On the internal signature and minimal electric network realizations of reciprocal behaviors

In a recent paper, it was shown that (i) any reciprocal system with a proper transfer function possesses a signature-symmetric realization in which each state has either even or odd parity; and (ii) any reciprocal and passive behavior can be realized as the driving-point behavior of an electric network comprising resistors, inductors, capacitors and transformers. These results extended classical results to include uncontrollable systems. In this paper, we establish new lower bounds on the number of states with even parity (capacitors) and odd parity (inductors) for reciprocal systems that need not be controllable

On the internal signature and minimal electric network realizations of reciprocal behaviors

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.In a recent paper, it was shown that (i) any reciprocal system with a proper transfer function possesses a signature-symmetric realization in which each state has either even or odd parity; and (ii) any reciprocal and passive behavior can be realized as the driving-point behavior of an electric network comprising resistors, inductors, capacitors and transformers. These results extended classical results to include uncontrollable systems. In this paper, we establish new lower bounds on the number of states with even parity (capacitors) and odd parity (inductors) for reciprocal systems that need not be controllable

Augmented Reticular Thalamic Bursting and Seizures in Scn1a-Dravet Syndrome

Loss of function in the Scn1a gene leads to a severe epileptic encephalopathy called Dravet syndrome (DS). Reduced excitability in cortical inhibitory neurons is thought to be the major cause of DS seizures. Here, in contrast, we show enhanced excitability in thalamic inhibitory neurons that promotes the non-convulsive seizures that are a prominent yet poorly understood feature of DS. In a mouse model of DS with a loss of function in Scn1a, reticular thalamic cells exhibited abnormally long bursts of firing caused by the downregulation of calcium-activated potassium SK channels. Our study supports a mechanism in which loss of SK activity causes the reticular thalamic neurons to become hyperexcitable and promote non-convulsive seizures in DS. We propose that reduced excitability of inhibitory neurons is not global in DS and that non-GABAergic mechanisms such as SK channels may be important targets for treatment

Multiphoton Quantum Optics and Quantum State Engineering

We present a review of theoretical and experimental aspects of multiphoton quantum optics. Multiphoton processes occur and are important for many aspects of matter-radiation interactions that include the efficient ionization of atoms and molecules, and, more generally, atomic transition mechanisms; system-environment couplings and dissipative quantum dynamics; laser physics, optical parametric processes, and interferometry. A single review cannot account for all aspects of such an enormously vast subject. Here we choose to concentrate our attention on parametric processes in nonlinear media, with special emphasis on the engineering of nonclassical states of photons and atoms. We present a detailed analysis of the methods and techniques for the production of genuinely quantum multiphoton processes in nonlinear media, and the corresponding models of multiphoton effective interactions. We review existing proposals for the classification, engineering, and manipulation of nonclassical states, including Fock states, macroscopic superposition states, and multiphoton generalized coherent states. We introduce and discuss the structure of canonical multiphoton quantum optics and the associated one- and two-mode canonical multiphoton squeezed states. This framework provides a consistent multiphoton generalization of two-photon quantum optics and a consistent Hamiltonian description of multiphoton processes associated to higher-order nonlinearities. Finally, we discuss very recent advances that by combining linear and nonlinear optical devices allow to realize multiphoton entangled states of the electromnagnetic field, that are relevant for applications to efficient quantum computation, quantum teleportation, and related problems in quantum communication and information.Comment: 198 pages, 36 eps figure

광자 띠꼬리 상태의 실험적 입증과 이에 기반한 레이저 특성의 제어

학위논문 (박사)-- 서울대학교 대학원 : 자연과학대학 물리·천문학부, 2018. 2. 전헌수.Shaping light to generate desired optical properties is one of the important topics in optics and photonics that has been studied for a long time. A complete control over the light intensity, polarization, frequency, phase, and even the spatio-temporal distribution of electromagnetic fields is the long-sought primary objective of light shaping, which can be the base technology for applied science and industry that handles the shape of light, leading to advanced optical functionalities and next generation photonic devices. The study of light shaping is considered to be the process of controlling the shape of light by manipulating the spatial and temporal optical properties of material, with understanding of electromagnetic properties of the medium in which light propagates. Historically, material properties of media have been a major methodology, which is represented by the dispersion relation on wavelength, birefringence on polarization, and nonlinearity. However, research on structural properties such as reflection, diffraction, and scattering at the interface, originated from the spatial arrangement of materials, is being actively carried out as well, consisting a large branch of modern photonics including photonic crystals, metamaterials, and topological photonics. The essence of studying light shaping is then to generate the structured light, using these material and structural methodologies, in order to improve an existing optical system and to develop new photonic devices. Thus, within a finite material pool, the issues of shaping light eventually result in a problem of the spatio-temporal arrangement of materials. The structure based on the periodic arrangement is used in many fields due to the intuitive design, but this approach is difficult to apply to optical systems which require complexity, because of the limited structural parameters. On the other hand, an optically disordered system which randomly arranges materials without specific restrictions provides vast degrees of structural freedom that increase according to the system size, but consumes a large amount of resources in order to predict optical properties and to form desired light shapes. That is, the structural degree of freedom and the predictability are complementary. In this thesis, a photonic crystal alloy is proposed as an ideal compromise that can easily predict and design optical properties while ensuring sufficient structural degrees of freedom to shape light with complexity corresponding to the real world. Here, the degree of freedom increases with the diversity of photonic atoms, however, the scattering strength at each lattice site can be controlled individually and independently to design the entire system in a pixelated scheme since the underlying crystalline structure is maintained. The spectral characteristics are then investigated to reveal that the eigenmode of the proposed system is the photonic band-tail state existing in the photonic band-gap. For this state, it is experimentally confirmed that the energy range in which the states are distributed is determined by the crystalline structure and the scattering strength, and that the spatial near-field distribution varies in a wide range, including the weak and strong localization, depending on the energy of the mode and the scattering strength of the structure. These observations prove the localization of the photonic band-tail state, which was theoretically predicted in 1987. In addition, the modal properties of the photonic band-tail states are distributed in a wide spectro-spatial range across the complete band-gap and from only a few lattices to the entire structure, which is a great advantage for light shaping. The band-tail laser, a conceptually novel laser device that uses the band-tail state as a resonant mode, is proposed, and the light shaping within a membrane is demonstrated by realizing the band-tail laser in a slab waveguide embedding InAsP/InP multiple-quantum-well structure. Using only the structural parameters of the photonic crystal alloy, monotonic control of modal density from multi-mode to single-mode, and precise manipulation of both the modal energy and modal extents of a single-mode operating band-tail laser are demonstrated. Furthermore, the near-field profile of a mode can be modulated in various shapes from the fundamental shape to high-order shapes including orbital angular momentum and spiral pattern. The design of light shaping, based on structural degrees of freedom in the band tail laser, is far more intuitive and effective than any disordered system, and the range of controllable modal properties and demonstrated shaping capabilities are superior to any known laser platform. The performance of band tail lasers is also comparable to the modern cavity lasers. Therefore, the photonic band-tail state and the band-tail laser, proposed in this thesis as a light shaping platform, could incorporate the currently known small library of lasing platform and even expand its boundary by realizing elaborate light shaping with various near-field shapes, which contributes to the development of various fields that deal with the shape of light.1. Introduction 1 1.1. Shaping light 1 1.1.1. Current status of light shaping 1 1.1.2. Shaping light within a membrane 2 1.1.3. Shaping light using periodic materials 4 1.1.4. Shaping light using scattering media 5 1.1.5. Summary 6 1.2. Photonic crystals 7 1.2.1. Theoretical proposal of E. Yablonovitch: Photonic analogy of semiconductor 7 1.2.2. Photonic band structure: Blochs theorem 8 1.2.3. Photonic band-gap: Inhibition of spontaneous emission 10 1.2.4. Photonic band-edges: Slow light effects 11 1.2.5. Shaping light using photonic crystals 11 1.2.6. Issues of photonic crystals approach: Insufficient parameters 13 1.2.7. Summary 14 1.3. Anderson localization 16 1.3.1. Theoretical proposals of P. W. Anderson: Localized eigenstates in a disordered lattice 16 1.3.2. Localization of a light: White paint theory 18 1.3.3. Pioneering experiments on photon localization 19 1.3.4. Shaping light using Anderson localization principle 22 1.3.5. Issues of Anderson localization approach: Controlling vast degrees of freedom 25 1.3.6. Summary 26 1.4. Objectives of this thesis 27 1.4.1. Development of an ideal platform for shaping a confined light 27 1.4.2. Characterization of eigenstates in the proposed platform 27 1.4.3. Demonstration of light shaping on chip-scale devices 28 1.4.4. Summary 28 1.5. Conclusion 29 2. Photonic crystal alloys 33 2.1. Introduction 33 2.1.1. Disordered photonic structures for light shaping 33 2.1.2. Previous studies on lattice disorder 35 2.1.3. Previous studies on compositional disorder 38 2.1.4. Major differences between the two systems 41 2.1.5. Summary 42 2.2. Photonic crystal alloys 43 2.2.1. Motivation: Preserving the crystalline symmetry 43 2.2.2. Quantification of the system 44 2.2.3. Fourier analysis: Ordered and disordered components 47 2.2.4. Summary 50 2.3. Optical activation 51 2.3.1. Motivation: Examining all eigenmodes in the system 51 2.3.2. Planar waveguide: Confining light within 2D slab structure 52 2.3.3. Multiple-quantum-well structure: Quantum confinement of charge carriers 53 2.3.4. Laser operation: Exclusive study of eigenstates 55 2.3.5. Summary 57 2.4. Experimental tools 58 2.4.1. Sample preparation 58 2.4.2. Photoluminescence measurement 60 2.4.3. Near-field measurement 63 2.4.4. Simulation method 69 2.4.5. Summary 70 2.5. Conclusion 71 3. Photonic band-tail states 75 3.1. Introduction 75 3.1.1. Theoretical predictions of S. John: Localized states inside the band-gap 75 3.1.2. Expected modal properties: Energy dependence of localization 76 3.1.3. Previous studies on photonic band-tail states 77 3.1.4. Prerequisites for photonic band-tail states 83 3.1.5. Summary 84 3.2. System of interest 85 3.2.1. Photonic crystal alloy with random configuration: Maintaining band properties 85 3.2.2. Hexagonal crystal structure: Wide band-gap 87 3.2.3. Slab waveguide embedding MQWs: Purcell enhancements of localized eigenstates 88 3.2.4. Summary 90 3.3. Photoluminescence characterization 91 3.3.1. Spectral response: Lasing modes developed inside band-gap 91 3.3.2. Statistical identification of photonic band-tail states 95 3.3.3. Band-gap narrowing: Explanation based on virtual crystal approximation 97 3.3.4. Exponentially increasing penetration depth 99 3.3.5. Gain overlap factor for lasing states 100 3.3.6. Bloch states vs. band-tail states 102 3.3.7. Lasing performance of band-tail states 104 3.3.8. Excitation dependence of modal energy 106 3.3.9. Summary 108 3.4. Near-field characterization 110 3.4.1. Eigenmode profiles: The most direct evidence of localization 110 3.4.2. Weak and strong localization 115 3.4.3. Quantification of modal extents 117 3.4.4. Localization of photonic band-tail states 118 3.4.5. Energy dependence of localization: Explanation based on envelope function of band-tail states 120 3.4.6. Mean free path and Ioffe-Regel factor 121 3.4.7. Eigenmode profiles of the other band-tail states 124 3.4.8. Eigenmode profiles in momentum space 125 3.4.9. Effective width in momentum space 129 3.4.10. Resolution dependence of Fourier space 131 3.4.11. Boundary dependence of modal extents 133 3.4.12. Excitation dependence of modal extents 134 3.4.13. Summary 137 3.5. Conclusion 140 4. Shaping band-tail lasers 145 4.1. Introduction 145 4.1.1. Random lasers: Laser in scattering media 145 4.1.2. Previous studies on shaping random laser 147 4.1.3. Recent approaches: Access to internal degree of freedom 151 4.1.4. Band-tail laser: Laser device based on band-tail states 153 4.1.5. Advantages for light shaping 154 4.1.6. Summary 155 4.2. Shaping modal densities 156 4.2.1. Main idea for shaping modal density: Controlling photonic density of states 156 4.2.2. Spectral response: The single-mode random laser 157 4.2.3. Near-field profiles: Elimination of peripheral modes 163 4.2.4. Lasing performances: Compared to state-of-the-art cavity lasers 165 4.2.5. Boundary dependence of modal properties 168 4.2.6. Dominant loss channel in a band-tail laser 170 4.2.7. Summary 172 4.3. Shaping modal properties 173 4.3.1. Main idea for shaping modal properties: Adjusting basis scattering elements 173 4.3.2. Spectral response: Wide and precise control of lasing modes 175 4.3.3. Degree of freedom in 2D parameter space: Exclusive modal control on both energy and confinement 178 4.3.4. Computational evidences of measured results 181 4.3.5. Computational evidences for the generality 183 4.3.6. Summary 185 4.4. Shaping near-field profiles 186 4.4.1. Main idea for shaping near-field profiles: Engineering a configuration to place scatterers 186 4.4.2. C6symmetric configuration for symmetric profiles 187 4.4.3. Spectro-spatial response: Rough tuning with configuration 188 4.4.4. Near-field shaping: From fundamental to high-order shapes 190 4.4.5. Orbital angular momentum and spiral pattern of confined light 193 4.4.6. Summary 195 4.5. Conclusion 197 5. Conclusion and outlook 201 References 205 국문 초록 217Docto

Augmented Reticular Thalamic Bursting and Seizures in Scn1a-Dravet Syndrome

Loss of function in the Scn1a gene leads to a severe epileptic encephalopathy called Dravet syndrome (DS). Reduced excitability in cortical inhibitory neurons is thought to be the major cause of DS seizures. Here, in contrast, we show enhanced excitability in thalamic inhibitory neurons that promotes the non-convulsive seizures that are a prominent yet poorly understood feature of DS. In a mouse model of DS with a loss of function in Scn1a, reticular thalamic cells exhibited abnormally long bursts of firing caused by the downregulation of calcium-activated potassium SK channels. Our study supports a mechanism in which loss of SK activity causes the reticular thalamic neurons to become hyperexcitable and promote non-convulsive seizures in DS. We propose that reduced excitability of inhibitory neurons is not global in DS and that non-GABAergic mechanisms such as SK channels may be important targets for treatment.In a mouse model of Dravet syndrome (DS) resulting from voltage-gated sodium channel deficiency, Ritter-Makinson et al. find that inhibitory neurons of the reticular thalamic nucleus are paradoxically hyperexcitable due to compensatory reductions in a potassium SK current. Boosting this SK current treats non-convulsive seizures in DS mice

Measurement techniques for the characterization of radio frequency gallium nitride devices and power amplifiers

The rapid growth of mobile telecommunications has fueled the development of the fifth generation (5G) of standards, aiming to achieve high data rates and low latency. These capabilities make use of new regions of spectrum, wider bandwidths and spectrally efficient modulations. The deployment of 5G relies on the development of radio-frequency (RF) technology with increased performance. The broadband operation at high-power and high-frequency conditions is particularly challenging for power amplifiers (PA) in transmission stages, which seek to concurrently maximize linearity and energy efficiency. The properties of Gallium Nitride (GaN) allow the realization of active devices with favorable characteristics in these applications. However, GaN high-electron mobility transistors (HEMTs) suffer from spurious effects such as trapping due to physical defects introduced during the HEMT growth process. Traps dynamically capture and release mobile charges depending on the applied voltages and temperature, negatively affecting the RF PA performance. This work focuses on the development of novel measurement techniques and setups to investigate trapping behavior of GaN HEMTs and PAs. At low-frequency (LF), charge dynamics is analyzed using pulsed current transient characterizations, identifying relevant time constants in state-of-the-art GaN technologies for 5G. Instead, at high-frequency, tailored methods and setups are used in order to measure trapping effects during the operation of HEMTs and PAs in RF modulated conditions. These RF characterizations emulate application-like regimes, possibly involving the control of the device’s output load termination. Therefore, an innovative wideband active load pull (WALP) setup is developed, using the acquisition capabilities of standard vector-network-analyzers. Moreover, the implications of performing error-vector-magnitude characterizations under wideband load pull conditions are studied. Finally, an efficient implementation of a modified-Volterra model for RF PAs is presented, making use of a custom vector-fitting algorithm to simplify the nonlinear memory operators and enable their realization in simulation environments

Ensemble of coupling forms and networks among brain rhythms as function of states and cognition

We acknowledge support from the W. M. Keck Foundation, and the US Israel Binational Science Foundation (BSF Grant 2020020). We also thank Dr. Sergi Garcia-Retortillo for stimulating discussions and helpful comments on the manuscript.The current paradigm in brain research focuses on individual brain rhythms, their spatiotemporal organization, and specific pairwise interactions in association with physiological states, cognitive functions, and pathological conditions. Here we propose a conceptually different approach to understanding physiologic function as emerging behavior from communications among distinct brain rhythms. We hypothesize that all brain rhythms coordinate as a network to generate states and facilitate functions. We analyze healthy subjects during rest, exercise, and cognitive tasks and show that synchronous modulation in the microarchitecture of brain rhythms mediates their cross-communications. We discover that brain rhythms interact through an ensemble of coupling forms, universally observed across cortical areas, uniquely defining each physiological state. We demonstrate that a dynamic network regulates the collective behavior of brain rhythms and that network topology and links strength hierarchically reorganize with transitions across states, indicating that brain-rhythm interactions play an essential role in generating physiological states and cognition.W.M. Keck FoundationUS-Israel Binational Science Foundation 202002