Questions tagged [foundations]

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

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2answers
204 views

How does the spectral decomposition of the Choi operator relate to Kraus operators?

In Nielsen and Chuang's QCQI, there is a proof states that Theorem 8.1: The map $\mathcal{E}$ satisfies axioms A1, A2 and A3 if and only if $$ \mathcal{E}(\rho)=\sum_{i} E_{i} \rho E_{i}^{\dagger} $$...
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1answer
98 views

How to deal with entanglement relativistically?

When discussing relativistic quantum mechanics, Dirac notation is dropped completely which makes the description of entangled particles difficult. However when discussing quantum entanglement and ...
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1answer
414 views

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 ...
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52 views

Can the Peres-Mermin square be reframed as a statement on the associated conditional outcome probabilities?

As mentioned in this answer, and links therein (assuming I'm understanding correctly), (non)contextuality can be defined as a property of a given set of conditional probability distributions, that is, ...
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1answer
51 views

How to compute the eigenvector of this complex matrix in Grover's algorithm?

We know that SO(3) matrix stands for the proper rotation in 3D space. But when I read this paper, there is a SO(3) matrix stands for the general query matrix of Grover's algorithm in SO(3) form: $$ \...
2
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1answer
37 views

Why do we use 'modes' in quantum optics?

In this material, it gives the definition of modes: The modes are basically defined by the properties of coherence and orthogonality: modes are orthogonal solutions of the wave equation. Since the ...
6
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1answer
52 views

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\...
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4answers
388 views

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 ...
6
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1answer
107 views

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-...
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4answers
124 views

Quantum teleportation and the reality of quantum states

This question is perhaps philosophical but it's been confusing me. Suppose Alice is teleporting some qubit state $|\phi\rangle$ to Bob via the quantum teleportation protocol. After Alice applies the ...
5
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2answers
92 views

What is the difference between no signaling and non locality at operational and ontological level?

I understand the basic definitions. Locality means Alice's measurements do not affect Bob's and system and that no-signalling means a party can't send information faster than light. I also know that ...
3
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1answer
94 views

Effect of quantum entanglement on measurement

I'm taking a quantum information systems class and thought of this while trying to wrap my head around some material, so I apologize if this comes off as dumb or founded on misunderstandings. Say you ...
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68 views

What happens to Quantum computing if Schroedingers equation gets a correction term to account for some new changes in fundamental physics? [closed]

We all know the current form of Schroedinger's equation. Due to some new observations, let's say it gets modified in a way that a correction term gets added. What are the ramifications for Quantum ...
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1answer
87 views

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 ...
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3answers
1k views

Why does quantum computing generally use matrix formulation of quantum mechanics rather than a continuous variable formulation?

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 ...
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337 views

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? ...
2
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1answer
371 views

What quantum gate is XNOR equivalent to?

The standard way to implement a reversible XOR gate is by means of a controlled-NOT gate or CNOT; this is the "standard quantum XOR operation". Physics.Stackexchange Is there a "standard quantum XNOR ...
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1answer
773 views

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 ...
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1answer
287 views

Equation for Quantum Gyroscopes

A quantum gyroscope is a very sensitive device to measure angular rotation based on quantum mechanical principles. The first of these has been built by Richard Packard and his colleagues at the ...
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1answer
1k views

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 ...