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Engineering bilinear mode coupling in circuit QED: Theory and experiment
摘要： Photonic states of high-Q superconducting microwave cavities controlled by superconducting transmon ancillas provide a platform for encoding and manipulating quantum information. A key challenge in scaling up the platform towards practical quantum computation is the requirement to communicate on demand the quantum information stored in the cavities. It has been recently demonstrated that a tunable bilinear interaction between two cavity modes can be realized by coupling the modes to a bichromatically driven superconducting transmon ancilla, which allows swapping and interfering the multiphoton states stored in the cavity modes [Gao et al., Phys. Rev. X 8, 021073 (2018)]. Here we explore both theoretically and experimentally the regime of relatively strong drives on the ancilla needed to achieve fast SWAP gates but which can also lead to undesired nonperturbative effects that lower the SWAP fidelity. We develop a theoretical formalism based on linear response theory that allows one to calculate the rate of ancilla-induced interaction, decay, and frequency shift of the cavity modes in terms of a susceptibility matrix. We go beyond the usual perturbative treatment of the drives by using Floquet theory, and find that the interference of the two drives can strongly alter the system dynamics even in the regime where the standard rotating wave approximation applies. The drive-induced ac Stark shift on the ancilla depends nontrivially on the drive and ancilla parameters which in turn modify the strength of the engineered interaction. We identify two major sources of infidelity due to ancilla decoherence. (i) Ancilla dissipation and dephasing lead to incoherent hopping among Floquet states which occurs even when the ancilla is at zero temperature; this hopping results in a sudden change of the SWAP rate, thereby decohering the SWAP operation. (ii) The cavity modes inherit finite decay from the relatively lossy ancilla through the inverse Purcell effect; the effect becomes particularly strong when the ac Stark shift pushes certain ancilla transition frequencies to the vicinity of the cavity mode frequencies. The theoretical predictions agree quantitatively with the experimental results, paving the way for using the developed theory for optimizing future experiments and architecture designs.
关键词： decoherence,transmon ancilla,superconducting cavities,ac Stark shift,quantum information,circuit QED,inverse Purcell effect,bilinear mode coupling,SWAP gates,Floquet theory
更新于2025-09-23 15:23:52
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New Silica Laser-Optimized Multimode Optical Fibers with Extremely Enlarged 100-??m Core Diameter for Gigabit Onboard and Industrial Networks
摘要： We present new type of silica graded index laser-optimized multimode optical fibers (LOMF) with extremely enlarged core diameter up to 100 μm and “typical” “telecommunication” cladding diameter 125 μm. This optical fiber was designed for harsh environment Gigabit onboard cable systems and industrial networks. It differs by special optimized graded refractive index profile, providing low differential mode delay (DMD) for selected guided modes. We present some results of tests, performed for manufactured pilot 520 m length of described LOMF 100/125, concerned with its geometry properties as well as key transmission parameters—attenuation and DMD map.
关键词： mode coupling,laser-based gigabit data transmission,higher-order modes,large core multimode optical fiber,differential mode delay,short-range optical networks,industrial networks,selected guided modes,on-board cable systems,few-mode regime
更新于2025-09-23 15:19:57
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Nonlinear Performance of Few-Mode Fiber Links with Intermediate Coupling
摘要： This paper reviews and extends the study of nonlinear performance of few-mode fiber links operating in all different linear coupling regimes for different mode delay maps. Nonlinear performance was estimated using the four-wave-mixing theory and the split-step Fourier method including semi-analytical solutions for linear mode coupling of arbitrary strength. The optimum link configurations minimizing the nonlinear penalty at practical levels of training sequence length are presented, including: the required coupling strength to give nonlinear distortion below that of the single-mode propagation without mode coupling, and the impact of mode delay maps. Finally, different approximate solution methods of the multimode nonlinear Schr?dinger equation are compared, highlighting the accuracy of a stochastic solution method including distributed linear mode coupling.
关键词： Mode-division multiplexing,few-mode fiber,linear mode coupling,fiber nonlinearity
更新于2025-09-19 17:15:36
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Plasmon lifetime enhancement in a bright-dark mode coupled system
摘要： Metallic nanoparticles can localize the incident light to hot spots as plasmon oscillations, where the intensity can be enhanced by up to four orders of magnitude. Even though the lifetime of plasmons is typically short, it can be increased via interactions with quantum emitters, e.g., spaser nanolasers. However, molecules can bleach in days. Here, we study the lifetime enhancement of plasmon excitations due to the coupling with longer-lifetime dark plasmon modes. We apply an analytical model based on harmonic oscillators to demonstrate that a coupled system of bright and dark plasmon modes decays more slowly than the bright mode alone. Furthermore, exact solutions of the three-dimensional Maxwell equations, i.e., finite-difference time domain, demonstrate that the lifetime of the coupled system significantly increases at the hot spot, which is not predictable by far-field response. The decay of the overall energy of such a coupled system, which can be extracted from experimental absorption measurements, is substantially different from the decay of the hot spot field. This observation enlightens the plasmonic applications in which the hot spot intensity enables the detection of the optical responses.
关键词： bright-dark mode coupling,finite-difference time domain,metallic nanoparticles,plasmon lifetime,hot spot
更新于2025-09-19 17:13:59
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Crosstalk Limitations due to Intercore Coupling on the BER Performance of an Optical Communication System with Homogeneous Multi-core Fiber
摘要： The effect of crosstalk due to inter-core coupling on the bit error rate (BER) performance of a fiber optic communication link with a homogeneous multi-core optical fiber (MCF) and a direct detection receiver with optical preamplifier is analytically evaluated and presented in this paper. Coupling coefficients due to inter-core coupling in a 7-core MCF is evaluated numerically with as a function of core-to-core distance (pitch) and relative refractive index contrast. Coupling length is determined against various index contrasts and at different core pitches. Crosstalk power, Signal to Crosstalk plus Noise Ratio (SCNR), BER and power penalty at any output core with light launched into other core of a 7-core MCF are determined analytically. The results show that there is mentionable deterioration in BER performance due to coupling induced crosstalk, and system suffers distinct power penalty at a given BER. For example, power penalty at BER of 10e-9 is found to be 4.0 dB and 4.3 dB for a MCF link of 10 km corresponding to relative refractive index difference of 0.0036 and 0.0030, respectively, for a pitch value of 30 μm and core radius of 4.5 μm.
关键词： Bit Error Rate,coupling length,mode coupling,coupling coefficient,multi-core fiber,crosstalk
更新于2025-09-16 10:30:52
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Discoveries and Explorations of Mode Splitting Phenomenon in Lossy Dielectric Waveguide
摘要： We discovered that a specific transmission mode in the fiber waveguide will split into two modes at near cut-off conditions when the fiber is coated with lossy dielectric nanofilms with higher refractive index. One of the two splitting modes is high lossy while the other is slightly lossy. We defined the “mode splitting coefficient” to describe the degree of mode splitting. We found that the biggest mode splitting coefficient was obtained at the mode cut-off wavelength using finite element method. Finally, we put forward an explanation towards the mode splitting phenomenon and expounded the relationship between the mode splitting and mode coupling.
关键词： Mode coupling,Mode splitting phenomenon,Finite element method,Lossy dielectric waveguide
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Continuum Generation in Higher-Order Modes of Photonic Crystal Fibers
摘要： Low-noise supercontinuum (SC) generation in photonic crystal ?bers (PCFs) can be achieved by using pump pulses of femtosecond (fs) duration and low soliton numbers [1]. The small cores sizes needed to obtain anomalous dispersion for pump wavelengths in the Yb gain band (typically 1030-1070 nm) implies a severe restriction on power for such pump pulses. One possible strategy for power scaling is to pump in higher-order ?ber modes, which can attain the desired dispersion properties in larger cores. This contribution aims to explore the properties of such continua, in particular the conditions necessary to retain a single-mode character of the output.
关键词： nonlinear mode coupling,photonic crystal fibers,higher-order modes,supercontinuum generation
更新于2025-09-16 10:30:52
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[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - The Loss Characteristics of Curved Fiber at Small Radius
摘要： Curved optical fiber sticking onto a round structure has many applications, such as mandrel acoustic sensors and fiber-length scratchable phase modulators. However, the components’ performances are limited by the transmission loss of the wound fibers. In this paper, the bending loss characteristic of curved fiber at small radius is experimentally demonstrated. A modified five-layer slab waveguide theory is used, which indicates that the bend loss has distinct oscillations at small radius. When the bending radius is smaller, the oscillation period changes more observably. In the experiment, single-mode fiber is bended on the outer surface of cylinders with various radius. The experimental result is consistent with theoretical analysis one.
关键词： bend loss,Fiber bending,mode coupling,whispering gallery modes (WGMs)
更新于2025-09-16 10:30:52
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Highly sensitive magnetic field sensor based on mode coupling effect in microstructured optical fibers
摘要： A highly sensitive magnetic field sensor based on mode coupling effect in a microstructured optical fiber (MOF) was theoretically investigated by using the finite element method. Magnetic fluid with refractive index higher than silica was designed to be filled into one cladding air hole in MOF to form a defect core. The coupling wavelength between fiber core modes and defect core modes can be modulated by external magnetic field. Simulation results show that the measuring sensitivity of magnetic field and figure of merit reached 1620? pm/Oe, 0.081/Oe in x-polarized mode and 1790? pm/Oe, 0.045/Oe in y-polarized mode, respectively. Meanwhile, the intensity of magnetic field depicts a good linear relationship with the coupling wavelength for both orthogonal polarized directions in the range of 25–175.9 Oe. The performance of the designed magnetic field sensor can be improved by optimizing the structural parameters in MOF.
关键词： Microstructured optical fiber,Mode coupling,Magnetic field sensor,Magnetic fluid
更新于2025-09-16 10:30:52
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Design of Plasmonic-Waveguiding Structures for Sensor Applications
摘要： Surface plasmon resonance has become a widely accepted optical technique for studying biological and chemical interactions. Among others, detecting small changes in analyte concentration in complex solutions remains challenging, e.g., because of the need of distinguishing the interaction of interest from other effects. In our model study, the resolution ability of plasmonic sensing element was enhanced by two ways. Besides an implementation of metal-insulator-metal (MIM) plasmonic nanostructure, we suggest concatenation with waveguiding substructure to achieve mutual coupling of surface plasmon polariton (SPP) with an optical waveguiding mode. The dependence of coupling conditions on the multilayer parameters was analyzed to obtain optimal ?eld intensity enhancement.
关键词： planar waveguide,mode coupling,surface polaritons,optical sensors
更新于2025-09-12 10:27:22