Quantum Information Processing Based On Cavity And Quantum Dot System

Quantum information is the study of information processing, such as informa-tion readout/write in, processing, encode, computing, and transmission, which can beaccomplished using quantum mechanical systems. Quantum information has many ad-vantages than classical information: the superposition of the quantum state provide theparallel computing that is much faster than classical computer; the quantum no-cloningtheory promise absolute security cryptogram; the entanglement network can connectthe quantum node that can achieve distributed quantum computation. Recently, manyquantum information process have been realized in various system such as nuclear mag-netic resonance (NMR), liner optics, ion trap, superconducting quantum interferencedevice (SQUID), quantum dot, and cavity QDE. Each system has its owns advantagesand disadvantages. The cavity QED and quantum dot have been considered two of themost promising candidates. My thesis include some theoretical studies about realizingquantum information process in cavity QED and quantum dots. The concrete researchcontent includes:(1) We propose schemes to prepare entanglement states in a bi-mode cavities viastimulated Raman adiabatic passage (STIRAP) and fractional stimulated Raman adi-abatic passage (f-STIRAP) techniques. Our scheme should be realizable in the nearfuture because of the existence of all experimental ingredients. Our numerical sim-ulation shows we can entangle the atoms or BEC condensate with high fidelities bychoosing proper laser pulses.(2) We present a feasible scheme for performing an optically controlled phase gatebetween two conduction electron spin qubits in adjacent self assembled quantum dots.Interaction between the dots is mediated by the tunneling of the valence hole state whichis activated only by applying a laser pulse of the right polarization and frequency. Com- bining the hole tunneling with the Pauli blocking effect, we obtain conditional dynamicsfor the two quantum dots, which is the essence of our gating operations. The most im-portant distinction between our paper and [Nature Phys.7,223(2010)] is that whilethe permanently interacting qubits are not scalable but the non-interacting qubits whileat rest are. Our results are of explicit relevance to the recent generation of verticallystacked self-assembled InAs quantum dots, and show that by a design which avoids un-intended dynamics the gate could be implemented in theory in the10ps range and witha fidelity over90%. Our proposal therefore offers an accessible path to the demonstra-tion of ultrafast quantum logic in quantum dots.(3) We present a proposal for deterministic entanglement between two quantumdots via classical interference. The quantum dots, detuningly driven by two lasers, canbe entangled with coherent cavity modes. After interference between the two out-putcavity modes, the two quantum dots can be entangled. Our scheme requires neitherdirectly coupling between qubits nor the detection of single photons. Moreover thequantum dots do not need to have the same frequencies and coupling constants.