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1500 questions
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
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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
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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
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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
2 answers
When would I consider using an outer product of quantum states, to describe aspects of a quantum algorithm?
I know the inner product has a relationship to the angle between two vectors and I know it can be used to quantify the distance between two vectors. Similarly, what's an use case for the outer product? You can exemplify with the simplest case. It…
R. Chopin
- 1,199
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- 17
7
votes
1 answer
Collective measurements: importance and realization
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
- 3,916
- 13
- 39
7
votes
2 answers
How to construct the "Inversion About the Mean" operator?
It seems like it should be simple, based on how Nielsen and Chuang talk about it, but I cannot seem to correctly implement the Inversion About the Mean operator ($2|\psi\rangle \langle\psi| - \mathcal{I}$) that is used in the Grover search…
nikojpapa
- 501
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- 9
7
votes
1 answer
Decomposition of an arbitrary 1-qubit gate into a specific gateset
Any 1-qubit special gate can be decomposed into a sequence of rotation gates ($R_z$, $R_y$ and $R_z$). This allows us to have the general 1-qubit special gate in matrix form: …
Ntwali B.
- 443
- 2
- 9
7
votes
2 answers
How can I get access to IBM Q 20 Tokyo and IBM Q 20 Austin?
How can I get access to IBM Q 20 Tokyo and IBM Q 20 Austin?
In the Q- experience site there is written that the access is for IBM clients only and in the profile there is a "promotional code" that you need to put to gain access to those chips.
How I…
Daniel Vainshtein
- 421
- 2
- 14
7
votes
1 answer
Is there a relation between the factorisation of the joint conditional probability distribution and Bell inequality?
[I'm sorry, I've already posted the same question in the physics community, but I haven't received an answer yet.]
I'm approaching the study of Bell's inequalities and I understood the reasoning under the Bell theorem (ON THE EINSTEIN PODOLSKY…
LadyOfShalott
- 73
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7
votes
1 answer
Is there a classical limit to quantum computing?
Why are quantum computers scalable?
With the subjects of spontaneous collapse models and decoherence in mind, it seems to me that the scalability of quantum computers is something which is not only physically difficult to achieve but also…
Jake Xuereb
- 466
- 2
- 7
7
votes
1 answer
Difference between coherence transfer, polarization transfer and population transfer?
I asked a question on Physics Stack Exchange but no one answered the question and I didn't get enough views on it. I am asking it on QCSE because the question is related to experimental quantum computation realized through NMR.
For an ensemble of…
Jitendra
- 255
- 3
- 6
7
votes
2 answers
What is the smallest quantum circuit to produce two-qubit state (a,b,b,b)?
How can I synthesis a two-qubit quantum state of the state vector (a,b,b,b) using basic quantum-gate circuit (arbitrary single-qubit rotation and controlled $Z$ gate)? And further, can I know a given circuit is the simplest?
cmc
- 173
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