Double Cavity Research Articles

Using coherent feedback loop for high quantum state transfer in optomechanics

We investigate the coherent feedback loop scheme to improve the quantum correlations transfer from optical to mechanical degrees of freedom in a double cavity optomechanical system. We use the Duan criterion to determine the separability of the two-mode mechanical states. The logarithmic negativity is employed to quantify the amount of the entanglement between mechanical modes in steady and dynamical regimes. We show that the entanglement can be significantly enhanced by a coherent feedback using a suitable tuning of the reflectivity parameter of the beam splitter located in each cavity. We also show that this enhancement is influenced by the temperature, the light squeezing parameter and the gain of the parameter amplifier. The entanglement dynamics in presence of the coherent feedback loop is also analyzed.

Multiple Fano resonance in MIM waveguide system with cross-shaped cavity

A Metal-Insulator-Metal (MIM) waveguide structures consists of cross-shaped cavity and baffle was proposed. The simulation results show that the tunable Fano resonance existed in cross-shaped cavity structures by adjusting the length parameters of horizontal and vertical cavities. Further, the position and alignment of the resonant peak wavelength can be easily changed. The sensitivity of the structure is up to 1075 nm/RIU and the figure of merit (FOM) is 9.95 × 104 by changing the parameters of structure. However, for improved double cross-shaped cavity structure, a linear refractive index sensitivity of 1100 nm/RIU with a figure of merit of about 1.08 × 105 can be obtained. The results clarified that the developed structure could have a great potential in nanosensor and spectral splitter.

Chiral drug fluorometry based on a calix[6]arene/molecularly imprinted polymer double recognition element grafted on nano-C-dots/Ir/Au.

A luminescent double recognition nanoprobe is described as a new strategy for the selective determination of chiral molecules. C-dots/Ir/Au fluorescent nanoparticles, synthesised under hydrothermal conditions, are used as a high-performance probe in combination with a molecularly imprinted polymer (MIP) and calix[6]arene as a double recognition element. Thiolated calix[6]arene is grafted on C-dots/Ir/Au as the first recognition element, which then forms a host-guest complex with the target molecule levodopa (L-DOPA). Subsequently, an MIP is prepared on the C-dots/Ir/Au (MIP/C-dots/Ir/Au) by chemical polymerisation. After the removal of L-DOPA, double recognition imprinting cavities are formed. The fluorescence intensity at 478nm of the nanoprobe is effectively quenched by adsorption of L-DOPA on MIP/C-dots/Ir/Au, which provides a method for L-DOPA determination. Owing to the double recognition strategy, this method has excellent selectivity which can effectively avoid interference from enantiomer D-DOPA, and a imprinting factor of 7.1 is obtained for L-DOPA. This accurate and reliable method, with a wide linear range (5 × 10-10 to 1.2 × 10-7molL-1) and a low limit of detection (1.45 × 10-10molL-1), was successfully applied to the determination of L-DOPA in real samples, giving standard recoveries of 89.7-110.0%. Thus, the proposed sensing method provides a viable approach for the determination of a single enantiomer. Graphical abstract Schematic presentation of the MIP/C-dots/Ir/Au for L-DOPA detection. A fluorescence double chiral recognition nanoprobe is prepared of C-dots/Ir/Au nanoparticles as signal probe, and a molecularly imprinted polymer (MIP) and calix[6]arene as a double recognition element. Owing to the double recognition strategy, this method has strong specificity and can effectively avoid interference from enantiomers and racemates.

Heatline visualization of mixed convection inside double lid-driven cavity having heated wavy wall

The current problem is performed to analyze the heatline visualization of the mixed convection mechanism and heat transfer in a double lid-driven square cavity having a heated wavy bottom surface. The moving vertical surfaces are under adiabatic conditions, and the top surface is at a cold temperature. The finite element method is employed to determine the dimensionless governing equations controlled by specific boundary conditions. The implications of the Reynolds number ( $$10 \le {\mathrm{Re}} \le 500$$ ), the directions of the constant moving wall ( $$\lambda _{\mathrm{l}}= \pm 1, \lambda _{\mathrm{r}}= \pm 1$$ ), Richardson number ( $$0.01 \le {\mathrm{Ri}} \le 100$$ ), Prandtl number ( $$0.015 \le \Pr \le 10$$ ) and the number of oscillations ( $$1 \le {\mathrm{N}} \le 4$$ ) are visualized by the streamlines, isotherms and the heatlines. The same direction of lid-driven cases leads to two primary circulation cells. The Richardson number increases as it imposes the increment of the vertical temperature gradient. At a high Prandtl number, the convection mode of heat transfer is fully established, and heat conduction occurs at a low Prandtl number. Moreover, the number of oscillations has the most significant direct impact on the streamlines and the temperature distributions compared to the flat surface. Higher Reynolds and Prandtl numbers result in an increment in the local and average Nusselt numbers. The result shows that one oscillation of the wavy surface with a low Richardson number yields to have an optimum heat transfer in the cavity.

Resonant tunneling diodes strongly coupled to the cavity field

We demonstrate resonant tunneling diodes, embedded in double metal cavities, strongly coupled to the cavity field, while maintaining their electronic properties. We measure the polariton dispersion and find a relative vacuum Rabi splitting of 11%, which explicitly qualifies for the strong-coupling regime. Additionally, we show that electronic transport has a significant influence on the polaritons by modulating the coupling strength. The merge between electronic transport and polaritonic physics in our devices opens up different perspectives of cavity quantum electro-dynamics and integrated photonics.

Heavy load characteristics of micro-beveled heavy-duty hydrostatic bearing lubricant oil film

This paper is based on the new Q1-205 micro-beveled double rectangular cavity heavy hydrostatic thrust bearing. According to the hydrostatic and dynamic pressure lubrication theory, the mathematical model of the dynamic and static bearing capacity of micro-beveled oil film is established under the conditions of considering the bearing oil supply system and the actual structural of the oil pad. Based on the finite volume method, the lubricating performance of the oil film is numerically simulated under heavy load of 10t, 15t, 20t, 25t and 30t, and the comprehensive influence law of oil cavity pressure, fluid velocity, vorticity and flow rate is revealed under the influence of extreme working conditions such as heavy load. Finally, the oil film pressure field affected by heavy load is tested under certain wedge parameters and rotational speed and verifies the theoretical analysis and simulation. It is found that the experimental and theoretical result of bearing is consistent with each other under heavy load. The dynamic pressure compensation effect of the bearing is better under the wedge oil pad condition. However, under heavy load, the extrusion and heating of lubricating oil are serious, which make the viscosity of lubricating oil drops sharply. In addition, the dynamic pressure effect of wedge oil pad is less affected by load. The compensation effect decreases slightly with the increase of load. The dynamic pressure compensation range of the bearing is 30%–10% under heavy load.

A Post-Loaded Rectangular Reentrant Cavity for Broadband Multiple-Beam Klystron

In an effort to enhance the bandwidth of a multiple-beam klystron having rectangular double reentrant cavity with circular cylindrical ferrule, reduction of the unloaded quality factor of the cavity was proposed by placing circular cylindrical posts extending from one of the cavity side-walls to the opposite wall in an orientation perpendicular to the electric field. A typical cavity was analyzed using 3D electromagnetic field solver CST Studio and the post-loading was found to reduce the unloaded quality factor by around 90% compared to that for no-post-loading. The proposed method was found to be the only method other than the use of passive loss to achieve this order of reduction in the quality factor with a minor increase in the cavity transverse dimensions. Post made of highly resistive material was found to have pronounced effect in reducing the quality factor. The 3D electromagnetic analysis was validated against measurements on a typical S-band cavity.

Planar hot-electron photodetector utilizing high refractive index MoS2 in Fabry–Pérot perfect absorber

Hot electron photodetection (HEPD) excited by surface plasmon can circumvent bandgap limitations, opening pathways for additional energy harvesting. However, the costly and time-consuming lithography has long been a barrier for large-area and mass production of HEPD. In this paper, we proposed a planar and electron beam lithography-free hot electron photodetector based on the Fabry–Pérot (F–P) resonance composed of Au/MoS2/Au cavity. The hot electron photodetector has a nanoscale thickness, high spectral tunability, and multicolour photoresponse in the near-infrared region due to the increased round-trip phase shift by using high refractive index MoS2. We predict that the photoresponsivity can achieve up to 23.6 mA W−1 when double cavities are integrated with the F–P cavity. The proposed hot electron photodetector that has a nanoscale thickness and planar stacking is a perfect candidate for large-area and mass production of HEPD.

Relative-cavity-length-controlled slow light in a cascaded magnon-photon system

We theoretically discuss the input–output characteristics of the cascaded magnon-photon system by focusing on the slow light effect caused by positive group delay. When two identical magnon-photon systems are cascaded, compared with the single cavity system, the bandwidth of the whole system is wider, but the group delay is smaller. The change of the group delay is different from that of the general linear system. Moreover, by changing the cavity length of the two microwave cavities, the system is slightly mismatched and the group delay could obviously increase. The slow light effect could be controlled by relative cavity length. The slow light effect of the mismatched double cavity system is more sensitive to external magnetic field than that of the single cavity system. The results provide a way to manipulate the transmission rate in optical information networks and a new view about the interconnection of microwave cavities.

Effects of a Rotating Cone on the Mixed Convection in a Double Lid-Driven 3D Porous Trapezoidal Nanofluid Filled Cavity under the Impact of Magnetic Field.

Effects of a rotating cone in 3D mixed convection of CNT-water nanofluid in a double lid-driven porous trapezoidal cavity is numerically studied considering magnetic field effects. The numerical simulations are performed by using the finite element method. Impacts of Richardson number (between 0.05 and 50), angular rotational velocity of the cone (between −300 and 300), Hartmann number (between 0 and 50), Darcy number (between 10 and ), aspect ratio of the cone (between 0.25 and 2.5), horizontal location of the cone (between 0.35 H and 0.65 H) and solid particle volume fraction (between 0 and 0.004) on the convective heat transfer performance was studied. It was observed that the average Nusselt number rises with higher Richardson numbers for stationary cone while the effect is reverse for when the cone is rotating in clockwise direction at the highest supped. Higher discrepancies between the average Nusselt number is obtained for 2D cylinder and 3D cylinder configuration which is 28.5% at the highest rotational speed. Even though there are very slight variations between the average Nu values for 3D cylinder and 3D cone case, there are significant variations in the local variation of the average Nusselt number. Higher enhancements in the average Nusselt number are achieved with CNT particles even though the magnetic field reduced the convection and the value is 84.3% at the highest strength of magnetic field. Increasing the permeability resulted in higher local and average heat transfer rates for the 3D porous cavity. In this study, the aspect ratio of the cone was found to be an excellent tool for heat transfer enhancement while 95% enhancements in the average Nusselt number were obtained. The horizontal location of the cone was found to have slight effects on the Nusselt number variations.

Position detection method and hydrodynamic characteristics of the water entry of a cylinder with multidegree motion

This study experimentally investigates the hydrodynamic characteristics of a cylinder with multidegree motion during water entry with different initial horizontal velocities and inclined angles. A mechanical device is designed to provide certain initial conditions for the cylinder, and the cavity evolution and cylinder position are recorded with a high-speed camera. To obtain precise hydrodynamic forces, a new image-processing method is established to detect the center and attitude angle of the cylinder based on a step edge model and the Grubbs criterion. Additionally, an algorithm is employed to correct the refraction effects in the raw data. Using the above methods, the phenomena of asymmetric cavities, cavity pinch-off, double cavities and cavity ripples are observed in the wake region of the cylinder. Before the cavity pinches off, the hydrodynamic force driving the cylinder motion is generated from the pressure difference between the wet and dry parts. After pinch-off, the hydrodynamic force is mainly dominated by the induced lift, which depends on the angular speed, and a high-pressure region created by the pinch-off cavity causes an instantaneous impulse force that causes quick decreases in the cylinder accelerations. In addition, for the cylinder lift coefficient, the average rate of change increases almost linearly with an increasing initial angle of attack during water entry. For the drag coefficient, the average rate of increase rises nearly linearly with increasing absolute value of the initial angle of attack before pinch-off. After cavity pinch-off, this rate increases almost linearly with increasing |v0|/α0L.

Optical transmission characteristics in the MDM waveguide coupled with N-rectangular resonators

A metal–dielectric–metal (MDM) waveguide coupled with N-rectangular cavities is proposed and its spectral features are derived and described based on the coupled-mode and multi-oscillator theory for the first time. The results of theoretical calculation and numerical simulation indicate that resonant modes are proportionally increased with the number of cavities, surprisingly, the wavelength at 716 nm is an F–P resonant mode for n = 1 and those new modes occur on both sides of 716 nm, thus a plasmonic tunable multi-modes filter and slow light effect are achieved. According to the field distributions, the resonant modes can be divided into several types: dipole, quadrupole, hexapole, eighth-pole modes and so on. Moreover, we find that the resonant transmissions are sensitively dependent on the widths and lengths of cavities as well as the vertical and horizontal distances between two cavities. In addition, the phenomena including magnitude modification, redshift, blueshift, and the disappearance and fusion of modes are clearly observed. Compared with those conventional MDM waveguides side-coupled with single or double cavities, our proposed device can provide more channels to manipulate the resonance wavelengths flexibly. Therefore, it may be applied in optoelectronic devices.

Design of second harmonic terahertz gyrotron cavity based on double confocal waveguide

Quasi-optical confocal cylindrical waveguide possesses a lot of good characteristics, such as big power capacity and low mode density, which can suppress the mode competition in beam-wave interaction. So quasi-optical waveguide has a great advantage in designing high harmonic terahertz gyrotrons. For the reason that part of electron beams located in a region of weak field intensity play a limited role in beam-wave interactions, the beam-wave interaction is not efficient in confocal cavity. Motivated by enhancing the beam-wave interaction efficiency of quasi-optical gyrotron, we propose a novel terahertz harmonic gyrotron cavity with double confocal waveguide in this paper. The transverse field distribution and the mode spectrum in double confocal waveguide are analyzed and presented. A 330 GHz second harmonic gyrotron with double confocal cavity is designed, theoretically analyzed and simulated by using a particle-in-cell (PIC) code. The results obtained for double confocal cavity are compared with the results for single confocal cavity, and the physical mechanism of beam-wave interaction enhancement in double confocal cavity is discussed. Theoretical results show that the double confocal cavity is able to increase the coupling strength of beam-wave interaction, thus, to improve the output power and the interaction efficiency of quasi-optical gyrotron. The PIC simulation results suggest that a high-order waveguide mode in double confocal cavity can steadily interact with the high harmonic cyclotron mode of electron beam without mode competition. Driven by a 40 kV, 2 A electron beam with a guiding center radius of 1.65 mm and velocity ratio equal to 1.5, output power of 9.9 kW at 328.93 GHz can be generated in the designed double confocal cavity. The beam-wave interaction efficiency increases from 5.3% in single confocal cavity to 12.4% in dual confocal cavity under the same operation parameters. The double confocal cavity has great potential applications in terahertz band. Moreover, this study indicates that the eigen mode in double confocal waveguide is a kind of hybrid mode superimposed by two independent single confocal waveguide modes. This mode characteristic will be beneficial to designing a multifrequency gyrotron oscillator operated in two modes and two cyclotron harmonics, simultaneously, with a single electron beam used, which provides a new possibility to develop the novel terahertz radiation source.

Transferring Einstein-Podolsky-Rosen State Cross Frequency Bands via Cavity Electro-Opto-Mechanical Converters

In order to transfer two-mode quantum state from optical input to microwave output, we propose a scheme based on double cavity electro-opto-mechanical converters. Principles and operation modes of cavity electro-opto-mechanical converter are introduced in detail, and theoretical model of transferring Einstein-Podolsky-Rosen state via our scheme is built. The dynamics and corresponding scattering matrixes of our scheme are analyzed carefully. Meanwhile, Ulhmann fidelity is utilized to quantify the similarity of initial state and final state, which also stands for the performance of our scheme. Influences of coupling rates and optical input bandwidth on fidelity are well discussed, and some significant factors are also taken into consideration, such as transmission spectrum, interaction rates and decoherence rates. Furthermore, Wigner distributions of initial state and final state as well as the von Neumann entropy are obtained to verify the performance of our scheme. The results show that our scheme could transfer the Einstein-Podolsky-Rosen state from optical input to microwave output with high fidelity (0.74), and the entropy ratio between initial and final states is about 0.78, which is quite close with the fidelity. Besides, Wigner distributions also show that initial state and final state are slightly different in phase structures. In case of strong coupling rates, ultralow temperature and narrow input bandwidth, the performance of our scheme could be further enhanced.

Optimization of Casting Yield in Multi-cavity Sand Moulds of Al-alloy Components

To produce casting with efficient use of material, energy, lead time and manpower is very essential to sustain in foundry industry. Mould with dense cast cavities or less number of cavities may lead to more solidification time, poor mechanical properties and defects like shrinkage, misrun and cold shut. It is proposed to design mould layout with selection of suitable combination of mould size and multiple number of cavities based on temperature distribution and solidification time which results in optimization of casting yield.Casting simulations are carried out for casting mould with single cavity based on mould size and variation of cavity –wall distance for Al-alloy component in green sand mould result in finding of minimum cavity wall gap. Double and multiple cavities moulds are simulated based on cavity-wall distance value and variation of cavity-cavity distance along with temperature distribution, solidification time and defects if any in cast part results in computing minimum cavity-cavity distance. Applying this in mould layout design, it leads into optimum mould layout and casting yield. AutoCAST-X1 simulation results are validated by experimentation for LM4 alloy cast in sand mould allocated with thermocouples and data acquisition system.

Teorijsko proučavanje kvaliteta dinamike aerostatično aksijalnog ležišta sa spoljašnjim kombinovanim prigušivanjem

The article considers the design, mathematical modelling and theoretical study of dynamics quality on aerostatic thrust bearing with external combined air double throttling and flow cavity. The use of the finite-difference method for solving boundary value problems for linearised and Laplace-transformed Reynolds equation allowed to obtain its solution with high accuracy. The quality indicators of bearing dynamics were studied depending on the damping and throttling resistances, as well as on the volume of the cavity. It is established that the presence of a cavity contributes to a significant improvement in the quality indicators of the bearing dynamics. Based on the analysis of the data obtained, conclusions are drawn confirming the hypothesis that with a targeted choice of the values of the external throttling system parameters, a design can be obtained that, in comparison with the known aerostatic bearings, will have much better dynamic characteristics.

Ground-state cooling of mechanical resonator in double optical cavity

<sec>The ground-state cooling of mechanical resonator is one of the fundamental problems in cavity quantum photomechanics. The so-called ground-state cooling is to make the number of steady-state phonons of the mechanical resonator less than one. In this paper, we first propose an electromagnetically-induced-transparency-like cooling mechanism in a double-cavity optomechanical system to cool a mechanical resonator. In the double-optical cavity optomechanical system, the right additional cavity, which is directly coupled to a standard optomechanical system, contains an ultra-cold two-level atomic ensemble. By selecting the optimal parameters to meet the cooling process of the mechanical resonator corresponding to the maximum value of the optical fluctuation spectrum and the heating process of the mechanical resonator corresponding to the minimum value of the optical fluctuation spectrum, the mechanical resonator can be cooled by monitoring the phonon number. We also exert the effects of the atomic additional cavity on the quantum Langevin equations and optical fluctuation spectrum. We find that the atomic double-cavity system may have a better ground-state cooling than the double-cavity in certain parameters.</sec><sec>To date, the researchers have proposed a number of theoretical cooling schemes in order to achieve the ground-state cooling of mechanical resonator. As far as we know, the sideband cooling for just a standard optomechanical system is a most famous scheme and the mechanical resonator is coupled to the optical field via radiation pressure force. By the quantum theory of mechanical resonator’s sideband cooling, the optical fluctuation spectrum determines the transition rate of both cooling and heating process of the mechanical resonator. That’s to say, the optical fluctuation spectrum at a mechanical resonator frequency <i>ω</i><sub>m</sub> is corresponding to the cooling transition, whereas the optical fluctuation spectrum at –<i>ω</i><sub>m</sub> is corresponding to the heating transition. They respectively correspond to anti-Stokes and Stokes effect in physics. Under resolvable sideband conditions, the optical field’s decay rate (the half-width of the single Lorentzian peak of optical fluctuation spectrum) is less than the frequency of the mechanical resonator. So, the ground-state cooling of the mechanical resonator can be obtained by making the maximum and minimum value of the optical fluctuation spectrum respectively correspond to the cooling anti-Stokes process and heating Stokes process.</sec><sec>In this paper, we mainly observe the electromagnetically-induced-transparency-like ground-state cooling in a double-cavity optomechanical system with an ensemble of two-level atoms. By adjusting the maximum and minimum value of the optical fluctuation spectrum at the position of <i>ω</i> = <i>ω</i><sub>m</sub> and <i>ω</i> = –<i>ω</i><sub>m</sub>, the mechanical resonator could be cooled down approximately to the ground state. Even when there exists an ensemble of two-level atoms in the right additional cavity, the mechanical resonator can be better cooled than just a cavity. These results may be conducive to the ground-state cooling of the mechanical resonator in the future experiment.</sec>

Magnetohydrodynamic convective flow of nanofluid in double lid-driven cavities under slip conditions

In this paper, we introduced a numerical analysis for the effect of a magnetic field on the mixed convection and heat transfer inside a two-sided lid-driven cavity with convective boundary conditions on its adjacent walls under the effects of the presence of thermal dispersion and partial slip. A single-phase model in which the water is the base fluid and a copper is nanoparticles is assumed to represent the nanofluid. The bottom and top walls of the cavity move in the horizontal direction with constant speed, while the vertical walls of the cavity are stationary. The right wall is mentioned at relatively low temperature and the top wall is thermally insulated. Convective boundary conditions are imposed to the left and bottom walls of the cavity and the thermal dispersion effects are considered. The finite volume method is used to solve the governing equations and comparisons with previously published results are performed. It is observed that the increase in the Hartmann number causes that the shear friction near the moving walls is enhanced and consequently the horizontal velocity component decreases.

Validation of a coupled pressure-equalization-thermal-mechanical model to study double-skin facades

Although double skin façades are a well-known façade system, still few experimental data and numerical approaches exist in literature that couple their thermal behaviour and pressure equalisation with the structural response. The reason is that, differently from insulating glazing units, the extent of the problem is trivial when designing ventilated double skins. Indeed, the leakage of the double skin cavity is large enough to avoid any response of the internal cavity pressure to its temperature variations. However, during the last years Closed Cavity Façades, a new trend of double skins, have been applied in order to achieve high performances in terms of thermal and acoustic insulation and providing at the same time valuable benefit with regards to maintenance cost reduction. The CCF low levels of air permeability are responsible for a strong correlation of pressure and temperature of its cavity and the phenomenon needs an accurate model to support the design. Indeed, an optimal design of the outer and inner skin should consider the skin interactions and their coupling through the cavity, under the dynamic temperature and variable mass within the cavity itself. The mass variation is governed by two counteracting effects: on one side the dry and clean air that is pumped into the cavity in order to avoid the risk of condensation, on the other side the mass flows through the skin openings that connects cavity with external and internal environment. Moreover, the pressure is also affected by the interior and exterior air pressures that induce a deflection of the inner and outer skin. A numerical calculation procedure was developed, integrated with commercial codes commonly used in façade design, in order to provide a unique assessment tool for the coupled thermal-mechanical design of double skin facades. The tool has been validated by means of an extensive experimental campaign and the different relevant effects have been described.

Flow characteristics of Axisymmetric Cavity Rear Wall Divergence Angle in a Scramjet Combustor

Non-reacting experimental study was performed on a rear wall angled cavity actuated supersonic flow of Mach 1.5 from a convergent divergent nozzle using a blowdown wind tunnel test setup. Ten different model combinations of double angled rear wall cavities is preferred for the study of improvements in the geometrical design of the combustor. Flow field properties of various cavity geometries were analyzed based on the key parameters like, wall static pressures, stagnation pressure loss to the flow and qualitative mixing of flow using momentum flux distribution. The static pressure is found to decrease inside the combustor with a decrease in the secondary dual rear wall angle below 90 degrees whereas value increases at the rear wall OWING to oscillation and recompression of shear layers inside the cavity region. In addition, the decrement in primary rear wall angle, an enhancement in mixing profile and a reduction in stagnation pressure loss are also observed.