Kyungsun Na, Gonzalo Ordonez, Sungyun Kim
It is shown that in a double-cavity, two-dimensional electron waveguide, the interplay between quasi-bound states of each cavity leads to the appearance of bound states in continuum for certain distances between the cavities. These bound states may be used to trap electrons in de-localized states distributed in both cavities.
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Bound state in the continuum and multiple atom state transfer applications in a waveguide QED setup
本研究在波导量子电动力学设置中实现了束缚于连续态的态，用于高保真度的多原子态转移，展示了其在量子信息处理中的应用潜力。
We develop a formalism for modelling exact time dynamics in waveguide quantum electrodynamics (QED) using the real-space approach. The formalism does not assume any specific configuration of emitters and allows the study of Markovian dynamics fully analytically and non-Markovian dynamics semi-analytically with a simple numerical integration step. We use the formalism to study subradiance, superradiance and bound states in continuum. We discuss new phenomena such as subdivision of collective decay rates into symmetric and anti-symmetric subsets and non-Markovian superradiance effects that can l…
In quantum communication and distributed quantum computing, one-dimensional waveguides provide directional transfer of quantum information. A single-mode waveguide has a density-of-states singularity at the lower cut-off frequency, which resembles sharp resonances of a cavity but with non-Markovian dynamics. Thus we put forward schemes of coupling atomic transitions and a waveguide continuum edge. We first present a scheme of spin-photon quantum interface operating in the non-Markovian regime for a $Λ$-type three-level system coupled to a waveguide. Then we show that strong coupling between at…
Bound state in the continuum and dynamics via phase modulation in giant-atom waveguide setups
本文研究了巨原子波导-量子电动力学系统中通过相调制控制束缚态连续谱和原子动力学的方法，揭示了相位工程在非本地光-物质接口中控制干涉、束缚态和量子动力学的重要性。
Rabi oscillation and fractional population via the bound states in the continuum in a giant atom waveguide QED setup
本文研究巨原子与耦合谐振器波导相互作用中的非马尔可夫动力学，揭示连续谱束缚态数量决定拉比振荡或分数布居行为，为控制开放量子系统耗散提供新途径。
Phase-controlled bound states in giant atom waveguide QED setup
本文研究巨原子通过两个远距离位点耦合的一维光子波导，发现相位调控的BOC和BIC，给出BOC存在条件及BIC频率与光子分布，并预测由BIC与BOC振荡诱导的量子拍，为利用束缚态操控波导系统提供新途径。
Quantum state preparation and transfer based on the bound state in the doublon continuum
研究通过强局域相互作用在耦合谐振器波导中产生双子连续谱束缚态，实现四原子纠缠态的高保真制备及量子纠缠态在不同节点间的相干传输，为波导平台的多粒子态生成与路由提供可扩展机制。
A quantum theory of light propagation in two optical channel waveguides tunnelling-coupled to a common continuum of modes (such as those of a slab waveguide) is presented, and classical and quantum interference effects are investigated. For classical light, the photonic system realizes an optical analogue of coherent population trapping in the continuum encountered in atomic physics, where destructive interference between different light leakage channels leads to the appearance of a trapped state embedded in the continuum. For nonclassical light, two-photon interference effects are predicted, …
Emergent Oscillating bound states in a semi-infinite linear waveguide with a point-like $Λ$-type quantum emitter driven by a classical field
本研究在半无限波导中耦合点状$\Lambda$型量子发射器，由经典场驱动，实现了振荡束缚态，打破了其仅存在于巨原子的限制。
Liouvillian gap closing--bound states in the continuum connection and diverse dynamics in a giant-atom waveguide QED setup
该研究在巨原子波导平台中揭示了李维拉维安间隙闭合与束缚态在连续谱形成之间的联系，并展示了通过调节BIC数量可实现多样化的动态行为。
High-fidelity Generation of Bell and W States in Giant Atom System via Bound State in the Continuum
本研究提出利用连续域束缚态在耦合谐振子波导的巨原子系统中生成高保真纠缠态的方案，Bell态保真度超98%，可扩展生成W态，纠缠态生成快且长期稳定，可在固态量子平台实现，拓展了相关系统在量子信息处理中的应用。
I review the four mechanisms of bound states in the continuum (BICs) in application to microwave and acoustic cavities open to directional waveguides. The most simple are the symmetry protected BICs which are localized inside the cavity because of the orthogonality of the eigenmodes to the propagating modes of waveguides. However, the most general and interesting is the Friedrich-Wintgen mechanism when the BICs are result of full destructive interference of outgoing resonant modes. The third type of the BICs, the Fabry-Perot BICs, occur in a double resonator system when each resonator can serv…
It is shown that two fundamentally different phenomena, the bound states in continuum and the spectral singularity (or time-reversed spectral singularity), can occur simultaneously. This can be achieved, in particular, in a rectangular core dielectric waveguide with embedded active (or absorbing) layer. In such a system a two-dimensional bound state in a continuum is created in the plane of a waveguide cross section and it is emitted or absorbed along the waveguide core. The idea can be used for experimental implementation of a laser or a coherent-perfect-absorber for photonic bound state that…
We propose a methodical approach to controlling and enhancing deviations from exponential decay in quantum and optical systems by exploiting recent progress surrounding another subtle effect: the bound states in continuum, which have been observed in optical waveguide array experiments within this past decade. Specifically, we show that by populating an initial state orthogonal to that of the bound state in continuum, it is possible to engineer system parameters for which the usual exponential decay process is suppressed in favor of inverse power law dynamics and coherent effects that typicall…
Photonic bound states in the continuum (BICs) are special localized and non-decaying states of a photonic system with a frequency embedded into the spectrum of scattered states. The simplest photonic structure displaying a single BIC is provided by two waveguides side-coupled to a common waveguide lattice, where the BIC is protected by symmetry. Here we consider such a simple photonic structure and show that, breaking mirror symmetry and allowing for non-nearest neighbor couplings, a doublet of quasi-BIC states can be sustained, enabling weakly-damped embedded Rabi oscillations of photons betw…
We present the basic ingredients of continuum optomechanics, i.e. the suitable extension of cavity-optomechanical concepts to the interaction of photons and phonons in an extended waveguide. We introduce a real-space picture and argue which coupling terms may arise in leading order in the spatial derivatives. This picture allows us to discuss quantum noise, dissipation, and the correct boundary conditions at the waveguide entrance. The connections both to optomechanical arrays as well as to the theory of Brillouin scattering in waveguides are highlighted. We identify the 'strong coupling regim…
Bound States in the Continuum in a Double Whispering Gallery Resonator
本文利用格林函数形式体系研究了单光子在一维波导耦合双回音壁谐振腔中的输运，揭示了两种连续谱束缚态的形成机制，并分析了波包存储动力学。
Geometric control of maximal entanglement via bound states in the continuum
通过几何设计控制巨原子波导中连续谱束缚态的最大纠缠特性。
The paper proposes an envelope soliton model of the electron. The soliton propagates within a waveguide which size varies with the potential. The soliton is the solution of the Schroedinger equation with the addition of a nonlinear term that is the negative of Bohm's Quantum potential. This potential is interpreted as representing the dispersion of the linear equation. The model is based on de Broglie's original wave-particle concept, which is based on the Special theory of relativity. The model thus illustrates that theory.
We present a calculation of the shot noise in a ballistic electron waveguide square root of NOT gate. A general expression for the shot noise in the leads connected to these types of gates is shown. We then parameterize an S-matrix which qualitatively describes the action of a square root of NOT gate previously found through numerical methods for GaAs/Al_xGa_{1-x}As based waveguides systems. Using this S-matrix, the shot noise in a single output lead and across two output leads is calculated. We find that the measurement of the shot noise across two output leads allows for the determination of…
We study a system made up of one or two two-level quantum emitters, coupled to a single transverse mode of a closed waveguide, in which photon wavenumbers and frequencies are discretized, and characterize the stable states in which one excitation is steadily shared between the field and the emitters. We unearth finite-size effects in the field-emitter interactions and identify a family of dressed states, that represent the forerunners of bound states in the continuum in the limit of an infinite waveguide. We finally consider the potential interest of such states for applications in the field o…
We discuss the properties of atom-photon bound states in waveguide QED systems consisting of single or multiple atoms coupled strongly to a finite-bandwidth photonic channel. Such bound states are formed by an atom and a localized photonic excitation and represent the continuum analog of the familiar dressed states in single-mode cavity QED. Here we present a detailed analysis of the linear and nonlinear spectral features associated with single- and multi-photon dressed states and show how the formation of bound states affects the waveguide-mediated dipole-dipole interactions between separated…
We present a small network for the testing of the entanglement of two ballistic electron waveguide qubits. The network produces different output conditional on the presence or absence of entanglement. The structure of the network allows for the determination of successful entanglement operations through the measurement of the output of a single qubit. We also present a simple model of a dynamic coulomb-like interaction and use it to describe some characteristics of a proposed scheme for the entanglement of qubits in ballistic electron waveguides.
Quantum sensing and metrology with free electrons
本文提出利用自由电子与波导光的强耦合，解决高光子数态的产生与探测难题，实现光学相位灵敏度提升十倍，并以兆赫兹速率生成数十光子NOON态，开创自由电子量子传感新技术。
Single-photon scattering and bound states in a one-dimensional waveguide with topological giant atom
本文研究CRW与有限SSH链构成的TGA经两个远端位点耦合时的单光子散射与束缚态，通过调制拓扑相位实现光子完全反射或透射，并获得连续谱上下两对束缚态。
Bound states in the continuum in a fluxonium qutrit
本文通过将fluxonium投影到三能级子空间，分析其第二激发能级在超导波导连续谱中形成的BIC，并评估噪声下的寿命与制备时间。
In this paper, the control of the edge-mode spectrum of integer-Hall-effect 2D waveguides by electric field is proposed and modeled with the effective mass approach. Under certain found conditions, the applied transversal electric field allows refining the modal spectrum from non-localized waves, and, additionally, it can switch the edge-mode from the propagating to the evanescent state, and it is interesting in the design of the edge-mode off and on logic components. These waveguides, arbitrary biased by potentials, are described by the Pauli spin-less charge equation, and they are simulated …
We propose a novel ultrafast electronic switching device based on dual-graphene electron waveguides, in analogy to the optical dual-channel waveguide device. The design utilizes the principle of coherent quantum mechanical tunneling of Rabi oscillations between the two graphene electron waveguides. Based on a modified coupled mode theory, we construct a theoretical model to analyse the device characteristics, and predict that the swtiching speed is faster than 1 ps. Due to the long mean free path of electrons in graphene at room temperature, the proposed design avoids the limitation of low tem…
The photonic bound state in the continuum (BIC) is discovered in a hybrid photonic circuit with low refractive index waveguide on a high refractive index thin membrane, where the optical dissipation is forbidden because of the destructive interference of different leakage channels. Based on the photonic BIC, the low mode area in a hybrid waveguide and high quality factor in a microresonator can be applied to enhance the light-matter interaction. Taking the fabrication-friendly polymer structure on diamond membrane as an example, those excellent optical performances can exist in a wide range of…
We study many-particle phenomena of propagating multi-mode photons and phonons interacting through Brillouin scattering-type Hamiltonian in nanoscale waveguides. We derive photon and phonon retarded Green's functions and extract their spectral functions in applying the factorization approximation of the mean-field theory. The real part of the self-energy provides renormalization energy shifts for the photons and the phonons. Besides the conventional leaks, the imaginary part gives effective photon and phonon damping rates induced due to many-particle phenomena. The results extend the simple sp…
In this paper, we provide a rigorous quantum mechanical derivation for the coherent photon transport characteristics of a two-level atom coupled to a waveguide without linearizing the coupling coefficient between the light and the atom. We propose a novel single frequency sampling method utilizing a UV-cutoff that allows us to treat the singularities in real space scattering potential despite the non-convergence property. We also study the conditions under which the linearization of the coupling coefficient is an accurate assumption and find the resulting spontaneous emission and transport cha…
Ultrahigh free-electron Kerr nonlinearity in all-semiconductor waveguides for all-optical nonlinear modulation of mid-infrared light
本研究通过全半导体波导实现超高水平自由电子 Kerr 非线性，用于中红外光的高效非线性调制，为光子集成电路发展提供新途径。
Electron quantum optics with beam splitters and waveguides in Dirac Matter
本文研究Dirac型物质中飞行电子的波函数分束与传播，分析分束器、超聚焦器和纳米带波导，指出波形、几何与能量需平衡以提升概率密度和寿命。
Excitation of a bound state in the continuum (BIC) through scattering is problematic since it is by definition uncoupled. Here, we consider a type of dressed BIC and show that it can be excited in a nonlinear system through multi-photon scattering and delayed quantum feedback. The system is a semi-infinite waveguide with linear dispersion coupled to a qubit, in which a single-photon, dressed BIC is known to exist. We show that this BIC can be populated via multi-photon scattering in the non-Markovian regime, where the photon delay time (due to the qubit-mirror distance) is comparable with the …
We characterize low-loss electron-beam evaporated niobium thin films deposited under ultra-high vacuum conditions. Slow deposition yields films with a high superconducting transition temperature ($9.20 \pm 0.06 \rm ~K$) as well as a residual resistivity ratio of $4.8$. We fabricate the films into coplanar waveguide resonators to extract the intrinsic loss due to the presence of two-level-system fluctuators using microwave measurements. For a coplanar waveguide resonator gap of $2~μ\rm m$, the films exhibit filling-factor-adjusted two-level-system loss tangents as low as $1.5 \times 10^{-7}$ wi…
In this paper, we propose an effective model including a macroscopic Hamiltonian to describe the interactions between a two-level atom and scattered light in a 1-D dielectric waveguide. The proposed formalism allows us to incorporate the effect of changing optical media inside the continuum while demonstrating a non-classical derivation of Fresnel Law. We obtain the transport characteristics of the two-level system, explore its high-Q bandreject filter property and discuss the implications of radiative and non-radiative dissipation. In addition, we apply our formalism to a modified Fabry-Pérot…
By restricting the spatial energy transmission of an electromagnetic wave, dielectric waveguides transmit light over long distances at sustained intensity. Waveguides have been used in the microwave and optical range to maintain strong signal intensities in connection with lasers, but guiding of intense short-wavelength radiation such as x-rays has proven more cumbersome. Here we investigate theoretically how tapered x-ray waveguides can focus and guide radiation from x-ray free electron lasers. Elliptical waveguides using a cladding material with high atomic number such as platinum can mainta…
Beyond symmetry-protected BICs: transmission through asymmetric crossbar junctions in one-dimensional waveguides
本文研究了一维波导非对称交叉结中的连续谱束缚态形成，通过求解 Helmholtz 方程发现准 BICs 表现为 Fano 共振中的尖锐透射共振及品质因子发散。
Understanding and controlling the transport properties of interacting fermions is a key forefront in quantum physics across a variety of experimental platforms. Motivated by recent experiments in 1D electron channels written on the $\mathrm{LaAlO_3}$/$\mathrm{SrTiO_3}$ interface, we analyse how the presence of different forms of spin-orbit coupling (SOC) can enhance electron pairing in 1D waveguides. We first show how the intrinsic Rashba SOC felt by electrons at interfaces such as $\mathrm{LaAlO_3}$/$\mathrm{SrTiO_3}$ can be reduced when they are confined in 1D. Then, we discuss how SOC can b…
We use optimal control in order to find the optimal shapes of pulses maximizing the population transfer between two bound states which are coupled via a continuum of states. We find that the optimal bounded controls acquire the bang-interior and interior-bang form, with the bang part corresponding to the maximum allowed control value and the interior part to values between zero and the maximum. Then, we use numerical optimal control to obtain the switching times and the interior control values. We compare our results with those obtained using Gaussian STIRAP pulses, and find that the optimal m…
A waveguide coincides with a strip having two narrows of diameter $ε$. Electron motion is described by the Helmholtz equation with Dirichlet boundary condition. The part of waveguide between the narrows plays the role of resonator and there can occur electron resonant tunneling. This phenomenon consists in the fact that, for an electron with energy $E$, the probability $T(E)$ to pass from one part of the waveguide to the other part through the resonator has a sharp peak at $E=E_{res}$, where $E_{res}$ denotes a "resonant" energy. In the present paper, we compare the asymptotics of $E_{res}=E_{…
Light-matter interaction at the transition between cavity and waveguide QED
本文通过冷原子与含纳米光纤的纤维环谐振器耦合实验，研究腔QED到波导QED的过渡，发现谐振器增长会使拉比振荡消失并出现非马尔可夫特征。
Access to the electron spin is at the heart of many protocols for integrated and distributed quantum-information processing [1-4]. For instance, interfacing the spin-state of an electron and a photon can be utilized to perform quantum gates between photons [2,5] or to entangle remote spin states [6-9]. Ultimately, a quantum network of entangled spins constitutes a new paradigm in quantum optics [1]. Towards this goal, an integrated spin-photon interface would be a major leap forward. Here we demonstrate an efficient and optically programmable interface between the spin of an electron in a quan…
We present exact analytical solutions for the zero-energy modes of two-dimensional massless Dirac fermions fully confined within a smooth one-dimensional potential V(x)= - α/cosh(βx), which provides a good fit for potential profiles of existing top-gated graphene structures. We show that there is a threshold value of the characteristic potential strength α/β for which the first mode appears, in striking contrast to the non-relativistic case. A simple relationship between the characteristic strength and the number of modes within the potential is found. An experimental setup is proposed for the…
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