Cavity Chain Research Articles

Steering non-Hermitian skin states by engineering interface in 1D nonreciprocal acoustic crystal

Topological insulators possess strong topological protection properties and can manipulate the wave propagation to combat disorder and defects. And now they have grown into a large research field in photonic and phononic crystals. However, the conventional topological band theory is used to describe a closed photonic/phononic crystal that is assumed to be a Hermitian system. In fact, actual physical systems often couple with external environment, and generate non-Hermitian Hamiltonians with complex eigenvalues. Recently, many novel topological properties have been induced by the interaction between non-Hermitian phase and topological phase. A prominent example is non-Hermitian skin effect that all eigenstates are localized to the boundary in open system, which is different from the conventional topological edge state. This unique physical phenomenon has inspired various applications, such as wave funneling, enhanced sensing, and topological lasing. In this work, we describe the non-Hermitian skin effect by using winding number domains. The sign of the winding number domain determines the rotation direction of the loops in the complex frequency plane, whose sign can be controlled by the nonreciprocal coupling direction. In this work, we design different topological skin interfaces between different domains with opposite winding numbers to manipulate the energy focusing on middle or two-end of non-Hermitian one-dimensional (1D) acoustic cavity chain. In experiment, we use an electroacoustic coupling method, in which a unidirectional coupler composed of microphones, speakers, phase shifters, and amplifiers is used to introduce positive and negative non-reciprocal couplings between the two acoustic cavities, and study the characteristics of these non-reciprocal couplings. Then, the non-reciprocal coupling cavities are extended into a chain structure, and the magnitudes and signs of the non-reciprocal couplings are flexibly controlled by using phase shifters and amplifiers. Through this method, we successfully construct the interfaces between different winding number domains, achieving a one-dimensional non-Hermitian skin effect at various interfaces. The experimental results indicate that the sound can be focused on the middle interface or two-end interfaces for different nonreciprocal coupling distributions, and the skin interface can also be switched from middle to two-end by exchanging the nonreciprocal coupling direction of the domains. Our research results provide greater flexibility for designing acoustic devices and also a new platform for exploring advanced topological acoustic systems for controlling sound propagation.

X -band two-stage rf pulse compression system with correction cavity chain

A compact $X$-band two-stage rf pulse compression system has been successfully designed, fabricated, and tested at Tsinghua $X$-band high-power test stand. The pulse compression system consists of a correction cavity chain, a first-stage, and a second-stage storage cavity. The correction cavity chain adopts a new design whose transmission loss and length are reduced by half compared with the old one. A detuning device is applied to the second-stage storage cavity so that the system can work in one-stage or alternatively two-stage compression mode. In the one-stage compression mode, a 150-ns, 70-MW flattop output, with a standard deviation of 1.5% in amplitude and 1\ifmmode^\circ\else\textdegree\fi{} in phase, was generated with a gain factor of 3. In the two-stage compression mode, a first two-stage pulse compression experiment with correction cavities in the $X$ band was performed. A peak power of 320 MW was achieved with a gain factor of 9.7 and full-width at half-maximum pulse durations of 53 ns.

Selective Topological Pumping for Robust, Efficient, and Asymmetric Sound Energy Transfer in a Dynamically Coupled Cavity Chain

One-way sound-wave propagation has been a research hotspot in acoustics during the past decade, with the production of acoustic diode, acoustic topological insulator, and parity-time-symmetric acoustic metamaterial. Here, we investigate topological pumping for sound waves in a coupled cavity chain along selective paths driven by dynamic modulation. We first showcase the adiabatic passage of sound energy in a heterostructured Su-Schrieffer-Heeger cavity chain. By solving the Dirac-like governing equation, we calculate the eigenspectrum of this model and prove the existence of a topologically protected interface state and end states. From the eigenspectrum, if no level crossing exists, energy transfer of the sound wave (or acoustic topological pumping) is reversed under adiabatic modulation, leading to the release and return of sound energy for a specific topological state. However, when the level crossing occurs, we find that topological pumping between the interface state and end states can be selectively excited, rendering complete transfer of the sound energy between two topological states. Moreover, topological pumping of sound waves can exist along the asymmetric paths under driven modulation. Our work has promising applications for robust, selective, and efficient sound energy transfer in acoustic network systems.

A quantitative calculation method of RF parameters for traveling wave accelerating structures

Equivalent circuit model of the coupled cavity chain has been widely used to analyze the properties of RF parameters of periodic accelerating structures. In this paper, the equivalent circuit model of disk-loaded waveguide traveling wave accelerating structure and its circuit equations are discussed and analyzed further. Based on analysis of relationship between the RF parameters of each cavity and the field distribution in the coupled cavity chain, a new method to calculate the frequency deviation of each cavity and the output coupling coefficient of the accelerating structure quantitatively is presented. This method is applied in a 10 MeV traveling wave accelerating structure tuning and results verify its correctness and effectiveness.

A Frequency-Agile Relativistic Magnetron With Axial Tuning

A frequency-agile relativistic magnetron with axial tuning is presented. To achieve axial tuning, reentrant cavity which has two radial parts connected by a coupling hole had been introduced. Resonant frequency of this cavity configuration can be tuned by adjusting the axial length of each coupling hole without any variation of other parameters. Multi-antenna output technique had been integrated with the reentrant cavity chain to obtain high conversion efficiency in the whole tuning range. Simulation results showed that this tube had a tuning range between 1.23 GHz to 1.70 GHz, corresponding to relative bandwidth of 32% about a center frequency of 1.465 GHz. In this tuning range, the maximum output power is 1.81 GW at 1.605 GHz, corresponding to an efficiency of 54.5%. This axial tuning RM is a promising compact high power microwave source with wide tuning range.

Demonstration of a cavity-based pulse compression system for pulse shape correction

A compact X-band correction cavity chain (CC) has been successfully designed, fabricated and high power tested for the Compact Linear Collider (CLIC) project. The CC consists of eight spherical cavities and four polarizers, and each spherical cavity has a ${Q}_{0}$ of 45 000 and a diameter of 7 cm. The compact CC can correct a decaying pulse shape generated by a storage cavity without need of low efficiency pulse modulation or a solution based on long delay lines. A flattop output with small ripples can be obtained if the CC and the storage cavity are matched. Experiments of the CC with a barrel open cavity (BOC) were conducted on the XBOX2 test facility at CERN, and the high power results match the theoretical calculations. The appliance of the CC only reduces the pulse compression efficiency by 6% relatively if the transmission attenuation is ignored.

Optomechanical properties of a degenerate nonperiodic cavity chain

The absorption of single-cavity and double-cavity optomechanical systems and periodic optomechanical lattices has previously been investigated extensively. In this paper, we present the absorption of a nonperiodic cavity chain, where the absorption value on the resonance point shows switchable dips or peaks, according to whether the optomechanical interaction is at an odd or even-numbered position in the chain. Meanwhile, the value of absorption due to the optomechanical interaction varies with the number of the bare cavities. The calculated results may have some novel applications, such as detecting the position of the movable mirror in a long cavity chain, which would be useful in quantum information processing based on optomechanical systems.

Influence of voltage rise time on operation frequency in magnetically insulated transmission line oscillator.

In the experiments of a magnetically insulated transmission line oscillator (MILO), the initiatory microwave frequency is slightly higher than the stable microwave frequency. This paper investigates the influence of the front edge of the voltage on microwave frequency. The theoretical analysis shows that the MILO operates at the 2π mode in the initiatory stage; therefore, the microwave frequency is determined by the single slow wave structure (SWS) cavity. During the stable operation, the MILO works at the π mode and the microwave frequency is decided by the structure parameters of the resonant cavity chain. It is a fact that the resonant frequency of a single SWS cavity is higher than that of the resonant cavity chain, so the reason why the initiatory microwave frequency is slightly higher than the stable microwave frequency can be explained. The simulation results agree with the theoretical results.

The dynamics of merge and inversion of cavity and slot modes in coupled cavity chain slow wave structure

The results of a theoretical study of the electrodynamic characteristics (EDC) in the dynamics of merge of the cavity and slot passbands of a slow-wave structure (SS) such as a coupled cavity chain (CCC) with the subsequent transition to a CCC with an inverted slot mode with a change in the opening angle of the coupling slot are presented. An analysis of the characteristics of CCC with combined and inverted bands with a traditional SS is carried out. The coupling impedance is presented for the first three spatial harmonics. The EDC CCC calculation was performed in the ANSYS HFSS program using the method of separation of closely spaced modes proposed by the authors. Suggested method made it possible to significantly increase the accuracy of the calculation of the dispersion characteristics of the CCC in the process of combining the passbands with the determination of the boundaries of not only the cavity, but also the slot passbands until the disappearance of the non-transmission band. The analysis of the distribution of the fields at given phase shifts in the cavity and slot CCC passbands revealed the features of their change during the inversion of the bands compared to traditional concepts. The field distributions in both passbands at different phase shifts have a hybrid (mixed) character of the fields of both the cavity and slot types waves.

Comparing gas transport in three polymers via molecular dynamics simulation.

People use polymers as materials for preparing separation media or containers. It is necessary to have a molecular level profound knowledge of gas transport in e bulk and interface regimes of different polymers, but few researchers have done a molecular level study of the bulk and interface behavior of gases in several types of non-homologen polymers thoroughly or developed expressions to correlate gas transport properties with cavity size distribution and chain oscillation flexibility. Therefore, in this work, molecular dynamics (MD) simulation was employed to study the transport of methane and n-butane molecules in the bulk and interface region of polyethylene (PE), poly(4-methyl-2-pentyne) (PMP) and polydimethylsiloxane (PDMS). Penetrant diffusivity, solubility and permeability in the bulk were studied first. The subdiffusion behavior of gas molecules is explored to obtain the mechanisms behind penetrant transport. Both penetrants have much smaller diffusivities in PE than in PMP and PDMS, and they have larger diffusivities in PDMS than in PMP. PE has lower accessible cavity fraction (ACF) and average oscillation amplitudes (AOAs) of the chains than PDMS and PMP. PE also has much smaller solubilities and permeabilities of both penetrants than PDMS and PMP. Though the permeabilities of both penetrants in PDMS are higher than the corresponding values in PMP, PMP has a higher selectivity of n-butane over methane than PDMS. Nonequilibrium MD simulation was performed to study the interface property and gas transport in the interface region. Equations to predict penetrant diffusivity and permeability from the accessible cavity fraction (ACF) and average amplitude of chain oscillation were developed successfully. Penetrant diffusivity and permeability are proportional to the value of ACF to the power of one third and that of ACF to the power of four thirds, respectively.

1007-6654(2018)01-0030-10

1007-6654(2018)01-0030-10

Rf design of a pulse compressor with correction cavity chain for klystron-based compact linear collider

We present an X-band high-power pulse compression system for a klystron-based compact linear collider. In this system design, one rf power unit comprises two klystrons, a correction cavity chain, and two SLAC Energy Doubler (SLED)-type X-band pulse compressors (SLEDX). An rf pulse passes the correction cavity chain, by which the pulse shape is modified. The rf pulse is then equally split into two ways, each deploying a SLEDX to compress the rf power. Each SLEDX produces a short pulse with a length of 244 ns and a peak power of 217 MW to power four accelerating structures. With the help of phase-to-amplitude modulation, the pulse has a dedicated shape to compensate for the beam loading effect in accelerating structures. The layout of this system and the rf design and parameters of the new pulse compressor are described in this work.

Ear malformations, hearing loss and hearing rehabilitation in children with Treacher Collins syndrome

ObjectiveThe aim of this study was to assess the main ear malformations, hearing loss and auditory rehabilitation in children with Treacher Collins syndrome. MethodsWe performed a retrospective study of 9 children with Treacher Collins syndrome treated in a central hospital between January 2003 and January 2013. ResultsThis study showed a high incidence of malformations of the outer and middle ear, such as microtia, atresia or stenosis of the external auditory canal, hypoplastic middle ear cavity, dysmorphic or missing ossicular chain. Most patients had bilateral hearing loss of moderate or high degree. In the individuals studied, there was functional improvement in patients with bone-anchored hearing aids in relation to conventional hearing aids by bone conduction. ConclusionsTreacher Collins syndrome is characterized by bilateral malformations of the outer and middle ear. Hearing rehabilitation in these children is of utmost importance, and bone-anchored hearing aids is the method of choice.

Ear malformations, hearing loss and hearing rehabilitation in children with Treacher Collins syndrome

ObjectiveThe aim of this study was to assess the main ear malformations, hearing loss and auditory rehabilitation in children with Treacher Collins syndrome. MethodsWe performed a retrospective study of 9 children with Treacher Collins syndrome treated in a central hospital between January 2003 and January 2013. ResultsThis study showed a high incidence of malformations of the outer and middle ear, such as microtia, atresia or stenosis of the external auditory canal, hypoplastic middle ear cavity, dysmorphic or missing ossicular chain. Most patients had bilateral hearing loss of moderate or high degree. In the individuals studied, there was functional improvement in patients with bone-anchored hearing aids in relation to conventional hearing aids by bone conduction. ConclusionsTreacher Collins syndrome is characterized by bilateral malformations of the outer and middle ear. Hearing rehabilitation in these children is of utmost importance, and bone-anchored hearing aids is the method of choice.

Mode stability analysis in the beam—wave interaction process for a three-gap Hughes-type coupled cavity chain

Based on space-charge wave theory, the formulae of the beam—wave coupling coefficient and the beam-loaded conductance are given for the beam—wave interaction in an N-gap Hughes-type coupled cavity chain. The ratio of the non-beam-loaded quality factor of the coupled cavity chain to the beam quality factor is used to determine the stability of the beam—wave interaction. As an example, the stabilities of the beam—wave interaction in a three-gap Hughes-type coupled cavity chain are discussed with the formulae and the CST code for the operations of the 2π, π, and π/2 modes, respectively. The results show that stable operation of the 2π, π, and π/2 modes may all be realized in an extended-interaction klystron with the three-gap Hughes-type coupled cavity chain.

Simulation of Three-Spin Interaction in Coupled Cavities Chain

We generalize usual second-order effective Hamiltonian approximation into third-order. Employing the generalized method, we propose a scheme to generate three-spin interaction using coupled cavity chain. We show that the third order term not only improves two parties interaction but also induces direct three-spin interaction which has not been simulated before. By controlling the frequency of laser field, one can obtain next nearest neighbor interaction on the same order with the nearest neighbor’s or the three-spin interaction on the same order as next nearest neighbor’s.

A tuning method for nonuniform traveling-wave accelerating structures

The tuning method of uniform traveling-wave structures based on non-resonant perturbation field distribution measurement has been widely used in tuning both constant-impedance and constant-gradient structures. In this paper, the method of tuning nonuniform structures is proposed on the basis of the above theory. The internal reflection coefficient of each cell is obtained from analyzing the normalized voltage distribution. A numerical simulation of tuning process according to the coupled cavity chain theory has been done and the result shows each cell is in right phase advance after tuning. The method will be used in the tuning of a disk-loaded traveling-wave structure being developed at the Accelerator Laboratory, Tsinghua University.

Arrays of waveguide-coupled optical cavities that interact strongly with atoms

We describe a realistic scheme for coupling atoms or other quantum emitters with an array of coupled optical cavities. We consider open Fabry–Perot microcavities coupled to the emitters. Our central innovation is to connect the microcavities to waveguide resonators, which are in turn evanescently coupled to each other on a photonic chip to form a coupled cavity chain. In this paper, we describe the components, their technical limitations and the factors that need to be determined experimentally. This provides the basis for a detailed theoretical analysis of two possible experiments to realize quantum squeezing and controlled quantum dynamics. We close with an outline of more advanced applications.

Effects of Cr Doping on the Structural and Electrochemical Properties of V<sub>6</sub>O<sub>13</sub>

It has been demonstrated that V6O13 is a very attractive cathode materials for rechargeable lithium-ion batteries. Cr3+ was doped to improve its electrochemical property. CrxV6O13(x =0.01~0.05) cathode materials were prepared using NH4VO3 and Cr2O3 as raw material by solid phase method in argon atmosphere. The best electrochemical properties of CrxV6O13 were obtained under the optimum conditions as follows: the argon flow rate is 85mL/min, the heating rate is 5°C /min, the holding time 1h at 180°C, 1h at 300°C and 30 min at 450°C. The structural and electrochemical properties were examined by means of X-ray diffraction, SEM and charge–discharge tests. The results demonstrated that the powders maintain double cavity chain structure regardless of the chromium doping. When the Cr doping of x = 0.03, capacity is highest. Maximum initial discharge capacity is 334mA•h/g, 80% of theoretical capacity. During discharge process there is 6.5 Li+ embedded in the Molecules of doping. After discharge cathode became Li6.5Cr0.03V6O13.

State transfer and entanglement with atomic ensembles in a one-dimensional fibre-coupled cavity chain

A simple scheme is presented to realize state transfer and entanglement with atomic ensembles in a one-dimensional fibre-coupled cavity chain. It is immune to atomic spontaneous emission, cavity decay and fibre decay by adiabatic dark state evolution. Moreover, with atomic-ensemble qubits instead of single-atom qubits, the process can be speeded up, which is important in view of decoherence. The most interesting aspect is that it can realize state transfer, the two-node maximum entanglement state between any selected two nodes and the m-node W state among any selected m nodes, which might be very useful in selective participation in distributed quantum information processing.