Tabish Qureshi

Aspects of tachyonic inflation with exponential potential

We consider issues related to tachyonic inflation with an exponential potential. We find an exact solution of the evolution equations in the slow roll limit in FRW cosmology. We also carry out a similar analysis in the case of brane assisted tachyonic inflation. We investigate the phase space behavior of the system and show that the dustlike solution is a late time attractor. The difficulties associated with reheating in the tachyonic model are also indicated.

CRITIQUE OF PROTECTIVE MEASUREMENTS

The recently proposed idea of {open_quotes}protective{close_quotes} measurement of a quantum state is critically examined, and generalized. Earlier criticisms of the idea are discussed, and their relevance to the proposal assessed. Several constraints on measuring apparatus required by {open_quotes}protective{close_quotes} measurements are discussed, with emphasis on how they may restrict their experimental feasibility. Though {open_quotes}protective{close_quotes} measurements result in an unchanged system state and a shift of the pointer proportional to the expectation value of the measured observable in the system state, the actual reading of the pointer position gives rise to several subtleties. We propose several schemes for reading the pointer position, both when the apparatus is treated as a classical system as well as when its quantum aspects are taken into account, that address these issues. The tiny entanglement which is always present due to deviation from extreme adiabaticity in realistic situations is argued to be the weakest aspect of the proposal. Because of this, one can never perform a protective measurement on a single quantum system with absolute certainty. This clearly precludes an ontological status for the wave function. Several other conceptual issues are also discussed. {copyright} {ital 1999} {ital The American Physical Society}

Cosmology with rolling tachyon

We examine the possibility of rolling tachyon to play the dual role of inflaton at early epochs and dark matter at late times. We argue that enough inflation can be generated with the rolling tachyon either by invoking the large number of branes or brane world assisted inflation. However, reheating is problematic in this model.We examine the possibility of rolling tachyon to play the dual roll of inflaton at early epochs and dark matter at late times. We argue that enough inflation can be generated with the rolling tachyon either by invoking the large number of branes or brane world assisted inflation. However, reheating is problematic in this model.

Understanding Popper's experiment

An experiment proposed by Karl Popper is considered by many to be a crucial test of quantum mechanics. Although many loopholes in the original proposal have been pointed out, they are not crucial to the test. We use only the standard interpretation of quantum mechanics to point out what is fundamentally wrong with the proposal, and demonstrate that Popper’s basic premise was faulty.

POPPER'S EXPERIMENT, COPENHAGEN INTERPRETATION AND NONLOCALITY

A thought experiment, proposed by Karl Popper, which has been experimentally realized recently, is critically examined. A basic flaw in Poppers argument which has also been prevailing in subsequent debates, is pointed out. It is shown that Poppers experiment can be understood easily within the Copenhagen interpretation of quantum mechanics. An alternate experiment, based on discrete variables, is proposed, which constitutes Poppers test in a clearer way. It refutes the argument of absence of nonlocality in quantum mechanics.

Wave–particle duality in N-path interference

Bohrs principle of complementarity, in the context of a two-slit interference experiment, is understood as the quantitative measures of wave and particle natures following a duality relation

Three-slit interference: A duality relation

{\mathcal D}^2+{\mathcal V}^2 \le 1

Einstein's Recoiling Slit Experiment, Complementarity and Uncertainty

. Here

Ghost Interference and Quantum Erasure

{\mathcal D}

Analysis of Popper's Experiment and Its Realization

is a measure of distinguishability of the two paths, and