Research

Overview: 

Decoherence is the process by which quantum information is lost from a system as it interacts with its environment. Decoherence thus puts fundamental limits to the precision of measurements. At the same time, precision measurement techniques are required to reach the experimental regimes necessary to study the effects of decoherence. At the fundamental level, much remains to be learnt about decoherence, and a better understanding of the behaviour of quantum systems will lead to improvements in quantum technologies and precision measurements. For example, it is well known that decoherence represents one of the greatest obstacles for the realisation of useful quantum computers. The aim of this research question is to improve precision measurement techniques and expand our understanding of decoherence. Our initial research will be focused around the four flagship projects described below.

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Projects:

Project 1: DM1 — Monitored quantum systems

Decoherence leads to the irreversible loss of entanglement leading to classical behaviour, thus hiding the fundamental quantum features of a system. Careful monitoring can, however, unscramble the decoherence and reveal what was hidden as, e.g. in our recent work, published in Nature, on “unveiling” the coherence of a quantum jump in a superconducting circuit. Alternatively, for composite quantum systems, there may exist, amidst the environmental noise, so-called “decoherence-free subspaces,” where entanglement is robust or develops naturally from the system-reservoir dynamics. This project will combine theoretical and experimental efforts to increase our understanding of entanglement and decoherence. 

Unveiling hidden coherence and entanglement in monitored quantum systems. We will extend our theoretical methods to learn how to unscramble decoherence for both coherent and incoherent driving of quantum systems. Coherent driving is special because a system driven by a field in a coherent state does not become entangled with that field. Any coherence revealed is hence local to the system, whereas for general driving the system and drive exhibit quantum coherence, introducing non-local entanglement. We will investigate the ramifications of coherent driving and its impact on the design of experimentally achievable monitoring. In contrast, incoherent driving implies a noisy input and raises unexplored questions, e.g. is there hidden coherence which might be revealed by appropriate monitoring, of inputs as well as outputs? This links directly to Einstein’s theory of atomic transitions, the original paradigm of “quantum jumps,” thus making our results directly relevant to the foundations of quantum theory. 

Spin-entangled electron and atom pairs. Using our world-leading single-atom manipulation techniques and state-of-the-art theoretical and numerical modelling, we will study how to generate and manipulate entangled states of atoms in optical tweezers and of electrons in superconducting devices. Atom-atom entanglement will be stored in a decoherence-free subspace, where damaging noisy inputs have opposite effects on the two atoms, leading to no net effect on the pair. This permits entanglement to be long-lived and robust to subsequent manipulations, such as the spatial separation of the atoms, which can be considered analogous to the separation of Cooper pairs in superconductors. We will investigate the process theoretically using a specially developed, non-equilibrium Green’s function theory based on the Nambu-Gor’kov-Schwinger-Keldysh formalism, providing new insights into decoherence as well as tests of Bell’s inequality in superconductors.

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Project 2: DM2 Ring Laser Gyroscopes

Large ring laser gyroscopes (RLGs) have revolutionized rotational seismology. The Chandler and annual wobbles in the Earth’s rotation, as well as diurnal polar motion, have all been observed. There is even potential for RLGs to measure the global mass redistribution arising as a result of climate change or other geophysical processes. In this project we aim to build on our world-leading expertise to develop the next-generation of RLGs and related devices. 

Michelson Centenary Ring (MCR). The MCR is our vision to bring the seminal 1925 Michelson, Gale, Pearson interferometer into the laser era. This involves the construction of a heterolithic ring laser whose beam paths enclose an area of 21 hectares — a high profile undertaking and nothing short of a landmark experiment in physics. This proposed device would have a raw sensitivity more than three orders of magnitude greater than the current world best (the German G-ring), and be capable of precision testing of general relativity. Whilst this far-reaching project will require substantive funding from several sources, the DWC thanks to its expertise and track-record is uniquely placed to lead the endeavour. We will undertake the necessary design work within the umbrella of the DWC, which will also support the full funding application process itself. 

Laser gyroscopes for monitoring infrastructure. We will take our expertise in absolute rotational sensing, originally developed for seismology, to civil engineering and infrastructure monitoring. There is strong interest from civil engineers in inter-storey drift and torsional excitation of tall buildings induced by seismic motion, which cannot be measured using conventional accelerometers. We will design and test combinations of fibre optic and ring laser gyroscopes, making use of the shake table at the University of Canterbury. This work will inform the development of practical and affordable sensors for reliable monitoring of large structures before, during, and after seismic activity. 

Passive ring resonator gyroscopes. We will use the ultra-stable C-II cavity as a passive resonant gyroscope to determine and (if possible) eliminate non-reciprocal biases that arise in the gain media of laser sources constructed by colleagues in Hannover. Although only at the level of 10−14 rad/s, such effects can limit sensitivity and need to be eliminated for future precision measurements. Moreover, we will develop novel passive gyroscopes based on monolithic microresonators. Whilst not as sensitive as large gyroscopes, microresonators promise unprecedented performance for their geometric size — so long as potential noise sources can be controlled. In addition to passive devices, we will also develop active microresonator gyroscopes (see also project FC1) with the overarching aim of achieving a bias stability suitable for commercial inertial navigation requirements.

Project 3: DM3 — Cavity QED

Cavity QED explores the interaction between atoms (or atom-like emitters) and photons in optical resonators. Enhanced light intensity in a resonator can push atom-photon coupling above decoherence rates, enabling coherent manipulation of quantum states. Moreover, transmission (loss) through resonator mirrors provides a well-defined input-output channel for quantum-noise-limited measurements of the system or quantum communication. In this project, we will study novel and topical platforms for cavity QED that address fundamental science as well as applications to quantum technology. 

Nanofibre cavity QED for time-delayed quantum feedback and control. Tapered optical nanofibres enable strong interactions between evanescent light and atoms near the nanofibre’s surface, even at the single-photon level. Standard optical fibres then provide an efficient photonic link between distant locations. Using these features, coherent coupling between atoms separated by over a metre was recently demonstrated, as well as strong coupling in the cavity itself. DWC researchers (and alumni) will continue to lead the way in this new field both experimentally and theoretically. In particular, we will implement photonic “circuits” consisting of several atom-nanofibre systems and long lengths of fibre, such that the propagation time of light along these fibres is comparable to the timescale of the atomic dynamics. This is uncharted territory for experiments, and will provide a landmark challenge for theory. For example, distant, connected atom-nanofibre systems will enable the investigation of collective atomic behaviour in macroscopically delocalised systems.  Such behaviour has implications for quantum information processing and our understanding of the fundamentals of many-body physics. This behaviour will be studied theoretically by employing the quantum stochastic Schrodinger equation with time delays to properly account for the nonlocal quantum correlations that emerge in the system. 

Deep strong coupling. It is standard when dealing with light-matter interactions to assume that the coupling is much slower than the resonant transitions. In contrast, the deep strong coupling regime is where the coupling speed is much faster than the resonant transitions. In this regime, strange new physics is predicted, along with new, faster ways of manipulating quantum states for sensing and quantum information applications. Here we aim to achieve and explore deep strong coupling between atomic spins and microwave photons. We recently made the first demonstration of a narrow (currently 35 MHz) magnon resonance in rare earth spins, and successfully reached the ultra-strong coupling regime. Redesigning the cavity to reduce the resonance frequency will enable us to reach the edge of the deep strong coupling regime. Moving further into the deep strong coupling regime will be achieved using the large anisotropic g factors characteristic of the rare earths. 

Plasmonic nanocavities. Optical nanocavities based on metallic nanoparticles allow for significantly higher light-matter coupling strength compared with traditional cavities. We will use this property to develop novel QED systems and quantum nanophotonic devices. We will first integrate highly-concentrated nanocrystals doped with rare-earth ions into core-shell nanocavities so as to demonstrate a new type of nanolaser. We will then develop new 2D semiconductor-based QED systems by leveraging our recently developed capabilities for controlling the quantum properties of polaritons in 2D semiconductors integrated with nanocavities. Using this unprecedented control, we aim to realise the initialisation and readout of spin information, and explore the potential of such devices for applications in all-optical computing.

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Project 4: DM4 — Quantum memories

Quantum memories based on rare-earth ion dopants are arguably the best available, offering high efficiencies, multi-hour coherence times, and large bandwidth storage of entanglement. 

Erbium possesses the unique and distinct advantage of having its optical transitions in the 1.5 µm wavelength range, where optical fibres are most transparent. A goal of this project is to dramatically increase the storage times available for 1.5 µm photons using so-called ZEFOZ transitions. Finding ZEFOZ transitions requires detailed knowledge of the dopants energy level structure and how it varies with magnetic field. Our recent groundbreaking work where we achieved the first crystal field characterisation of rare earth ion dopants in no symmetry (C1) sites will allow us to find the high field ZEFOZ transitions for 167Er:Y2SiO5, where extremely long coherence times are expected. 

In parallel with this work we will further develop and apply our crystal field techniques for other systems. This includes Eu3+ and Pr3+ in Y2SiO5, which have been extensively used for quantum memory work but without a detailed understanding of the energy level structure. We will also investigate the largely unexplored Ho3+:Y2SiO5, whose unusually large hyperfine structure is attractive for developing high bandwidth memories. We expect that, in all of these systems, improved knowledge of the crystal fields will lead to improved quantum memories

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Overview:

Self-organisation — the formation of large-scale ordered structures from initial disordered states — is a ubiquitous phenomenon that manifests itself in a variety of systems. It plays a key role in the emergence and persistence of complex structures that appear spontaneously in nature, including animal coats, fluid turbulence, and at the most sophisticated level, life itself. Self-organisation is also key to many technological applications, including ultra-short pulsed lasers, neural networks, and self-assembling nanostructures that could lead to breakthroughs in efficient and cheap nanotechnology. We will use the DWC’s world-leading expertise in photonic and quantum systems to (i) solve fundamental questions related to self-organisation and associated nonequilibrium dynamics, and (ii) harness self-organisation effects for the development of new technologies. During the first four years, we propose to focus on the four areas described below that move from understanding the fundamentals of quantum systems to applying self-organisation to create new laser sources for NZ manufacturing.

Projects:

Project 1: SO1 – Clusters, Cascades and dissipation in quantum turbulence

Two dimensional (2D) Bose-Einstein condensates offer unique opportunities to explore self-organisation in a highly controllable quantum system. In 1949, Onsager predicted that 2D quantum vortex systems self-organise into vortex clusters, stimulating the study of 2D quantum turbulence as a minimal model for the universal phenomena of fluid turbulence, including the celebrated Kolmogorov energy cascade. Recent experiments published in Science have observed Onsager’s predictions for the first time, with PI Bradley’s group providing essential theoretical support for the experimental effort. We will expand on these pioneering experiments, and undertake a comprehensive investigation into turbulence and associated vortex clustering in 2D quantum fluids. Our project brings together the theoretical expertise at UoO and the sophisticated experimental facilities and expertise at UoA. Our experiment will be built around a 2D 87Rb condensate trapped in a sheet of light. A digital mirror device will be used to induce quantum turbulence in the trapped atoms, whilst velocity-selective Bragg scattering will be used to visualise the handedness of the vortices. Using this experimental configuration, we will study the transient dynamics of vortex clustering, and explore the different kinds of energy cascades that can emerge in 2D vortex (and/or acoustic wave) turbulence. Numerical simulations will be used to guide and interpret our experiments. We will also develop theoretical descriptions of a range of phenomena associated with 2D quantum turbulence, including sympathetic cooling in multicomponent systems and anomalous dissipation in spinor systems, thus paving the way for future experimental studies. Our investigations will shed light on the ubiquitous physics of turbulence and self-organisation of large-scale structures.

Project 2: SO2 — Understanding self-organisation in multi-scale systems

Self-organisation is a manifestation of emergent behaviour that arises from the coupling between the different parts of a complex system. This project will investigate such emergent behaviours from a fundamental point of view, examining their dependence on parameters that control the coupling as well as the underlying topology. Our main focus will be on the development of new mathematical tools that can be applied to diverse self-organisation phenomena in contemporary photonic and quantum systems, providing new understanding and insights.

To explore novel emergent dynamics, we will first consider a class of prototypical system that has attracted significant attention in the context of integrated optics: coupled networks of microcavity lasers. Motivated by applications to optical information processing and neuro-inspired computing, the focus will be on the coupling of excitable and self-pulsing systems. We will study the networks’ synchronisation and locking properties in

the presence of different temporal and spatial scales by first developing and then applying advanced mathematical and computational techniques so as to identify qualitative changes and rearrangements of critical boundaries or thresholds that organise transient and long-term behaviour. Our theoretical findings will then be tested via direct comparison with experimental measurements performed in close collaboration with our colleagues at CNRS, who already have the necessary infrastructure in place. Our secondary aim is to help elucidate the nonlinear dynamics that underpin the emergence of selforganised structures in quantum and photonic systems. In particular, we will analyse the equations of motion that govern these systems’ behaviour, and examine the bifurcation structure of the self-organised states. Moreover, we will develop new numerical methods to determine the onset of various instabilities that have hitherto eluded existing techniques. The theoretical findings from this aim will be directly used to inform subsequent DWC experimental projects.

Project 3: SO3 – Universality in non-equilibrium dynamics

In nonequilibrium systems, self-organisation is typically linked to a symmetry breaking phase transition. It is well-known that sudden quenching across such a transition leads to the formation of disconnected domains, each of which chooses to break symmetry independently. The microscopic details of the domains’ subsequent evolution may be extremely complicated, but a simple scaling regime can emerge at a macroscopic level. Formally known as dynamic scaling, in this regime the spatial correlations grow universally in time with a power law that can be used to identify the dynamic universality class.

The development of non-thermal fixed point theory has extended the concept of scaling to isolated quantum systems even in the absence of a symmetry breaking phase transition, culminating with the recent experimental observation of universal dynamics in quantum gases. The rich symmetries of quantum gases (e.g. conferred by the spin degrees of freedom) and their properties such as hydrodynamic transport and long range interactions make these systems ideal for uncovering new universality classes and understanding unifying principles. Our team has made critical advances towards understanding the phase ordering dynamics in planar ferromagnetic superfluids; in this project, we will study such dynamics in new types of quantum fluids and optical systems, connecting to established strengths of the DWC in quantum gases, nonlinear photonics, and atoms in cavities.

First we will develop a theory to explain recent observations, where a quasi-one-dimensional spinor quantum gas was found to exhibit an unexpected scaling exponent not predicted by theory. Our hypothesis is that this anomalous scaling arises from the confinement used in the experiment, which allowed the tightly confined degrees of freedom to be partially accessible to the quantum fluid. We will derive a quantitative theory for this regime and perform simulations using c-field methods. A second application will be to magnetic binary superfluids recently realised in Innsbruck. These superfluids are unique in that they have long-ranged and anisotropic dipole-dipole interactions between the particles. In a planar geometry, this system is expected to form an exotic striped fluid phase (with superfluid and crystalline-spin order). In addition to collaborating with the Innsbruck group to find a practical procedure to form and observe the striped phase, we will develop a theory for the ordering dynamics of these stripes. Such dynamics for crystalline order are largely unexplored and may realize a new dynamic universality class; we will develop an order parameter correlation function and simulation techniques to study the ordering dynamics.

An important aspect of this project is to extend the concepts of coarsening and non-thermal fix point theory, which have been developed in the field of condensed matter and high-energy physics, to the quantum fluid and photonic systems extensively studied in the DWC. Notably, immediate connections are available with the fibre-cavity emulation (QCE1) and quantum turbulence (SO1) projects, as well as the quantum matter experiment (QCE3). The universal dynamics of these systems are largely unexplored and they have many features that make them of interest, such as the potential for control over the strength of quantum fluctuation effects, dissipation and reservoir interactions.

Project 4: SO4 — New sources of ultra-short pulses

The formation of dissipative solitons in mode-locked lasers is a paradigmatic example of self-organisation in optics. The resulting periodic trains of ultra-short pulses are central to numerous applications, from medicine to machining, while their spectral structure underpins the optical frequency combs that have revolutionised the field of precision metrology. Ultra-short pulses (and correspondingly broad frequency combs) can also be generated by coherently driving a passive Kerr nonlinear resonator with a continuous wave laser (see also FC1). Pulses generated in this manner are known as temporal Kerr cavity solitons (CSs); they were first observed in 2010 in an optical fibre ring resonator, and have subsequently been recognised as the temporal counterparts of “Kerr” optical frequency combs generated in monolithic microresonators. Thanks to their rich dynamics and countless applications, mode-locked lasers and passive Kerr resonators are amongst the most active research areas in photonics today. Here, we will use the DWC’s world-leading expertise to explore novel paradigms of ultra-short pulse and frequency comb generation in such systems.

Temporal Kerr CSs. We will first study the generation of bright CS-like structures in resonators with normal group-velocity dispersion. To this end, we will build a suitable optical fibre ring resonator and use it to examine CS existence and characteristics in the normal dispersion regime. We will then seek to realise multimode CSs characterised by the phase-locking of several different mode families of the resonator, in analogy with recent reports of spatiotemporal mode-locking in multimode fibre lasers. We will first expand an existing experiment involving a highly-controllable fibre ring resonator with two polarisation modes to investigate how interactions between mode families can enable spatiotemporal phase-locking. We will then experiment with a system where the number of transverse modes approaches infinity: a cylindrical resonator with no intrinsic geometric modal confinement. CSs have recently been theoretically predicted to arise in such a system via simultaneous temporal and spatial localisation of light; our aim is to achieve the first experimental observations of such localisation, thus paving the way for an entirely new platform for ultra-short pulse generation.

Mode-locked lasers. In collaboration with RIKEN (Japan), we will develop new high-power (> 100 W average) mode-locked thin-disk lasers for micro-machining. We will use the f-2 f scheme to lock the carrier-envelope-offset phase of the laser to fully control the underlying electric field, and improve laser ablation. The resulting source could also be operated as an optical frequency comb, thus providing crucial research infrastructure for NZ science and metrology. We also seek to develop a fibre-based laser system capable of delivering light across the entire mid-IR spectrum (2–10 µm) with multi-W average power. To this end, we will build a mode-locked oscillator based on erbium-doped ZBLAN fibres to produce a pulse train at 2.8 µm. The pulses will then undergo simultaneous amplification and spectral broadening (supercontinuum generation) in a custom-designed nonlinear amplifier followed by additional spectral broadening in customised chalcogenide fibres. Our nonlinear amplifier will be based on novel doped fluoride fibres that we will develop together with our collaborators (companies ALPhANOV and Le Verre Fluore); the fibres will be optimised to deliver unprecedented mid-IR performance. The resulting mid-IR source will be ideally suited to enhance the performance of imaging and sensing techniques used in the DWC.

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Overview:

Engineered photonic and atomic systems are ideal platforms for proof-of-principle testing of new ideas and applications of unconventional states of matter. Trapped-atom gases offer a level of controllability for their single- and multi-particle properties unparalleled in any other physical system, while structured light offers flexible atomic manipulation and realisation of optical analogues. We will use such systems for simulating a variety of physical phenomena at the forefront of physics research, and develop tools and techniques enabling future quantum simulation experiments. Our long-term goal is to use table-top quantum and photonic systems as analog computers to solve model problems that are too hard for classical computers, e.g. the birth of a model universe from quantum fluctuations.

Projects:

Project 1: QCE1 — Emulating solid-state and quantum physics with fibre cavities

Optical fibre systems are attractive for elucidating universal nonlinear wave phenomena — an area where DWC researches have made seminal contributions. Here we will leverage our world-class expertise in driven passive optical fibre cavities to emulate a range of novel effects. Our immediate objectives include:

Chimera states are peculiar structures characterised by the spatiotemporal coexistence of coherent and incoherent domains. Using fibre cavities, we have recently achieved the first experimental observations of chimera-like states in a system with local coupling, and demonstrated their controlled creation and annihilation. Here we will build from our initial observations, and experimentally investigate the chimera’s statistical properties and dynamics: we seek to experimentally resolve the chimera’s Lyapunov spectrum and associated metrics, and to study their transport behaviour under different conditions. The chimera’s turbulent character and emergence from a nonequilibrium phase transition provides a natural link between our work and projects SO1 and SO3.

Ferromagnetism and Ising Hamiltonian. With control of cavity birefringence, we will generate and sustain optical polarisation domain walls (PDWs). These structures are analog to domain walls appearing in numerous phase transitions in solid-state and quantum physics. By tracking the positions of PDWs, we will be able to perform stochastic room temperature simulations of solid-state physics in real time. PDW dynamics are also related to the Ising Hamiltonian, originally proposed for spin interactions, and found to map to numerous complex (NP-hard) combinatorial optimization problems that are increasingly important in our society, e.g. for drug discovery, or analysis of social networks. We will use PDWs to develop an Ising machine aimed at solving these otherwise intractable problems. We also plan to use this platform for the emulation of topological materials (QCE4) and synthetic dimensions, as well as the study of the dynamic scaling of nonthermal fixed points (SO3) as opportunities arise.

Project 2: QCE2 — Enabling quantum simulations with rare earths in optical tweezer

Rare earth elements such as erbium and dysprosium (Dy) exhibit large anisotropic dipolar interactions that make them well-suited for quantum simulations of interacting spins. In this project, we will develop a new platform for the manipulation and control of individual Dy atoms, and use the platform to investigate how exotic quantum states of matter emerge out of fundamental few-atom interactions. Our specific aims are as follows:

Single dysprosium atoms in optical tweezers. Leveraging our experience in manipulating individual, laser-cooled Rb atoms in optical tweezers, we will first build a new experimental apparatus capable of loading and detecting single Dy atoms in optical tweezer arrays. This will provide a unique research capability within the DWC that is distinct and complementary to the worldwide focus on large ensembles of Dy.

Multiple atom manipulation. We will then demonstrate the manipulation of multiple Dy atoms by extending methods previously demonstrated for Rb atoms: efficient loading of tweezer arrays, single-site addressability, effective cooling, and the ability to merge loaded traps into one. This will allow us to build few-body systems of Dy atom-by-atom and study their fundamental interactions.

Dipolar quantum many-body dynamics. We will finally combine experiments and theory to study how many-body effects emerge from few-body physics in samples with dipolar interactions. To this end, we will apply our recent advances in the theory of short-range interacting atoms to dipolar interactions relevant to Dy, and develop pertinent computational tools for simulating the few-atom quantum dynamics. Experimentally, our capability to prepare individual atomic spins offers unprecedented flexibility in engineering quantum states, and will allow us to study a wealth of phenomena such as the formation of droplet crystals and the possibility of magnetically bound molecules.

Project 3: QCE3 – Experimental Atomtronics

The field of atomtronics seeks to develop atomic analogs of electronic circuit components, and use the rich internal structure of atoms as a technological platform. Here we will investigate, control, and exploit the dynamics of interacting quantum systems through a prototyping “board” for atomic systems based upon optical tweezers. The board will be highly reconfigurable, and its nodes (tweezer trapping sites) can be populated with three kinds of quantum matter: Bose-Einstein condensates, degenerate Fermi gases, and single atoms. Interactions between nodes can be mediated by light, or by long-range dipolar fields of Rydberg atoms facilitated by the phenomenon of Rydberg blockade. Our board will be capable of straddling both quantum and photonic technologies, and enable chemistry at the quantum and even single-atom level using ultracold samples. The initial focus of our project will be to develop an experimental realisation of the prototyping board itself. Once realised, we will use the fine atomtronic control enabled by the board to demonstrate:

Strong photon-photon interactions will be created from atomic dipole-dipole interactions by using optical interaction resonances. We will use double electromagnetically-induced transparency (EIT) to enact strong interactions between a 780 nm photon and a 767 nm photon, thus paving the way for new experiments and applications in quantum nonlinear optics.

Single photon source. We will develop a single-photon source emitting directed photons on demand — the holy grail for quantum communications. A dipole-allowed microwave transition of a single Rydberg atom will be coupled to a similar transition in a separate quantum degenerate ensemble via dipole-dipole interactions, thus converting a single atomic excitation to a collective excitation (spin-wave). This can then be read-out in the forward direction with a control field, when desired. Our target implementation uses 40K and ⁸⁷Rb, to generate photons in the 1.5 µm telecommunications band. Our platform will interface with the cold atom experiment in FC3 via optical fibres, hybridising and bridging two disparate quantum technologies.

Project 4: QCE4 – Topological materials and coupled superfluids

The rich external and internal structure of coupled condensates makes them ideal platforms for emulating fundamental physical processes, and for realising atomtronic analogs of solid-state devices. For example, we have shown that coupled superfluids can emulate a Josephson vortex transmission line, while others have shown that superfluid vortices can carry Majorana quasiparticles useful for quantum computing applications. We aim to combine these two approaches, studying ways to manipulate Majorana-based quantum bits via coupled-superfluid dynamics by means of analytic modelling and numerical simulation. Using our world-leading expertise on topological excitations in superfluids, we will develop analytical models of Majorana vortex dynamics in harmonically trapped superfluids, narrow channels, and Josephson transmission lines. These will be tested using specially developed, efficient numerical methods for solving the time-dependent mean field theory of p-wave and s-wave topological fermionic superfluids, allowing a direct comparison between theory and simulation as well as providing insight into areas not amenable to analytic solutions. We will then develop and extend state-of-the-art numerical simulation tools based on the exact diagonalisation quantum Monte Carlo method and machine learning to study the many-body quantum physics of topological superfluids and their Majorana-carrying topological excitations.

Project 5: Project QCE5 — Nonlinear dynamics at the quantum limit

Open quantum systems constitute a promising platform for simulating many-body physics. There is consequently growing interest to better understand the dynamics and behaviour of such systems — both in the fully quantum and semiclassical regimes. Here we will study two prototypical, experimentally accessible open quantum systems: the driven-dissipative Bose-Hubbard dimer, realized in semiconductor microcavities, superconducting circuits, and photonic crystals; and the paradigmatic Dicke model realised with an optically coupled Bose-Einstein condensate. We will apply advanced methods from the theory of dynamical systems to analyse the governing equations of these systems in the semiclassical limit, and use the findings to inform quantum many-body simulations as well as experiments, especially for cases with only very few photons and/or atoms. Motivated by future applications of low-energy quantum devices for memory storage and information processing, we will focus in particular on self-trapping, symmetry breaking and the Josephson effect symmetry in the photonic crystal Bose-Hubbard dimer realised by our colleagues at CNRS, and novel transitions to superradiance in the unbalanced Dicke model with two independent coupling strengths. We will determine allowed states of collective behaviour using the theory of phase transitions, including superradiant steady states, coherent oscillations, and even intermittent chaotic switching.

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Overview:

Photonic technologies enable compact, rapid, and minimally invasive imaging or sensing of human tissues, food samples, bacteria, and pollutants, the latter being at the core of the GEMM initiative. They offer unique opportunities for improvements to our health and the environment. This research area is multidisciplinary and collaborative by its very nature, and encompasses many distinct measurement methods and applications areas. In the first four years, we will focus on the following six flagship projects:

Projects:

Project 1:  HE1 Improving the quality of NZ’s primary produce

We will work with NZ farmers and trade organisations such as Zespri to help them improve the quality of their produce, while minimising costs and environmental damage. Our focus is on developing new non-destructive techniques and demonstrate their practical usefulness for new application areas. This work will build on our existing spectroscopic and data interpretation methods that have already been used to evaluate some of NZ’s primary produce. While the individual techniques below are useful by themselves, the challenge now is to realise a step-change in capabilities by fusing different analysis methods into practical tools that will deliver primary producers unprecedented information and understanding of the physical and chemical properties of their produce. Optical coherence tomography (OCT) is an interferometric technique that allows high-resolution, non-invasive, in vivo imaging deep into biological objects with a resolution as small as a few micrometres, i.e. smaller than most cells. Recently, we have developed techniques that allow deeper imaging in tissue and detection of subtle changes in tissue composition. We now propose to develop new OCT tools specifically for primary produce assessment using functionalities such as elastography, flow or polarisation measurements. These new probes will be targeted, in the first instance, for the assessment of berry ripeness and resistance to potentially harmful diseases and parasites. Laser-based ultrasonic sensing has been developed as a non-destructive and non-contact means to image the internal properties of different media. This technique measures through the entire fruit, unlike conventional methods which only measure at the surface. We are now able to infer important physical properties of products of the primary industry, such as ripeness (fruit) and stiffness (timber). Working directly with producers, we will extend this work to provide rapid assessment of fruit and timber quality, allowing producers to optimise the entire supply chain (e.g. the ripest fruit goes to the closest market). Raman spectroscopy uses inelastic scattering of laser light to observe vibrational signatures of the chemicals within a sample providing valuable information on substances as diverse as hops and fish oil. Such methods are biased to the surface of a sample. We will develop time-resolved methods and spatially offset Raman techniques that allow for sub-surface analysis, thus increasing the capability of this method. By extending and combining all these methods and fusing the data the ability to understand the quality of materials will be enhanced. We will customise combinations of the above techniques to produce a step-change in how NZ’s primary producers understand their products and manage them. For example, these techniques will be used to assess kiwifruit for areas of chill damage allowing better management of kiwifruit once they are picked.

Project 2: HE2 Laser lab on a chip

In 2016, Havelock North residents were affected by an outbreak of Campylobacter in the water supply, causing four deaths, and costing NZ$ 21m. This incident highlighted fundamental limitations of current water quality testing practices. Despite twice-weekly tests and a 24 hour turnaround time (worldwide standard), the community was still exposed to Campylobacter for five days before action was taken. We will develop an optofluidic chip that will enable near real time (30 minutes), monitoring of water quality — reliably and at low cost. The chip will build upon our expertise in fluorescence techniques for the enumeration of bacteria and single cell identification. In addition to its inherent compactness and low cost, our optofluidic approach will enable multiple different tests to be performed on the same chip, while simultaneously providing long optical path lengths for enhanced sensitivity. The risk of fouling will be mitigated by separating the optical components of the system from the fluid streams. By enabling cheap and immediate testing of water quality, we anticipate that our chip will have a significant impact on the health and environment of communities in NZ and worldwide.

Project 3: HE3 Multiscale biomedical imaging to understand deterioration of human tissue

Meaningful prevention, treatment, and management of diseases and injuries requires knowledge of the body’s internal structures and how those structures age and deteriorate. To develop such knowledge, we will custom-build advanced imaging systems specifically tailored to the need of medical researchers and health practitioners working on tissue degeneration and regeneration. Four areas will be initially considered.

Soft tissue imaging with OCT. We will use polarisation sensitive OCT, combined with spectroscopic probes and a force sensor to completely characterise soft tissues in load bearing conditions. This will provide deep insights into the complex multiscale nature of load transfer, from the microscale to the bulk mechanical properties of tissues, and will highlight the relationships between structure and function. The knowledge acquired will revolutionise soft tissue disease management and treatment, in particular by enabling early detection of osteoarthritis. It will also benefit engineered constructs or prosthetics that mimic soft tissue mechanical properties.

Photoacoustic imaging of blood flow in bones. Blood supply to bones is of major importance. It can trigger diseases when inadequate, e.g. osteoporosis and bone death. It is also a health indicator, as arthritis, gout, infection, or cancer increase bone vascularization. Yet, dedicated imaging tools are lacking. Based on some of our earlier work, we propose to create a new modality based on ultrasound and photoacoustics to image blood flow in bones, non-invasively and potentially in real-time. We will progress from localising vasculature to blood flow measurements, and finally perform an in vivo feasibility study in healthy volunteers.

Live brain activity with two-photon microscopy. While two-photon microscopy has shown great potential for imaging neuronal activity, its use to answer fundamental neuroscience questions is limited by the prohibitive price of commercial systems. Combining our expertise in laser and microscopy, we will develop a cost effective two-photon microscope dedicated to this issue, with the aim to provide access to more than 100 individual brain cells simultaneously. As a first application, we will study how sensory neuronal networks are altered in a mouse model of autism, which will provide new insights into the treatment and diagnosis of such disorders. We also anticipate that this work will trigger new collaborations and further studies into different disorders.

New light sources and algorithms for biomedical imaging. Significant resources are committed worldwide to biomedical imaging, and NZ can only compete by being smarter and more agile. The DWC, with its demonstrated ability to develop custom laser sources and original numerical methods, has a history of imaging breakthroughs. We will continue to break new grounds by exploiting optical microresonators  as new OCT sources to increase resolution and imaging depth. Using new mid-IR sources, we will achieve world-leading axial resolution by moving into quantum OCT, improve nonlinear microscopy as well as Raman spectroscopy techniques. New machine learning algorithms will also be developed to analyse OCT images and retrieve clinically relevant parameters, e.g. early signs of eye and skin diseases. To enhance resolution and computation speed, we plan to apply machine learning techniques in new and unconventional ways.

Project 4: HE4 Optical Probes for Biopsy Free Monitoring of Tissue and Bone

Non-communicable and age-related diseases are particularly difficult to detect — especially at an early stage where treatment is most effective. For example, the diagnostic accuracy of prostate cancer (the second most common male cancer worldwide) ranges from 20–80 %, requiring invasive, costly, and repeated biopsies. In this project, we will build upon a suite of photonic technologies developed by members of the DWC to realise novel screening tools suitable for clinical use. We will combine multiple imaging and sensing modalities with advanced data fusion and machine learning techniques to achieve higher diagnostic accuracy, thus reducing the need for invasive biopsies and other costly screening tests. We aim to develop three different medical probe technologies for early detection of skin cancer, prostate cancer, and coeliac disease, all of which pose challenges for conventional screening in NZ. These technologies will leverage the detailed chemical and physical information provided by molecular spectroscopy, optical coherence tomography (OCT), and photoacoustic imaging to distinguish anomalous cells from healthy surrounding tissue. These probes will allow us to acquire the knowledge to be in a position to develop versatile probes to distinguish anomalous cells from healthy surrounding tissue for a range of diseases and allow us to use our expertise to build new collaboration with medical practitioners in NZ and worldwide.

Surface contact and needle probes. We will first focus on a handheld contact probe that uses Raman spectroscopy for rapid detection of skin cancer. In particular, we seek to turn an existing prototype into a clinically viable device. We will also incorporate polarisation sensitive OCT in order to permit full visualisation of the skin structure, thus enhancing the device’s performance. Building on the contact probe, we will develop a needle probe that will allow for in situ and real time mapping of the prostate with unprecedented accuracy, thus facilitating early detection of prostate cancer.

Spatially-offset Raman spectroscopy (SORS) probe. Needle probes provide accurate information on tissue health, but can cause patient discomfort. Here we will utilise SORS to develop complementary contact probes capable of measuring tissue at selected depths. We will develop a SORS probe that allows potential tumours to be interrogated anywhere in the prostate without a needle and potentially without the need of OCT technology to obtain depth information, thus allowing for unprecedented tumour delineation including in surgical settings.

Endoscopes. Molecular spectroscopy can be used to improve endoscopic diagnosis and monitoring of gastrointestinal diseases. Here we will investigate the potential of multi-way vibrational spectroscopic and fluorescence techniques to detect coeliac disease. Specifically, we will use a combination of different spectroscopic techniques together with methods of multivariate analysis and machine learning to classify tissues according to disease states. Based on the results of initial ex vivo studies, the most promising combinations of methods will be incorporated into a device capable of making in vivo diagnosis of a range of gastrointestinal illnesses. We will additionally work on incorporating OCT capabilities into the device so as to obtain sub-surface structural information that can further guide the diagnoses.

Project 5: HE5  Bio-active Molecules and Nanoparticles for Biological Sensing and Treatment

Non-toxic and chemically inert, lanthanide-ion-doped, upconverting nanoparticles can convert low-energy near-infrared photons into high-energy visible photons. This upconversion fluorescence has tremendous importance for a broad spectrum of applications in bio-imaging, drug delivery, theranostics and nanomedicine. Here we will exploit this new technology for biomedical sensing and imaging as well as for treatment. Using high-resolution spectroscopy and detailed modelling of the electronic structure and energy transfer processes, we will first optimise the performance of upconverting nanoparticles. This research will include the effect of high magnetic fields, which can radically enhance fluorescence yields. We will then target heating and temperature sensing for cancer treatment and detection. Heat treatment is typically performed by allowing nanoparticles (typically 50 nm) to deposit in tumours, favoured by a correspondingly higher blood flow, and delivering IR radiation by fibre-optics (which will also be used for temperature sensing). Starting with phantoms, and progressing to real (dead) tissue samples, we will check the location of the particles with our partner (MARS Ltd)’s 3D, multi-wavelength X-rays scanners. In combination with thermal modelling, we will then develop appropriate treatment planning procedures. Next, we will utilise photoacoustic imaging for non-invasive real time monitoring of the photothermal therapy process. We also plan to extend this work to functionalised nanoparticles to target specific molecules, thereby allowing for molecule specific photoacoustic imaging to monitor specific disease processes or drug delivery. Separately, we will look at photo-active molecules and molecular cages that open and close using light. HNO-based therapeutics show considerable promise in clinical trials for acute heart failure, but are so unstable as to prevent storage. We will develop on-demand HNO donors triggered by light. Their use in conjunction with the small fibre-optic probes mentioned above will allow for the simultaneous detection and treatment of diseases within tissues, a dramatic shift with respect to current techniques. We will also unravel the mechanisms of HNO’s key reactions in biology.

Project 6: HE6  Sensing and Protecting our Cultural and Natural World

The indigenous Māori culture and a globally unique natural environment are central to the identity of Aotearoa New Zealand. Many of the photonic technologies developed in the DWC are ideally suited to help better understand and protect our cultural and natural heritage. Here we will apply a diverse range of techniques to examine cultural materials and to elucidate the geophysical world around us. Our initial objectives include:

Analysis of Māori textiles. We will explore the efficacy of microscopy, spectroscopy and Raman microscopy to characterise cultural materials (e.g. plant materials, consolidants, adhesives) and deterioration mechanisms (light fastness of naturally dyed New Zealand plant fibres). This work has important implications for community access to taonga in the museum sector, where concerns about deterioration caused by light have major consequences for public display of Māori textiles.

Geophysical and environmental sensing. New Zealand is one of the most geologically active regions of the world. We will establish the elastic properties of rocks under subsurface conditions for very high temperature and pressure, implement fibre-optic sensors of strain and temperature in the Alpine fault, and use ring laser rotational sensors (see project DM2) to develop novel imaging capabilities of seismic ground motion. This work will be extended to look at geo-thermal reservoirs and for structural monitoring with our partners at NTU in Singapore.

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Overview:

Efficient, reliable and secure communication systems are at the heart of the economy, our well-being, entertainment, and exploration — including scientific exploration. While these systems come in many forms and scales, from bluetooth (radio) to provably secure quantum communications, they are all ultimately based on quantum and photonic technologies. Here we will leverage the DWC’s core expertise to explore and develop new technologies and protocols for the communication systems of the future. In the first four years, we will focus on the following four flagship research projects.

Projects:

Project 1: FC1 — Microresonator optical frequency combs

An optical frequency comb is a laser light source whose spectrum is comprised of thousands equally spaced frequency components.  Their invention in the early 2000s triggered a raft of scientific advances, ranging from unprecedentedly precise measurements of the fundamental constants of nature to the development of the world’s most accurate clocks; the Nobel Prize followed in 2005. Frequency combs can also offer attractive prospects for telecommunications, but improvements in comb performance are still needed for practical viability. This project will exploit the newly developed technology of optical microresonators to create the next generation of comb sources optimised for communications applications. As described below, we will investigate comb generation in both in quadratic χ (2) and Kerr χ (3) nonlinear resonators.

χ (2) resonators. We will first build on our groundbreaking demonstration of electro-optic combs obtained through resonant optical-microwave mixing recently published in Nature, and perform full optimisation of this new comb source. We envisage that advances in microwave cavity design, and the use of new materials, will significantly improve the efficiency and increase the operating frequencies. In parallel, we will experimentally investigate our recent predictions of using second harmonic generation and parametric down conversion to enable generation of combs in the visible and mid-IR spectral regions, where low-power, high-quality combs are currently lacking while they would be extremely valuable for Raman spectroscopy applications HE.

χ (3) resonators. We will study comb generation in integrated χ (3) silicon-nitride and silica microresonators sourced from our external partners. Synchronous pumping of the resonators with pulsed light will provide both efficient comb generation as well as electronic control of the comb spacing. Moreover, we will harness the nonlinear filtering provided by the intracavity comb dynamics to realise combs with significantly lower phase noise than the input driving field. Results on novel soliton dynamics will also be investigated for their communication applications. Finally, we will study crystalline microresonators doped with active ions, such as erbium, where external driving will be replaced by internal lasing action, relaxing the stringent coherence requirements placed on the lasers used to drive microresonator combs.

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Project 2: Project FC3 — Bi-directional microwave to optical conversion

Communication between different quantum systems over macroscopic distances is an open problem central to the development of viable quantum technologies. While optical photons are ideal for transmitting information, they do not easily interact with microwave-based qubits which underlie the most promising quantum information schemes. To solve this problem, we will develop efficient methods to convert microwave photons to optical photons and vice-versa. Three distinct schemes will be explored experimentally, as described below. All experiments will take advantage of various optical and microwave resonant designs, and they will operate in cryogenic temperatures thanks to a large-volume 3He/4He dilution cryostat recently commissioned by The University of Otago and the DWC as a shared resource.

Electro-optic. We have identified the electro-optical process as the most promising approach in the short term. In a preliminary experiment at room temperature, we achieved what was then a record efficiency of 0.1%. Other groups have now vindicated our approach and further improved it. Here we plan to use superconducting microwave cavities and better designed high-Q optical microresonators and couplers to push the conversion efficiency beyond 50%.

Rare earth. Rare earth ions in solids exhibit narrow transitions ideally suited for microwave-to-optical conversion, as we have recently demonstrated. Here we will first improve the conversion efficiency, currently limited to 10-5, by using isotopically pure ions, working at low temperature, and incorporating high-Q resonator designs. Next, we will consider fully concentrated crystals, which promise extreme nonlinearities, and therefore efficient broadband conversion. Our work will include basic spectroscopic studies of the materials and the most promising systems will be used for upconversion experiments.

Cold atoms. Highly excited electronic states (Rydberg states) in cold atomic ensembles are exceptionally responsive to microwave fields and exhibit optical nonlinearities at the single photon level. Recent room-temperature experiments have obtained high conversion efficiency in the classical regime; we will progress this to the quantum limit by using cryogenic temperatures. The setup will include an optical conveyor-belt to transport atoms, and we expect to reach conversion efficiencies above 90%. We further envisage interfacing this platform with the Otago quantum gas apparatus (project QCE3) via optical fibres carrying streams of single photons, thus demonstrating a bridge between disparate quantum technologies.

Once sufficiently high efficiencies are reached, we will proceed to convert microwave quantum states into optical states. We will focus on states that are simple to prepare in the microwave domain, but have thus far been impossible to generate in the optical domain. An optical three photon state, sought after for the past 20 years, is a primary target, as it will enable linear quantum computing and secret key sharing. We will also pursue full bi-directionality of the conversion so as to demonstrate entanglement of two different quantum systems. This would drastically scale the size of quantum systems and bring practical quantum computing a step closer.

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