November 2017
Abstracts of the QSIT Lunch Seminar, Thursday, November 2, 2017
Perturbative metamaterials: Designing functionality with discrete models
Marc Serra Garcia – Condensed Matter Theory and Quantum Optics (Huber group), ETH Zurich
The challenge in metamaterials design is to find material geometries that lead to the desired functionalities. Discrete, or reduced-order models provide a concise description of complex phenomena, such as negative refraction, or topological surface states. Hence, a promising approach towards new metamaterials is to combine geometric building blocks to replicate discrete models presenting the desired features. However, there is no reliable way to solve such an inverse problem. In this talk, I will introduce a new class of metamaterials, which we term “perturbative metamaterials”, consisting of weakly interacting unit cells. The weak interaction allows us to associate each element of the discrete model to individual geometric features of the metamaterial, thereby enabling a systematic design process. We demonstrate our approach by designing 2D elastic metamaterials that realize Veselago lenses, zero-dispersion bands, and topological surface phonons. I will present an example where this design process is used to demonstrate a novel topological phase of matter and will propose the use of this technique to the design of systems for quantum computing applications.
Strong Coupling Cavity QED with Double Quantum Dot Charge Qubits: The Story Continues
David van Woerkom – Quantum Device Lab (Wallraff group), ETH Zurich
We study the dynamics of a double quantum dot (DQD) charge qubit realized in a GaAs/AlGaAs two dimensional electron gas and strongly coupled to a high impedance SQUID array resonator. DQD qubit dephasing rate down to γ2/2π = 3 MHz allows us to perform time resolved measurements realized in the dispersive regime, which we use to discriminate between the contribution of relaxation and pure dephasing processes to the decoherence rate. We realize measurements of Rabi-oscillations, Ramsey-fringes, charge relaxation and Hahn-echo for a the DQD charge qubit, with time scales T∗2 ∼ 25 ns, T1 ∼ 100 ns and T2,echo ∼ 50 ns extracted for interdot detuning and tunnel rate of δ = 0 and 2t ∼ 4 GHz respectively. In a new set of devices, we realized proof of concept experiments in which the coupling between a Transmon qubit and a DQD charge qubit is mediated by a tunable high impedance SQUID array resonator, which acts as a quantum bus enabling long range coupling between dissimilar qubits. The device is equipped with a flux line to tune the Transmon frequency on nanosecond time scales, and with a 50 Ω coplanar waveguide resonator capacitively coupled to the Transmon for read out. Realizing a well-controlled interface between semiconductor and superconductor based quantum computing architectures may allow to harness the best of both device architectures, for example by providing an interface between strongly coupled charge state and high coherence spin states of electrons and possibly nuclei. We are confident that the methods and techniques developed in this work are transferable to QD devices based on other material systems.