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8:50 AM
@glS Got sufficient sleep so hopefully this will work this time?
0
A: Quantify the probability in guessing the Hamiltonian?

More AnonymousThis is my attempt. We start with the following tricks: We assume $M$ is a large number. This enables us to say the distribution observed $\{ M \}$ is the most probable distribution. We count the frequency of the of a particular eigenvalues with $\tilde \lambda_k$ with $m_i$. Hence, for a par...

 
 
1 hour later…
10:02 AM
@Mithrandir24601 any quick thoughts^ if this is sensible?
@Mithrandir24601 Also I could pose the same question for the infrared divergences as well
Where usually most people assume gravity plays no role
@Mithrandir24601 Also point 6 looks like entropy. Can I say I have my own version of entropy?
0
A: Quantify the probability in guessing the Hamiltonian?

More AnonymousThis is my attempt. We start with the following tricks: We assume $M$ is a large number. This enables us to say the distribution observed $\{ M \}$ is the most probable distribution. We count the frequency of the of a particular eigenvalues with $\tilde \lambda_k$ with $m_i$. Hence, for a par...

 
 
1 hour later…
glS
11:11 AM
@MoreAnonymous "We assume M is a large number. This enables us to say the distribution observed {M} is the most probable distribution." I guess $M$ is the number of measurements, that is, the number of collected samples. What do you mean "the most probable distribution?" the distribution is uniquely determined by state being measured and observable
 
@glS So compared to the other possible distrubutions one could get from multinomial theorem ... We assume ours is the most probable
 
glS
@MoreAnonymous but what I mean is that there isn't "a most probable" distribution here. As far as I understand, you have a state $|\psi\rangle$ that you are measuring multiple times in some basis. The distribution is simply givens by the squared overlaps of $|\psi\rangle$ in the measurement basis. It's unique, so why talk of "the most probable one"?
 
@glS Ah cause my eigenkets are variables (in the sense you can vary them)
 
glS
@MoreAnonymous why?
 
@glS How would I other wise reach the maximum (most probable) distribution point (6). Also I think there are 2 equals sign in point 3
Note the 2nd one is gained by empirical probability
And must match after the maximization
@glS I think I'm saying using the distribution of eigenvalues it should be possible to construct the eigenbasis and thus the Hamiltonian . Also slight edit done.
 
glS
11:21 AM
ok so I still don't get what state is being measured here. You have some $|\psi\rangle$ and you measure it in the eigenbasis of some Hamiltonian, correct? Then you collect many samples and thus find the overlaps of $|\psi\rangle$ in this basis. If you change the measurement basis you are not measuring the Hamiltonian anymore
 
@glS Correct! You use units and dimensions and see it's energy and there is an intermediate operator point 3
 
glS
@MoreAnonymous I don't know what "use units and dimensions and see it's energy" means, but that's beside the point. If there is an intermediate operator than my sentence is not correct
 
@glS You don't know the Hamilontian the space is one where you are varying all possible Hamiltonains
 
glS
so you are not measuring in the energy eigenbasis then?
 
@glS I think My formulations allows one to go from eigenvalue distribution to eigenvectors to Hamiltonian
Note it has its assumptions
 
glS
11:25 AM
@MoreAnonymous I don't know what this means
and you haven't answered the question
 
@glS I am measuring eigenenergies but alternate between measurements of O and H (point 3)
Also the question has been edited ... Do read it before the section "Why this is a difficult problem"
 
glS
@MoreAnonymous that is not clear at all from the question. It should be in the background section
so, you have a state $|\psi\rangle$, and you measure this state sometimes in the energy eigenbasis and sometimes in some other random measurement bases?
 
@glS Yes
But only the eigenenergy ones are recorded
 
glS
@MoreAnonymous then what's the point in doing the other measurements?
 
@glS If I measure energy twice I would get the same eigenenergy
(I think)
"otherwise the same energy eigenvalue would be on the list" point 3
 
glS
11:34 AM
@MoreAnonymous no, you would get one of the possible outcomes, we already discussed this. Then if you measure immediately after the first measurement yes you do get the same outcome
but that's not what you are doing
 
Yes. So essentially u have a list of energies which look like:

1/2
3/2
1/2
5/2
Now, since u dont have:

1/2
1/2
1/2
1/2
U conclude a measurement of a different observable was done
 
glS
Please use normal notation. I don't know what those lists mean. What state are you measuring?
 
@glS Sorry I personally find it easier to think like this
@glS You do not know the states (you only have the eigenenergies)
So basically the variables are the possible Hamiltonians and the eigenvectors
/energy -eigenfunctions
and you are given . only the distribution of eigenvalues
If you think this is impossible to solve (even non-probabilistically) I think you can use an argument of counting number of variables and number of equations? (I think it is solvable and hence the solution)
@glS Am I making less or more sense?
 
glS
if you are measuring the same state $|\psi\rangle$ multiple times, regardless your knowing the state or not, doing measurements and discarding the results is pointless
the state is reset before every measurement, so it's not like the post-measurement states matter in this case
 
@glS Wait I'm slightly confused (I might be thinking of this too physically). But I think we're on the same page but for different reasons :/
can I ask if the answer makes sense? (with your current understanding of the question)?
 
glS
11:51 AM
@MoreAnonymous I don't understand the question, that's the problem
 
Alright here's another go at reformulating it: in the usual formulation of QM one has: energy eigenbasis + eigenvalues -> Hamiltonian
 
glS
I don't get the point of these "intermediary measurements" that you do and discard. If you measure $|\psi\rangle$ in a basis $|u_k\rangle$ and then measure $|\psi\rangle$ in a basis $|v_k\rangle$, the results in the different bases do not affect one another
 
(spectral theorem)
Can I have energy eigenvalues -> eigenbasis ?
(or atleast guess them)
Just to be more specific: eigenvalues -> energy eigenbasis
If not, can I effectively guess this?
@glS is this reformulation better? or worse?
 
glS
@MoreAnonymous that's just words, I don't know what you mean by that. The only interpretation I can think of is the one we discussed a few days ago, when I told you that no I don't see how that makes sense.
 
@glS Does it work if you read the answer with this perspective (provided by words)? Also can you find the permalink or something for that version (we've done this too many times :( ) So I'm not sure which version
Honestly I'd like to include diagrams,etc maybe I should do that in the answer?
 
glS
12:26 PM
no because then I stop at the first point, as per beginning of the present discussion
because I don't know what does it mean "most probable distribution" here
 
Anonymous
1:06 PM
@MoreAnonymous How's this a quantum computing question?
 
@SanchayanDutta its quantum information imo
@glS yes a diagram would help
So lets say the possible eigenvalues . are 1/2 3/2 5/2 all of different probabilities
then we would expect to see the 1/2 more than the 3/2 for example
And that is essentially what I mean
by most probable
@SanchayanDutta Also is the question sensible to you btw?
Regardless of classification?
 

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