1,373 research outputs found

    On Time-Resolved 3D-Tracking of Elastic Waves in Microscale Mechanical Metamaterials

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    Toward an active CMOS electronics-photonics platform based on subwavelength structured devices

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    The scaling trend of microelectronics over the past 50 years, quantified by Moore’s Law, has faced insurmountable bottlenecks, necessitating the use of optical communication with its high bandwidth and energy efficiency to further improve computing performance. Silicon photonics, compatible with CMOS platform manufacturing, presents a promising means to achieve on-chip optical links, employing highly sensitive microring resonator devices that demand electronic feedback and control due to fabrication variations. Achieving the full potential of both technologies requires tight integration to realize the ultimate benefits of both realms of technology, leading to the convergence of microelectronics and photonics. A promising approach for achieving this convergence is the monolithic integration of electronics and photonics on CMOS platforms. A critical milestone was reached in 2015 with the demonstration of the first microprocessor featuring photonic I/O (Chen et al, Nature 2015), accomplished by integrating transistors and photonic devices on a single chip using a monolithic CMOS silicon-on-insulator (SOI) platform (GlobalFoundries 45RFSOI, 45 nm SOI process) without process modifications, thus known as the "zero-change" approach. This dissertation focuses on leveraging the fabrication capabilities of advanced monolithic electronic-photonic 45 nm CMOS platforms, specifically high-resolution lithography and small feature size doping implants, to realize photonic devices with subwavelength features that could potentially provide the next leap in integrated optical links performance, beyond microring resonator based links. Photonic crystal (PhC) nanobeam cavities can support high-quality resonance modes while confining light in a small volume, enhancing light-matter interactions and potentially enabling ultimate efficiencies in active devices such as modulators and photodetectors. However, PhC cavities have been overshadowed by microring resonators due to two challenges. First, their fabrication demands high lithography resolution, which excludes most standard SOI photonic platforms as viable options for creating these devices. Secondly, the standing-wave nature of PhC nanobeam cavities complicates their integration into wavelength-division multiplexing (WDM) optical links, causing unwanted reflections when coupled evanescently to a bus waveguide. In this work, we present PhC nanobeam cavities with the smallest footprint, largest intrinsic quality factor, and smallest mode volume to be demonstrated to date in a monolithic CMOS platform. The devices were fabricated in a 45 nm monolithic electronics–photonics CMOS platform optimized for silicon photonics, GlobalFoundries 45CLO, exhibiting a quality factor in excess of 100,000 the highest among fully cladded PhC nanobeam cavities in any SOI platform. Furthermore to eliminate reflections, we demonstrate an approach using pairs of PhC nanobeam cavities with opposite spatial mode symmetries to mimic traveling-wave-like ring behavior, enabling efficient and seamless WDM link integration. This concept was extended to realize a reflectionless microring resonator unit with two microrings operating as standing-wave cavities. Using this scheme with standing-wave microring resonators could lead to an optimum geometry for microring modulators with interdigitated p-n junctions in terms of modulation efficiency in a manner that allows for straightforward WDM cascading. This work also presents the first demonstration of resonant-structure-based modulators in the GlobalFoundries 45CLO platform. We report the first-ever demonstration of a PhC modulator in a CMOS platform, featuring a novel design with sub-wavelength contacts on one side allowing it to benefit from the "reflection-less"' architecture. Additionally, we also report the first demonstration of microring modulators. The most efficient devices exhibited electro-optical bandwidths up to 30 GHz, and 25 Gbps non-return-to-zero (NRZ) on-off-keyed (OOK) modulation with 1 dB insertion loss and 3.1 dB extinction ratio. Finally, as the complexity of silicon photonic systems-on-a-chip (SoC) increases to enable new applications such as low-energy data links, quantum optics, and neuromorphic computing, the need for in-situ characterization of individual components becomes increasingly important. By combining Near-field scanning optical microscopy (NSOM) with a flip-chip post-processing technique, this dissertation demonstrates a method to non-invasively perform NSOM scans of a photonic device within a large-scale CMOS-photonic circuit, without interfering with the performance and packaging of the photonics and electronics, making it a valuable tool for future development of high performance photonic circuits and systems

    Microwave-shielded ultracold polar molecules

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    Since the realization of Bose--Einstein condensates and degenerate Fermi gases, ultracold atoms with tunable interactions have become an essential platform for studying quantum many-body phenomena. Notable examples include the realization of BCS--BEC crossover and the simulation of the Bose/Fermi Hubbard model. Ultracold polar molecules could enrich the quantum gas toolbox with their long-range dipole-dipole interaction, which offers not only new opportunities in many-body physics, such as realizing the topological superfluid and the extended Hubbard model, but also applications in quantum chemistry, quantum computation, and precision measurements. However, the large number of internal degrees of freedom of molecules present a significant challenge in both cooling them to quantum degeneracy and controlling their interactions. Unlike atomic gases, a dense molecular sample suffers from fast collisional losses, preventing the implementation of evaporative cooling and the observation of scattering resonances. In this thesis, we describe how we solved the long-standing issue of collisional losses by microwave shielding, created a degenerate Fermi gas of NaK molecules, and discovered a new type of scattering resonances via which we created the first ultracold tetratomic molecules in the 100-nK regime. By synchronizing the rotation of polar molecules with a circularly polarized microwave electric field, we equip the molecular sample with a highly tunable intermolecular potential. This not only stabilizes the gas against inelastic collisions but also enables field-linked scattering resonances for precise control over scattering lengths. At long range, the molecules interact via their induced rotating dipole moments. As they approach each other, their orientations realign to produce a repulsive force, thereby mitigating inelastic collisions at close distances. With an elastic-to-inelastic collision ratio of 500, we have achieved evaporative cooling of the molecular gas down to 21 nK and 0.36 times the Fermi temperature, setting a new record for the coldest polar molecular gas to date. Thanks to the collisional stability of microwave-shielded molecules, we can directly load them into predominantly a single layer of a magic 3D optical lattice, achieving a peak filling fraction of 24%. These ultracold molecules, owing to their long lifetimes in their ground state and their long-range dipolar coupling, provide a unique platform to study quantum magnetism. With the achieved high filling fraction, we are prepared to study non-equilibrium spin dynamics such as rotational synchronization and spin squeezing. We demonstrated that the interaction between microwave-shielded polar molecules is highly tunable via the microwave power, detuning, and polarization. When the interaction potential is deep enough to host field-linked bound states at the collisional threshold, a shape resonance is induced, allowing us to tune the scattering rate by three orders of magnitude. The field-linked resonances enables controls over the scattering length in a similar fashion as Feshbach resonance for ultracold atoms, promising the realization of strongly correlated phases, such as dipolar pp-wave superfluid. It also paves the way to investigate the interplay between short-range and long-range interactions in novel quantum matters, such as exotic supersolid. Moreover, through a field-linked resonance, we associated for the first time weakly bound tetratomic molecules in the 100-nK regime, with a phase space density of 0.04. The transition from a Fermi gas of diatomic molecules to a Bose gas of tetratomic molecules paves the way for dipolar BCS--BEC crossover. With microwave-shielded polar molecules, we have realized a quantum gas featuring highly tunable long-range interactions. The technique is universal to polar molecules with a sufficiently large dipole moment, and thus offers a general strategy for cooling and manipulating polar molecules, and for associating weakly bound ultracold polyatomic molecules. Utilizing the toolbox developed in ultracold atoms, this platform possesses the potential to unlock an entirely new realm of quantum simulation of many-body physics

    Kerr Enhanced Backaction Cooling in Magnetomechanics

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    Precise control over massive mechanical objects is highly desirable for testing fundamental physics and for sensing applications. A very promising approach is cavity optomechanics, where a mechanical oscillator is coupled to a cavity. Usually, such mechanical oscillators are in highly excited thermal states and require cooling to the mechanical ground state for quantum applications, which is often accomplished by utilising optomechanical backaction. However, this is not possible for increasingly massive oscillators, as due to their low frequencies conventional cooling methods are less effective. Here, we demonstrate a novel cooling scheme by using an intrinsically nonlinear cavity together with a low frequency mechanical oscillator. We demonstrate outperforming an identical, but linear, system by more than one order of magnitude. While currently limited by flux noise, theory predicts that with this approach the fundamental cooling limit of a linear system can not only be reached, but also outperformed. These results open a new avenue for efficient optomechanical cooling by exploiting a nonlinear cavity

    Beam scanning by liquid-crystal biasing in a modified SIW structure

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    A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

    An efficient quantum memory in 167Er3+:Y2SiO5

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    This thesis investigates whether a quantum memory suitable for quantum communication applications can be developed using an erbium doped crystal. To assess the potential of the storage material, 167Er3+:Y2SiO5, the performance of two quantum memory protocols are characterised, the Atomic Frequency Comb (AFC) and Rephased Amplified Spontaneous Emission (RASE). As such, this work is a spiritual successor to two previous PhD projects, Kate Ferguson's non-classical demonstration of the RASE protocol using praseodymium, and Milos Rancic's high resolution spectroscopy and demonstration of long hyperfine coherence times in erbium. A telecom compatible quantum memory is vital for the DLCZ quantum repeater protocol, a critical device for quantum communications networks. A quantum memory designed for communications networks will need to meet several requirements: operate in the fibre optic telecommunications band, high recall efficiency, long storage time, and high bandwidth. Erbium is of interest as it has an optical transition within the telecommunications C-band (1530-1565 nm) and Rancic's thesis demonstrated the hyperfine coherence time needed for long storage times, 1.3 s. However, efficient quantum memories using erbium have not been demonstrated to date. This thesis will present an efficient quantum memory using erbium and discuss a pathway to demonstrate all the above criteria simultaneously. Techniques that were developed in Rancic's thesis are expanded in this thesis to create a new memory preparation process. The preparation process uses the long hyperfine lifetimes and large hyperfine splittings found in 167Er3+:Y2SiO5. Using this preparation, two quantum memory protocols were demonstrated, the Atomic Frequency Comb (AFC) and Rephased Amplified Spontaneous Emission (RASE), from Ferguson's thesis. In the AFC experiments, non-classical storage was demonstrated with a delay time of 0.66 us, an efficiency of 22%, and a bandwidth of 6 MHz. In the RASE experiments, an efficiency of 47% was demonstrated with a spin-state storage time of 27 us, and the potential to store 40 temporal modes. The initial results have shown orders of magnitude increases in storage times and efficiency over previous erbium memories. However, the efficiencies shown are not high enough for a quantum repeater demonstration. Cavity-enhancement offers a way to increase the efficiencies of both the AFC and RASE demonstrations. In the AFC chapter, cavity enhancement was discussed as a way to increase the efficiency, theoretically, to 96.6% with a 100 MHz bandwidth. These predicted efficiencies and bandwidths, using erbium, would meet three of the requirements needed for applications in a communications network, while Rancic has already demonstrated the remaining requirement in the same material. The next step for this work will be to realise the predicted efficiency and bandwidth, and then implement hyperfine rephasing for long storage times. In summary, this thesis expands on the works of Ferguson and Rancic to demonstrate quantum memories based in erbium. The demonstrations are promising so far, and proposed improvements to the experiment suggest that a quantum memory fit for quantum networks applications is possible. Furthermore, a pathway to an improved quantum memory is presented. Such a memory could be used in an initial quantum repeater demonstration

    Efficient wireless coverage of in-building environments with low electromagnetic impact

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    The city of tomorrow is a major integrating stake, which crosses a set of major broad spectrum domains. One of these areas is the instrumentation of this city and the ubiquity of the exchange of data, which will give the pulse of this city (sensors) and its breathing in a hyper-connected world within indoor and outdoor dense areas (data exchange, 5G and 6G). Within this context, the proposed doctorate project has the objective to realize cost- and energy- effective, short-range communication systems for the capillary wireless coverage of in-door environments with low electromagnetic impact and for highly dense outdoor networks. The result will be reached through the combined use of: 1) Radio over Fiber (RoF) Technology, to bring the Radio Frequency (RF) signal to the different areas to be covered. 2) Beamforming antennas to send in real time the RF power just in the direction(s) where it is really necessary

    Integrated widely tunable laser systems at 1300 and 1550 nm as swept sources for optical coherence tomography

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    Nonlinear Cavity Optomechanics in Diamond

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    Diamond has been proven to be a particularly useful material for implementing quantum technologies due to the various defects known as color centers. These color centers can be coupled to both photons and phonons; therefore, they enable the realization of a hybrid quantum system that consists of spins, photons, and phonons. Cavity optomechanics provides a platform to increase the interaction time between photons and phonons. By increasing the average number of photons and phonons, the coupling rates will be enhanced, and better control over the system could emerge as a result. This is integral to quantum technologies such as quantum networks, computers, and sensors. Cavity optomechanical systems are inherently nonlinear systems, which can be easily seen when the number of photons and phonons increases. This work studies nonlinear cavity optomechanics in diamond as we explore relatively under-studied dynamical regimes of optomechanical systems by increasing the number of phonons
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