| Abstract |
It comprises two parts.
The first part is about spin polarization noise in thermal alkali vapors. Spin noise is a fundamental source of noise, imposing the, so called, fundamental quantum limits to precision measurements employing spin polarized targets. However, being, as it is, of magnetic origin, spin noise can be manipulated to reveal system
specific information and in this, first part of the thesis, we use it to extract such parts of information, experimentally. Part I is organized as follows. In the first chapter, the general properties of alkali metals and their atomic structure are discussed. We build the formalism used to attack calculations in alkali systems,
a formalism based on spherical tensor algebra, and present the various interactions and relaxation processes relevant to the description of a thermal vapor.
Finally, since light beams are used to probe the properties of the medium, the impact of these properties on the characteristics of passing light are analyzed. It is important to note at this point that the chapter has been written out rather exhaustively, with an eye on it serving as a textbook reference for spherical tensor algebra calculations in the context of alkali metals. In the second chapter, a description of our laboratory is given; quoting suppliers, equipment and such.
In the third, and final, chapter of this part, the experimental work performed is presented. This involved extracting the transverse relaxation rate of an alkali vapor, which is the main decoherence rate in the system, and providing a proof of principle on the ability of spin noise measurements to serve as a Quantum Random Number Generator.
The second part is about quantum biology. The incentive for this work has been the magnetoreception ability of certain species of plants and animals and, particularly, the proposed explanation of the avian compass by means of magnetic field effects in radical ion pairs (RIPs). RIPs are formed in spin correlated states,
by a charge transfer process between two free radicals. This correlated state evolves coherently between the singlet and triplet subspaces, an evolution which can be in
uenced by magnetic fields before charge recombination occurs, thus making the RIP act as a magnetic sensor. The author's work on the subject was to theorize on the implications of initially exciting RIPs in coherent triplet states, rather than in the singlet state. Part II is organized as follows. In the first chapter, a round-up of experimental observations on magnetic field effcts
on radical ion pairs is presented and magnetoreception, being the incentive for this work, is discussed. This chapter, like the first chapter of part I, is written as a general reference/introduction to the field of spin chemistry. In the second chapter, the mathematical formalism traditionally pertaining to the description
of RIP reactions is given and a new, conceptually dfferent, master equation by I. Kominis is introduced. In the final chapter, the excitation of RIPs in triplet, rather than singlet, states is discussed. Specifically, we analyze how a coherent triplet state can provide not only alignment, but also orientational, information
for an external magnetic field in a radical pair which demonstrates isotropic hyperfine interaction; an impossibility for singlet-born pairs. We also discuss the case of a triplet excited state in a pair with anisotropic hyperfine interaction and show how the angular sensitivity, in the context of the new theory and in specific
ranges of parameters, demonstrates radically diffrent behavior than expected from the traditional, phenomenological approach.
|
Spin noise, decoherence and magnetic effects in alkali atoms and biomolecules
