As systems/structures get smaller we need to take into account noise and quantum effects and so, we need to develop some quantum devices. Quantum devices work using quantum principles like qubits that have already been developed, i.e., superconducting qubits that are going to be discussed in chapter 1. Initially, scientists wanted to use qubits to do quantum computations, this is not easy so scientists developed methods to do something different, e.g. quantum metamaterials. Here in this thesis we describe two examples of quantum devices. Our first device is the parametric quantum amplifier. Used when we need to amplify very weak signals. Amplifying a weak signal on the nanoscale is a very big challenge, this is due to classical and quantum noise, and so, we need to employ quantum physics to resolve this issue. The proposed two-qubit system amplifies weak signals at very small scales. We have shown that we can construct a multitude of novel devices on the nano-scale with the use of qubits Our second device uses harmonic mixing. It can be used where rectification is needed, for example, when we need to rectify some fluctuations and in principle some quantum fluctuations in order to pump either an excited or ground state of the two qubit device. In this thesis we propose how to do this. Firstly, we propose that if we apply harmonic mixing of two signals for two qubits, using the structure of the equation and basically the structure of quantum mechanics we can pump a desirable quantum state. We can pump either the upper or ground state by changing the signal.

<p>This thesis explores the use of nonlinear crystals from theKTiOPO₄(KTP) family with the aim to extend the possibleapplications for laser sources and to gain more knowledge aboutthe material’s benefits and limits. The work focussed onoptical parametric oscillators (OPOs) and optical parametricamplifiers (OPAs), which employ second order nonlinearprocesses. Both devices transfer energy from a laser beam at aparticular wavelength to a different wavelength, which istuneable. In OPOs two new beams at different wavelengths aregenerated, whereas in OPAs an existing weak beam is amplified.The essential part of these devices, which enables theoccurrence of the energy conversion, is a nonlinear crystal. Inthis work the ferroelectric crystals KTP and RbTiOPO₄(RTP) have been utilized.</p><p>By modifying the material’s structure,quasi-phasematching can be obtained, which is a crucialrequirement for achieving efficient energy conversion betweenthe incident and the generated waves. The fabrication ofquasi-phasematched crystals is dependent on the controlledreversion of the material’s spontaneous polarisation,which is accomplished by periodic electric field poling.</p><p>Nanosecond pulses of more than 200 kW were generated in the“eye-safe”region by employing a double pass OPA.Small signal gains exceeding 75 dB were obtained for anessentially diffraction limited beamwithout spectralbroadening of the seed. By subsequent signal coupling intofibres substantial broadening was accomplished. A systematicmeasurement series of several RTP crystals allowed us toaccurately determine the wavelength and temperature dispersionof the refractive index, which are two essential requirementsfor further employment of this material. The OPOs based on RTPwere widely tuneable by controlling the temperature. It wasalso concluded that RTP behaves similar to KTP in parametricdevices, thus being a material, which can sustain high powers,possesses large nonlinear coefficients and can operate in abroad wavelength region.Efficient Raman oscillation concurrent with parametricoscillation was observed and analysed in several KTP samples.This gave further insight into the processes taking placeinside the material when performing as a frequency converter,if the generated idler lies in the absorption band.This thesis also covers the investigation of afemtosecond optical parametric chirped pulse amplifier.Temporally stretched seed pulses were amplified to 85 µJ,resulting in a gain above 60 dB, and subsequent recompressionresulted in 270 fs pulses.</p><p><b>Keywords:</b>nonlinear optics, KTiOPO₄, optical parametric oscillator, optical parametricamplifier, RbTiOPO₄, quasi-phasematching, electric field poling,stimulated Raman scattering.</p>

This thesis explores the use of nonlinear crystals from theKTiOPO4(KTP) family with the aim to extend the possibleapplications for laser sources and to gain more knowledge aboutthe material’s benefits and limits. The work focussed onoptical parametric oscillators (OPOs) and optical parametricamplifiers (OPAs), which employ second order nonlinearprocesses. Both devices transfer energy from a laser beam at aparticular wavelength to a different wavelength, which istuneable. In OPOs two new beams at different wavelengths aregenerated, whereas in OPAs an existing weak beam is amplified.The essential part of these devices, which enables theoccurrence of the energy conversion, is a nonlinear crystal. Inthis work the ferroelectric crystals KTP and RbTiOPO4(RTP) have been utilized. By modifying the material’s structure,quasi-phasematching can be obtained, which is a crucialrequirement for achieving efficient energy conversion betweenthe incident and the generated waves. The fabrication ofquasi-phasematched crystals is dependent on the controlledreversion of the material’s spontaneous polarisation,which is accomplished by periodic electric field poling. Nanosecond pulses of more than 200 kW were generated in the“eye-safe”region by employing a double pass OPA.Small signal gains exceeding 75 dB were obtained for anessentially diffraction limited beamwithout spectralbroadening of the seed. By subsequent signal coupling intofibres substantial broadening was accomplished. A systematicmeasurement series of several RTP crystals allowed us toaccurately determine the wavelength and temperature dispersionof the refractive index, which are two essential requirementsfor further employment of this material. The OPOs based on RTPwere widely tuneable by controlling the temperature. It wasalso concluded that RTP behaves similar to KTP in parametricdevices, thus being a material, which can sustain high powers,possesses large nonlinear coefficients and can operate in abroad wavelength region.Efficient Raman oscillation concurrent with parametricoscillation was observed and analysed in several KTP samples.This gave further insight into the processes taking placeinside the material when performing as a frequency converter,if the generated idler lies in the absorption band.This thesis also covers the investigation of afemtosecond optical parametric chirped pulse amplifier.Temporally stretched seed pulses were amplified to 85 µJ,resulting in a gain above 60 dB, and subsequent recompressionresulted in 270 fs pulses. <b>Keywords:</b>nonlinear optics, KTiOPO4, optical parametric oscillator, optical parametricamplifier, RbTiOPO4, quasi-phasematching, electric field poling,stimulated Raman scattering. / NR 20140805

We explore the optical parametric amplifier, an optical device where a pump field creates a pair of lower-frequency fields: signal and idler. The pump field is usually treated classically, but this thesis focuses on scenarios where the pump must be treated quantum mechanically. One of these scenarios is the growing field of nonlinear interferometry, where the fundamental sensitivity of a probed relative phase can beat the classical bounds and reach the maximum limit allowed by quantum mechanics, the Heisenberg limit. Indeed, we show that a fully quantum nonlinear interferometer displays a Heisenberg scaling in terms of the mean number of input pump photons. This result goes beyond the well-accepted Heisenberg scaling with respect to the down-converted photons inside the interferometer, which predicts unphysical phase sensitivities starting at a particular input pump energy. Our theoretical findings are particularly useful when designing a nonlinear interferometer with bright pump fields or optimized optical parametric amplifiers for quantum metrology and quantum imaging applications. The quantum nature of the pump field may also play a central role concerning other physical phenomena, like Hawking radiation in the context of black holes. As suggested by several authors, both the optical parametric amplifier and Hawking radiation comprise the creation of fundamental particle pairs. Thus, if the optical parametric amplifier is fully treated quantum mechanically, we may get insight into an open problem in modern physics, namely the black hole information paradox. According to this paradox, the information stored in a black hole can be destroyed once the black hole has evaporated by emitting Hawking radiation, contradicting quantum mechanics. Despite the experimental efforts to build systems that reproduce event horizons and gravitational effects in the laboratory, the evaporation of black holes due to the emission of Hawking radiation remains a challenging task. In this thesis, we experimentally investigate the impact of an evolving pump field in an optical parametric amplifier by optimizing a parametric down-conversion process. We measure the pump and signal photon number properties, finding that the pump field gets chaotic and the signal coherent when the pump displays some sizeable depletion. We arrive at similar conclusions about the pump field from its measured Wigner function. Our experiment is the first step towards a successful experiment that could suggest that information in the black hole is not destroyed but encoded in the emitted Hawking radiation starting at some point in the black hole evolution. We finally discuss further experimental improvements to investigate the parallel between the optical parametric amplifier and Hawking radiation.

No description available.

This dissertation details the development of the world’s first cryogenically cooled Fe:ZnSe-based chirped pulse amplifier, a mid-wave infrared source for strong-field physics experimentation. The long upper-state lifetime provided by cryogenically cooling the Fe:ZnSe gain medium allows free-running, diode-pumped Er:YAG lasers to be used as pump lasers. The amplifier is seeded by a novel two-stage optical parametric amplifier pumped at 1 μm, which is potentially carrier-envelope phase-stable. The system is capable of producing 247-fs pulses at 333 Hz and 4.6 mJ with a center wavelength of 4.07 μm, although exact characteristics vary for different repetition rates and arrangements. The spectral bandwidth avoids strong atmospheric CO2 absorption centered around 4.3 μm, allowing operation in ambient air with good beam quality. The laser is simple, stable, reliable, and boasts a high repetition rate and average power compared to other systems. By focusing the 18-GW beam in air, harmonics up to the ninth order were observed indicating its potential for use in strong-field experimentation. Few-cycle pulses were generated by passing the beam, at a repetition rate of 400 Hz, through a large-diameter gas-filled hollow-core fiber followed by dispersion compensating bulk CaF2. A krypton-filled fiber at 370 kPa yielded 1.14-mJ, 42-fs pulses centered at 4.07-μm, while an oxygen-filled fiber at 310 kPa delivered 0.78-mJ, 39-fs pulses spanning 3 to 5.5 μm. This work is a step toward a high repetition rate mid-wave infrared driver of isolated attosecond, keV-level, X-ray pulses. Fe:ZnSe is a unique gain medium with potential to become a disruptive technology across a variety of fields, especially in strong-field science, in which many physical phenomena are enhanced at longer wavelengths.

Thesis (MSc)--University of Stellenbosch, 2011. / Please refer to full text to view abstract.

abstract: Kinetic inductance springs from the inertia of charged mobile carriers in alternating electric fields and it is fundamentally different from the magnetic inductance which is only a geometry dependent property. The magnetic inductance is proportional to the volume occupied by the electric and magnetic fields and is often limited by the number of turns of the coil. Kinetic inductance on the other hand is inversely proportional to the density of electrons or holes that exert inertia, the unit mass of the charge carriers and the momentum relaxation time of these charge carriers, all of which can be varied merely by modifying the material properties. Highly sensitive and broadband signal amplifiers often broaden the field of study in astrophysics. Quantum-noise limited travelling wave kinetic inductance parametric amplifiers offer a noise figure of around 0.5 K ± 0.3 K as compared to 20 K in HEMT signal amplifiers and can be designed to operate to cover the entire W-band (75 GHz – 115 GHz).The research cumulating to this thesis involves applying and exploiting kinetic inductance properties in designing a W-band orthogonal mode transducer, quadratic gain phase shifter with a gain of ~49 dB over a meter of microstrip transmission line. The phase shifter will help in measuring the maximum amount of phase shift ∆ϕ_max (I) that can be obtained from half a meter transmission line which helps in predicting the gain of a travelling wave parametric amplifier. In another project, a microstrip to slot line transition is designed and optimized to operate at 150 GHz and 220 GHz frequencies, that is used as a part of horn antenna coupled microwave kinetic inductance detector proposed to operate from 138 GHz to 250 GHz. In the final project, kinetic inductance in a 2D electron gas (2DEG) is explored by design, simulation, fabrication and experimentation. A transmission line model of a 2DEG proposed by Burke (1999), is simulated and verified experimentally by fabricating a capacitvely coupled 2DEG mesa structure. Low temperature experiments were done at 77 K and 10 K with photo-doping the 2DEG. A circuit model of a 2DEG coupled co-planar waveguide model is also proposed and simulated. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2016

Parametric amplifiers are essential for analyzing and measuring the weak signals generated byquantum circuits at cryogenic temperatures. This project aims to realize a low noise travelingwave parametric amplifier (TWPA) by exploiting the nonlinear current dependence of thekinetic inductance of superconducting NbTiN nanowires. We fabricate an inductor in theform of a compact meandering nanostructure on small chips. We describe the microwavecircuit design, the simulations performed and the fabrication recipes. We present the resultsfrom the initial measurements at low-temperature (4.2 K - 0.3 K) performed in a 3He dipstickcryostat.We analyzed two different structures in this thesis. The first design implements a co-planarwaveguide structure that operates as a multi-modal cavity with resonances that can be modifiedby adjusting geometrical parameters. In contrast, the second design attempts to eliminate theseresonances by matching the impedance of the device with that of the input and output signallines. For this reason, we adopted a microstrip structure with a top-layered ground plane.In addition, the second design allows for phase matching of the signal and idler frequenciesinvolved in parametric amplification through dispersion engineering. Finally, we determineimportant parameters like the temperature dependence of the kinetic inductance, phase velocity,and characteristic impedance of the devices at cryogenic temperatures. / Parametriska förstärkare är viktiga för att analysera och mäta svaga signalerna som genererasav kvantkretsar vid kryogeniska temperaturer. Detta projekt syftar till att realisera enresande våg parametrisk förstärkare med lågt brus (TWPA) genom att utnyttja det ickelinjäraströmberoendet hos den kinetiska induktansen i supraledande NbTiN- nanotrådar. Vitillverkar en spole i form av en kompakt slingrande nanostruktur på små chips. Vibeskriver mikrovågskretsdesignen, simuleringarna som utförs samt tillverkningsprocesserna.Vi presenterar resultaten från de initiala mätningarna vid låga temperaturer (4.2 K - 0.3 K)utförda i en 3He stickkryostat.Vi analyserade två olika strukturer i detta arbete. Den första designen implementerar enkoplanar vågledarstruktur som fungerar som en multimodal kavitet med resonanser som kanmodifieras genom att justera geometriska parametrar. Däremot syftar den andra designenatt eliminera dessa resonanser genom att matcha enhetens impedans med den för ingångs-och utgångssignallinjerna. Av denna anledning valde vi en mikrostripstruktur med ettjordplan i toppskiktet. Dessutom tillåter den andra designen fasanpassning av signalen ochidlerfrekvenserna som är en del av den parametriska förstärkningen genom dispersionsteknik.Slutligen tar vi reda på viktiga parametrar som temperaturberoendet för den kinetiskainduktansen, fashastigheten och den karakteristiska impedansen för proven vid kryogeniskatemperaturer.

Nonlinear optical interaction in quasi-phase-matched structures opens up unique possibilities to build compact and efficient parametric devices such as optical parametric oscillators, generators, and amplifiers with tailored spectral properties. The focus of this thesis is on novel parametric interactions with periodically-poled KTiOPO4 (PPKTP) as the parametric gain medium. Optical parametric oscillators (OPOs) are attractive light sources for many applications, particularly in spectroscopy, and plays a central role in this thesis. Special attention is put on simple, yet powerful, spectral-manipulation and bandwidth-narrowing techniques for OPOs. The overall knowledge gained from these studies has been used for device construction of several tunable ultraviolet sources for biological sensing. In the case of bandwidth narrowing, the observation of decreasing spectral bandwidth in a noncollinear, idler-resonant OPO, as compared with a signal-resonant one, has been found to be due to the interplay between the material properties and the angular dispersion of PPKTP. To further reduce the bandwidth, we have shown that it is very beneficial to replace the output mirror in an OPO with a bulk Bragg grating. In fact, even close to degeneracy, where the bandwidth is typically wide, this approach is able to decrease the bandwidth drastically. Moreover, different OPO cavity designs have been examined in order to spectrally manipulate the resonant waves. By deploying a grating in a ring OPO cavity, it becomes possible to access the resonant wave and spectrally manipulated it in a zero-dispersion arrangement; the filtered wave is subsequently sent back into its own cavity as a seed signal, in a self-seeding arrangement. This particular cavity design decreases the bandwidth close to ~ 1000 times as compare to the free-running mode. An interesting phenomenon arises when two mutually coherent laser beams are used to pump a linear OPO cavity. When the pump beams intersect within the PPKTP crystal, an interference grating is formed and acts as a catalyst for the generation of new spectral sidebands through multiple cascaded four-wave mixing, in the pump, the idler and the signal directions. The spacing of these sidebands is determined geometrically by the incident pump angle, while the signals are continuously tunable over the c-band telecom window (λ ~ 1.5 μm) by rotating the cavity. Ultrabroad bandwidths have been generated in an optical parametric generator (OPG) pumped by an amplified picosecond Ti:sapphire laser. In the collinear direction the output spectrum extends over three octaves in the mid-infrared region. This enormously broad spectrum is also Fourier-filtered and subsequently used for narrowband seeding of an optical parametric amplifier (OPA). Finally, the spectral range between 285 nm and 340 nm is of importance for detection of biological substances through fluorescence spectroscopy. With this spectral region in mind a practical way to generate a tunable parametric device in the ultraviolet region is presented in the thesis. The developed ultraviolet laser is used for studies of the characteristics of biological particles. The ultraviolet source and the results from these studies, will be utilized in an integrated detection system, a so called early-warning system. / QC 20100923