\Phi\in\mathrm T(\mathcal X,\mathcal Y)$ be a CPTP map.
Any such channel admits a Kraus decomposition of the form
$$\Phi(X)=\sum_a A_a X A_a^\dagger,$$
for a set of operators $A_a\in\mathrm{Lin}(\mathcal X,\mathcal Y)$ satisfying $\sum_a…
glS
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What design considerations set the frequency bounds for superconducting qubits?
Superconducting qubits generally have frequencies within the range of 4 - 8 GHz. What design considerations give the upper and lower bounds for what is a feasible design. I.e, why can't they be higher or lower in frequency?
psitae
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Showing that Matrix Inversion is BQP-complete - HHL Algorithm
I am trying to understand an argument that Matrix Inversion is BQP-complete for certain conditions on the matrix. This is explained here on page 39 (this paper is a primer to the HHL algorithm and gives some more detailed calculations, more detail…
IntegrateThis
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Does the Choi-Jamiolkowski isomorphism really establish a connection between kinematics and dynamics?
I understand the mathematical construction of the Choi-Jamiolkowski isomorphism aka channel-state duality. It all makes sense formally, yet I still struggle to grasp its physical (or quantum-informational) meaning. Does the isomorphism between…
quantumorsch
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Calculating power of a quantum computer for RSA
As discussed in this question, the expected security of 1024-bit RSA is 80-bits:
NIST SP 800-57 §5.6.1 p.62–64 specifies a correspondence between RSA modulus size $n$ and expected security strength $s$ in bits:
Strength RSA modulus size
80 …
R1-
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Quantum fidelity simplified formula while both of the density matrices are single qubit states
I have a question while reading the quantum fidelity definition in Wikipedia Fidelity of quantum states, at the end of the Definition section of quantum fidelity formula, it says Explicit expression for qubits. If rho and sigma are both qubit…
tatakai
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8
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Quantum Fourier Transform without SWAPs
The Quantum Fourier Transform from Nielsen and Chuang chapter 5 is pictured here:
In the textbook the author refers to "swap gates at the end of the circuit which reverse the order of the qubits".
My questions are:
Is it possible to transform the…
forky40
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What is the definition of Bell state on a n-qubit system?
Question 1: The bell state for a 2-qubit system has been defined in Nielsen and Chuang's book as the set of maximally entangled states spanned by $\{|00\rangle + |11\rangle, |00\rangle - |11\rangle, |01\rangle + |10\rangle, |01\rangle- |10\rangle…
John Jacob
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How to interpret $-\rvert1\rangle \otimes \rvert1\rangle = -\rvert11\rangle$?
I'm having trouble accepting, intuitively, that $-\rvert1\rangle \otimes \rvert1\rangle = -\rvert11\rangle = \rvert1\rangle \otimes -\rvert1\rangle$.
It's my understanding that $ -\rvert1\rangle$ is just $\rvert1\rangle $ but time or space delayed…
Dragonsheep
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What are the main obstacles to overcome to build silicon-photonic quantum computers?
In superconducting quantum computers, we use mostly superconducting qubits or trapped ions. However, those systems are quite large because their environment either requires near absolute zero temperature (for superconducting to happen), or vacuum…
Aleksandar Kostovic
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What exactly makes quantum computers faster than classical computers?
What feature of a quantum algorithm makes it better than its classical counterpart? Are quantum computers faster than classical ones in all respects?
Tobias Fritzn
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How does measurement calibration work?
One of the possible ways to improve the results of an experiment on the IBM machine using the Qiskit language is to use the measurement calibration methods. This is the link to the documentation.
I understood that the calibration matrix is made…
Marco Ballarin
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Nielsen and Chuang's proof for 'approximating arbitrary unitary gates is generically hard'
The following statement is found on the page 199 of Nielsen and Chuang's book (10th Anniversary Edition) in the proof for the fact that 'approximating arbitrary unitary gates is generically hard':
Suppose we have $g$ different types of gates…
Nan
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Calculating the expectation value of a unitary operator on a quantum computer
What is the smartest way of calculating the expectation value of some unitary $U$ in some state $|\psi\rangle$?
There are two ways I know:
quantum phase estimation algorithm;
Hadamard test.
Are there more efficient techniques to do that?
Andrey Kardashin
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