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bio website home.lu.lv/~sd20008
location Cambridge, UK
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visits member for 2 years, 9 months
seen Apr 16 at 7:20

I am a post-doctoral researcher at University of Cambridge working in the field of quantum computing.


Apr
9
awarded  Critic
Apr
9
comment Is there a simple expression for the coherent information of a Pauli channel?
Where have you noticed this (can you give a reference)? Also, what do you mean by $H(\Lambda)$?
Feb
28
comment Properties of controlled z-rotations
Can you describe more precisely what exactly is the property you want after the local unitaries are applied? Do you mean c-c-c-z in the first line rather than c-z-z-z?
Feb
10
comment Conjugate of unknown qubit?
In the case without CTCs you can argue by linearity -- a map that sends a state to its complex conjugate is not linear. I don't know the formal definition of CTCs, so I don't know if this argument would also carry over to the CTC case.
Feb
4
answered Is there a unitary, linear bijection between (1) Maximally Entangled and (2) Factorizable States?
Jan
31
comment How does one devise a Grover quantum oracle despite the no-cloning theorem?
Transforming $|x\rangle$ to $|f(x)\rangle$ is not reversible. Such oracle could be applied only once, since the input $x$ is lost after the first application. The oracle workspace is used in the following sense: $|x\rangle|0\rangle \xrightarrow{\textrm{Oracle}} (-1)^{f(x)}|x\rangle|0\rangle$. The extra $|0\rangle$ register is the workspace that starts in $|0\rangle$ and is returned in $|0\rangle$ and is used to reversibly compute $f(x)$ (i.e., compute $f(x)$, apply it as a phase of the first register and then uncompute).
Jan
7
comment Proving the unitary relation of ensemble decompositions
Your are right, I overlooked that $\psi$s and $\phi$s need not be orthonormal in your question. Norbert's answer then is what you are looking for!
Jan
5
comment Proving the unitary relation of ensemble decompositions
I once wrote a blog post about this: marozols.wordpress.com/2012/05/09/…
Jan
4
comment Is the process on initialization of qubits unitary?
Since initialization destroys the previous value, it is not reversible and hence not unitary. The fact that unitary erasure of information is not possible (or the "no-erasure theorem") is the time-reversed counterpart of the famous no-cloning theorem. See nature.com/nature/journal/v404/n6774/abs/404164a0.html and sciencedirect.com/science/article/pii/S0375960103010478
Sep
24
awarded  Autobiographer
Dec
6
awarded  Commentator
Dec
6
comment Super-dense coding protocol with a key
I also recommend to read the post suggested by Piotr! ;)
Sep
28
answered Is there a physical motivation to study finite fields?
Aug
29
awarded  Yearling
May
14
comment What are the limitations of performing music in space?
Another instrument that would completely fail is rainstick. Also, a gong would have to be strapped down properly before it can be played.
May
14
awarded  Scholar
May
14
accepted What are the limitations of performing music in space?
May
14
awarded  Student
May
14
asked What are the limitations of performing music in space?
May
8
comment Positivity in the Pauli/Bloch/coherence vector representation
Yes, this is the way to do it. The star product is defined in terms of a symmetric tensor $d_{ijk}$ which in turn is defined via $\{\lambda_i,\lambda_j\} = 2 d_{ijk} \lambda_k$ for $i \neq j$. For fixed $k$ there are only $d$ pairs $(i,j)$ that give a non-zero $d_{ijk}$, so that should let you compute the star product in $d^2$ time.