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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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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5answers
139 views

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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3answers
97 views

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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2answers
63 views

If classical physics emerges in some limit of quantum mechanics, shouldn't there be intermediate classical-quantum computers?

Presumably quantum mechanics really is the way the universe works, and it appears we don't really understand where the boundary between quantum mechanical phenomena like interference end and classical ...
4
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1answer
41 views

Are inseparable states with positive partial transposition nonlocal?

In Horodecki, Horodecki and Horodecki (1998), Mixed-state entanglement and distillation: is there a ``bound'' entanglement in nature?, the authors remark in the conclusions (beginning of pag. 4, ...
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2answers
2k views

Why doesn't the Gottesman-Knill theorem render quantum computing almost useless?

The Gottesman-Knill theore states (from Nielsen and Chuang) Suppose a quantum computation is performed which involves only the following elements: state preparations in the computational basis, ...
3
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1answer
57 views

Classical and quantum limits to classical copying?

The no-cloning theorem can be sharpened to give quantitative bounds on the fidelity with which an arbitrary quantum state can be copied. Is there a similar picture available for classical copying? ...
2
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1answer
103 views

How does quantum contextuality relate to mutually commuting observables?

I am trying to get a better understanding of what is the idea behind quantum contextuality. Quoting from the wikipedia page (emphasis mine): Quantum contextuality is a foundational concept in ...
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0answers
22 views

Construction of optimal ensemble to show quantum steerability

In Wiseman et al. (2007), in the process of deriving necessary and sufficient conditions for the steerability of some classes of states, the authors show (lemma 1, page 3) how to construct an optimal ...