Effects Of Detuning Research Articles

Cost-effective photonics-based THz wireless delivery system using a directly modulated DFB-LD

We present a cost-effective photonics-based THz wireless delivery system using a directly modulated distributed feedback laser diode (DFB-LD). A DFB-LD with non-return to zero (NRZ) modulation up to 25 Gbps and a uni-traveling-carrier photodiode (UTC-PD) with a horn antenna is employed to transmit a THz wave into free space in the photonics-based THz signal transmitter. A Schottky barrier diode (SBD) with a horn antenna is used to directly detect the THz wave from free space at the THz signal receiver. To achieve the best bit error rate performance, we varied the optimal THz carrier frequency in a photonics-based THz wireless delivery system. After THz carrier frequency optimization, bit error rates were measured by varying THz link operating conditions, such as the data rate, photocurrent of UTC-PD, and wireless transmission distance. We successfully transmitted a 25 Gb/s NRZ signal over 1.6 and 2.2 m wireless transmission distances before and after managing the adiabatic chirp characteristic of directly modulated DFB-LD using the laser-to-filter detuning effect, respectively, while satisfying the 7% hard decision-forward error correction (HD-FEC) threshold (3.4×10−3).

Parametric Study of Impulse Semi-active Mass Damper with Developing Directional Active Joint

High-rise buildings can easily suffer structural damage from dynamic excitation, which can be reduced with a tuned mass damper (TMD). However, TMDs can experience detuning or large displacement of the mass block. To prevent detuning, a newly developed directional active joint (DAJ) installed for automatic decoupling between the control mass block and the structure is proposed. The switching timing of several weight ratios for this DAJ and the response weighted control law were investigated with the vector form instinct finite element method and the fourth-order Runge–Kutta method. A ten-story building under excitation of near fault and far-field seismic records as the original structure and under TMD and semi-active mass damper (SAMD) (VwnA1) control was investigated to compare the displacement reaction of the top floor, efficiency of shock absorption and change in the shock absorption effect when the basic vibration frequency of the structure was misestimated. With the SAMD, the structure’s maximum displacement reaction was reduced by 37–42%. Regardless of the structural frequency misestimation ratio, the maximum displacement and average root mean square absorption rate at the top floor was only 4%, and the detuning phenomenon had little effect on it. With the TMD, a higher or lower misestimation ratio of the structure frequency caused a worse shock absorption effect. The SAMD is less sensitive to the basic vibration frequency of the structure and can indeed prevent the detuning effect of the TMD.

Seismic Resistance and Parametric Study of Building under Control of Impulsive Semi-Active Mass Damper

When high-rise buildings are shaken due to external forces, the facilities of the building can be damaged. A Tuned Mass Damper (TMD) can resolve this issue, but the seismic resistance of TMD is exhausted due to the detuning effect. The Impulsive Semi-Active Mass Damper (ISAMD) is proposed with fast coupling and decoupling at the active joint between the mass and structure to overcome the detuning effect. The seismic proof effects of a high-rise building with TMD and ISAMD were compared. The numerical analysis results indicate that: (1) the reduction ratio of the maximum roof displacement response and the mean square root of the displacement reduction ratio of the building with the ISAMD were higher than 30% and 60%, respectively; (2) the sensitivity of the efficiency index to the frequency ratio of the ISAMD was very low, and detuning did not occur in the building with the ISAMD; (3) to achieve stable seismic resistance of the ISAMD, its frequency ratio should be between 2 and 4; (4) the amount of displacement of the control mass block of the ISAMD can be reduced by enhancing the stiffness of the auxiliary spring of the ISAMD; and (5) the proposed ISAMD has a stable control effect, regardless of the earthquake distance.

Theoretical Analysis and Numerical Simulation for Cavity Ring‐Down Spectroscopy

To investigate the process of the creation of the ring‐down events in cavity ring‐down spectroscopy, theoretical formulae are derived for the interaction of the field in a cavity with the injection light, and a corresponding program for numerical simulation is developed. Using these theoretical formulas, the effects of the frequency detuning between the injection and the cavity mode, the absorption of the medium in the cavity, the residual injection, and the oscillation of the high‐order transverse modes are analyzed. A specific method for improving the measurement of the ring‐down time is proposed. With numerical simulation, the phenomenon of the intensity modulation during the frequency coupling of the cavity mode with the injection light is investigated. As the coherence of the injection light degrades, the light distribution in the cavity gradually develops from a smooth state to random states. Finally, it converges to a state at which the injection light is incoherent. The simple experimental results confirm that the limited coherence of the injection light causes the randomness of the development of the cavity field, and the results are used for the demonstration of the effectiveness and accuracy of the proposed method in solving for the ring‐down time.

The resonant frequency measurement method for superconducting cavity with Lorentz force detuning

The precise measurement of resonance frequency is very important to tune the cavity and stabilize the RF field. The minimal-reflection method is usually used to measure the cavity resonance frequency, but the accuracy may not meet the stability requirement for the superconducting cavity with narrow bandwidth. The falling-edge method with high precision has been used for the resonance frequency measurement of the normal conducting cavity, but it cannot be used directly for the superconducting cavity due to the effect of Lorentz Force Detuning (LFD). This paper presents the solution for applying the falling-edge method to measure the resonance frequency of superconducting cavity with LFD. The periodic iteration algorithm is developed to calculate the frequency detuning and phase shift caused by the dynamic Lorentz Force within RF falling-edge. The phase shift due to the deviation of initial resonance frequency is derived by subtracting the LFD item from the phase measurement, and the initial resonance frequency can be determined finally. The method has been tested on the superconducting cavity at CAFE facility, and the effectiveness has been demonstrated.

Effect of Detuning of Clamping Force of Tie Rods on Dynamic Performance of Rod-Fastened Jeffcott Rotor

In view of the advantages of lightweight, high strength, easy cooling, and easy assembly, the rod-fastened rotor is widely used in the aeroengine and heavy gas turbine. However, because of assembly, stress relaxation, material creep, and other reasons, the clamping force of the tie rods will be out of tune during the long-term operation of the rotor. The detuning of the clamping force of the tie rods not only affects the contact stiffness of the contact interface but also causes the rod-fastened rotor with a certain residual shaft bow, which will affect the dynamic characteristics of the rod-fastened rotor. Based on the statistical model of rough surface contact (GW contact model), this paper presents a method to calculate the equivalent flexural stiffness of rough surface considering the detuning of the clamping force of the tie rods and gives the calculation method of the residual shaft bow deformation of the rod-fastened Jeffcott rotor with detuning of the tie rods. The effect of the preload, the rate of detuning of the tie rods, the number of detuning tie rods on the natural frequency, and the response of residual shaft bow of the rod-fastened Jeffcott rotor at a certain speed are investigated. The results show that the detuning of the tie rods makes the flexural stiffness of the rotor inconsistent along with two main stiffness directions of the rotor, which makes the natural frequency of the rotor divided into two. The negative detuning of the tie rods decreases the natural frequency of the rotor, while the positive detuning of the tie rods increases the natural frequency of the rotor. The smaller preload or the larger rate of detuning of the tie rods makes the detuning of the tie rods have a greater influence on the natural frequency of the rotor. These results will provide a theoretical reference for the dynamic analysis and design of the rod-fastened rotor.

Dynamics of a delayed Duffing-type energy harvester under narrow-band random excitation

In this paper, a Duffing-type energy harvester with time delay circuit under narrow-band random excitation is studied by using the method of multiple scales. The analytical expressions of the steady-state responses near the principal resonance and their stable conditions are derived. Results show that the phenomenon of stochastic jump is found, and the operational bandwidth of the nonlinear energy harvester can be extended. The effects of frequency detuning, noise intensity, time delay, piezoelectric coupling, and time constant ratio on the dynamical behaviors are discussed. From the viewpoint of improving system performance and optimizing harvester design, a proper choose of time delay and feedback gain is proposed by the power conversion efficiency and the RMS voltage. It indicates that the negative feedback gain is favorable for an energy harvester to provide more electrical output power and miniaturize design. Moreover, the Monte Carlo simulations are given to verify the validity of the theoretical method.

Tripartite entanglement in a Laguerre–Gaussian rotational-cavity system with an yttrium iron garnet sphere

We propose a scheme that can realize the tripartite entanglement between the Laguerre–Gaussian (L–G) cavity mode, magnon mode, and phonon (rotating) mode in a hybrid rotating cavity optomechanical system with an yttrium iron garnet sphere inside the cavity. The excited magnon mode and the L–G cavity mode are related through the magnetic dipole interaction, and the L–G cavity mode can exchange orbital angular momentum (OAM) with the rotating mirror. In this way, the magnon mode and the rotating mirror are connected through the L–G cavity mode. Our results show that physical parameters such as OAM of the L–G cavity mode, detuning of the magnon mode, and effective detuning of the cavity mode play different roles in establishing entanglements.

Measuring orbital angular momentum of vortex beams in optomechanics

Measuring the orbital angular momentum (OAM) of vortex beams, including the magnitude and the sign, has great application prospects due to its theoretically unbounded and orthogonal modes. Here, the sign-distinguishable OAM measurement in optomechanics is proposed, which is achieved by monitoring the shift of the transmission spectrum of the probe field in a double Laguerre-Gaussian (LG) rotational-cavity system. Compared with the traditional single LG rotational cavity, an asymmetric optomechanically induced transparency window can occur in our system. Meanwhile, the position of the resonance valley has a strong correlation with the magnitude and sign of OAM. This originally comes from the fact that the effective detuning of the cavity mode from the driving field can vary with the magnitude and sign of OAM, which causes the spectral shift to be directional for different signs of OAM. Our scheme solves the shortcoming of the inability to distinguish the sign of OAM in optomechanics, and works well for high-order vortex beams with topological charge value ±45, which is a significant improvement for measuring OAM based on the cavity optomechanical system.

Manipulating the steady-state entanglement via three-level atoms in a hybrid levitated optomechanical system

We theoretically investigate the generation of steady-state entanglement in a levitated optomechanical system with a cascade three-level atomic medium and a dielectric nanosphere. There are two cavity modes, driven by two external laser beams with different frequencies, which are responsible for trapping and cooling the nanosphere. Atoms prepared in coherent superposition are injected into the cavity to manipulate the optical fields and the effective optomechanical coupling. We show that the entanglement between the nanosphere and the cavity modes can be enhanced by selecting properly the initial population of the lower atomic level. In particular, when the atoms are prepared at that level, the corresponding optomechanical entanglement increases with the increase of the atom-field coupling strength. We also investigate in detail the influence of the effective cavity field detunings, the atomic detunings, the driving power, and the nanosphere's radius and found that there exist optimal values of the effective cavity field detuning and the driving power that maximize the optomechanical entanglement. By selecting the system's parameters properly, we further demonstrate the generation of genuine tripartite entanglement between three degrees of freedom in the system. The findings here may help flexible control of the steady-state entanglement in hybrid optomechanical systems.

Development of a superconducting radio frequency double spoke cavity for CSNS

China Spallation Neutron Source (CSNS) has been in operation for about 2 years, and an upgrade is proposed to compensate the space charge effect. A superconducting radio frequency (SRF) linac with double spoke cavities and medium-beta elliptical cavities has been designed to increase the injection energy from 80MeV to 300MeV, and institute of high energy physics (IHEP) has developed a prototype double spoke cavity at β0 0.5. The cavity shape was optimized to minimize Ep/Eacc while keeping Bp/Eacc reasonably low. Meanwhile, mechanical design was applied to check stress, Lorentz force detuning and microphonic effects, and to minimize pressure sensitivity. A new input power coupling scheme was proposed to avoid electrons hitting directly on ceramic window. After fabrication and post processing of cavity, the cavity was vertical tested for several times, and mechanical polishing was applied to improve the performance. The cavity finally reached Bp of 140mT at Eacc = 16.1MV/m and Q0=1.42×1010 under vertical test at 2K.

Constrained optimal design of seismic base absorbers based on an extended KDamper concept

In this paper, an extended KDamper (EKD) concept is proposed, for implementation as a seismic base absorber. The complexity of the EKD renders the conventional minmax (H∞) approaches ineffective. For this reason, a dedicated constrained optimization problem is proposed for the selection of the optimal system parameters. The EKD is designed according to seismic design codes and the constraints and limitations of the EKD components are evaluated based on engineering criteria. In order to better observe the efficiency of the proposed configuration, an acceleration filter is placed, as an additional constraint. Therefore, each set of optimized parameters of the EKD refers to the maximum structure acceleration, expressed as a percentage of PGA. A database of artificial accelerograms, compatible with the EC8 response spectra is generated. Sensitivity analysis is performed, and the effect of detuning is observed. Subsequently, the EKD is implemented as a seismic base absorber in a multi-story building. The performance of the proposed control strategy is compared not only to the original structure but also to the cases of conventional and highly damped base isolation systems, as well as to the KDamper. The EKD presents an improved superstructure dynamic behavior, comparable with a base isolated system. At the same time, the base relative displacement is drastically reduced, in the order of a few centimeters, rendering the implementation of the EKD feasible using conventional structural elements, without the need for special types of bearings. In addition, the base shear is reduced, as compared to the original structure, with the implementation of the proposed configuration, and thus, EKD can be considered a possible retrofitting option for seismic protection.

Synthetic flux attachment

Topological field theories emerge at low energy in strongly-correlated condensed matter systems and appear in the context of planar gravity. In particular, the study of Chern-Simons terms gives rise to the concept of flux attachment when the gauge field is coupled to matter, yielding flux-charge composites. Here we investigate the generation of flux attachment in a Bose-Einstein condensate in the presence of non-linear synthetic gauge potentials. In doing so, we identify the U(1) Chern-Simons gauge field as a singular density-dependent gauge potential, which in turn can be expressed as a Berry connection. We envisage a proof-of-concept scheme where the artificial gauge field is perturbatively induced by an effective light-matter detuning created by interparticle interactions. At a mean field level, we recover the action of a "charged" superfluid minimally coupled to both a background and a Chern-Simons gauge field. Remarkably, a localised density perturbation in combination with a non-linear gauge potential gives rise to an effective composite boson model of fractional quantum Hall effect, displaying anyonic vortices.

Stimulated Raman adiabatic passage: Effects of system parameters on population transfer

The stimulated Raman adiabatic passage (STIRAP) procedure is a robust and complete population transfer method which has various applications in chemistry and atomic physics. The bright-state STIRAP (b-STIRAP) is an alternative population transfer process with an intuitive pulse sequence. The simultaneous use of both STIRAP and b-STIRAP is beneficial in quantum manipulation. Adjusting the system parameters in both processes can be useful for the enhancement of transfer efficiency. Hence, we have studied the effects of single-photon detuning, transition time, pulse width, and pulse delay parameters on the population transfer via STIRAP and b-STIRAP techniques. Moreover, the impact of the field amplitude is investigated and analyzed in the b-STIRAP method. It is shown that the robustness of the complete transition can be improved by tuning the field amplitude in the single-photon resonance condition.

A High-Q Resonant Inductive Link Transmit Driver With Adaptive-Predictive Phase-Continuous Tuning and Deviation Frequency Calibration for Enhanced FSK/PSK Modulation and Power Transfer

Inductively coupled power transfer systems often use high- $Q$ antenna circuits to reduce losses and increase transmission range. However, the narrow bandwidth due to the high $Q$ -factor conventionally constrains the modulation rate on the carrier, creating a tradeoff between power transfer efficiency and data rate. In this article, we show how instantaneous tuning of the antenna can permit frequency and phase modulation data rates beyond the $Q$ -factor limitations, provided that the drive and antenna resonance frequencies are kept the same at all times. It is also necessary to ensure that the modulation symbol boundaries are precisely aligned with the tracking of the resonance tuning to ensure phase continuity and optimum power transfer. With instantaneous tuning, phase modulation can be implemented by defined numbers of cycles at an offset frequency, provided the offset is precisely controlled. We describe how the required instantaneous resonance tuning can be achieved using a switched fractional capacitor technique and present a system architecture that can follow abrupt frequency changes due to the modulation while tracking changes to the resonant condition due to environmental detuning effects at each modulation frequency. An integrated mixed-signal driver/modulator/tuner demonstrator system is presented, operating from 10 kHz–2 MHz using a 0.18- $\mu$ m 1.8–50-V CMOS/laterally-diffused metal-oxide semiconductor (LDMOS) process. The system maintains phase continuity in the antenna current throughout frequency shift keying (FSK) and phase-shift keying (PSK) modulation and employs self-calibration of the PSK modulation frequencies to achieve precise angles of phase rotation for QPSK. The antenna tuning, modulation, and frequency calibration are verified with experimental results.

PT -symmetry-breaking-enhanced cavity optomechanical magnetometry

$\mathcal{PT}$-symmetry-breaking enhanced cavity optomechanical magnetometer is proposed, which is achieved by monitoring the change of intensity of a nonlinear four-wave mixing (FWM) process in a gain-cavity-assisted cavity optomechanical system (COMS). Compared with the traditional single loss COMS, the FWM intensity can be enhanced by two orders of magnitude when the gain-cavity-assisted COMS operates at the $\mathcal{PT}$-symmetry-breaking phase. Meanwhile, the sensitivity of magnetic field sensing can be increased from $10^{-9}$T to $10^{-11}$T. This originally comes from the fact that the effective detuning and decay of loss-cavity can be effectively modified in the $\mathcal{PT}$-symmetry-breaking phase. Our work shows that an ultrahigh-sensitivity magnetometer can be achieved in the $\mathcal{PT}$-symmetry-breaking COMS, which will have wide applications in the field of quantum sensing.

Effect of the nearby levels on the resonance fluorescence spectrum of the atom–field interaction

We study the resonance fluorescence in the Jaynes-Cummings model when nearby levels are taking into account. We show that the Stark shift produced by such levels generates a displacement of the peaks of the resonance fluorescence due to an induced effective detuning and also induces an asymmetry. Specific results are presented assuming a coherent and a thermal fields.

Nonreciprocal Transmission and Nonreciprocal Entanglement in a Spinning Microwave Magnomechanical System

AbstractThis study presents nonreciprocal transmission and nonreciprocal magnon–phonon entanglement in a spinning microwave magnomechanical system. This system consists of microwave photons, magnon modes, and phonons. These are created by the vibrational mode of a yttrium iron garnet sphere. This investigation reveals that nonreciprocity is caused by the light that is circulating in a resonator that is experiencing a Fizeau shift. This leads to a difference in the effective detuning frequency of the photon for forwarding and backward drives. A super‐strong transmission isolation rate (>100 dB) and a strong entanglement isolation rate (≈50 dB) are obtained by applying the experimental parameters. This scheme opens a new route for exploiting a variety of nonreciprocal effects, and it provides the theoretical basis for the design and realization of magnetically controllable isolators and diodes.

Distributing entangled state using quantum repeater protocol: Trapped atomic ions in optomechanical cavities

Distribution of the entangled state of trapped atomic ions to long distance using quantum repeater protocol is considered. Indeed, the long distance is divided into short parts, and then using entanglement generation and entanglement swapping techniques in optomechanical cavities, the entanglement is distributed. To do the task, we perform interaction between trapped atomic ions in optomechanical cavities, operate proper measurements on trapped ions and also make Bell state measurement as a well-known way to swap the entanglement. Accordingly, the entanglement is distributed between target ions with satisfactory values of success probability and entanglement degree. The effects of detuning and amplitude of pump laser on the entanglement and success probability are evaluated. The fluctuations of entanglement and success probability are decreased by increasing of detuning. Via increasing the amplitude of pump laser, the maxima of entanglement are repeated more times and success probability undergoes the collapse-revival phenomenon.

Unidirectional spin transport of a spin-orbit-coupled atomic matter wave using a moving Dirac δ -potential well

We study the transport of a spin-orbit-coupled atomic matter wave using a moving Dirac $\delta$-potential well. In a spin-orbit-coupled system, bound states can be formed in both ground and excited energy levels with a Dirac $\delta$ potential. Because Galilean invariance is broken in a spin-orbit-coupled system, moving of the potential will induce a velocity-dependent effective detuning. This induced detuning breaks the spin symmetry and makes the ground-state transporting channel be spin-$\uparrow$ ($\downarrow$) favored while makes the excited-state transporting channel be spin-$\downarrow$ ($\uparrow$) favored for a positive-direction (negative-direction) transporting. When the $\delta$-potential well moves at a small velocity, both the ground-state and the excited-state channels contribute to the transportation, and thus both the spin components can be efficiently transported. However, when the moving velocity of the $\delta$-potential well exceeds a critical value, the induced detuning is large enough to eliminate the excited bound state, and makes the ground bound state the only transporting channel, in which only the spin-$\uparrow$ ($\downarrow$) component can be efficiently transported in a positive (negative) direction. This work demonstrates a prototype of unidirectional spin transport.