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<jats:p>High-efficiency terahertz (THz) wave generation with multiple frequencies by optimized cascaded difference frequency generation (OCDFG) is investigated at 100 K using a nonlinear crystal consisting of a periodically poled lithium niobate (PPLN) part and an aperiodically poled lithium niobate (APPLN) part. Two infrared pump waves with a frequency difference <jats:italic>ω</jats:italic> <jats:sub>T1</jats:sub> generate THz waves and a series of cascaded optical waves in the PPLN part by cascaded difference frequency generation (CDFG). The generated cascaded optical waves with frequency interval <jats:italic>ω</jats:italic> <jats:sub>T1</jats:sub> then further interact in the APPLN part by OCDFG, yielding the following two advantages. First, OCDFG in the APPLN part is efficiently stimulated by inputting multi-order cascaded optical waves rather than the only two intense infrared pump waves, yielding unprecedented energy conversion efficiencies in excess of 37% at 1 THz at 100 K. Second, THz waves with <jats:italic>M</jats:italic> times <jats:italic>ω</jats:italic> <jats:sub>T1</jats:sub> are generated by mixing the <jats:italic>m</jats:italic>th-order and the (<jats:italic>m</jats:italic> + <jats:italic>M</jats:italic>)th-order cascaded optical waves by designing poling period distributions of the APPLN part.</jats:p>

<jats:p>High fidelity two-qubit gates are fundamental for scaling up the superconducting qubit number. We use two qubits coupled via a frequency-tunable coupler which can adjust the coupling strength, and demonstrate the CZ gate using two different schemes, adiabatic and diabatic methods. The Clifford based randomized benchmarking (RB) method is used to assess and optimize the CZ gate fidelity. The fidelities of adiabatic and diabatic CZ gates are 99.53(8)% and 98.72(2)%, respectively. We also analyze the errors induced by the decoherence. Comparing to 30 ns duration time of adiabatic CZ gate, the duration time of diabatic CZ gate is 19 ns, revealing lower incoherence error rate <jats:inline-formula> <jats:tex-math> <?CDATA ${{r}^{^{\prime} }}_{{\rm{incoherent}},{\rm{int}}}=0.0197(5)$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:msup> <mml:mi>r</mml:mi> <mml:mo>′</mml:mo> </mml:msup> <mml:mrow> <mml:mi mathvariant="normal">incoherent</mml:mi> <mml:mo>,</mml:mo> <mml:mi mathvariant="normal">int</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>0.0197</mml:mn> <mml:mo stretchy="false">(</mml:mo> <mml:mn>5</mml:mn> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_30_4_044212_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> compared to <jats:italic>r</jats:italic> <jats:sub>incoherent, int</jats:sub> = 0.0223(3).</jats:p>

<jats:p>A distant-neighbor quantum-mechanical method is used to study the nonlinear optical wave mixing in graphene nanoflakes (GNFs), including sum- and difference-frequency generation, as well as four-wave mixing. Our analysis shows that molecular-scale GNFs support quantum plasmons in the visible spectrum region, and significant enhancement of nonlinear optical wave mixing is achieved. Specifically, the second- and third-order wave-mixing polarizabilities of GNFs are dramatically enhanced, provided that one (or more) of the input or output frequencies coincide with a quantum plasmon resonance. Moreover, by embedding a cavity into hexagonal GNFs, we show that one can break the structural inversion symmetry and enable otherwise forbidden second-order wave mixing, which is found to be enhanced by the quantum plasmon resonance too. This study reveals that the molecular-sized graphene could be used in the quantum regime for nanoscale nonlinear optical devices and ultrasensitive molecular sensors.</jats:p>

<jats:p>Optimal creation of photon Fock states is of importance for quantum information processing and state engineering. Here an efficient strategy is presented for speeding up generation of photon Fock state in a superconducting circuit via counterdiabatic driving. A transmon qubit is dispersively coupled to a quantized electrical field. We address a Λ-configuration interaction between the composite system and classical drivings. Based on two Gaussian-shaped drivings, a single-photon Fock state can be generated adiabatically. Instead of adding an auxiliary counterdiabatic driving, our concern is to modify these two Rabi drivings in the framework of shortcut to adiabaticity. Thus an accelerated operation with high efficiency can be realized in a much shorter time. Compared with the adiabatic counterpart, the shortcut-based operation is significantly insusceptible to decoherence effects. The scheme could offer a promising way to deterministically prepare photon Fock states with superconducting quantum circuits.</jats:p>

<jats:p>Recent evidence suggests that the multiple charge-separation pathways can contribute to photosynthetic performance. In this work, the influence of coupled-dipoles on photosynthetic performance was investigated in a two-charge separation pathways quantum heat engine (QHE) model. And the population dynamics of the two coupled sites, <jats:italic>j</jats:italic>–<jats:italic>V</jats:italic> characteristics, and power involving this photosynthetic QHE model were evaluated for the photosynthetic performance. The results illustrate that the photosynthetic performance can be greatly enhanced but quantum interference is deactivated by the coupled-dipoles between the two-charge separation pathways. However, the photosynthetic performance can also be promoted by the deactivated quantum interference owing to the coupled-dipoles. It is a novel role of the coupled-dipoles in the energy transport process of biological photosynthetic, and some artificial strategies may be motivated by this photosynthetic QHE model in the future.</jats:p>

<jats:p>Contactless manipulation of multi-scale objects using the acoustic vortex (AV) tweezers offers tremendous perspectives in biomedical applications. However, it is still hindered by the weak acoustic radiation force (ARF) and torque (ART) around the vortex center. By introducing the elevation angle to the planar transducers of an <jats:italic>N</jats:italic>-element ring array, the weak-focused acoustic vortex (WFAV) composed of a main-AV and <jats:italic>N</jats:italic> paraxial-AVs is constructed to conduct a large-scale object manipulation. Different from the traditional focused AV (FAV) generated by a ring array of concave spherical transducers, a much larger focal region of the WFAV is generated by the main lobes of the planar transducers with the size inversely associated with the elevation angle. With the pressure simulation of the acoustic field, the capability of the rotational object driving in the focal plane for the WFAV is analyzed using the ARF and the ART exerted on an elastic ball based on acoustic scattering. With the experimental system built in water, the generation of the WFAV is verified by the scanning measurements of the acoustic field and the capability of object manipulation is also analyzed by the rotational trapping of floating particles in the focal plane. The favorable results demonstrate the feasibility of large-scale rotational manipulation of objects with a strengthened ART and a reduced acousto-thermal damage to biological tissues, showing a promising prospect for potential applications in clinical practice.</jats:p>

<jats:p>We report instability of the single-walled carbon nanotubes (SWCNT) filled with non-Newtonian Jeffrey fluid. Our objective is to get the influences of relaxation time and retardation time of the Jeffrey fluid on the vibration frequency and the decaying rate of the amplitude of carbon nanotubes. An elastic Euler–Bernoulli beam model is used to describe vibrations and structural instability of the carbon nanotubes. A new vibration equation of an SWCNT conveying Jeffrey fluid is first derived by employing Euler–Bernoulli beam equation and Cauchy momentum equation taking constitutive relation of Jeffrey fluid into account. The complex vibrating frequencies of the SWCNT are computed by solving a cubic eigenvalue problem based upon differential quadrature method (DQM). It is interesting to find from computational results that retardation time has significant influences on the vibration frequency and the decaying rate of the amplitude. Especially, the vibration frequency decreases and critical velocity increases with the retardation time. That is to say, longer retardation time makes the SWCNT more stable.</jats:p>

<jats:p>The interaction between cavitation bubble and solid surface is a fundamental topic which is deeply concerned for the utilization or avoidance of cavitation effect. The complexity of this topic is that the cavitation bubble collapse includes many extreme physical phenomena and variability of different solid surface properties. In the present work, the cavitation bubble collapse in hydrophobic concave is studied using the pseudopotential multi-relaxation-time lattice Boltzmann model (MRT-LB). The model is modified by involving the piecewise linear equation of state and improved forcing scheme. The fluid–solid interaction in the model is employed to adjust the wettability of solid surface. Moreover, the validity of the model is verified by comparison with experimental results and grid-independence verification. Finally, the cavitation bubble collapse in a hydrophobic concave is studied by investigating density field, pressure field, collapse time, and jet velocity. The superimposed effect of the surface hydrophobicity and concave geometry is analyzed and explained in the framework of the pseudopotential LBM. The study shows that the hydrophobic concave can enhance cavitation effect by decreasing cavitation threshold, accelerating collapse and increasing jet velocity.</jats:p>

<jats:p>A simplified theoretical model for the linear Rayleigh–Taylor instability of finite thickness elastic–plastic solid constantly accelerated by finite thickness viscous fluid is performed. With the irrotational assumption, it is possible to consider viscosity, surface tension, elasticity or plasticity effects simultaneously. The model considers thicknesses at rigid wall boundary conditions with the velocity potentials, and deals with solid elastic–plastic transition and fluid viscosity based on the velocity continuity and force equilibrium at contact interface. The complete analytical expressions of the amplitude motion equation, the growth rate, and the instability boundary are obtained for arbitrary Atwood number, viscosity, thicknesses of solid and fluid. The thicknesses effects of two materials on the growth rate and the instability boundary are discussed.</jats:p>

<jats:p>A thermal multiphase lattice Boltzmann (LB) model is used to study the behavior of droplet impact on hot surface and the relevant heat transfer properties. After validating the correctness of the codes through the <jats:italic>D</jats:italic> <jats:sup>2</jats:sup> law, the simulations of intrinsic contact angle and the temperature-dependent surface tension are performed. The LB model is then used to simulate the droplet impact on smooth and micro-hole heated surface. On the smooth surface, the impinging droplet is reluctant to rebound, unless the intrinsic wettability of the solid surface is fairly good. On the micro-hole surface, however, the micro-holes provide favorable sites for generating a high-pressure vapor cushion underneath the impinging droplet, which thereby facilitates the continuous droplet rebound. For the continuously rebounding droplet. The time evolution of volume and temperature display obvious oscillations. The achievable height of the rebounding droplet increases as the intrinsic wettability of the solid surface becomes better, and the maximum transient heat flux is found to be directly proportional to the droplet rebounding height. Within a certain time interval, the continuous rebounding behavior of the droplet is favorable for enhancing the total heat quantity/heat transfer efficiency, and the influence of intrinsic wettability on the total heat during droplet impingement is greater than that of the superheat. The LB simulations not only present different states of droplets on hot surfaces, but also guide the design of the micro-hole surface with desirable heat transfer properties.</jats:p>