Synchronisation of micro-mechanical oscillators inside one cavity using feedback control

The purpose of this work is to develop a systematic approach towards synchronisation of two micro-mechanical oscillators inside one optical cavity using feedback control. We first obtain the linear quantum stochastic state space model for the optomechanical system considered in this paper. Then we design a measurement-based optimal controller, aimed at achieving complete quantum synchronisation of the two mechanical oscillators with different natural frequencies, in the linear quadratic Gaussian setting. In addition, simulation results are provided, which show how system parameters impact on the control effect. These findings shed light on the synchronised network of oscillators that can be used for memory and quantum state transfer.This research was supported by the Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology (project number CE110001027), AFOSR Grant FA2386-12-1-4075, and the Australian Research Council Discovery Project program.

Synchronization along quantum trajectories

We employ a quantum trajectory approach to characterize synchronization and phase-locking between open quantum systems in nonequilibrium steady states. We exemplify our proposal for the paradigmatic case of two quantum Van der Pol oscillators interacting through dissipative coupling. We show the deep impact of synchronization on the statistics of phase-locking indicators and other correlation measures defined for single trajectories, spotting a link between the presence of synchronization and the emergence of large tails in the probability distribution for the entanglement along trajectories. Our results shed new light on fundamental issues regarding quantum synchronization providing new methods for its precise quantification.Comment: v2: 9 + 3 pages, 5 figures. v3: few typos corrected, close to the published versio

Brillouin cavity optomechanics: Single-quantum-level operations towards quantum memory applications

Cavity-enhanced Brillouin scattering interactions with gigahertz-frequency acoustic phonons offer a promising pathway towards the quantum coherent control of mechanical oscillators. In this thesis, I experimentally investigate single-quantum-level operations applied to thermal me- chanical oscillators by combining optical measurement techniques with Brillouin interactions in crystalline whispering-gallery-mode microresonator devices. These operations are explored for applications in quantum state engineering and optical quantum memories. Generating and characterising non-classical states of mechanical motion currently represents a key challenge in quantum cavity optomechanics, and the realisation of a quantum memory would enable the development of many quantum technologies. The advances reported here contribute to both of these active areas of research. In a series of three experiments, single- and multi-phonon addition and subtraction opera- tions applied to thermal mechanical states are explored. I present the first experimental inves- tigation of single-phonon addition and subtraction operations using a joint click-dyne detection scheme, where the effect of such operations are verified by observing a characteristic doubling of the mean occupation of the state. These techniques are then extended to multi-phonon subtraction. Here, the -parameterised Wigner function of the resulting non-Gaussian states are determined, advancing the state-of-the-art for optics-based mechanical state tomography. Finally, an interferometric detection scheme is employed that implements a superposition of phonon subtractions in two time bins, and the phase coherence between these two operations is demonstrated and studied. In this thesis, I also theoretically investigate the prospects of an optical quantum memory based on Brillouin cavity optomechanics. Using realistic parameters, I show that efficient storage and retrieval of single photons is feasible, and I identify two key applications: temporal multiplexing and temporal mode manipulation. The deleterious effect of thermal noise in such optomechanical quantum light storage is also considered. To conclude, an outlook towards some near-term and long-term experimental goals that can build upon on the achievements reported is presented.Open Acces

Versatile Femtosecond Laser Synchronization for Multiple-Timescale Transient IR Spectroscopy

Several ways to electronically synchronize different types of amplified femtosecond laser systems are presented, based on a single freely programmable electronics hardware: Arbitrary-detuning asynchronous optical sampling, as well as actively locking two femtosecond laser oscillators, albeit not necessarily to the same round-trip frequency. They allow us to rapidly probe a very wide range of timescales, from picoseconds to potentially seconds, in a single transient absorption experiment without the need to move any delay stage. Experiments become possible that address a largely unexplored aspect of many photochemical reactions, in particular in the context of photo-catalysis as well as photoactive proteins, where an initial femtosecond trigger very often initiates a long-lasting cascade of follow-up processes. The approach is very versatile, and allows us to synchronize very different lasers, such as a Ti:Sa amplifier and a 100~kHz Yb-laser system. The jitter of the synchronisation, and therewith the time-resolution in the transient experiment, lies in the range from 1~ps to 3~ps, depending on the method. For illustration, transient IR measurements of the excited state solvation and decay of a metal carbonyl complex as well as the full reaction cycle of bacteriorhodopsin are shown. The pros and cons of the various methods are discussed, with regard to the scientific question one might want to address, and also with regard to the laser systems that might be already existent in a laser lab

Coherent Resonant Properties of Cardiac Cells

Materials / States of matte

Chapter Coherent Resonant Properties of Cardiac Cells

Materials / States of matte

New materials, regimes and applications of fibre laser technology

Nonlinear optics enables the manipulation of spectral and temporal characteristics of optical pulses interacting with a dielectric medium. Optical fibres, as a uniquely practical medium, provide an environment for effectively exploiting the nonlinear effects. This has facilitated the rapid growing interest in this field focused on the investigation of fibrebased sources incorporated with various novel saturable absorber devices for ultrashort pulse generation. This thesis reports a series of experiments exploring the ongoing research in the field of nonlinear optics, including the development of ultrafast mode-locked fibre sources and their applications in supercontinumm generation and third order parametric interactions in new carbon materials. Firstly, the integration of carbon-based materials with rare-earth doped media allows the demonstration of ultrafast mode-locked laser sources operating at wavelengths across the near-infrared region in a compact, low cost and environmentally robust scheme. Power scaling of such sources can be achieved by operating in the all-normal dispersion regime making use of a glass-substrate saturable absorber device that exhibits a higher damage threshold. Supercontinuum generation has been used as an effective method for spectral broadening. Pumping with a conceptually simple and reliable fibre-based system, a continuum covering from 2 to 3 μm is generated in a highly nonlinear GeO2 fibre. This experiment demonstrates a robust and long-term stable source of radiation in an important band, coincident with a portion of the atmospheric transmission window. Finally, the demonstration of a simple and compact nano-material based dual-wavelength system shows the performance of such devices as a simultaneous saturable absorber and passive synchroniser. An experimental study of coherent frequency mixing at large frequency shifts in a graphene sample, pumped by a two-colour fibre-integrated source, proves the strong nonlinear response of this new carbon material.Open Acces

Long-range optical trapping and binding of microparticles in hollow-core photonic crystal fibre.

Optically levitated micro- and nanoparticles offer an ideal playground for investigating photon-phonon interactions over macroscopic distances. Here we report the observation of long-range optical binding of multiple levitated microparticles, mediated by intermodal scattering and interference inside the evacuated core of a hollow-core photonic crystal fibre (HC-PCF). Three polystyrene particles with a diameter of 1 µm are stably bound together with an inter-particle distance of ~40 μm, or 50 times longer than the wavelength of the trapping laser. The levitated bound-particle array can be translated to-and-fro over centimetre distances along the fibre. When evacuated to a gas pressure of 6 mbar, the collective mechanical modes of the bound-particle array are able to be observed. The measured inter-particle distance at equilibrium and mechanical eigenfrequencies are supported by a novel analytical formalism modelling the dynamics of the binding process. The HC-PCF system offers a unique platform for investigating the rich optomechanical dynamics of arrays of levitated particles in a well-isolated and protected environment.This work was supported by Max Planck Society. R. Z. acknowledges funding from the Cluster of Excellence "Engineering of Advanced Materials" at the Friedrich-Alexander University in Erlangen, Germany

Absolute frequency measurement of an 171Yb lattice clock and optical clock comparisons

The measurement of time and frequency is at the heart of many technological applications and scientific measurements alike. In fact, the SI-unit the second is by quite a margin the SI-unit with the best relative uncertainty (ca. 10^{-16}), given by the accuracies of Cs fountain clocks probing the F = 3 - F = 4 ground-state transition in 133Cs. Still, demands for even higher accuracy and especially stability (a Cs fountain needs up to two weeks for the statistics to reach its declared uncertainty) are uttered in support of technological advancements (e.g. geodesy and GNSS systems) as well as fundamental science (physics beyond the standard model, tests of relativity). Nowadays optical lattice clocks confining a large number of neutral atoms in Stark shift free optical traps (the Stark shift free condition is characterised by a so-called magic wavelength of the trap) propose good candidates for a future redefinition of the SI-second in terms of an optical transition. Their accuracy and stability already surpass the Cs-fountains by two and three orders of magnitude, respectively. With further improvements to be expected in the near future, the application of optical lattice clocks to relativistic gravimetry, quantum computing, quantum simulation and fundamental physics keeps evolving. This thesis describes the development and characterisation of an 171Yb lattice clock at INRIM as well as its first frequency measurement campaigns and technolo- gies towards improved optical frequency measurements. The lattice clock confines cold atoms in a 1D optical dipole trap at the magic wavelength, which also cancels any Doppler- and recoil-related effects on the ultra-narrow clock transition. The first chapter offers a general overview of the physics behind lattice clocks and opti- cal frequency measurements. In the second chapter the 171Yb lattice clock developed during this work is expounded, including the trapping, state-preparation and state-probing of ultracold atoms inside the optical lattice. An exhaustive uncertainty budget for the clock transition is given and discussed showing already a performance beyond state-of- the-art Cs fountain clocks. An absolute frequency measurement obtained during this work is laid out. The result represents the lowest uncertainty achieved in a measurement of this transition against a primary frequency standard so far and is in agreement with previous values obtained by other groups around the world. A proof-of-principle experiment demonstrating for the first time the feasibility of transportable optical lattice clocks for geodesy and metrology applications outside of laboratory environments is described in chapter three. This experiment was conducted in collaboration with PTB and NPL and included a geodetic measurement with a transportable optical lattice clock that agreed with conventional methods as well as an optical 171Yb-87Sr frequency ratio measurement, enlarging the database on this particular ratio and thereby contributing to a possible redefinition of the SI-unit the second in terms of an optical transition or frequency-ratio matrix in the future. The fourth chapter discusses improvements added to the Yb lattice clock after the aforementioned measurements, in particular the stabilisation of the cooling and trapping lasers on a single stable low-drift cavity using mirrors coated for three disparate wavelengths across the optical spectrum. The simultaneous offset sideband locking and a throughout characterisation of the cavity are discussed. The last chapter is about the characterisation and optimisation of the NPL universal oscillator, which was conducted during my secondment at the NPL research facilities in the UK. The universal oscillator consists out of a femtosecond frequency comb, an ultra stable master laser and six slave oscillators. The femtosecond comb is transferring the stability of the superior master oscillator cavity to all six slave oscillators, which includes five lasers ranging from the infrared to the visible region. The principle of operation is explained and the obtained high performance of the spectral purity transfer set forth and discussed. This experiment demonstrated an unprecedented spectral purity transfer performance in a multi-branch configuration, opening the way for the interrogation of whole clock ensembles by just one master oscillator