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8 votes

What is the stabilizer rank of the W state?

I think it's doable to get at least an upper bound of $\lceil n/2 \rceil$ for the stabiliser rank of $W_n$. Note that, as you wrote, $W_2 = |01\rangle + |10\rangle $ is a stabiliser state, so has ...
Vincent's user avatar
  • 171
4 votes

Is purity convex in time?

The following is only a partial answer: While your argument rightly shows that normal $\mathcal L$ (which means $e^{t\mathcal L}$ is unital) is sufficient for convex purity, numerics suggest this even ...
Frederik vom Ende's user avatar
2 votes
Accepted

CHSH game sharing more general states

For a general two-qubit state, including mixed ones, the maximal violation was found by the Horodeccy in 1995. If you write the state in the Block decomposition as $$\rho = \frac{1}{4} \sum_{i,j = 0}^{...
Mateus Araújo's user avatar
2 votes
Accepted

How to calculate the number of m-partitions of an N-partite quantum state?

This is a purely combinatorics problem. Let us index our registers by $1,\cdots,N$. We have $m$ "bags" $P_1,\cdots,P_m$ into which which we want to put our indexes. For the first index ($1$)...
Tristan Nemoz's user avatar
  • 6,702
2 votes

Do we consider the entangled-based protocol E91 to be a device-independent protocol?

Ekert's original protocol was never specified in a device independent way but, as you suggest, it's very close by virtue of the reliance on Bell inequalities. (He has commented to me that, with ...
DaftWullie's user avatar
  • 59.3k
1 vote
Accepted

Why do we need to put the control qubit in superposition in Bell State?

The reason relates to the task of entanglement generation. For the generation of a Bell state, we want to make the state of the second qubit is maximally correlated with that of the first, such that ...
Rohan Mehta's user avatar
1 vote

Do we consider the entangled-based protocol E91 to be a device-independent protocol?

I think you can safely say that E91 was the beginning of device-independent protocols. It has all the basic ideas in there and the intuition for why device-independent security holds is there too. ...
Rammus's user avatar
  • 5,968

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