MACROSCOPIC GAS ENSEMBLES AS QUANTUM MEMORY

Abstract

Manipulation and control of quantum systems has attracted a lot of attention in the recent decade due to enormous possibilities of simplifying the solution of certain physical and mathematical problems that were thought to be intractable with classical systems. Notable examples of such problems being the factorization of large numbers and solving the structure of complex molecules by utilizing the underlying complexity of quantum systems. Quantum information processing (QIP) deals with the use of the ability of manipulating and controlling the internal state of isolated quantum systems and the coupling of quantum systems for solving the above mentioned problems. In case of a QIP system, a single building block having two degrees of freedom is referred to as a Qubit (equivalent to bit in classical computers). There are variety of systems that have been studied extensively for usability in QIP. For e.g. Quantum optic systems (two level atoms and photons), solid state systems (Josephson junction), and NMR systems where an ensemble of molecules is used for QIP. The basic criteria for any system to qualify as a Qubit have been laid out by DiVincenzo. Most of the systems based on isolated single Qubits have been technically challenging to work with, for e.g. they require state of the art technologies in the area of Ultra high vacuum, lasers, optics and RF electronics. An alternative that has been proposed in the recent times has been to use macroscopic atomic vapour cells where the entire vapour cell acts as a single pure-Qubit. The collective internal electronic spin states of these atoms in the gaseous form is used a Qubit. The state of the Qubit is prepared through optical pumping and the spin state is read out through birefringence of the atomic vapor to the incident probe light. However, the challenging part in these systems is to increase the spin relaxation times. The spin relaxation normally is associated with the inelastic collisions between the atoms in the gas phase and walls of the cells. This thesis addresses the issue of increasing the spin relaxation time. It is well know that, spin relaxation time can be increased by coating the vapor cells with long hydrocarbon chains. The coatings like paraffin (Tetracontane) are known to allow a spin polarized atom to experience thousands of collisions with cell walls without getting depolarized. During the course of this Master’s thesis, efforts have been made to fabricate paraffin coated glass vapor cells filled with Rubidium atoms and to measure their spin relaxation lifetimes.