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1500 questions
6
votes
2 answers
Can we rotate Bloch vectors for qudits like we do with qubits in the Bloch sphere?
I have been looking into the Bloch vectors for qudits and have been wondering if we can do rotations that are similar to the rotations in the qubit Bloch sphere.
Like, once we create a Bloch vector for a qutrit, it exists in 8-dimensional space. In…
Parmeet Singh EP 066
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6
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1 answer
Can D-Wave machines solve QUBO problems more efficiently than gate model devices?
I'm new to quantum annealing and D-Wave computer. I saw that it has about 5000 qubits which can solve a QUBO problem with 5000 variables.
From my understanding, if we use a gate model device, say, an IBM quantum device to solve a QUBO problem, the…
peachnuts
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6
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2 answers
Are bucket-brigate (q)RAM architectures also advantageous in the classical case?
One of the main ideas introduced in Giovannetti et al. 2007
(0708.1879) is the so-called bucket-brigade (q)RAM architecture.
The authors state (first paragraph, second column, first page, in v2) that this new (at the time) (q)RAM architecture…
glS
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6
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2 answers
How to prove that Z operator rotates points on Bloch sphere about Z axis through 180°?
My idea was to apply $Z$ operator , which leads us back to the point where we started from, and also show that after applying the $Z$ operator just we are not at the same point where we started (this is for showing that we are not rotating by a…
Archil Zhvania
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6
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1 answer
How to calculate the state given by two qubits?
Let's say two qubits are both in $|+\rangle$ state. We need to find $a_1$, $a_2$, $a_3$, and $a_4$ in $|\phi\rangle = a_1|00\rangle + a_2|01\rangle + a_3|10\rangle + a_4|11\rangle$, how do we find these amplitudes? How do we do it in general case,…
Archil Zhvania
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6
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1 answer
How to implement a Square root of Swap gate that swaps 2n-qubits on the IBM Q (composer)?
I am looking for an implementation using the quantum gates provided by the IBM composer of the following quantum function:
input $2n$ qubits
output $2n$ qubits wherein $50\%$ of the cases the state of the $2$ sets of $n$ qubits are swapped and in…
JanVdA
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6
votes
2 answers
Simulating flag qubits and conditional branches using Stim
In a quantum error correcting code using flag qubits, it's common to have flag measurements that tell you it's necessary to do some extra measurements for safety. So, for example, I want to say:
if measurement_result_was_true:
…
Craig Gidney
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6
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Prove that $|(\langle \psi|_{A} \otimes \langle \phi|_{B})|\theta\rangle_{AB}|^{2}<1$ for entangled $|\theta\rangle_{AB}$
I am trying to show that $|\langle \psi|_{A} \otimes \langle \phi|_{B}|\theta\rangle_{AB}|^{2}<1$ given $|\theta\rangle$ is an entangled state, and as such has schmidt rank >1. Decomposing it, we get…
GaussStrife
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Should one learn the math of quantum computing from a "pure" perspective, or are quantum computing texts "good enough"?
Math for quantum computing includes advanced linear algebra, functional analysis, group and representation theory, probability theory, and more.
There are plenty of pure math books out there for those, but there are also quantum…
user2521987
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Clifford gates are transversal What exactly does this transversal mean? What is the difference between non-Clifford gates and Clifford gates?
Clifford gates are transversal What exactly does this transversal mean? What is the difference between non-Clifford gates and Clifford gates? Why is it simple for Clifford gates to implement transversal for quantum fault tolerance? Please explain…
Wang
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6
votes
1 answer
Why does quantum phase estimation complexity scale with maximum representable energy?
In Quantum simulation of chemistry with sublinear scaling in
basis size Ryan Babbush and other authors from Google Quantum team argue, when talking about performing Quantum Phase Estimation in 1st quantization, that
The reason for our greatly…
Pablo
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6
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2 answers
What is the form of a unitary $U$ that preserves the marginals on a given state, $\text{Tr}_A(U\rho_{AB} U^\dagger) = \rho_B$?
Suppose for some quantum state $\rho_{AB}$ and unitary $U_{AB}$, one has
$$\text{Tr}_A(U\rho U^\dagger) = \rho_B$$
does this imply that $U_{AB} = U_A\otimes I_B$?
Also, the same question as above, but if it holds for all states, $\rho_{AB}$, is that…
user1936752
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6
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1 answer
Does QFT exploit entanglement?
I was studying the quantum circuit for the Quantum Fourier Transform (QFT) on the Mike & Ike, and they write the result of the transformation as a product state.
More precisely they wrote the output of the QFT in the form
$$\frac{1}{\sqrt{2^n}} …
wasalbi
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6
votes
1 answer
Where is definitive documentation for OpenQASM 2.0 and 3.0
I have gotten conflicting information about OpenQASM; some sources point to version 3 while others say 3 is not ready. I want to refer to a document that will tell me what instructions actually work with the official library.
Anna Naden
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6
votes
1 answer
In a transmon qubit, what corresponds to the ground and excited states?
In a transmon qubit, we have ground and energy eigenstates but what is actually happening in the circuit here? How do the current and voltage look?
It looks like its made up of things you would find normally in a classical circuit so whats different…
snickers_stickers
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