The project is focused in theory, fabrication and characterization of quantum information processing devices manipulating q-bits. Strong coupling between quantum dots and high-Q cavity was demonstrated, enabling both classical and quantum mechanical switching.
A comprehensive theoretical analysis of the cavity quantum electrodynamics (QED) in single-photon Mach-Zehnder Interferometer (SMZI) based switches and single quantum gates that are intended for the processing of quantum information encoded in the polarization of single photons inside integrated photonic crystal (PC) quantum networks is presented. These devices rely on manipulating the geometrical phase of single photons by means of the Single-Photon Faraday Effect (SPFE), which can be described in terms of a detuned single mode quantum field strongly interacting with a two-level system or quantum dot (QD) inside nanocavities. The feasibility of such devices depends on the ability for the field in each arm of the interferometer to couple in their respective nanocavities, successfully interact with the quantum dot, and when the appropriate phase is accumulated couple out; all these steps being performed with minimum phase error and losses. Using the Jaynes-Cummings model, the cavity dynamics is studied for various detuning energies and coupling energies, and it is shown that the design of these devices can achieve low phase error and robustness against fabrication errors.
Classical computation relies heavily on information manipulation. Each component of a hardware needs to communicate with others, and this is done by encoding information into strings of bits and application of logical operations. When dealing with quantum technologies, there arises a new set of paradigms and devices, based on manipulations of qubits, the quantum analogues of conventional bits. This work investigates the generation and distribution of quantum entanglement, a uniquely non-classical correlation, across spin chains, which serve as promising platforms for quantum information processing. We systematically compare two distinct entanglement generation protocols: Protocol 1 (P1), based on alternating weak and strong couplings that create a band structure enabling an effective trimer-model approximation, and Protocol 2 (P2), which employs symmetric boundary couplings and virtual excitations to establish a direct effective interaction between the chain ends. Our results demonstrate that a protocol based on virtual excitations and optimized boundary couplings consistently outperforms its counterpart in speed, achieved entanglement, and robustness against fabrication imperfections and noise. Furthermore, by employing effective model reductions and open quantum systems techniques we provide a comprehensive framework for understanding the resilience of distributed entanglement in solid-state quantum devices. The characteristics of the virtual-coupling protocol highlight its potential for experimental implementation in scalable quantum technologies.
Quantum computers require technologies that offer both sufficient control over coherent quantum phenomena and minimal spurious interactions with the environment. We show, that photons confined to photonic crystals, and in particular to highly efficient waveguides formed from linear chains of defects doped with atoms can generate strong non-linear interactions which allow to implement both single and two qubit quantum gates. The simplicity of the gate switching mechanism, the experimental feasibility of fabricating two dimensional photonic crystal structures and integrability of this device with optoelectronics offers new interesting possibilities for optical quantum information processing networks.