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1500 questions
15
votes
6 answers
Is there any online Bloch sphere simulator?
While writing this answer I realized it would be really helpful if I could show the OP a video or .gif of how qubit states in Bloch spheres transform under certain unitary operations. I googled up a bit and could find only these two…
Sanchayan Dutta
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How is the Grover-Algorithm applied to a database?
Question
I want to use the Grover-Algorithm to search an unsorted database for an element $x$. Now the question arises, how do I initialize index and value of the database with the qubits?
Example
Let's say I have $4$ qubits. Thus, $2 ^ 4 = 16$…
alex
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3 answers
Simulate hamiltonian evolution
I'm trying to figure out how to simulate the evolution of qubits under the interaction of Hamiltonians with terms written as a tensor product of Pauli matrices in a quantum computer. I have found the following trick in Nielsen and Chuang's book…
Apo
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Relation between quantum entanglement and quantum state complexity
Both quantum entanglement and quantum state complexity are important in quantum information processing. They are usually highly correlated, i.e., roughly a state with a higher entanglement corresponds to a higher quantum state complexity, or a…
XXDD
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15
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5 answers
General construction of $W_n$-state
Two of the most well known entangled states are the GHZ-state $|\psi\rangle = 1/\sqrt{2}\left( |0\rangle^{\otimes n} + |1\rangle^{\otimes n}\right)$ and the $W_n$-state, with $W_3 = 1/\sqrt{3}\left(|100\rangle + |010\rangle + |001\rangle\right)$.…
nippon
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3 answers
What do they mean by "qubit can't be copied"?
What does it mean by ''qubit can't be copied'' ?
In a note, it is saying that:
Copying a qubit means $$U|\psi\rangle_A|0\rangle_B=|\psi\rangle_A|\psi\rangle_B$$
i.e; applying a unitary transformation on the qubit state. It is explained as, if the…
tarit goswami
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4 answers
Are there any examples of anyone applying quantum algorithms to problems in computational biology?
As the title suggests, I'm searching for published examples of quantum algorithms being applied to problems in computational biology. Clearly the odds are high that practical examples don't exist (yet) – what I'm interested in is any proof of…
Greenstick
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4 answers
What use has quantum computing been?
Most of us on this site believe that quantum computing will work. However, let's play devil's advocate. Imagine that we suddenly hit some fundamental stumbling block that prevented further development towards a universal quantum computer. Perhaps…
DaftWullie
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15
votes
1 answer
What is a Haar random quantum state?
Can somebody please explain me what is a Haar random state? I am not able to find any friendly resource to read about it.
Shweta Aggrawal
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2 answers
Jones Polynomial
There are many fairly standard quantum algorithms that can all be understood within a very similar framework, from Deutsch's algorithm Simon's problem, Grover's search, Shor's algorithm and so on.
One algorithm that seems to be completely different…
DaftWullie
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15
votes
3 answers
How to permute (reshuffle) an n-bit input?
I am interested in a quantum algorithm that gets as input an n-bit sequence and that produces as output a reshuffled (permuted) version of this n-bit sequence.
E.g. if the input is 0,0,1,1 (so n=4 in this case) then the possible answers…
JanVdA
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15
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3 answers
Is acting with a positive map on a state not part of a larger system allowed?
In the comments to a question I asked recently, there is a discussion between user1271772 and myself on positive operators.
I know that for a positive trace-preserving operator $\Lambda$ (e.g. the partial transpose) if acting on a mixed state $\rho$…
Quantum spaghettification
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15
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2 answers
Is it true to say that one qubit in an entangled state can instantaneously affect all others?
When a qubit is measured, there is a ‘collapse of the wave-function’ as a result is randomly chosen.
If the qubit is entangled with others, this collapse will also effect them. And the way it affects them depends on the way we chose to measure our…
James Wootton
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2 answers
Does a study guide exist that starts from a "purely CS background" and advances towards "making a new quantum programming language"?
I am from a computer science background and I find it difficult to decide on the resources I should focus on while learning quantum computing, since there is so much to read/watch. My ultimate goal is to make a programming language acting as an…
Kushajveer
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3 answers
What is the difference between "code space", "code word" and "stabilizer code"?
I keep reading (e.g. Nielsen and Chuang, 2010; pg. 456 and 465) the following three phases; "code space", "code word" and "stabilizer code" - but am having a difficult time finding definitions of them and more importantly how they differ from one…
Quantum spaghettification
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