Second-order Coupling Effects Research Articles

High-fidelity and Robust Stimulated Raman Transition with Parameter-modulated Optimal Control

High-fidelity and robust quantum control is essential for large-scale quantum information processing. The stimulated Raman transition that utilizes second-order coupling effect is a valuable and conventional technique for manipulating states in multi-level quantum systems, but its accuracy is limited by the driving-induced Stark shift. Here, we propose a new parameter-modulated method to effectively compensate the Stark-shift effect, so that we are able to realize high-fidelity and robust stimulated Raman transition with optimal control. Additionally, its robustness against different systematic errors can be further improved via optimization its average fidelity under these specific errors. Besides, our method has potential applications for high-fidelity and robust quantum control in high-order coupling scenarios.

Dynamic Modeling and Analysis of a Rotating Piezoelectric Smart Beam

In active vibration control study, piezoelectric actuators and sensors are bonded on the surface of a beam. They can change the frequency and modal characteristics of the system. This paper presents an analysis of the frequency response to a rotating piezoelectric smart beam. Hamilton’s principle along with the assumed mode method are employed to derive the governing equations of the first-order approximate coupling model for the piezoelectric smart beam. The coupling is taken into account as the second-order coupling effect of the axial elongation caused by the transverse displacement of the beam. Then, the equations are transformed into a dimensionless form after identifying the necessary parameters. The dimensionless natural frequencies of the piezoelectric smart beam corresponding to the bending and stretching vibrations are obtained through a numerical simulation, with comparison made of those of the beam with no actuator or sensor. Furthermore, the implication is investigated of the structural parameters and bond location on the piezoelectric actuators and sensors. Besides, the common case of a smart beam bonded with multiple pairs of piezoelectric actuators and sensors is studied, and the effects of the first natural frequency and tip deformation are analyzed. The research provides a theoretical reference for the optimization of structural parameters and location of piezoelectric actuators and sensors, thereby preventing the resonance when the excitation frequency is approximately equal to the natural frequency of the beam.

Effect of second-order coupling on photon-pair statistics in waveguide structures

We investigate a quasi-one-dimensional periodic array of coupled waveguides, with one extended and one bound dimension, incorporating both first- and second-order coupling. We study the evolution of optical fields in this system, and measure quantum correlations when path-entangled photon pairs are launched into them. We observe a surprisingly large and nontrivial effect of second-order coupling on these correlations---while quantum correlations are symmetric when only first-order coupling is present, the introduction of next-nearest-neighbor coupling often breaks the symmetry to reflections.

Effect of second-order coupling on optical bistability in a hybrid optomechanical system

We theoretically investigate an optomechanical system consisting of two coupled cavities, a bare optomechanical cavity and a traditional one. An optical parametric amplifier (OPA) is placed inside the traditional cavity. Optomechanical cavity has an oscillating mirror and a fixed one. In addition to the first order coupling between mechanical resonator of the system and the radiation pressure of optomechanical cavity, we consider a second order interaction between them. The evaluation of the system’s behavior shows bistability in the mean photon number of optomechanical cavity. Our results show that, the second order coupling leads to degenerate solutions for the equation of mean photon number of optomechanical cavity. We see that the strength of SOC can change the domain of bistability region of optomechanical cavity. Also, properties of the field driving OPA have remarkable effects on the stability of optomechanical cavity. Moreover, we show that the domain of bistability region can be modified by changing of optical properties of the system.

The Importance of Vibronic Coupling for Efficient Reverse Intersystem Crossing in Thermally Activated Delayed Fluorescence Molecules.

Factors influencing the rate of reverse intersystem crossing (k rISC) in thermally activated delayed fluorescence (TADF) emitters are critical for improving the efficiency and performance of third‐generation heavy‐metal‐free organic light‐emitting diodes (OLEDs). However, present understanding of the TADF mechanism does not extend far beyond a thermal equilibrium between the lowest singlet and triplet states and consequently research has focused almost exclusively on the energy gap between these two states. Herein, we use a model spin‐vibronic Hamiltonian to reveal the crucial role of non‐Born‐Oppenheimer effects in determining k rISC. We demonstrate that vibronic (nonadiabatic) coupling between the lowest local excitation triplet (3LE) and lowest charge transfer triplet (3CT) opens the possibility for significant second‐order coupling effects and increases k rISC by about four orders of magnitude. Crucially, these simulations reveal the dynamical mechanism for highly efficient TADF and opens design routes that go beyond the Born‐Oppenheimer approximation for the future development of high‐performing systems.

Fast universal quantum gates on microwave photons with all-resonance operations in circuit QED.

Stark shift on a superconducting qubit in circuit quantum electrodynamics (QED) has been used to construct universal quantum entangling gates on superconducting resonators in previous works. It is a second-order coupling effect between the resonator and the qubit in the dispersive regime, which leads to a slow state-selective rotation on the qubit. Here, we present two proposals to construct the fast universal quantum gates on superconducting resonators in a microwave-photon quantum processor composed of multiple superconducting resonators coupled to a superconducting transmon qutrit, that is, the controlled-phase (c-phase) gate on two microwave-photon resonators and the controlled-controlled phase (cc-phase) gates on three resonators, resorting to quantum resonance operations, without any drive field. Compared with previous works, our universal quantum gates have the higher fidelities and shorter operation times in theory. The numerical simulation shows that the fidelity of our c-phase gate is 99.57% within about 38.1 ns and that of our cc-phase gate is 99.25% within about 73.3 ns.

Enhancement of Localization in a Driven Four-Well System with Second-Order Coupling

We study theoretically the effect of second-order coupling (SOC) on the tunneling dynamics in a planar four-well system with only one well periodically modulated. We find that SOC between next-nearest neighboring wells facilitates localization. Due to SOC, the suppression of tunneling occurs over a finite range of parameters, in stark contrast to the normal coherent destruction of tunneling in the nearest-neighbor tight-binding approximation. This counter-intuitive phenomenon of SOC-enhanced localization can be attributed to the existence of a localized Floquet state rather than the degeneracy of quasi-energy levels in such a system.

Heteronuclear second-order coupling effects in platinum-lead-bonded compounds

As part of NMR investigations of chemical shifts and couplings of heavy nuclei bonded to each other we have been examining compounds with direct platinu ti nd platinum-lead bonds and now report second-order coupling effects betwee 19 and zo7Pb in platinum-lead compounds. This communication has bee prompted by the recent report (I) of isotopic heteronuclear second-order ~0~~1~~ between ‘17Sn and “‘Sn in (Ru(SnC1,),C1)4and (Os(SnC1,),C1)4-. As an example we take the compound cis-Pt(PPh,),(Ph)(PbPh3) for which the 31P NMR spectrum (2) in dichloromethane consists of two main doublets (6 24.85 ppm, 6 20.80 ppm) arising from the nonequivalent phosphines (2J(31P-3’ Hz). The doublet at higher frequency has satellites (‘J(‘95Pt-31P) = 2 2J(207Pb-31P) = 3460 Hz), which are consistent with a phosphorus tram to and the doublet at lower frequency has couplings (1J(g5Pt-31P) = 1965 Hz, 31P) = 260 Hz), which are consistent with a phosphorus cis to the lead atom. The “*Pt NMR spectrum at 21.3 1 MHz (Fig. 1) of cis-Pt(PPh3),(Ph)(PbFhs) has a central doublet of doublets resulting from coupling to the different phospbor~s atoms and two sets of *“Pb satellites (with the same phosphorus couplings) each f intensity approximately 12% relative to the central multiplet. The two sets of llites are not symmetrically disposed about the central multiplet, their tion being 180 Hz above the frequency of the main multiplet. The *07P spectrum at 20.84 MHz (Fig. 1) is of similar appearance (with different ph uplings) with lg5Pt satellites ( 16% of the central multiplet) unsymmetrically dissed about the central multiplet by 180 Hz to the lower frequency side of the spectrum. Spectra recorded at higher field (lg5Pt at 42.70 MHz, 207Pb at 41.74 MHz) show the asymmetry is decreased to 85 Hz. That the asymmetry is attributable to second-order coupling effects in the satellite spectrum rather than a large isotope effect is endorsed by several experimental observations. The above variation of the asymmetry with frequency is quite the opposite of that expected for an isotope effect, The central multiplets of both spectra have sharp, well-defined lines. In the platinum-195 spectrum this central multiplet corresponds to lg5Pt bonded to lead nuclei with spin 0 (*O’Pb 24%, “‘Pb 52%). gnitude of the asymmetry of the satellites suggests that for a genuine isoto ct the peaks of the central multiplet should be significantly broadened, if split into two multiplets, corresponding to lg5Pt bonded to each of those two nuclei.

Heteronuclear second-order coupling effects in high-resolution Tin NMR spectra

Heteronuclear second-order coupling effects in high-resolution Tin NMR spectra

Mercury tiltmeter as an infrasonic detector: Theory, observations, and applications

Observations of acoustic gravity waves at Eilat by a mercury tiltmeter are reported and interpreted. Waves belonging to the first gravity mode (GR0) and three acoustic modes (S0, S1, S2) that originated at the Chinese nuclear air blast of October 14, 1970, were simultaneously recorded on infrasonic microbarographs and the newly installed MIT (Massachusetts Institute of Technology) tiltmeters. The explosion (yield, about 5 Mt) produced at a distance of 5024 km a surface overpressure of about 300 μb at 240 sec. This overpressure in turn caused a horizontal displacement of 3 μ and a tilt of 3 × 10−10 rad at the same period. Plane-wave theory is used to show that the incident sound wave can excite a surface wave at the recording site through a second-order coupling effect. The induced waves propagate in the earth with the sound phase velocity and decay exponentially with depth. This theory is in good agreement with the observations. It is shown that the surface sound pressure and the induced ground motion are tied by a simple relation from which the mean rigidity of the upper crust at the recording site can be derived. The local rigidity of the granitic upper crust at Eilat is thus found to be 3.22 × 1011 dynes/cm2. Sensitivity of the tiltmeter to infrasonic waves in the period range 20–400 sec is estimated to be 10−12 rad/μb at zero site noise and electronic snr ratio of 1:1, with a detectability threshold at about 20 μb.