Towards Distributed Quantum Information Processing Using Coupling Of Neutral Atoms to Plasmonic Nanostructures

Abstract

Communication and transfer of quantum information between two physically separated quantum systems – distributed quantum information processing (QIP), is one of the key steps towards scalable and networked quantum computing. In this direction, we propose to experimentally develop and demonstrate a novel experimental platform for achieving strong coupling between ultracold Rubidium (Rb) atoms and plasmonpolariton modes in conducting nanostructures. These schemes provide an alternative mechanism to the more complex and well known cavity-quantum electrodynamics (CQED) systems for achieving strong coupling. The thesis has two major components of work namely, a) Design and construction of an experimental apparatus for production of samples of utlracold 87Rb atoms down to temperatures to where quantum degeneracy can be achieved. b) The second part is to design and characterize plasmonic nanostructures for trapping individual neutral 87Rb atoms. A significant portion of the work describes the construction of an experimental setup to produce 87Rb Bose-Einstein Condensate (BEC). This machine would allow production of high density, high number ultracold samples of large number of atoms at temperatures from a few 100’s of K down to 100’s of nK. In the next phase of the experiment, individual atoms from the BEC will be isolated by transferring the condensate into a 3-D optical lattice potentials and tuning the lattice parameters to achieve a Mottinsulator phase. Ultracold sample of 87Rb BEC is made using the standard techniques of laser cooling and trapping in a magneto-optic trap, transferring in a novel, modified Quadrupole-Ioffe magnetic trap. This is followed by forced RF evaporative cooling to achieve the desired phase space densities for achieving BEC. The second major part of the work done in the thesis is the design, fabrication and characterization of the nanostructures. Existing proposals for trapping and coupling single atoms in conducting tips having paraboloidal shape have certain technical challenges. One of the major technical challenge is the lack of a method for reproducibly fabricating the tips of a given geometry using a top-down approach. Hence, an alternative approach for producing these nanostructures has been devised. Instead of nanotips, cylindrical pillars of 10’s of nm’s in height and diameters varying from 10’s of nm’s to 100’s of nm’s have been designed and fabricated in-house using Electron-Beam Lithography (EBL) . Finite Difference Time Domain (FDTD) analysis has been used to optimize the geometry. Near-field Scanning Optical Microscopy (NSOM/SNOM) has been used to characterize the optical near fields of these structure