Recent content by mtak0114

Hi I would like to know if I have a system of coupled harmonic oscillators whether the standard position operator for an uncoupled oscillator is valid, i.e. x_i = \frac{1}{\sqrt{2}} (a_i+a_i^\dagger)? where i labels the ions. To give some context I am looking at a problem involving a...

During my PhD I have done very little programming but I have done a a fair bit of programming during my undergraduate degree. I don't know if you would call it substantial though... This is something that I realize that I would probably need to scratch up on if I am to enter the work force.

So to give a bit more context: My PhD topic is a bit exotic where I was primarily focussed on developing a consistent theory of Quantum information in the context of relativity. But I have also balanced this with application driven research where I was involved in various theoretical aspects of...

So I am about to finish my PhD and am stressing a lot about my future. I have two possible options which I am thinking of either staying in physics and getting a post-doc or moving into industry or perhaps finance. So this is my thought process: I really enjoy certain aspects of physics but...

So would it be correct to say that the Dirac equation includes effects due to both electric and magnetic dipole moments of the electron? but given that the former are not observed they are suppressed? When one goes to QED however is such a suppression necessary or does the theory predict...

Thanks Bill that makes sense, but is that assuming that F^{\mu\nu} is just the magnetic field {\bf B} in the rest frame otherwise I can't see how \sigma_{\mu\nu}F^{\mu\nu} reduces to such a term in the rest frame. Is it possible to see the converse, that QFT implies that spin does not couple...

Hi I have a simple question: We know from non-relativistic quantum mechanics that the spin of an electron couples only to the magnetic field, i.e. it processes around the magnetic field. How is this resolved in the relativistic context where it would seem that the spin should couple to...

Hi could someone please explain the story (if there is one) about the Dirac equation with an anomalous magnetic moment term, I have seen this in several old papers but it never seems to be mentioned in textbooks. Was this an old confusion in formulating QFT. In this context I believe the Dirac...

Thanks for the help I think an example might help me gain some intuition, for a qubit would the following two projectors constitute a POVM ? P_0 = |0 \rangle \langle0 | and P_1 = |1 \rangle \langle 1 | If so if I choose to measure along different directions on the bloch sphere, say x...

Thanks for the reply that's quite helpful. I have not heard of the Dilation theorem. Do you have any good sources detailing some theory and examples perhaps of this in regards to measurement. I had a look at Nielsen and Chuang which had a tiny bit but was a bit of detail. Specifically what...

Hi I have a question about POVMs im confused as to how they correspond to actual measurements we do in a lab, and how non-orthogonal measurements fit into this context. For example we have some POVM with elements E_i. I read in Nielsen and Chuang that we do a measurement and get outcome m...

1. Show that an arbitrary density operator for a mixed state qubit may be written as 2. \rho = \frac{I+r^i\sigma_i}{2}, where ||r||<1 (Nielsen and Chuang pg 105) 3. So my attempt was as follows Given that a \rho is hermitian it may be written as a linear combination of the pauli...

Hi I am confused about these two related but different terms Lorentz invariance/covariance and General invariance/covariance As I understand it a Lorentz invariant is a scalar which is the same in all inertial reference frames i.e. it acts trivially under a Lorentz transformation an example...

Yes but is this the correct picture? What I mean is regardless of the hamiltonian if the state forms a closed loop on the bloch sphere will there still be a geometric phase? thanks again Mark

thanks for the references, I had a look at the book but there is still something I'm confused about, the parameter space which people refer to seem to refer to either those parameters which the hamiltonian depend on or the projective hilbert space - the bloch sphere for say a spin half particle...