Juan Miguel Arrazola
  • Member for 9 years, 9 months
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What is the motivation for the definition of concurrence in quantum information?
7 votes

To the best of my knowledge, the initial motivation for defining the concurrence involves the fact that for pure bipartite entangled states, the reduced density matrices of each subsystem are not pure....

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Show that Bell states cannot be decomposed as tensor products of single qubits' states
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5 votes

All you need to show is that there do not exist any $a,b,c$ or $d$ satisfying the conditions $\frac{1}{\sqrt{2}}(|00\rangle)+|11\rangle)=(a|0\rangle+b|1\rangle)\otimes(c|0\rangle+d|1\rangle)$ and $|...

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Types of photon qubit encoding
4 votes

In general, any two orthogonal modes of light provide a way of constructing a two-level quantum system that can serve as a qubit. The possibilities are immense! Of course, not every option will be ...

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Fast algorithm for maximizing the quantum fidelity
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4 votes

I have luckily found an answer to this question: The fidelity is concave in both its arguments i.e. $F(\lambda \rho_1+(1-\lambda)\rho_2,\lambda \sigma_1+(1-\lambda)\sigma_2 )\geq \lambda F(\rho_1,\...

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How to compute the pure extensions of a given mixed state?
4 votes

It is a general result that any mixed quantum state can be viewed as the reduced state of a pure state in a larger dimensional Hilbert space. This is referred to as a purification, and some people ...

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Is the collapse of the wave function inherently time asymmetric?
4 votes

As suggested in the answer above, in general, decoherence increases the entropy associated with a quantum system and as such has the same type of time-reversal asymmetry that appears in thermodynamics....

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Quantum key distribution (QKD) upper and lower bounds
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3 votes

Closing the gap between lower and upper bounds for the tolerated errors in quantum key distribution protocols is a long-standing problem in the field. In general, to give a lower bound on the key rate,...

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What's wrong with this faster-than-light gedankenexperiment?
3 votes

The flaw in your argument is that the claim "entanglement will instantly replicate the photons' paths and such the pattern onto Bob's screen [sic]" is incorrect. The statistics for the measurement ...

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Why do local hidden variable theories predict a triangular pattern for the graph?
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3 votes

Bell's theorem basically states that some predictions of quantum mechanics cannot be obtained from a local hidden variable model of the theory. Some people (like Nielsen and Chuang) refer to this as ...

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Why do some physicists believe that scalable quantum computing is possible?
2 votes

You might find this lecture by Scott Aaronson insightful. https://www.scottaaronson.com/democritus/lec14.html He basically makes a very convincing defence of quantum computing against arguments made ...

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Variations of double slit experiment with their results to look up
2 votes

You might be interested in this paper https://arxiv.org/abs/0811.2068. Here, they perform an experimental test of Born's rule using not two, but three slits.

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A good book for Quantum Cryptography
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2 votes

There aren't really many books on quantum cryptography. The only one I am aware of is a book titled Applied Quantum Cryptography (C. Kollmitzer and M. Pivk, eds., Springer, 2010). The Nielsen and ...

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why non orthogonal states are indistinguishable?
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2 votes

Two states $\rho_0$ and $\rho_1$ are perfectly distinguishable if there exists a POVM measurement $\{P_0,P_1\}$ such that $$\operatorname{Tr}(\rho_0P_0)=1$$ $$\operatorname{Tr}(\rho_0P_1)=0$$ $$\...

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Quantum Teleportation Fidelity
2 votes

It might also be useful to think of the following: How can we possibly verify that the teleported state is indeed equal to the initial state? We can't just look at quantum systems and know what their ...

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Again about all-win lottery
2 votes

Even if all your other arguments were correct, note that being in either one of two states with equal probability is not the same as being in a quantum state $\frac{1}{\sqrt{2}}| 0\rangle + \frac{1}{\...

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mixture of maximally mixed and maximally entangled state
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1 votes

To answer this question, we will first compute the values of $\lambda$ for which $\rho(\lambda)$ is PPT and separately compute the values for which it is entangled. Let $T$ be the transpose map, such ...

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Bell State, if Bob applies a Pauli Gate?
1 votes

In your question, you were also wondering what would happen if both Alice and Bob apply the same Pauli gate on their respective qubit. To complement Mark's answer, I would like to expand on this point....

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using a unitary matrix to transpose
1 votes

The transpose is not a unitary map. One simple way to understand this is by recalling that the transpose is not a completely positive map. More precisely, let $T$ be the transpose map. Then the state $...

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Is it possible to create an entangled pair of photons if they originate initially from operations at two separate sites?
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1 votes

If the two photons are the only systems you are considering, the short answer is no, you cannot entangle them by performing only local operations. This is a consequence of the fact that entanglement ...

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Multiqubit state tomography by performing measurement in the same basis
0 votes

I think that a concise way to understand why one-particle measurements cannot always recover any mixed state is to make use of the following fact: If a POVM does not span the space of operators on the ...

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