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visits member for 2 years, 11 months
seen May 5 '12 at 20:03

Scientist


Apr
30
awarded  Yearling
May
4
comment Information conservation during quantum measurement in $\psi$-epistemic interpretations
May be interesting: mathoverflow.net/questions/95537/…
Apr
30
awarded  Yearling
Apr
4
comment Negative probabilities in quantum physics
Feynman wrote in this essay: "Trying to think of negative probabilities gave me a cultural shock at first, but when I finally got easy with the concept I wrote myself a note so I wouldn't forget my thoughts."
Apr
4
awarded  Necromancer
Mar
26
comment Multiqubit state tomography by performing measurement in the same basis
@Piotr Migdal: Using other words I am simply showing that the set of that nonorthogonal measurements is not "informationally complete".
Mar
26
comment Multiqubit state tomography by performing measurement in the same basis
Even measurement in single basis produces $2^n-1$ parameters. My preliminary estimation give equation $\sum_k C^n_k C^{k+2}_k$, but seems Chris' curve corresponds a bit different values.
Mar
25
comment Multiqubit state tomography by performing measurement in the same basis
Indeed, I see - $\rho_1 = (1 + \sigma_z \otimes \sigma_x)/4$, $\rho_2 = (1 + \sigma_x \otimes \sigma_z)/4$.
Mar
25
comment Multiqubit state tomography by performing measurement in the same basis
@Peter Shor: I already wrote, I do not require that - we may distinuish the swap of all components due to assymetry between $\sigma_0 \otimes \sigma_k$ and $\sigma_k \otimes \sigma_0$.
Mar
25
comment Multiqubit state tomography by performing measurement in the same basis
@Peter Shor: they are equal only for $k,j \neq 0$ but it is not so for terms with $\sigma_0 =1$ (so my note about "a swap operator" in earlier answer was misleading).
Mar
22
answered Multiqubit state tomography by performing measurement in the same basis
Mar
9
comment Analyticity and Causality in Relativity
I doubt an answer may be short. From experience of discussion about that problem (also confirmed by answers and comments here) I learn, that even statement of the problem is not very simple. One my colleague even had idea to use it as PhD theme ...
Feb
29
answered Quantum memories: What are they?
Feb
20
comment Constructing a Hamiltonian (as a polynomial of $q_i$ and $p_i$) from its spectrum
I think, the Newton interpolation formula may be used instead of Gaussian elimination in this case
Feb
18
answered Constructing a Hamiltonian (as a polynomial of $q_i$ and $p_i$) from its spectrum
Jan
21
comment Time reversal symmetry and T^2 = -1
I could better understand a question $Pin(3,1)$ vs $Pin(1,3)$. How we could answer what we are using in Euclidean case? Even in Lorentzian case we sometimes have to talk about experimental data (e.g. discovery of antiparticles, search for Majorana neutrino, etc.) to clarify such questions.
Dec
5
answered Charged black holes in equilibrium
Dec
3
comment Charged black holes in equilibrium
It is quite common to claim that even single black hole does not result a stationary spacetime lightandmatter.com/html_books/genrel/ch07/ch07.html
Nov
29
comment Is this a simple Lie algebra?
In such a case OP could write $[i\sigma_a,i\sigma_b]=\cdots$. It is not a convention, it is rather a convenient trick to work with Lie algebra of unitary group, because the algebra is anti-Hermitian matrices. If to use the convention without warning we could not distinguish $sl(2,C)$ and $su(2)$
Nov
24
comment Hilbert-Schmidt basis for many qubits - reference
Maybe the discrete Wigner function is a bit other story, because they need to use trace on $GF(2^n)$ and exchange components in Hilbert-Schmidt scalar product.