Materia cuántica exótica generada con ingeniería de Floquet

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Física de Materiales, leída el 17-09-2019This thesis investigates three time periodic quantum mechanical systems, all of which are of particular interest for research related to ultracold atoms in optical lattices. In the first system (Chapter 2), a synthetic uniform magnetic eld is created through the shaking of a two dimensional square optical lattice [1]. In this way an effective magnetic field can be felt by ultra cold atoms trapped in the lattice. Simple continuous shaking, however, produces non-uniform effective masses (tunneling amplitudes) which lead to non-uniform ux configurations. This is addressed both analytically and numericallyin this work. In addition, the limitations of continuous shaking schemes are discussed and several non-continuous shaking protocols are analyzed and compared. At the end of this investigation, the shaking schemes that yield a uniform effective mass and magnetic flux are identified...En la presente tesis doctoral se muestran los resultados obtenidos en la investigacion de tres sistemas cuanticos periodicos en el tiempo, todos ellos de gran interes dentro de la investigacion relacionada con atomos ultrafríos en redes opticas. En el primer sistema (Capitulo 1), un campo magnetico uniforme es creado de manera artificial a partir del sacudido periodico de una red optica bidimensional cuadrada [1]. De este modo, los atomos ultrafríos atrapados en dicha red pueden experimentar un campo magnetico efectivo. Una perturbacion simple y continua produce, sin embargo, masas efectivas no uniformes (amplitudes de tuneleo) que dan lugar a configuraciones de flujo no uniforme. Ambos puntos son abordados de manera analítica y numerica. Ademas de ello, las limitaciones de una perturbacion continua son discutidas y varios protocolos de perturbacion discontinua son analizados y comparados. Finalmente, los protocolos de perturbacion que producen una masa efectiva y un flujo magnetico uniformes son identificados...Depto. de Física de MaterialesFac. de Ciencias FísicasTRUEunpu

Cat states in a driven superfluid: role of signal shape and switching protocol

We investigate the behavior of a one-dimensional Bose-Hubbard model whose kinetic energy is made to oscillate with zero time-average. The effective dynamics is governed by an atypical many-body Hamiltonian where only even-order hopping processes are allowed. At a critical value of the driving, the system passes from a Mott insulator to a superfluid formed by a cat-like superposition of two quasi-condensates with opposite non-zero momenta. We analyze the robustness of this unconventional ground state against variations of a number of system parameters. In particular we study the effect of the waveform and the switching protocol of the driving signal. Knowledge of the sensitivity of the system to these parameter variations allows us to gauge the robustness of the exotic physical behavior.Comment: 9 pages, 5 figure

'Sawfish' Photonic Crystal Cavity for Near-Unity Emitter-to-Fiber Interfacing in Quantum Network Applications

Photon loss is one of the key challenges to overcome in complex photonic quantum applications. Photon collection efficiencies directly impact the amount of resources required for measurement-based quantum computation and communication networks. Promising resources include solid-state quantum light sources, however, efficiently coupling light from a single quantum emitter to a guided mode remains demanding. In this work, we eliminate photon losses by maximizing coupling efficiencies in an emitter-to-fiber interface. We develop a waveguide-integrated 'Sawfish' photonic crystal cavity and use finite element simulations to demonstrate that our system transfers, with 97.4% efficiency, the zero-phonon line emission of a negatively-charged tin vacancy center in diamond adiabatically to a single-mode fiber. A surrogate model trained by machine learning provides quantitative estimates of sensitivities to fabrication tolerances. Our corrugation-based design proves robust under state-of-the-art nanofabrication parameters, maintaining an emitter-to-fiber coupling efficiency of 88.6%. To demonstrate its potential in reducing resource requirements, we apply the Sawfish cavity to a recent one-way quantum repeater protocol.Comment: Main part: 16 pages, 7 figure

Cat states in a driven superfluid: role of signal shape and switching protocol

We investigate the behavior of a one-dimensional Bose-Hubbard model whose kinetic energy is made to oscillate with zero time-average. The effective dynamics is governed by an atypical many-body Hamiltonian where only even-order hopping processes are allowed. At a critical value of the driving, the system passes from a Mott insulator to a superfluid formed by a cat-like superposition of two quasi-condensates with opposite non-zero momenta. We analyze the robustness of this unconventional ground state against variations of a number of system parameters. In particular we study the effect of the waveform and the switching protocol of the driving signal. Knowledge of the sensitivity of the system to these parameter variations allows us to gauge the robustness of the exotic physical behavior