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Is Gil Kalai's argument against topological quantum computers sound?
In a lecture, recorded on Youtube, Gil Kalai presents a 'deduction' for why topological quantum computers will not work. The interesting part is that he claims this is a stronger argument than the argument against fault tolerant computing in…
Discrete lizard
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Does quantum computing threaten blockchain?
As per Wikipedia, blockchains are a way to maintain "a continuously growing list of records, called blocks, which are linked and secured using cryptography [... and] inherently resistant to modification of the data."
Blockchains are in current…
Daniel Tordera
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Why do we use the standard gate set that we do?
The typically used gate set for quantum computation is composed of the single qubits Cliffords (Paulis, H and S) and the controlled-NOT and/or controlled-Z.
To go beyond Clifford we like to have full single qubit rotations. But if we are being…
James Wootton
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What is the quantum circuit equivalent of a (delayed choice) quantum eraser?
Quantum computers are efficiently able to simulate any other quantum system. Hence there must be some sort of equivalent of a (possibly simulated) quantum eraser setup. I would like to see such an equivalent drawn as a quantum circuit, ideally in…
user1039
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Scalability of ion trap quantum computers
My understanding is that the magnetic fields needed to hold the ions in place in ion trap quantum computers are very complex, and for that reason, currently, only 1-D computers are possible, therefore reducing the ease of communication between…
auden
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Will deep learning neural networks run on quantum computers?
Deep Learning (multiple layers of artificial neural networks used in supervised and unsupervised machine learning tasks) is an incredibly powerful tool for many of the most difficult machine learning tasks: image recognition, video recognition,…
Bob Swain
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How does approximating gates via universal gates scale with the length of the computation?
I understand that there is a constructive proof that arbitrary gates can be approximated by a finite universal gate set, which is the Solovay–Kitaev Theorem.
However, the approximation introduces an error, which would spread and accumulate in a long…
M. Stern
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How to compactly represent multiple qubit states?
Since access to quantum devices capable of quantum computing is still extremely limited, it is of interest to simulate quantum computations on a classical computer. Representing the state of $n$ qubits as a vector takes $2^n$ elements, which greatly…
Kiro
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What is the difference between the "Fubini-Study distances" $\arccos|\langle\psi|\phi\rangle|$ and $\sqrt{1-|\langle\psi|\phi\rangle|}$?
I sometimes see the "Fubini-Study distance" between two (pure) states $|\psi\rangle,|\phi\rangle$ written as
$$
d(\psi,\phi)_1=\arccos(|\langle\psi|\phi\rangle|),
$$
for example in the Wikipedia page.
Other sources (e.g. this paper in pag. 16), use…
glS
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How and why does swap test works?
I am having some trouble understanding why a SWAP test would work. I meant I read that and understood the concepts as follows:
If the two input states are equal, the output register always results
in a state of $|1\rangle$, so a $1$ outcome will be…
Hamza
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How to calculate an Expected Value of some operator acting on qubits?
I'm trying to implement the Variational Quantum Eigensolver in Qiskit.
Suppose, I have an operator $A = \sigma_1^z\sigma_2^z$ acting on some two-qubit state $|\psi\rangle$. After a measurement I get a set of probabilities corresponding to states…
C-Roux
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Why isn't there a contradiction between the existence of CNOT gate/entanglement and the no-cloning theorem?
Of course I am not implying that I am right and the no cloning theorem is wrong, but I am trying to figure out what is wrong with my reasoning and yet I couldn't find the mistake.
Based on Wikipedia
In physics, the no-cloning theorem states that…
u185619
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Is swap gate equivalent to just exchanging the wire of the two qubits?
Is swap gate equivalent to just exchanging the wire of the two qubits?
if yes why not just switching the wire whenever we want to apply a swap gate?
Sam
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What does "bipartite" mean?
This is a really easy question, but my mother language is not English and I get confused quite a lot reading Preskill notes.
What does a bipartite system mean? Is this just that it "lives" in a tensor product of two Hilbert spaces? Does it mean that…
CFRedDemon
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Why is an entangled qubit shown at the origin of a Bloch sphere?
I'm unclear why the Bloch sphere representation of a maximally entangled qubit shows the state of the bit as being at the origin of the sphere.
For example, this illustration
shows the effect of the simple circuit
over time, with $q_0$ on the…
orome
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