Robust interface between flying and topological qubits

Hybrid architectures, consisting of conventional and topological qubits, have recently attracted much attention due to their capability in consolidating the robustness of topological qubits and the universality of conventional qubits. However, these two kinds of qubits are normally constructed in significantly different energy scales, and thus this energy mismatch is a major obstacle for their coupling that supports the exchange of quantum information between them. Here, we propose a microwave photonic quantum bus for a direct strong coupling between the topological and conventional qubits, in which the energy mismatch is compensated by the external driving field via the fractional ac Josephson effect. In the framework of tight-binding simulation and perturbation theory, we show that the energy splitting of the topological qubits in a finite length nanowire is still robust against local perturbations, which is ensured not only by topology, but also by the particle-hole symmetry. Therefore, the present scheme realizes a robust interface between the flying and topological qubits. Finally, we demonstrate that this quantum bus can also be used to generate multipartitie entangled states with the topological qubits.Comment: Accepted for publication in Scientific Report

Out-of-equilibrium physics in driven dissipative coupled resonator arrays

Coupled resonator arrays have been shown to exhibit interesting many- body physics including Mott and Fractional Hall states of photons. One of the main differences between these photonic quantum simulators and their cold atoms coun- terparts is in the dissipative nature of their photonic excitations. The natural equi- librium state is where there are no photons left in the cavity. Pumping the system with external drives is therefore necessary to compensate for the losses and realise non-trivial states. The external driving here can easily be tuned to be incoherent, coherent or fully quantum, opening the road for exploration of many body regimes beyond the reach of other approaches. In this chapter, we review some of the physics arising in driven dissipative coupled resonator arrays including photon fermionisa- tion, crystallisation, as well as photonic quantum Hall physics out of equilibrium. We start by briefly describing possible experimental candidates to realise coupled resonator arrays along with the two theoretical models that capture their physics, the Jaynes-Cummings-Hubbard and Bose-Hubbard Hamiltonians. A brief review of the analytical and sophisticated numerical methods required to tackle these systems is included.Comment: Chapter that appeared in "Quantum Simulations with Photons and Polaritons: Merging Quantum Optics with Condensed Matter Physics" edited by D.G.Angelakis, Quantum Science and Technology Series, Springer 201

Complex systems in quantum technologies

124 p.En esta Tesis, se propone una serie de protocolos de información cuántica, analizando la viabilidad con la tecnología actual, en plataformas de iones atrapados y circuitos superconductores. Encontramos que los protocolos propuestos tienen que adaptarse a las ventajas e inconvenientes de cada plataforma. Se prueba que un qubit protegido, basado en una representación dual de una cadena fermiónica topológica, puede ser codificado en un sistema de trampa de iones, debido a sus propiedades específicas. Se analiza la simulación cuántica de fermiones, encontrando una mayor eficiencia debido a puertas colectivas que son realizables con la tecnología de iones atrapados. Dentro de este espíritu, estimamos las posibilidades de los circuitos superconductores de simular modelos de espines, sistemas fermiónicos y bosónicos. Extendemos estos conceptos a la simulación cuántica de sistemas dinámicos clásicos, encontrando que una simulación de la dinámica de Boltzmann discreta puede ser codificada en sistemas acoplados de qubits con bosones. Estos son los primeros pasos para explorar las simulaciones de dinámica de fluidos en un ordenador cuántico