Quantum Computing Stack Exchange
Quantum Computing Stack Exchange

Questions tagged [foundations]

For questions about quantum foundations. Examples include questions about fundamental axioms, interpretations, contextuality, or generalized probabilistic theories.

34 questions
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What is the use of categorical quantum mechanics?

I recently noticed that Oxford's computer science department has started offering a grad course on categorical quantum mechanics. Apparently they say that it is relevant for the study of quantum foundations and quantum information, and that it uses…
Sanchayan Dutta
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What exactly are Quantum XOR Games?

I have done some research & found a few different papers that discuss xor games (classic & quantum). I am curious if someone could give a concise introductory explanation as to what exactly xor games are & how they are or could be used/useful in…
user820789
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Are correlations stronger than those allowed by quantum mechanics possible?

We know how a quantum correlation setup can help us with a better probability of winning games like the CHSH. But what is the upper bound that physics can allow? Is it the quantum correlation setup? Or can we exceed them in general sense to get much…
Siddhant Singh
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Superposition of quantum gates

In the standard model of quantum computation a gate is a unitary that acts on a subsystem. Physically, it can be implemented by some device. Now, any device is also a part of our quantum world, thus it has a quantum state. This quantum state, in…
Danylo Y
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What is the rank of a quantum channel?

I read the following sentence in a paper: We consider a quantum channel $\mathcal{E}_{\omega}(\rho)=\sum_{i=1}^{r} K_{i} \rho K_{i}^{\dagger}$ where $r$ is the rank of the channel. I didn't find the definition of the rank of the quantum channel…
Sherlock
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Will two entangled qubits be affected by gravity?

Will two entangled qubits be affected by gravity? I mean if one is near blackhole's horizon and other is on earth will the effect of relativity be experienced on the measurement? will there be any delay or error in measurement?
varun palakodeti
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Can we think that any multi-qubit quantum gate has a constant complexity from physics perspective?

It's known that any multi-qubit quantum gate can be represented as a product of a number of CNOT and single-qubit gates. The total number of these simple gates required is exponential (in the number of qubits) on average, and thus we can say that an…
Danylo Y
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What are the 2022 Nobel Prize winning papers of Alain Aspect, John Clauser, and Anton Zeilinger, and how do they fit into the timeline of QIS?

The 2022 Nobel Prize in Physics was awarded to Alain Aspect, John Clauser, and Anton Zeilinger for "experiments with entangled photons... pioneering quantum information science". Presumably there were noteworthy publications of each. Are there…
Mark Spinelli
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Why do we need Hilbert spaces when talking about qubits and quantum computation?

I was just curious to know why do we need Hilbert Spaces when talking about the qubits and quantum computation in general. I mean why can't we just work with inner product spaces, rather than going for complete inner product spaces. I am guessing it…
Upstart
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Biggest variance of $h=\sum_i H_i$?

What's the biggest variance of $h=\sum_i H_i$ where $H_i$ is the hamiltonian act on the ith qubit? If the n qubits state is separable, i.e., the state is $\mid\psi_1\rangle\otimes\mid\psi_2\rangle\otimes\cdots\mid\psi_n\rangle$. Obviously, the…
narip
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Doing non-unitary operations on quantum computer

So I am trying to implement non-unitary operations on Qiskit. There is an option to perform conditional operations in Qiskit. Suppose I prepare a qubit state in superposition. $|\psi\rangle=\sqrt{\frac{1}{2}}\left(|0\rangle+|1\rangle\right)$ Then I…
Chetan Waghela
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How can quantum interference happen in real world if a wave function does not have any physical meaning?

I understood quantum interference as a heart of quantum computing, because it enables two possibilities to cancel each other. Quantum algorithms utilize this property to reduce the probability of returning wrong answers and thus give higher chance…
suhdonghwi
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Difference between Bell's inequality and CHSH

In this section of the Scholarpedia article on Bell's theorem, the first paragraph comments that Bell's original inequality is not ideal for experimental verification because it requires perfect anti-correlation of the variables, and for that reason…
Pedro
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Why does quantum computing generally use matrix formulation of quantum mechanics rather than a continuous variable formulation?

The book Elements of Quantum Computing draws a distinction between "Wave Mechanics" and "Matrix Mechanics" (p. 38). I believe the reason we use a matrix formulation is that we are not dealing with continuous quantities like position, but finite…
LeWoody
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Prove that if Kraus operators of $\Phi$ form an ONB then $\Phi$ is the replacement map

This problem is from a "passing remark" in this lecture notes. With the help of some colleagues I managed to find a way for this supposedly elementary fact, but I would like to see if there is an alternative the details of which I will explain at…
Evangeline A. K. McDowell
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