Questions tagged [nonclassicality]
For questions about the nonclassical properties of quantum systems, that is, properties of quantum systems that are incompatible with classical physics. Nonclassicality is a more general notion than that of entanglement, and the term can be used to loosely refer to different notions, such as nonlocality, steerability, non-Gaussianity, and many more.
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What are some examples of uncomputability with quantum computers?
It is sometimes said that quantum effects lead to non computable results in the weak sense that quantum computers might allow truly random actions (at least according to some interpretations). I think ...
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Are there non-stabilizer multi-qubit states that are easy to simulate?
The Gottesman-Knill theorem states that the following process is efficiently simulatable on a classical computer:
start of with a set of qubits in a computational basis
apply any amount of $H, S$ and ...
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Entanglement-assisted communication ability of a quantum depolarizing channel vs. a classical binary symmetric channel
Consider a quantum qubit depolarizing channel which takes a quantum state $\rho$ to output
$$N(\rho) = (1-p)\rho + p\frac{\mathbb{1}_2}{2}.$$
If I restrict $\rho$ to be either $\vert0\rangle\langle 0\...
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QuTiP lecture: Single-Atom-Lasing
I have tried to run one of the examples in QuTip lectures: single atom lasing.
Although I have used the prepared code represented in reference, I have received error and I have not been able to ...
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Circuit from finite group of gates and classical simulations
Let $ G $ be a finite group of quantum gates. Is it true that any circuit made using only gates from the finite group $ G $ can be efficiently simulated on a classical computer?
Here by circuit made ...
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How can classical bits be copied if qubits cannot be copied?
The no-cloning theorem of quantum mechanics tells us there can be no general quantum circuit that can copy arbitrary qubit states, i.e. a quantum gate or circuit cannot send $|0\rangle |\psi\rangle\...
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Defining joint-measurability on ensembles of states
Joint Measurability for a collection of POVMs $\{\Omega_j\}_j$ where $j$ is the index of the POVMs with associated effects $\{\Omega^\omega_j\}_{\omega}$ is defined as
$$\Omega^\omega_j = \sum_{\theta}...
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Quantum fourier transform with classical vibrations
Is there any difference in effect between a quantum circuit and a carefully constructed analogue one relying on interference? For example, why couldn't I take a series of $N$ carefully shaped pipes, ...
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How is the additivity of accessible information, $\frac{1}{n} I_{\rm acc}(\rho^{\otimes n})=I_{\rm acc}(\rho)$, proved?
Let $\rho^{XA}$ be a classical-quantum state of the form
$$ \rho^{XA} = \sum_{x\in X} p_x |x\rangle\langle x|\otimes \rho_x^A, $$
and let the accessible information be given by
$$ I_{acc}(\rho^{XA}) = ...
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Why is the quantum discord of $\rho$ zero iff $\rho=\sum_j p_j \pi_j\otimes \rho_j$ for mutually orthogonal projections $\pi_j$?
In (Wiseman 2012), the author mentions (equation (4), page 6), that a state $\rho$ has zero quantum discord (more precisely, zero Alice-discord) if and only if it can be written in the form
$$\rho = \...
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Why are commuting density operators said to be "classical states"?
In quantum information it is commonly said that a set of states $S=\{ \rho_i \}_i$ is classical if $[\rho_m, \rho_n] = 0, \,\forall \rho_m,\rho_n \in S$. This is meant in the sense that all observed ...
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Why are diagonal Hamiltonians considered classical?
I've been following UT QML course (http://localhost:8888/tree/UNI/PHD/UT-QML) and during their lecture on the Ising hamiltonian, they point out that the hamiltonian of an Ising model without a ...
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Understanding Hardy's proof of "nonlocality without inequalities"
I'm reading the proof of "nonlocality without inequality" presented in (Hardy 1992).
In this protocol, we consider two particles (say, an electron and a positron) evolving almost independently: they ...
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Does a classical computer really require $2^n$ complex numbers to represent the state of $n$ qubit quantum computer?
One often reads that the key reason why classical computers (probabilistic or deterministic) are unable to simulate quantum algorithms such as Simon's or Shor's efficiently is that a classical ...
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Does the CHSH inequality fully characterise the local polytope?
Consider the standard two-party CHSH scenario. Each party can perform one of two measurements (denoted with $x,y\in\{0,1\}$) and observe one of two outcomes (denoted with $a,b\in\{0,1\}$).
Let $P(ab|...
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