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1500 questions
29
votes
4 answers
Are quantum computers just a variant on Analog computers of the 50's & 60's that many have never seen nor used?
In the recent Question "Is Quantum Computing just Pie in the Sky" there are many responses regarding the improvements in quantum capabilities, however all are focussed on the current 'digital' computing view of the world.
Analog computers of old…
Philip Oakley
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29
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4 answers
How can I implement an n-bit Toffoli gate?
I want to create a Toffoli gate controlled by n qubits, and implement it in QISKit. Can this be done? If so, how?
Ali Javadi
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29
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5 answers
Does Moore's law apply to quantum computing?
Plain and simple. Does Moore's law apply to quantum computing, or is it similar but with the numbers adjusted (ex. triples every 2 years). Also, if Moore's law doesn't apply, why do qubits change it?
Alex Jone
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29
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3 answers
Is there any potential application of quantum computers in machine learning or AI?
A lot of people believe that quantum computers can prove to be a pivotal step in creating new machine learning and AI algorithms that can give a huge boost to the field. There have even been studies that our brain may be a quantum computer, but so…
Piyush Kathuria
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29
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3 answers
How does measurement of one qubit affect the others?
To represent a quantum computer's state, all the qubits contribute to one state vector (this is one of the major differences between quantum and classical computing as I understand it). My understanding is that it's possible to measure only one…
auden
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28
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2 answers
What is the difference between quantum annealing and adiabatic quantum computation models?
From what I understood, there seems to be a difference between quantum annealing and adiabatic quantum computation models but the only thing I found on this subject implies some strange results (see below).
My question is the following: what is…
Adrien Suau
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28
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3 answers
What is the difference between superpositions and mixed states?
My understanding so far is: a pure state is a basic state of a system, and a mixed state represents uncertainty about the system, i.e. the system is in one of a set of states with some (classical) probability. However, superpositions seem to be a…
Norrius
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28
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2 answers
Why is it important to eliminate the garbage qubits?
Most reversible quantum algorithms use standard gates like Toffoli gate (CCNOT) or Fredkin gate (CSWAP). Since some operations require a constant $\left|0\right>$ as input and the number of inputs and outputs is equal, garbage qubits (or junk…
Be Brave Be Like Ukraine
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27
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Circuit construction for Hamiltonian simulation
I would like to know how to design a quantum circuit that given a Hermitian matrix $\hat{H}$ and time $t$, maps $|\psi\rangle$ to $e^{i\hat{H}t} |\psi\rangle$.
Thank you for your answer.
Tam'si Ley
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27
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4 answers
Why can't there be an error correcting code with fewer than 5 qubits?
I read about 9-qubit, 7-qubit and 5-qubit error correcting codes lately. But why can there not be a quantum error correcting code with fewer than 5 qubits?
Aleph
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27
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3 answers
What are magic states?
I wonder what are magic states, and a magic state gadget. While I'm reading a paper, these terms frequently appear.
김동민
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26
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4 answers
Is error correction necessary?
Why do you need error correction? My understanding is that error correction removes errors from noise, but noise should average itself out. To make clear what I'm asking, why can't you, instead of involving error correction, simply run the…
auden
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26
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1 answer
How to understand the Haar measure from a quantum information perspective?
I found it a little difficult to understand it using Wikipedia and some mathematical documents. How to understand the Haar measure from a quantum information theory perspective? Are there any materials that explain it?
raycosine
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26
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Explicit Conversion Between Universal Gate Sets
I'm interested in the conversion between different sets of universal gates. For example, it is known that each of the following sets is universal for quantum computation:
$\{T,H,\textrm{cNOT}\}$
$\{H,\textrm{c}S\}$, where $S=T^2$ and $S^2=Z$, and…
DaftWullie
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26
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3 answers
What exactly are anyons and how are they relevant to topological quantum computing?
I have been trying to get a basic idea of what anyons are for the past couple of days. However, the online articles (including Wikipedia) seem unusually vague and impenetrable as far as explaining topological quantum computing and anyons goes.
The…
Sanchayan Dutta
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