arXiv subjects

N. J. Lambert

Publications and source records attributed to N. J. Lambert.

13 recordsLinked to original sources

arXiv2026

Multifrequency Floquet Engineering of Magnon Polaritons

Floquet engineering of cavity magnon-polaritons by periodically modulating the magnon frequency has recently attracted much interest as a way to manipulate the energy spectrum of magnon-photon hybrid systems. However, modulating the frequency of magnons by a time-varying bias magnetic field can be challenging. We demonstrate cavity magnon-polariton Floquet engineering by modulating the microwave cavity frequency, allowing large modulation depth and bandwidth. We apply commensurate two-frequency Floquet modulations with the higher frequency at twice and three times the lower frequency, and demonstrate that the resulting spectrum depends on the relative amplitude and phase of the two drive tones. In comparison with single-frequency Floquet modulations, the spectrum has qualitatively different features; in particular, new anticrossings appear between previously uncoupled sidebands. Our platform offers an alternative way to manipulate Floquet quasi-energy levels in hybrid systems.

cond-mat.mes-hall↗

arXiv2025

Coherent control of magnon-polaritons using an exceptional point

The amplitude of resonant oscillations in a non-Hermitian environment can either decay or grow in time, corresponding to a mode with either loss or gain. When two coupled modes have a specific difference between their loss or gain, a feature termed an exceptional point emerges in the excitations' energy manifold, at which both the eigenfrequencies and eigenmodes of the system coalesce. Exceptional points have intriguing effects on the dynamics of systems due to their topological properties. They have been explored in contexts including optical, microwave, optomechanical, electronic and magnonic systems, and have been used to control systems including optical microcavities, the lasing modes of a PT-symmetric waveguide, and terahertz pulse generation. A challenging problem that remains open in all of these scenarios is the fully deterministic and direct manipulation of the systems' loss and gain on timescales relevant to coherent control of excitations. Here we demonstrate the rapid manipulation of the gain and loss balance of excitations of a magnonic hybrid system on durations much shorter than their decay rate, allowing us to exploit non-Hermitian physics for coherent control. By encircling an exceptional point, we demonstrate population transfer between coupled magnon-polariton modes, and confirm the distinctive chiral nature of exceptional point encircling. We then study the effect of driving the system directly through an exceptional point, and demonstrate that this allows the coupled system to be prepared in an equal superposition of eigenmodes. We also show that the dynamics of the system at the exceptional point are dependent on its generalised eigenvectors. These results extend the established toolbox of adiabatic transfer techniques with a new approach for coherent state preparation, and provide a new avenue for exploring the dynamical properties of non-Hermitian systems.

physics.class-ph↗

arXiv2021

An ultra-stable microresonator-based electro-optic dual frequency comb

Optical frequency combs emit narrow pulses of light with a stable repetition rate. Equivalently, the generated light spectrum consists of many discrete frequencies spaced by this same repetition rate. These precision light sources have become ubiquitous in applications of photonic technologies because they allow coherent sampling over a broad part of the optical spectrum. The addition of another comb, with a slightly different line spacing, results in a dual comb. Widely used in spectroscopy, dual combs allow one to read out the broad frequency response of a sample in a simple electronic measurement. Many dual comb applications require a high level of mutual coherence between the combs, but achieving this stability can be demanding. Here, by exploiting the rich structure of the nonlinear electro-optic tensor in lithium niobate, we generate ultra-stable dual combs with the two combs naturally having orthogonal polarizations. Our combs have relative linewidths down to 400 microhertz, and require no stabilization or post-processing methods. The ultra-high stability of the spectrum emitted by our device, along with its simplicity of operation and energy efficiency, offer a route to the deployment of robust and versatile dual comb sources.

physics.optics↗

arXiv2020

Random telegraph signal analysis with a recurrent neural network

We use an artificial neural network to analyze asymmetric noisy random telegraph signals (RTSs), and extract underlying transition rates. We demonstrate that a long short-term memory neural network can vastly outperform conventional methods, particularly for noisy signals. Our technique gives reliable results as the signal-to-noise ratio approaches one, and over a wide range of underlying transition rates. We apply our method to random telegraph signals generated by a superconducting double dot based photon detector, allowing us to extend our measurement of quasiparticle dynamics to new temperature regimes.

cond-mat.mes-hall↗

arXiv2018

Selection rules for cavity-enhanced Brillouin light scattering from magnetostatic modes

We experimentally identify the magnetostatic modes active for Brillouin light scattering in the optical whispering gallery modes of a yttrium iron garnet sphere. Each mode is identified by magnetic field dispersion of ferromagnetic-resonance spectroscopy and coupling strength to the known field distribution of the microwave drive antenna. Our optical measurements confirm recent predictions that higher-order magnetostatic modes can also generate optical scattering, according to the selection rules derived from the axial symmetry. From this we summarize the selection rules for Brillouin light scattering. We give experimental evidence that the optomagnonic coupling to non-uniform magnons can be higher than that of the uniform Kittel mode.

cond-mat.mes-hall↗

arXiv2017

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 quasiparticle poisoning rate to be significantly worse than that of a unisolated double dot, and conclude that quasiparticle exchange between the dot and the leads is an important relaxation mechanism.

cond-mat.mes-hall↗

arXiv2015

Magneto-optical coupling in whispering gallery mode resonators

We demonstrate that yttrium iron garnet microspheres support optical whispering gallery modes similar to those in non-magnetic dielectric materials. The direction of the ferromagnetic moment tunes both the resonant frequency via the Voigt effect as well as the degree of polarization rotation via the Faraday effect. An understanding of the magneto-optical coupling in whispering gallery modes, where the propagation direction rotates with respect to the magnetization, is fundamental to the emerging field of cavity optomagnonics.

cond-mat.mes-hall↗

arXiv2015

Cavity mediated coherent coupling of magnetic moments

We demonstrate the long range strong coupling of magnetostatic modes in spatially separated ferromagnets mediated by a microwave frequency cavity. Two spheres of yttrium iron garnet are embedded in the cavity and their magnetostatic modes probed using a dispersive measurement technique. We find they are strongly coupled to each other even when detuned from the cavity modes. We investigate the dependence of the magnet-magnet coupling on the cavity detuning $Δ$, and find a $1/Δ$ dependence also characteristic of cavity-coupled superconducting qubits. Dark states of the coupled magnetostatic modes of the system are observed, and ascribed to mismatches between the symmetries of the modes and the drive field.

cond-mat.mtrl-sci↗

arXiv2015

Dispersive read-out 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.

cond-mat.mtrl-sci↗

arXiv2015

Identification of spin wave modes 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 (YIG) 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, are able to identify the modes themselves.

cond-mat.mtrl-sci↗

arXiv2014

Splitting a single Cooper-pair with microwave light

We measure an aluminum superconducting double quantum dot and find that its electrical impedance, specifically its quantum capacitance, depends on whether or not it contains a single broken Cooper pair. In this way we are able to observe, in real time, the thermally activated breaking and recombination of Cooper pairs. Furthermore, we apply external microwave light and break single Cooper pairs by the absorption of single microwave photons.

cond-mat.mes-hall↗

arXiv2014

The energy landscape of a superconducting double dot

We consider the energetics of a superconducting double dot, comprising two superconducting islands coupled in series via a Josephson junction. The periodicity of the stability diagram is governed by the competition between the charging energy and the superconducting gap, and the stability of each charge state depends upon its parity. We also find that, at finite temperatures, thermodynamic considerations have a significant effect on the stability diagram.

cond-mat.mes-hall↗

arXiv2013

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.

cond-mat.mes-hall↗