Nick Lambert

Identification of spin wave modes in yttrium iron garnet strongly coupled to a co-axial cavity

We demonstrate, at room temperature, the strong coupling of the fundamental and non-uniform magnetostatic modes of an yttrium iron garnet ferrimagnetic sphere to the electromagnetic modes of a co-axial cavity. The well-defined field profile within the cavity yields a specific coupling strength for each magnetostatic mode. We experimentally measure the coupling strength for the different magnetostatic modes and, by calculating the expected coupling strengths, we are able to identify the modes themselves.

Magneto-optical coupling in whispering-gallery-mode resonators

Engineering and Physical Sciences Research Council (Grant IDs: EP/M50693X/1, EP/L027151/1), European Research Council (Grant ID: 648613), Hitachi (research fellowship), Royal Society (University Research Fellowship), Winton programme for the Physics of Sustainability

Dispersive readout of ferromagnetic resonance for strongly coupled magnons and microwave photons

We demonstrate the dispersive measurement of ferromagnetic resonance in a yttrium iron garnet sphere embedded within a microwave cavity. The reduction in the longitudinal magnetization at resonance is measured as a frequency shift in the cavity mode coupled to the sphere. This measurement is a result of the intrinsic non-linearity in magnetization dynamics, indicating a promising route towards experiments in magnon cavity quantum electro-dynamics.

Cavity mediated coherent coupling of magnetic moments

We would like to acknowledge support from Hitachi Cambridge Laboratory, EPSRC Grant No. EP/K027018/1 and ERC Grant No. 648613. A.J.F. is supported by a Hitachi Research Fellowship. A.C.D. is supported by the ARC via the Centre of Excellence in Engineered Quantum Systems (EQuS), Project No. CE110001013.

A charge parity ammeter.

A metallic double dot is measured with radio frequency reflectometry. Changes in the total electron number of the double dot are determined via single electron tunnelling contributions to the complex electrical impedance. Electron counting experiments are performed by monitoring the impedance, demonstrating operation of a single electron ammeter without the need for external charge detection.

Quantum capacitance and charge sensing of a superconducting double dot

We study the energetics of a superconducting double dot, by measuring both the quantum capacitance of the device and the response of a nearby charge sensor. We observe different behaviour for odd and even charge states and describe this with a model based on the competition between the charging energy and the superconducting gap. We also find that, at finite temperatures, thermodynamic considerations have a significant effect on the charge stability diagram.

Realization of fully tunable FinFET double quantum dots with close proximity plunger gates

This paper presents the realization of a FinFET double quantum dots transistor on ultrathin silicon-on-insulator. In this platform, three Al FinFET gates surround the Si device layer channel forming electrically tunable potential barriers; Si plunger side gates are included to enable precise control of the quantum dots potential. This device is fabricated using a multi-layer electron beam lithography process that is fully compatible with metal oxide semiconductor technology. Low temperature electrical measurements and coulomb oscillation characteristics have demonstrated the capability of this structure to form double quantum dots with adjustable interdot coupling.

Cooper pair tunnelling and quasiparticle poisoning in a galvanically isolated superconducting double dot

We increase the isolation of a superconducting double dot from its environment by galvanically isolating it from any electrodes. We probe it using high frequency reflectometry techniques, find 2e-periodic behaviour, and characterise the energy structure of its charge states. By modelling the response of the device, we determine the time averaged probability that the device is poisoned by quasiparticles, and by comparing this with previous work, we conclude that quasiparticle exchange between the dots and the leads is an important relaxation mechanism.

VLSI Compatible Parallel Fabrication of Scalable Few Electron Silicon Quantum Dots

144 highly tuneable high density lithographically defined Si double quantum dots (DQDs) are fabricated for the first time in parallel via a scalable VLSI compatible fabrication process for the realisation of single electron qubits for quantum computing. 25 nm DQDs with less than 5 nm in dimensional variation are achieved via the use of Hydrogen silsesquioxane resist and electron beam lithography. Repeatable coulomb oscillations and coulomb diamonds signifying single electron tunneling are observed in the electrical characteristics of a Si DQD structure. This demonstrates the viability and dimensionality of our system and paves the way for single electron spin manipulation in scalable Si based systems.

VLSI compatible parallel fabrication of scalable few electron silicon quantum dots

One-hundred ninety-two highly tuneable high density lithographically defined Si dual double quantum dots (DQDs) are fabricated for the first time in parallel via a scalable VLSI compatible fabrication process for the realization of single electron qubits for quantum computing. 25 nm DQDs with less than 5 nm in dimensional variation are achieved via the use of Hydrogen silsesquioxane resist and electron beam lithography. Repeatable coulomb oscillations and coulomb diamonds signifying single electron tunnelling are observed in the electrical characteristics of a Si DQD structure. This demonstrates the viability and dimensionality of our system and paves the way for single electron spin manipulation in scalable Si-based systems.