benrg
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What is the meaning of the state $|1\rangle-|1\rangle$?
7 votes

Sanchayan Dutta's answer correctly points out that $|1\rangle-|1\rangle$ doesn't actually arise in your example problem, but it doesn't answer the question in the title: what is $|1\rangle-|1\rangle$? ...

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Is the CNOT in the standard three-qubit circuit for the GHZ state necessary?
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5 votes

If you initialize three qubits to $|0\rangle$, apply a Hadamard gate to each, then measure each in the computational basis, the result will be an independent coin flip for each bit: that is, any of ...

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How do local quantum gates affect an entangled state?
5 votes

All of your math is correct. Both of the states that you calculated are entangled states. An entangled state is one in which there exist measurable properties of subsystems that are correlated. In (1),...

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Quantum tensor product closer to Kronecker product?
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5 votes

The tensor product of two objects with $m$ and $n$ components is an object with $mn$ components that consists of the pairwise products of the components of the inputs. The Kronecker product and the $v ...

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How does a quantum computer execute a process by leveraging superposition?
2 votes

Your intuition is correct if you think of the superpositions as classical probability distributions, which is how they are usually described in popularizations. What's unique to quantum mechanics is ...

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What is meant by $\log(m)$ qubits
2 votes

As DaftWullie said in a comment, $\log m$ is most likely a shorthand for $\lceil\log_2 m\rceil$. Traditionally in computer science, one looks only at the asymptotic complexity of algorithms. ...

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How to write a classical version of Shor's algorithm
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2 votes

In Shor's (quantum) algorithm, you compute the modular exponent only a small number of times—far smaller than $N$. The algorithm is probabilistic, and if you're lucky you may compute it only once. ...

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How exactly does Grovers algorithm "crack" symmetric key encryption?
2 votes

Grover's algorithm is a Circuit SAT solver that finds a satisfying assignment in around $2^{n/2}$ evaluations of the circuit, where $n$ is the number of inputs. You can build a circuit that takes a ...

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If quantum speed-up is due to the wave-like nature of quantum mechanics, why not just use regular waves?
2 votes

What makes quantum wave mechanics different from classical is that the wave is defined over a configuration space with a huge number of dimensions. In nonrelativistic undergraduate quantum mechanics (...

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Why can't quantum computation replace classical computation?
1 votes

Your question talks about the theoretical capabilities of theoretical computers. Anyone who says that quantum computers won't replace classical computers is probably talking about the actual ...

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Quantum parallelism and Deutsch's algorithm - what is $U_f$ really?
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1 votes

Where does that single evaluation of $f(x)$ actually occur? Is it in the construction of $U_f$? $U_f$ is an implementation of $f$ in quantum gates. The evaluation of $f$ occurs in the course of ...

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Grover algorithm for a database search: where is the quantum advantage?
1 votes

Grover's algorithm is a (quantum-)circuit-SAT solver. I suppose it could also be a literal black box solver, but it would only work with black boxes that don't decohere your entangled input state, and ...

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Is running a large random brute force on quantum computer possible at the moment?
1 votes

From the question title, it sounds like you're interested in brute-force password cracking. There is a quantum algorithm for this that outperforms brute force, in principle. It's called Grover's ...

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What is the point of Grover's algorithm, really?
0 votes

Grover's algorithm is a CIRCUIT-SAT solver. Given a circuit with $n$ boolean inputs, it finds a satisfying input in $O(2^{n/2})$ evaluations of the circuit in the worst case, which is interesting ...

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Quantum teleportation and the reality of quantum states
0 votes

The ontology of pure states is tricky, but if you believe in pure states then mixed states are fairly straightforward, I think. Teleportation of a third qubit seems unnecessary in this thought ...

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