Dr. Fesseha Kassahun
I am currently an associate professor of physics at the Addis Ababa University, where I have worked for more than 23 years starting with the rank of graduate assistant. I have taught several courses both at the undergraduate and graduate levels. In particular, I have taught classical electrodynamics and quantum mechanics at the undergraduate level and quantum mechanics and quantum optics at the graduate level. I have also formulated and supervised 21 MSc and 2 PhD research projects. I am these days exclusively involved in the PhD program. There are at present six graduate students working for their PhD under my supervision. I have found the task of teaching physics to be difficult and intellectually challenging. One has to do, especially at the graduate level, a lot of hard work in order to come up with a certain material that his students can easily understand. On the other hand, what I have observed over the years is that the teaching process does not seem to have the effect of inculcating deep-rooted scientific interest in the students. And worst of all, this process does not appear to have the effect of influencing their view of life one way or the other.
I had the opportunity to write two books, one on quantum mechanics entitled Fundamentals Of Quantum Mechanics and another one on quantum optics entitled Fundamentals Of Quantum Optics. In the first book the formalism of quantum mechanics is developed by introducing postulates stated in terms vectors and operators and then establishing the forms of the relations that appear in the postulates or that follow from them in position or momentum space. A discussion included in this book maintains the standpoint that a system cannot evolve both as a free and interacting entity at the same time. It evolves in time either as a free or an interacting system. Hence the dynamics of a free system should be governed by the free Hamiltonian, with the dynamics of an interacting system governed by the interaction Hamiltonian. It is not therefore possible to have a quantum description in which the time evolution of a system is carried partly by the state vector and partly by the operators. I have spent a lot of time and energy in the process of writing the second book. I had to struggle hard to come up with logical, consistent, and conceptually sound exposition of the various topics covered in the book. Among other distinct features, I would like to mention the approach adopted to derive the master equation for a cavity mode or a two-level atom coupled to a squeezed vacuum reservoir and to establish the correlation properties of the noise operators or forces associated with quantum or c-number Langevin equations.
I have some research work on fundamental problems in quantum mechanics and quantum optics. Despite the simplicity of evaluating the propagator for a quadratic Hamiltonian by means of the van Vleck-Pauli relation, the question of the validity of this relation had not been investigated from the point of view of operator ordering. I have somehow managed to obtain, employing path integration, an exact expression for the propagator in Cartesian coordinates for a quadratic Hamiltonian with arbitrary ordering [J. Math. Phys. 33, 2179 (1992)]. In addition, I have obtained an alternative method of evaluating the coherent-state propagator using path integration and by introducing the notion of a coherent-state propagator action. This action is calculated by taking a quadratic term in the Lagrangian as alpha(t)alpha(0) [Phys. Rev. A 46, 5379 (1992)]. It is perhaps worth mentioning that some authors working in quantum optics have already started to apply the newly established methods of evaluating the propagator. It is indeed fascinating to realize that the propagator formulation, in which the Euler-Lagrange equations play a central role, provides a fully quantum description of a system. Moreover, the effect of placing a parametric amplifier in the cavity of a three-level laser has been investigated in a paper published in Physical Review A [Phys. Rev. A 63, 033811 (2001)]. It is found that one effect of the parametric amplifier is to increase the squeezing of the cavity mode by a maximum of 50%. It is gratifying to find out that this paper is repeatedly cited in the literature. It also appears to be appropriate to disclose that the determination of the squeezing spectrum by way of the Q function demands sophisticated quantum thinking [Opt. Commu. 151, 384 (1998)].
I still enjoy doing research of one kind or another. I am currently working along with my PhD students on various problems in quantum optics. I would like to mention that I want to do research for the sole purpose of trying to understand certain aspects of the interaction of light with matter. Very often I find what I do in physics to be quite exciting. I also have a profound appreciation for the quantum theory of light. If one is doing physics without getting excited or having some sense of appreciation, he must then be narrowly missing intellectual life of the highest form. I really wonder to see that the vast majority of the people lead predominantly pragmatic life, which is driven by practically oriented goals. And very few people lead predominantly academic life, which is inspired by theoretically oriented goals*.
Finally, I would like to say something on the question of God. It seems that God has not created man. On the contrary, it appears that man has created God in his own image. I am now fully convinced that
- there is no any document which can be taken as the word of God
- there is no intervention by God in the affairs of human beings
- there is no intelligent design behind the creation of the universe**
In light of the above points, I am inclined to believe that there is no God. On the other hand, although the current scientific explanation of the origin of the universe is far from being fully convincing, Darwin's theory of evolution provides an excellent account of the substantially modified animal called human being. I would like to finish by asking the question 'have you ever tried to figure out your reaction to the hard fact that somebody lives for a certain period of time and then suddenly disappears altogether'.
*These are goals that have no immediate practical applications.
**We demand that there should be intelligent design behind a universe created by God. Alternatively, we assert that there should not be intelligent design behind a universe created by blind forces operating randomly.
EPS-NA: Thank you Dr. Fesseha!