京都大学 / 新制・課程博士 / 博士(工学) / 甲第24630号 / 工博第5136号 / 新制||工||1981(附属図書館) / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 水落 憲和, 教授 関 修平, 教授 梶 弘典 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

We investigate the resonant characteristics of superconducting meandering nanowires to design a nonlinear kinetic inductance traveling-wave parametric amplifier. The devices are patterned out of 15 nm thick NbTiN films. They consist of a coplanar waveguide, that shrinks into 100 nm wide meandering nanowires. For a total kinetic inductance of ∼1 μH, our simulations show that these structures behave as resonators with fundamental mode frequency around 1 GHz and a phase velocity of the signal as low as c/1000. The resonance peaks correspond to the presence of current antinodes within the meandering structure. Samples were fabricated at the Albanova Nanolab facility and measured in a sample-in-vacuum dipstick at 300 mK. Frequency sweeps in the 0.1-10 GHz range confirm the presence of these resonance peaks. In addition, we investigate the current nonlinearity of our devices. Analysis of the temperature dependence of the resonant peaks revealed the critical temperature of the film, TC = 14.0 ± 0.5 K. The dispersion relations showed that the device impedance exceeds the resistance quantum RQ = 6.5 kΩ when close to resonance or below 87 MHz. A second design was realized in order to reduce the device’s characteristic impedance to ≈ 50 Ω. This design, accomodating a micro stripline, embedded a significantly longer nanowire, with a total kinetic inductance ∼10 μH. Measurements showed a dramatically reduced impedance to ≈ 700 Ω, but still not matched to 50 Ω, giving rise to a dense frequency comb of standing modes in the 0-3 GHz bandwidth, with a constant spacing of ≈ 45 MHz. / Vi undersöker egenskaperna hos supraledande slingrande nanotrådar i syfte att designa en ickelinjär kinetisk induktans parametrisk förstärkare. Våra prov är mönstrade ur 15 nm tjocka NbTiN-filmer. De består av en koplanär vågledare som krymper till 100 nm breda slingrande nanotrådar. Med en sammanlagd kinetisk induktans på ∼1 μH visar våra simuleringar att dessa strukturer beter sig som resonatorer med en funda- mental modfrekvens runt 1 GHz och en fashastighet för signalen så låg som c/1000. Resonanserna motsvarar närvaron av strömantinoder inom den slingrande strukturen. Proverna tillverkades i Albanovas Nanolab och mättes i en prov-i-vakuum-sticka runt 300 mK. Frekvenssvepen i området 0,1-10 GHz bekräftar förekomsten av dessa res- onanser. Dessutom undersökte vi den strömberoende ickelinjäriteten i våra enheter. Analys av resonansernas temperaturberoende ger ett värde på filmens kritiska temper- atur, TC = 14.0 ± 0.5 K. Dispersionsförhållandena visade att provens impedans över- stiger resistanskvantumet RQ = 6, 5 kΩ nära resonanserna. En andra design realiserades för att reducera provens karakteristiska impedans till ≈ 50 Ω. Denna design, med en mikrostripline, har en betydligt längre totaltsträcka med en sammanlagd kinetisk induk- tans på ∼10 μH. Mätningarna visade en dramatiskt reducerad impedans på ≈ 700 Ω, men inte till det matchade värdet på 50 Ω, vilket gav upphov till en tät frekvenskam inom bandbredden 0- 3 GHz, med ett avstånd på ≈ 45 MHz mellan resonanserna.

Integrated quantum photonic circuits have gained increasing interest in the field of quantum information, due to their compactness, the intrinsic stability and the potential scalability. Photons are the promising candidate for quantum information processing. Among all the optical platforms, femtosecond-laser waveguide writing technique has shown the extraordinary versatility in producing different components of a complete quantum system. In the last decade, femtosecond-laser writing has greatly expanded its applications in quantum technology. The aim of this thesis is to study and optimize the fundamental optical devices for integrated quantum circuits using femtosecond-laser waveguide writing technique. We investigate relevant theory of optical waveguides, the methods to fabricate and characterize laser-written waveguides in glass. In this work, we demonstrate the femtosecond-laser writing of integrated devices including Mach-Zehnder interferometer and path-encoded CNOT quantum gate. These devices can further serve as building blocks to produce complete integrated quantum system. / Integrerade kvantfotoniska kretsar har fått ett ökande intresse inom området kvantinformation, på grund av deras kompakthet, den inneboende stabiliteten och den potentiella skalbarheten. Fotoner är den lovande kandidaten för bearbetning av kvantinformation. Bland alla optiska plattformar har femtosekund-laservågledarskrivteknik visat den extraordinära mångsidigheten i att producera olika komponenter i ett komplett kvantsystem. Under det senaste decenniet har femtosekundlaserskrivning kraftigt utökat sina tillämpningar inom kvantteknologi. Syftet med denna avhandling är att studera och optimera de grundläggande optiska enheterna för integrerade kvantkretsar med hjälp av femtosekund-laservågledarskrivteknik. Vi undersöker relevant teori om optiska vågledare, metoderna för att tillverka och karakterisera laserskrivna vågledare i glas. I detta arbete demonstrerar vi femtosekundlaserskrivning av integrerade enheter inklusive Mach-Zehnder-interferometer och vägkodad CNOT-kvantgrind. Dessa enheter kan vidare fungera som byggstenar för att producera kompletta integrerade kvantsystem.

Anderson localization occurs when an otherwise conductive solid becomes insulatingdue to a sufficiently large degree of disorder in the medium. The electron band energy(as a function of disorder) at which this transition between extended and localizedelectron states occur is called the mobility edge (ME) and is energy-dependent only in3-dimensional systems. In lower dimensional systems, energy-independent ME (allstates localized or all extended) has been demonstrated by replacing disorder withquasi-periodic potential. However, recent theoretical findings indicate that neitherdisorder nor quasi-periodic potential is necessary for a material to exhibit electronlocalization and existence of energy-dependent pseudo ME at finite system size.In this thesis work, we use light in coupled silicon nitride waveguides to simulatesingle-particle transport of a solid-state medium and investigate the coexistence ofdelocalized and localized states in disorder-free photonic lattices of finite systemsize. This was achieved by implementing a simulated linearly increasing electricpotential on even-numbered sites by varying the refractive index of the wave guide(ch. 3). Through our experimental setup, we successfully achieved a coexistence oflocalized and delocalized states, where the degree of localization varies depending onthe strength of the applied electric field.The findings have implications for the field of quantum technology, whereunderstanding and controlling quantum states is crucial. The ability to achievelocalization in the absence of disorder opens new possibilities for designing andengineering photonic devices for quantum information processing tasks. / Anderson-lokalisering uppstår när ett annars ledande fast material blir isolerande pågrund av en tillräckligt stor grad av oordning i mediet. Elektronbandsenergin (som enfunktion av oordning) vid vilken denna övergång mellan förlängda och lokaliseradeelektrontillstånd sker kallas mobilitetskanten (ME) och är energiberoende endasti 3-dimensionella system. I lägre dimensionella system har energioberoende ME(alla tillstånd lokaliserade eller alla förlängda) påvisats genom att ersätta oordningmed kvasi-periodisk spänning. Nya teoretiska fynd indikerar dock att varkenoordning eller kvasi-periodisk spänning är nödvändig för att ett material ska uppvisaelektronlokalisering och förekomsten av energiberoende pseudo-ME för system avfinita storlekar.I detta examensarbete använder vi ljus i kopplade vågledare av kiselnitrid föratt simulera transport av en partikel i ett fast tillståndsmedium och undersökersamexistensen av icke-lokaliserade och lokaliserade tillstånd i finita system utanoordning med fotoniska gitter. Detta uppnåddes genom att implementera ensimulerad linjärt ökande elektrisk potential på varje jämnt numrerat gitterläge platsgenom att öka vågledarbredderna och noll elektrisk spänning på varje udda. Genomvårt experimentella upplägg lyckades vi uppnå lokaliserade och förlängda tillstånd, därgraden av lokaliseringen varierade beroende på styrkan av det tillämpade elektriskafältet.Fynden har implikationer för kvantteknologi, där förståelse och kontroll avkvanttillstånd är avgörande. Förmågan att uppnå lokalisering i frånvaro avoordning öppnar nya möjligheter för att designa och konstruera fotoniska enheter förkvantinformationsprocesser.

<p dir="ltr">Quantum information science and technology has been at the forefront of science and technology since MIT mathematician Peter Shor discovered a quantum algorithm to factor large numbers in 1994. Advancement in quantum theory also advances practical technological applications. Quantum technology can be applied both in civilian society and the military field from encryption, artificial intelligence, sensing, to communications. This multi-purpose applicability, therefore, has the potential to alter international security as scientifically advanced nation-states vie for quantum supremacy. This research examines the applications of quantum science and how these applications can potentially impact international security. Because nation-states fund and support quantum science research, sources of method will include academic journals and online resources as well as government reports. Practical applications of quantum technology, including quantum computing, quantum sensing, and quantum communication, will constitute the primary scope of this research.</p>

In this work, we explored one material from the broad family of 2D semiconductors, namely WSe2 to serve as an enabler for advanced, low-power, high-performance nanoelectronics and optoelectronic devices. A 2D WSe2 based field-effect-transistor (FET) was designed and fabricated using electron-beam lithography, that revealed an ultra-high mobility of ~ 625 cm2/V-s, with tunable charge transport behavior in the WSe2 channel, making it a promising candidate for high speed Si-based complimentary-metal-oxide-semiconductor (CMOS) technology. Furthermore, optoelectronic properties in 2D WSe2 based photodetectors and 2D WSe2/2D MoS2 based p-n junction diodes were also analyzed, where the photoresponsivity R and external quantum efficiency were exceptional. The monolayer WSe2 based photodetector, fabricated with Al metal contacts, showed a high R ~502 AW-1 under white light illumination. The EQE was also found to vary from 2.74×101 % - 4.02×103 % within the 400 nm -1100 nm spectral range of the tunable laser source. The interfacial metal-2D WSe2 junction characteristics, which promotes the use of such devices for end-use optoelectronics and quantum scale systems, were also studied and the interfacial stated density Dit in Al/2D WSe2 junction was computed to be the lowest reported to date ~ 3.45×1012 cm-2 eV-1. We also examined the large exciton binding energy present in WSe2 through temperature-dependent Raman and photoluminescence spectroscopy, where localized exciton states perpetuated at 78 K that are gaining increasing attention for single photon emitters for quantum information processing. The exciton and phonon dynamics in 2D WSe2 were further analyzed to unveil other multi-body states besides localized excitons, such as trions whose population densities also evolved with temperature. The phonon lifetime, which is another interesting aspect of phonon dynamics, is calculated in 2D layered WSe2 using Raman spectroscopy for the first time and the influence of external stimuli such as temperature and laser power on the phonon behavior was also studied. Furthermore, we investigated the thermal properties in 2D WSe2 in a suspended architecture platform, and the thermal conductivity in suspended WSe2 was found to be ~ 1940 W/mK which was enhanced by ~ 4X when compared with substrate supported regions. We also studied the use of halide-assisted low-pressure chemical vapor deposition (CVD) with NaCl to help to reduce the growth temperature to ∼750 °C, which is lower than the typical temperatures needed with conventional CVD for realizing 1L WSe2. The synthesis of monolayer WSe2 with high crystalline and optical quality using a halide assisted CVD method was successfully demonstrated where the role of substrate was deemed to play an important role to control the optical quality of the as-grown 2D WSe2. For example, the crystalline, optical and optoelectronics quality in CVD-grown monolayer WSe2 found to improve when sapphire was used as the substrate. Our work provides fundamental insights into the electronic, optoelectronic and quantum properties of WSe2 to pave the way for high-performance electronic, optoelectronic, and quantum-optoelectronic devices using scalable synthesis routes.

This research study aims to investigate the capacity of single photons to carry information through polarization and time ordering and proposes a protocol called Beyond Pulse Position Modulation (BPPM) to improve photon-based communication reliability over longer distances with limited power. Such a protocol may be used in any communication scenario where energy efficiency is important, e.g., in satellite communication or where pulse position modulation (PPM) typically is used. The study compares various metrics such as information bits per symbol, photon, and time bin to evaluate the system’s efficiency and conducts a comparative analysis of BPPM, Pulse Position Modulation (PPM), On-Off Keying (OOK), andGeneral protocol’s effectiveness. (The simulations were conducted using the Python programming language with Visual Studio Code IDE.) / Denna forskningsstudie syftar till att undersöka informationskapaciteten hos enstaka fotoner då dessa kodats med avseende på polarisering och tidsordning. Ett nytt protokoll som kallas Beyond Pulse Position Modulation (BPPM) använder felkorrigering för att förbättra kommunikationstillförlitligheten över längre avstånd med begränsad effekt. Ett sådant protokoll kan användas i vilket kommunikationsscenario som helst där energieffektivitet är viktigt, t.ex. vid satellitkommunikation eller där pulspositionsmodulering (PPM) vanligtvis används. Studien jämför olika mätvärden som informationsbitar per symbol, per foton och per tidslucka för att utvärdera systemets effektivitet och genomför en jämförande analys av BPPM, Pulse Position Modulation (PPM), On-Off Keying (OOK) och ett protokoll med fixt antal fotoner per block avseende protokollens effektivitet. (Simuleringarna utfördes med Python-programmeringsspråket med Visual Studio Code IDE.)

Die verlässliche Erzeugung einzelner Photonen mit wohldefinierten Eigenschaften in allen Freiheitsgraden ist entscheidend für die Entwicklung photonischer Quantentechnologien. Derzeit basieren die wichtigsten Einzelphotonenquellen auf dem Prozess der spontanen parameterischen Fluoreszenz (SPF), bei dem ein Pumpphoton in einem nichtlinearen Medium spontan in ein Paar aus Signal und Idlerphotonen zerfällt. Resonator-überhöhte SPF, also das Plazieren des nichtlinearen Mediums in einem optischen Resonator, ist ein weit verbreitetes Verfahren, um Einzelphotonenquellen mit erhöhter Helligkeit und angepassten spektralen Eigenschaften zu konstruieren. Das Anpassen der spektralen Eigenschaften durch gezielte Auswahl der Resonatoreigenschaften ist besonders für hybride Quantentechnologienvon Bedeutung, welche darauf abzielen, unterschiedliche Quntensysteme so zu kombinieren, dass sich deren Vorteile ergänzen. Diese Arbeit stellt eine umfassende theoretische und experimentelle Analyse der dreifach resonanten SPF vor. Das aus der Literatur bekannte theoretische Modell wird diesbezüglich verbessert, dass der Einfluss sämtlicher Eigenschaften des Resonators auf die wichtigen experimentellen Größen (z.B. die Erzeugungsrate) gezielt ausgewertet werden kann. Dieses verbesserte und hoch genaue Modell stellt eine wichtige Grundlage für die Entwicklung und Optimierung neuartiger Photonenpaarquellen dar. Im experimentellen Teil dieser Arbeit wird der Aufbau und die Charakterisierung einer dreifach resonanten Photonenpaarquellen präsentiert. Die neu entwickelte digitale Regelelektronik sowie ein hochstabiler, schmalbandiger Monochromator welcher auf monolitischen, polarisationsunabhängigen Fabry-Pérot Resonatoren basiert, werden vorgestellt. Indem diese temperaturstabilisierten Resonatoren als Spetrumanalysator verwendet werden, wird zum ersten Mal die Frequenzkammstruktur des Spektrums der erzeugten Signal- und Idlerphotonen nachgewiesen. Des Weiteren wird der Einfluss der Pumpresonanz auf die Korrelationsfunktion und die Zweiphotoneninterferenz von Signal- und Idlerphotonen simuliert und vermessen. Abschließend werden Experimente aus dem Bereich der hybriden Quantennetzwerke präsentiert, in welchen Quantenfrequenzkonversion verwendet wird um die erzeugten Signalphotonen in das Telekommunikationsband zu transferieren. Dabei wird nachgewiesen, dass das temporale Wellenpaket durch die Konversion nicht beeinflusst wird und aufgezeigt, wie Quantennetzwerke von kommerziellen Telekommunikationstechnologien profitieren können. / The consistent generation of single photons with well-defined properties in all degrees of freedom is crucial for the development of photonic quantum technologies. Today, the most prominent sources of single photons are based on the process of spontaneous parametric down-conversion (SPDC) where a pump photon spontaneously decays into a pair of signal and idler photons inside a nonlinear medium. Cavity-enhanced SPDC, i.e., placing the nonlinear medium inside an optical cavity, is widely used to build photon-pair sources with increased brightness and tailored spectral properties. This spectral tailoring by selective adjustment of the cavity parameters is of particular importance for hybrid quantum technologies which seek to combine dissimilar quantum systems in a way that their advantages complement each other. This thesis provides a comprehensive theoretical and experimental analysis of triply-resonant cavity-enhanced SPDC. We improve the theoretical model found in the literature such that the influence of all resonator properties on the important experimental parameters (e.g., the generation rate) can be analyzed in detail. This convenient and highly accurate model of cavity-enhanced SPDC represents an important basis for the design and optimization of novel photonpair sources. The experimental part of this thesis presents the setup and characterization of a triply-resonant photon-pair source. We describe the digital control system used to operate this source over days without manual intervention, and we present a highly stable, narrow-linewidth monochromator based on cascaded, polarization-independent monolithic Fabry-Pérot cavities. Utilizing these temperature-stabilized cavities as a spectrum analyzer, we verify, for the first time, the frequency comb spectral structure of photons generated by cavity-enhanced SPDC. We further simulate and measure the impact of the pump resonance on the temporal wave-packets and the two-photon interference of signal and idler photons. Finally, we present a series of experiments in the context of hybrid quantum networks where we employ quantum frequency conversion (QFC) to transfer the generated signal photons into the telecommunication band. We verify the preservation of the temporal wave-packet upon QFC and highlight how quantum networks can benefit from advanced commercial telecommunication technologies.