arXiv subjects
Publications and source records attributed to A. V. Gopala Rao.
The Bloch sphere provides an elegant way of visualizing a qubit. Analogous representation of the simplest composite state of two-qubits has attracted significant attention. Here we present a detailed mathematical analysis of the real-matrix parametrization and associated geometric picturization of arbitrary two-qubit states - up to their local SL2C equivalence, in terms of canonical ellipsoids inscribed within the Bloch sphere.
We revisit the problem of the Lorentz transformation of time-intervals in special relativity. We base our discussion on the time-interval transformation formula $ cΔt' = γ(cΔt - \vecβ \cdot Δ\vec{r}) $ in which $ Δt'$ and $ Δt $ are the time-intervals between a given pair of events, in two inertial frames $ S $ and $ S'$ connected by an general boost. We observe that the Einstein time-dilation-formula, the Doppler formula and the relativity of simultaneity, all follow when one the frames in the time-interval transformation formula is chosen as the canonical frame of the underlying event-pair. We also discuss the interesting special case $ Δt' = γΔt $ of the time-interval transformation formula obtained by setting $ \vecβ \cdot Δ\vec{r}=0 $ in it and argue why it is really \textbf{not} the Einstein time-dilation formula. Finally, we present some examples which involve material particles instead of light rays, and highlight the utility of time-interval transformation formula as a calculational tool in the class room.
Statistical ensemble formalism of Kim, Mandel and Wolf (J. Opt. Soc. Am. A 4, 433 (1987)) offers a realistic model for characterizing the effect of stochastic non-image forming optical media on the state of polarization of transmittedlight. With suitable choice of the Jones ensemble, various Mueller transformations - some of which have been unknown so far - are deduced. It is observed that the ensemble approach is formally identical to the positive operator valued measures (POVM) on the quantum density matrix. This observation, in combination with the recent suggestion by Ahnert and Payne (Phys. Rev. A 71, 012330, (2005)) - in the context of generalized quantum measurement on single photon polarization states - that linear optics elements can be employed in setting up all possible POVMs, enables us to propose a way of realizing different types of Mueller devices.
The Classification of Polarization elements, the polarization affecting optical devices which have a Jones matrix representation, according to the types of eigenvectors they possess, is given a new visit through the Group-theoretical connection of polarization elements. The diattenuators and retarders are recognized as the elements corresponding to boosts and rotations respectively. The structure of homogeneous elements other than diattenuators and retarders are identified by giving the quaternion corresponding to these elements. The set of degenerate polarization elements is identified with the so called `null' elements of the Lorentz Group. Singular polarization elements are examined in their more illustrative Mueller matrix representation and finally the eigenstructure of a special class of singular Mueller matrices is studied.