Alex 'qubeat'

541 reputation

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	location	Russia
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visits	member for	2 years
	seen	May 5 '12 at 20:03
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Scientist

	541 reputation	bio	website		visits	member for	2 years
34 badges		location	Russia		seen	May 5 '12 at 20:03

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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.