Most Popular
1500 questions
7
votes
1 answer
Definition of locality in Bell experiments
Continuing from my previous question on Brunner et al.'s paper (arXiv); so given a standard Bell experimental setup:
where independent inputs $x,y \in \{0, 1\}$ decide the measurement performed by Alice & Bob on quantum state $S$ with outcomes $a,b…
ahelwer
- 4,288
- 2
- 15
- 36
7
votes
2 answers
In Bell nonlocality, why does $P(ab|xy)\neq P(a|x)P(b|y)$ mean the variables are not statistically independent?
I've been working through the paper Bell nonlocality (arXiv) by Brunner et al. after seeing it in user glS' answer here. Early on in the paper, the standard Bell experimental setup is defined:
Where $x, y \in \{0,1\}$, $a, b \in \{-1, 1\}$, and the…
ahelwer
- 4,288
- 2
- 15
- 36
7
votes
3 answers
Can one ever find the elements of a superposition state?
Given some set of basis states $\{\vert 0\rangle, \vert 1\rangle, \vert 2\rangle...\vert N\rangle\}$ and an unknown superposition of the form $\frac{1}{\sqrt{2}}(\vert i \rangle + \vert j \rangle)$, what exactly forbids us from computing $i$ and…
Al Jones
- 71
- 1
7
votes
0 answers
Is it better to use fewer gates or fewer working qubits?
I have a script that takes a while to simulate. I can modify it in such a way where I can use fewer qubits at a time, but it will require more iterations of manipulation. I believe this will cut down on simulation time, but does is it worse when…
nikojpapa
- 501
- 3
- 9
7
votes
1 answer
How are Rigetti and IBM QX device parameters related to Kraus operators?
Rigetti reports the following parameters: (https://www.rigetti.com/qpu)
T1, T2* times
1-qubit gate fidelity (F1q)
2-qubit gate fidelity (F2q) and,
read-out fidelity (Fro)
IBM QX reports the following:…
Edifice
- 429
- 2
- 10
7
votes
2 answers
How is the Deutsch-Jozsa algorithm faster than classical for practical implementation?
There is something I really misunderstand about the Deutsch-Jozsa algorithm.
To check if $f$ is balanced or constant, we use the following algorithm:
where $U_f$ gives $(x,y) \rightarrow (x, y \oplus f(x))$.
Let's take $n=1$ for simplicity (thus…
Marco Fellous-Asiani
- 2,220
- 2
- 15
- 42
7
votes
2 answers
Clarification needed: "Simulation" of $e^{-iHt}$ and its time complexity
On page 3 here it is mentioned that:
However, building on prior works [32, 36, 38] recently it has been
shown in [39] that to simulate $e^{−iHt}$ for an $s$-sparse Hamiltonian
requires only $\mathcal{O}(s^2||Ht||\text{poly}(\log N,
…
Sanchayan Dutta
- 17,945
- 8
- 50
- 112
7
votes
1 answer
In which paper was the CHSH game first presented?
The CHSH inequality was presented in the paper Proposed Experiment to Test Local Hidden-Variable Theories published in 1969 by J.F. Clauser, M.A. Horne, A. Shimony, and R.A. Holt. I'm interested in which paper first presented their proposed…
ahelwer
- 4,288
- 2
- 15
- 36
7
votes
1 answer
Why is the CNOT gate matrix a valid representation for two-qubit states?
Can anyone explain how the CNOT matrix below is a valid presentation for the four-qubit states that follow after?
|0 0> -> |0 0>
|0 1> -> |0 1>
|1 0> -> |1 1>
|1 1> -> |1 0>
Source: Wikipedia
DrHamed
- 181
- 1
- 8
7
votes
1 answer
Is the common depiction of a surface code to be taken literally as a real-space image of the actual hardware?
I'm currently reading the paper "Surface codes: Towards practical large scale quantum computing" and have a couple of very basic questions that if answered will help me contextualize and organize the information in this paper much better. I…
Malcolm Regan
- 773
- 5
- 11
7
votes
1 answer
Does the GLOA have any advantage over the Solovay-Kitaev algorithm?
The Solvay Kitaev algorithm was discovered long before the Group Leaders Optimization algorithm and it has some nice theoretical properties. As far as I understand, both have exactly the same goals: given a finite dimensional unitary operator, they…
Sanchayan Dutta
- 17,945
- 8
- 50
- 112
7
votes
1 answer
Weak Fourier Sampling vs Strong Fourier Sampling?
I'm having trouble understanding the difference between weak fourier sampling and strong fourier sampling. From this paper:
...two important variants of the Fourier sampling paradigm have been
identified: the weak standard method, where only…
Raekye
- 307
- 1
- 4
7
votes
1 answer
Relation between $\mathrm{QMA}$ and $\mathrm{P^{QMA}}$
What is the relation between $\mathrm{QMA}$ and $\mathrm{P^{QMA}}$ and how do we prove it? Are these classes equal?
BlueLagoon
- 73
- 2
7
votes
1 answer
How significant are the variants of Grover's Algorithm?
I found a paper by Grover titled "How significant are the known collision and element distinctness quantum algorithms?", in which he expressed criticism to several famous algorithms, including Ambainis's algorithm for element distinctness. More…
183orbco3
- 173
- 4
7
votes
1 answer
What are "collective measurements", and how do they differ from "normal" measurements?
I am reading the paper Polar codes for classical-quantum channels
by Wilde and Guha, and it is stated the fact that collective measurements are necessary in order to aciheve the Holevo symmetric information as it can be seen from the HSW theorem.…
Josu Etxezarreta Martinez
- 4,136
- 15
- 42