arXiv subjects
Publications and source records attributed to Joydip Ghosh.
A controlled-NOT logic gate based on conditional spectroscopy has been demonstrated recently for a pair of superconducting flux qubits [Plantenberg et al., Nature 447, 836 (2007)]. Here we study the fidelity of this type of gate applied to a phase qubit coupled to a resonator (or a pair of capacitively coupled phase qubits). Our results show that an intrinsic fidelity of more than 99% is achievable in 45ns.
An approach to the construction of the CNOT quantum logic gate for a 4-dimensional coupled-qubit model with weak but otherwise arbitrary coupling has been given recently [M. R. Geller et al., Phys. Rev. A, 012320 (2010)]. How does the resulting fidelity depend on the form of qubit-qubit coupling? In this paper we calculate intrinsic fidelity curves (fidelity in the absence of decoherence versus total gate time) for a variety of qubit-qubit interactions, including the commonly occurring isotropic Heisenberg and XY models, as well as randomly generated ones. For interactions not too close to that of the Ising model, we find that the fidelity curves do not significantly depend on the form of the interaction, and we calculate the resulting interaction-averaged fidelity curve for the non-Ising-like cases and a criterion for determining its applicability.
In this paper we have presented a generalized treatment of a photon scattering by a harmonic oscillator initially at ground state. We have predicted the scattering cross-section of the oscillator and showed how the treatment invariably requires the formalisms of renormalization. As a special case of our treatment, we discussed about Rayleigh and Thomson Scattering and computed the total cross-section in order to be consistent with experimental results. Two approximations are adopted in order to simplify the problem but without any digression from our goal. A second order perturbation theory is employed where the first excited state of the harmonic oscillator is considered to be the only intermediate state and A dipole approximation is utilized. Throughout this paper we have used Gaussian units.
The shifting of spectral lines due to induced correlation effect, discovered first by Wolf for the single scattering case which mimics the Doppler mechanism has been extended and developed further by the present authors known as Dynamic Multiple scattering(DMS). We have explored DMS theory for explaining anomalous redshifts in quasars. Our recent work, based on the statistical analysis of the Véron-Cetty data(2003) supports that quasar redshifts fit the overall Hubble expansion law, as in the case of galaxies, for z less than equal to 0.295 but not for higher redshifts, indicating clearly the inadequacy of the Doppler effect as the sole mechanism in explaining the redshifts for high redshift quasars for z greater than equal to 0.295. We found that the redshift posseses an additive, discordant component due to frequency shifting from the correlation induced mechanism which increases gradually for ~ 0.295 < z < 3.0, however, appearing to follow the evolutionary picture of the universe with absolute dependence on the physical characteristics i.e., environmental aspects of the relevant sources through which the light rays pass, after being multiply scattered.