A. Caviglia
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1
Quantum networks, in which quantum information is distributed over long distances between many physical nodes, hold great promise for the realization of networked quantum computation, quantum communication, and distributed quantum sensing. A high fidelity interface between a long-lived quantum memory and optical photons for the long-distance distribution of entanglement form the fundamental building block of any practical quantum network. In recent years, integrated optomechanical crystals (OMCs) have emerged as a promising physical platform for quantum technologies, including quantum network applications. The flexible operation wavelength of OMCs, including the telecom C-band where fiber transmission losses are minimized, as well as the long lifetimes of their mechanical mode render OMCs a natural candidate for the storage and distribution of quantum information in long-distance quantum networks. However, initial demonstrations using one-dimensional nanobeam OMCs suffer from weak thermal anchoring to the substrate, resulting in low purity of the optomechanically generated single photons. To address this issue, quasi-two-dimensional (2D) OMCs have been developed, allowing for more efficient dissipation of generated thermal phonons into the cryogenic environment. In this thesis, we demonstrate the purity and coherence of optomechanically generated single photons from quasi-2D OMCs. Moreover, we directly measure the photon indistinguishability by two-photon interference through Hong-Ou-Mandel experiment....
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Quantum networks, in which quantum information is distributed over long distances between many physical nodes, hold great promise for the realization of networked quantum computation, quantum communication, and distributed quantum sensing. A high fidelity interface between a long-lived quantum memory and optical photons for the long-distance distribution of entanglement form the fundamental building block of any practical quantum network. In recent years, integrated optomechanical crystals (OMCs) have emerged as a promising physical platform for quantum technologies, including quantum network applications. The flexible operation wavelength of OMCs, including the telecom C-band where fiber transmission losses are minimized, as well as the long lifetimes of their mechanical mode render OMCs a natural candidate for the storage and distribution of quantum information in long-distance quantum networks. However, initial demonstrations using one-dimensional nanobeam OMCs suffer from weak thermal anchoring to the substrate, resulting in low purity of the optomechanically generated single photons. To address this issue, quasi-two-dimensional (2D) OMCs have been developed, allowing for more efficient dissipation of generated thermal phonons into the cryogenic environment. In this thesis, we demonstrate the purity and coherence of optomechanically generated single photons from quasi-2D OMCs. Moreover, we directly measure the photon indistinguishability by two-photon interference through Hong-Ou-Mandel experiment....
This thesis is an experimental investigation of the superconducting state of the two dimensional electron gas formed at the interface between amorphous LaAlO3 and (111) KTaO3. The superconducting phase diagram of (111) KTaO3 is explored by means of electrical transport measurements both above and far below the resistive transition applying small magnetic fields as well as some of the highest available on the planet.
In Chapter 1 we give a brief introduction to the physics of interfacial oxide superconductors.
In Chapter 2 we investigate the extreme resilience of the superconducting state to planar magnetic fields and find the highest critical fields ever reported at oxide interfaces. By considering paramagnetic and orbital pair breaking on equal footing, we find that the magnitude of the critical fields is enabled by the cooperation of an atomically thin superconducting layer and strong spin-orbit scattering.
In Chapter 3 we study the quantum corrections to conductivity that affect the resistive transitions at (111) LaAlO3/KTaO3 interfaces. We find that, thanks to electron-phonon scattering, electrons experience significant decoherence which enables sizeable conductivity contributions from quasiparticle-interference and Maki-Thompson superconducting fluctuations.
Finally in Chapter 4 we discover that the very low temperature switching behavior of our samples are compatible with the spontaneous formation of a Josephson junction array at this interface. Investigating the resistive switching in time-reversal-symmetric conditions we find that the superconducting patches can couple through non-harmonic current-phase relations and sizeable capacitive contributions. This results in a stochastic distribution of switching currents. In the presence of an externally applied magnetic field, we observe non reciprocal responses that affect both the average and width of the switching currents distributions. We propose a simple model in which phase frustration and a non-harmonic CPR can rectify thermally activated fluctuations in the array. ...
In Chapter 1 we give a brief introduction to the physics of interfacial oxide superconductors.
In Chapter 2 we investigate the extreme resilience of the superconducting state to planar magnetic fields and find the highest critical fields ever reported at oxide interfaces. By considering paramagnetic and orbital pair breaking on equal footing, we find that the magnitude of the critical fields is enabled by the cooperation of an atomically thin superconducting layer and strong spin-orbit scattering.
In Chapter 3 we study the quantum corrections to conductivity that affect the resistive transitions at (111) LaAlO3/KTaO3 interfaces. We find that, thanks to electron-phonon scattering, electrons experience significant decoherence which enables sizeable conductivity contributions from quasiparticle-interference and Maki-Thompson superconducting fluctuations.
Finally in Chapter 4 we discover that the very low temperature switching behavior of our samples are compatible with the spontaneous formation of a Josephson junction array at this interface. Investigating the resistive switching in time-reversal-symmetric conditions we find that the superconducting patches can couple through non-harmonic current-phase relations and sizeable capacitive contributions. This results in a stochastic distribution of switching currents. In the presence of an externally applied magnetic field, we observe non reciprocal responses that affect both the average and width of the switching currents distributions. We propose a simple model in which phase frustration and a non-harmonic CPR can rectify thermally activated fluctuations in the array. ...
This thesis is an experimental investigation of the superconducting state of the two dimensional electron gas formed at the interface between amorphous LaAlO3 and (111) KTaO3. The superconducting phase diagram of (111) KTaO3 is explored by means of electrical transport measurements both above and far below the resistive transition applying small magnetic fields as well as some of the highest available on the planet.
In Chapter 1 we give a brief introduction to the physics of interfacial oxide superconductors.
In Chapter 2 we investigate the extreme resilience of the superconducting state to planar magnetic fields and find the highest critical fields ever reported at oxide interfaces. By considering paramagnetic and orbital pair breaking on equal footing, we find that the magnitude of the critical fields is enabled by the cooperation of an atomically thin superconducting layer and strong spin-orbit scattering.
In Chapter 3 we study the quantum corrections to conductivity that affect the resistive transitions at (111) LaAlO3/KTaO3 interfaces. We find that, thanks to electron-phonon scattering, electrons experience significant decoherence which enables sizeable conductivity contributions from quasiparticle-interference and Maki-Thompson superconducting fluctuations.
Finally in Chapter 4 we discover that the very low temperature switching behavior of our samples are compatible with the spontaneous formation of a Josephson junction array at this interface. Investigating the resistive switching in time-reversal-symmetric conditions we find that the superconducting patches can couple through non-harmonic current-phase relations and sizeable capacitive contributions. This results in a stochastic distribution of switching currents. In the presence of an externally applied magnetic field, we observe non reciprocal responses that affect both the average and width of the switching currents distributions. We propose a simple model in which phase frustration and a non-harmonic CPR can rectify thermally activated fluctuations in the array.
In Chapter 1 we give a brief introduction to the physics of interfacial oxide superconductors.
In Chapter 2 we investigate the extreme resilience of the superconducting state to planar magnetic fields and find the highest critical fields ever reported at oxide interfaces. By considering paramagnetic and orbital pair breaking on equal footing, we find that the magnitude of the critical fields is enabled by the cooperation of an atomically thin superconducting layer and strong spin-orbit scattering.
In Chapter 3 we study the quantum corrections to conductivity that affect the resistive transitions at (111) LaAlO3/KTaO3 interfaces. We find that, thanks to electron-phonon scattering, electrons experience significant decoherence which enables sizeable conductivity contributions from quasiparticle-interference and Maki-Thompson superconducting fluctuations.
Finally in Chapter 4 we discover that the very low temperature switching behavior of our samples are compatible with the spontaneous formation of a Josephson junction array at this interface. Investigating the resistive switching in time-reversal-symmetric conditions we find that the superconducting patches can couple through non-harmonic current-phase relations and sizeable capacitive contributions. This results in a stochastic distribution of switching currents. In the presence of an externally applied magnetic field, we observe non reciprocal responses that affect both the average and width of the switching currents distributions. We propose a simple model in which phase frustration and a non-harmonic CPR can rectify thermally activated fluctuations in the array.
This thesis explores the growth, fabrication and measurement of freestanding complex oxide membranes. Complex oxides such as SrRuO3 and NdNiO3 are fabricated into a freestanding membrane form, with their numerous intrinsic properties and phenomena characterised and investigated. New techniques describing solutions to the current fabrication hurdles of freestanding complex oxide membranes is discussed, along with the comparison of SrRuO3 and NdNiO3 freestanding membranes and their epitaxial counterparts.
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This thesis explores the growth, fabrication and measurement of freestanding complex oxide membranes. Complex oxides such as SrRuO3 and NdNiO3 are fabricated into a freestanding membrane form, with their numerous intrinsic properties and phenomena characterised and investigated. New techniques describing solutions to the current fabrication hurdles of freestanding complex oxide membranes is discussed, along with the comparison of SrRuO3 and NdNiO3 freestanding membranes and their epitaxial counterparts.
Photonic topological edge states
A nanoscale investigation
The aimof this thesis is to investigate the impact of symmetry on light and how it alters its characteristics. Our research centers around the examination of complex photonic crystals rooted in the concept of photonic topological insulators, which are analogs of topological insulators initially introduced in condensed matter physics. Unlike typical insulating materials, these possess a unique ability to conduct along their surface or edges. Leveraging this fundamental property, photonic topological insulators have gained attention for designing transport circuits resistant to back-reflection and scattering mechanisms....
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The aimof this thesis is to investigate the impact of symmetry on light and how it alters its characteristics. Our research centers around the examination of complex photonic crystals rooted in the concept of photonic topological insulators, which are analogs of topological insulators initially introduced in condensed matter physics. Unlike typical insulating materials, these possess a unique ability to conduct along their surface or edges. Leveraging this fundamental property, photonic topological insulators have gained attention for designing transport circuits resistant to back-reflection and scattering mechanisms....
Master thesis
(2021)
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Amber Mozes, A. Caviglia, M. Matthiesen, A. Caviglia, T. van der Sar, A. Endo
Terahertz time-domain spectroscopy (THz-TDS) is an extremely useful method to probe material electrodynamics. The THz regime comprises rich physics, enabling to determine compositional, electronic and vibronic degrees of freedom through THz spectroscopy of a material under study. However, to study nanometre size thin films with THz-TDS, we need to overcome a large mismatch in length scales, since the THz wavelength is on the order of millimeters. A solution lies in the THz probing of metasurfaces, artificial materials made of conductive structures with length scales much smaller than the probing wavelength. Such a metamaterial induces enhanced electromagnetic field strengths near the surface, enabling nonlinear spectroscopy without the need for strong-field terahertz sources. Additionally, they provide sensitivity to the local (micron-scale) electrodynamic environment. In the ideal case, one can infer significant information about the thin film electrodynamics via the resonance frequency and dissipation in the metasurface. This thesis project comprises the optimization of terahertz (THz) resonant electric split ring resonator (eSRR) metasurfaces for enhanced-light matter coupling, suitable for material characterization. Experimental characterization is combined with finite element simulations, to obtain the transmission spectra and near-field electric, magnetic fields and current densities. In simulation, the eSRR design is optimized to obtain an up to four times stronger response at resonance than the designs described in literature. The optimized design is studied on different substrates, revealing the ability to extract a resonance even close to a substrate Reststrahlen band. This thesis concludes with characterization of the metal-insulator transition of transition metal oxide NdNiO3. From the resonance frequency and quality factor it is possible to track this phase transition from time-domain terahertz spectroscopy, thereby revealing the ability to probe extremely thin films, with an outlook on out of equilibrium studies.
...
Terahertz time-domain spectroscopy (THz-TDS) is an extremely useful method to probe material electrodynamics. The THz regime comprises rich physics, enabling to determine compositional, electronic and vibronic degrees of freedom through THz spectroscopy of a material under study. However, to study nanometre size thin films with THz-TDS, we need to overcome a large mismatch in length scales, since the THz wavelength is on the order of millimeters. A solution lies in the THz probing of metasurfaces, artificial materials made of conductive structures with length scales much smaller than the probing wavelength. Such a metamaterial induces enhanced electromagnetic field strengths near the surface, enabling nonlinear spectroscopy without the need for strong-field terahertz sources. Additionally, they provide sensitivity to the local (micron-scale) electrodynamic environment. In the ideal case, one can infer significant information about the thin film electrodynamics via the resonance frequency and dissipation in the metasurface. This thesis project comprises the optimization of terahertz (THz) resonant electric split ring resonator (eSRR) metasurfaces for enhanced-light matter coupling, suitable for material characterization. Experimental characterization is combined with finite element simulations, to obtain the transmission spectra and near-field electric, magnetic fields and current densities. In simulation, the eSRR design is optimized to obtain an up to four times stronger response at resonance than the designs described in literature. The optimized design is studied on different substrates, revealing the ability to extract a resonance even close to a substrate Reststrahlen band. This thesis concludes with characterization of the metal-insulator transition of transition metal oxide NdNiO3. From the resonance frequency and quality factor it is possible to track this phase transition from time-domain terahertz spectroscopy, thereby revealing the ability to probe extremely thin films, with an outlook on out of equilibrium studies.
In this study, ultrathin films of the itinerant 4d ferromagnet SrRuO3 were epitaxially deposited on SrTiO3 and capped with a thin LaAlO3 layer. Top gates and a dielectric layer were patterned onto contacted films and magnetotransport properties were characterized at low temperatures as a function of top gate voltage. A particular focus was placed on the anomalous Hall resistivity. The magnitude of the Hall signal and the sheet resistance were shown to vary with top gate voltage. In particular, the anomalous Hall loops were compared to numerical tight-binding models. The model is proposed as an alternate explanation to the skyrmion picture and as a complement to the two-channel phenomenological model put forth to explain the unusual low-temperature anomalous signal of ultrathin SrRuO3 . Model predictions were found to be valid at
low temperatures in semiconducting Ru-deficient SrRuO3 films. ...
low temperatures in semiconducting Ru-deficient SrRuO3 films. ...
In this study, ultrathin films of the itinerant 4d ferromagnet SrRuO3 were epitaxially deposited on SrTiO3 and capped with a thin LaAlO3 layer. Top gates and a dielectric layer were patterned onto contacted films and magnetotransport properties were characterized at low temperatures as a function of top gate voltage. A particular focus was placed on the anomalous Hall resistivity. The magnitude of the Hall signal and the sheet resistance were shown to vary with top gate voltage. In particular, the anomalous Hall loops were compared to numerical tight-binding models. The model is proposed as an alternate explanation to the skyrmion picture and as a complement to the two-channel phenomenological model put forth to explain the unusual low-temperature anomalous signal of ultrathin SrRuO3 . Model predictions were found to be valid at
low temperatures in semiconducting Ru-deficient SrRuO3 films.
low temperatures in semiconducting Ru-deficient SrRuO3 films.
This thesis is an experimental investigation of the physical properties of different transition metal oxide ultra-thin films. A common feature of these various materials and structures is that they exhibit a solid-state phase transition from a metallic to an insulating state, which is triggered upon changing sample composition, or by varying an external stimulus such as temperature, illumination or gas pressure. The experiments performed cover a broad spectrum of condensed matter, from material growth, structural characterisation and nanodevice fabrication to low-temperature magnetotransport, synchrotron microscopy and gas sensing.
...
This thesis is an experimental investigation of the physical properties of different transition metal oxide ultra-thin films. A common feature of these various materials and structures is that they exhibit a solid-state phase transition from a metallic to an insulating state, which is triggered upon changing sample composition, or by varying an external stimulus such as temperature, illumination or gas pressure. The experiments performed cover a broad spectrum of condensed matter, from material growth, structural characterisation and nanodevice fabrication to low-temperature magnetotransport, synchrotron microscopy and gas sensing.