Initial Motional State Research Articles

Research on Stable Motion Control Method of Underwater Robot Based on Collaborative Filtering Technology

As countries in the world continue to deepen marine research and development and the need for national defense construction, unmanned underwater robots are playing an increasingly important role in scientific experiments, seabed oil and gas exploration and testing, and military affairs. The motion stability of underwater robots is the key to ensure the safe and reliable operation of underwater robots, and it is the main content of stability control research to make underwater robots return to the initial state of motion after being disturbed. Therefore, it becomes very important to study stability control methods. It’s necessary. This thesis first analyzes the motion characteristics of collaborative filtering technology in water, and establishes a dynamic model of an underwater robot system composed of main thrusters, double vertical thrusters and double-sided thrusters, and performs basic fluid flow for underwater robots.

How to put quantum particles on magic bullet trajectories that can hit two targets without a clear line-of-sight

Quantum particles move in strange ways, even when they propagate freely in space. As a result of the uncertainty principle, it is not possible to control the initial conditions of particle emission in such a way that the particle will definitely pass through two precisely defined positions along its path, even if it is possible to line up the two positions with the emitter. However, there is also an upside to the quantum mechanical laws of motion: constructive quantum interferences can actually raise probabilities to values higher than those permitted by classical causality. Here, it is shown that conventional interferometric methods can be used to prepare photons in a quantum state in which a non-vanishing fraction of particles will hit both of two possible targets, even though the direct line-of-sight connecting the two targets is blocked at the source. The demonstration of the effect is complicated by the uncertainty principle because the physical detection of a particle at one target disturbs the motion of the particle, making it impossible to determine whether the initial state of motion would have allowed the particle to hit the other target or not. It is nonetheless possible to determine the minimal fraction of “magic bullet” particles that must have hit both targets by showing that the number of particles hitting target A is larger than the number of particles missing target B. Quantum interference effects can thus be used to optimize the path of particles in free space beyond the classical limit of motion along a straight line.

Interferometer for force measurement via a shortcut to adiabatic arm guiding

We propose a compact atom interferometer to measure homogeneous constant forces guiding the arms via shortcuts to adiabatic paths. For a given sensitivity, which only depends on the space-time area of the guiding paths, the cycle time can be made fast without losing visibility. The atom is driven by spin-dependent trapping potentials moving in opposite directions, complemented by linear and time-dependent potentials that compensate the trap acceleration. Thus, the arm states are adiabatic in the moving frames and nonadiabatic in the laboratory frame. The trapping potentials may be anharmonic, e.g., optical lattices, and the interferometric phase does not depend on the initial motional state or on the pivot point for swaying the linear potentials.Received 10 March 2020Accepted 20 May 2020Corrected 17 September 2020DOI:https://doi.org/10.1103/PhysRevResearch.2.023328Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAtom interferometryAtom lasersAtom opticsCold atoms & matter wavesAtomic, Molecular & OpticalQuantum Information

Ultra-intense laser pulse characterization using ponderomotive electron scattering

We present a new analytical solution for the equation of motion of relativistic electrons in the focus of a high-intensity laser pulse. We approximate the electron’s transverse dynamics in the averaged field of a long laser pulse focused to a Gaussian transverse profile. The resultant ponderomotive scattering is found to feature an upper boundary of the electrons’ scattering angles, depending on the laser parameters and the electrons’ initial state of motion. In particular, we demonstrate the angles into which the electrons are scattered by the laser scale as a simple relation of their initial energy to the laser’s amplitude. We find two regimes to be distinguished in which either the laser’s focusing or peak power are the main drivers of ponderomotive scattering. Based on this result, we demonstrate how the intensity of a laser pulse can be determined from a ring-shaped pattern in the spatial distribution of a high-energy electron beam scattered from the laser. We confirm our analysis by means of detailed relativistic test particle simulations of the electrons’ averaged ponderomotive dynamics in the full electromagnetic fields of the focused laser pulse.

Fast phase gates with trapped ions

We implement faster-than-adiabatic two-qubit phase gates using smooth state-dependent forces. The forces are designed to leave no final motional excitation, independently of the initial motional state in the harmonic, small-oscillations limit. They are simple, explicit functions of time and the desired logical phase of the gate, and are based on quadratic invariants of motion and Lewis-Riesenfeld phases of the normal modes.

Quantum State Transfer Using the Four-Ion Cluste State

We demonstrate that a four-ion cluster state can be used to realize the quantum state transfer in the ion-trap systems. The scheme does not involve Bell-state measurement and is insensitive to both the initial motional state and heating.

Detection of motional ground state population of a trapped ion using delayed pulses

Efficient preparation and detection of the motional state of trapped ions is important in many experiments ranging from quantum computation to precision spectroscopy. We investigate the stimulated Raman adiabatic passage (STIRAP) technique for the manipulation of motional states in a trapped ion system. The presented technique uses a Raman coupling between two hyperfine ground states in 25Mg+, implemented with delayed pulses, which removes a single phonon independent of the initial motional state. We show that for a thermal probability distribution of motional states the STIRAP population transfer is more efficient than a stimulated Raman Rabi pulse on a motional sideband. In contrast to previous implementations, a large detuning of more than 200 times the natural linewidth of the transition is used. This approach renders STIRAP suitable for atoms in which resonant laser fields would populate nearby fluorescing excited states and thus impede the STIRAP process. We use the technique to measure the wavefunction overlap of excited motional states with the motional ground state. This is an important application for force sensing applications using trapped ions, such as photon recoil spectroscopy, in which the signal is proportional to the depletion of motional ground state population. Furthermore, a determination of the ground state population enables a simple measurement of the ion's temperature.

Controlled Teleportation of an Arbitrary Two-ion State by Using Five-ion Cluster State in Ion-trap Systems

We demonstrate that a five-ion cluster state can be used to realize the deterministic controlled teleportation of an arbitrary two-ion state in ion-trap systems. The scheme does not involve Bell-state measurement and is insensitive to both the initial motional state and heating.

Scheme for Implementing Quantum Dense Coding by Using GHZ-Like State in Ion-Trap Systems

An experimentally feasible scheme for implementing quantum dense coding by using a GHZ-like state is proposed. In ion-trap systems, we demonstrated that the probability of implementing quantum dense coding is 100 %. In addition, our approach is insensitive to both the initial motional state and heating.

Generation of a genuine six-partite entangled state in trapped-ion system

Recently, a genuine six-qubit entangled state |six> has been proposed [Chen P X, et al. Phys Rev A, 2006, 74: 032324]. This state does not belong to the well-known three types of multipartite entangled states, i.e., Greenberger-Horne-Zeilinger (GHZ) state, W state, and linear cluster state. This state has many potential applications in quantum information processing. We propose a scheme for generating such a genuine six-qubit entangled state for trapped ions in thermal motion. The scheme is insensitive to both the initial motional state and heating.

On the phase dependence of the interconversion of the motional modes in a Penning trap by quadrupolar excitation

The interconversion of the radial motional modes in a Penning trap (magnetron and cyclotron modes) by an external quadrupolar rf-field with a frequency near the true cyclotron frequency ω c plays an important role in the measurement cycle of Penning trap mass spectrometry. Ions to be measured are prepared in a state of magnetron motion which is then resonantly converted into cyclotron motion. The data analysis is usually carried out under the assumption that the initial motional state of the ions has been a pure magnetron state. In reality, however, a small component of cyclotron motion is always present in the ion's initial motional state. This component introduces a dependence on the initial phases of the quadrupolar rf-field and of the magnetron and cyclotron oscillators. This paper explores how excitation curves, conversion times and conversion line shapes depend on these phases and on the initial radius of the cyclotron motion. Since most experiments cannot control all of these phases the data must be interpreted in terms of phase-averaged quantities. These are slightly more general than those for pure magnetron motion. Most importantly, there are no shifts of the maxima and minima of phase-averaged conversion profiles compared to those predicted with pure magnetron motion in the initial state, so that the mass determinations are not affected. The theory predicts experimental data points to fall not on a mathematical curve, as for pure magnetron motion in the initial state, but within bands about the phase-averaged curves, with a finite width roughly proportional to the radius of the initial cyclotron motion. The scattering of data points can give rise to a loss of contrast of measured conversion line shapes. The component of cyclotron motion in the initial state introduces an additional parameter into the analytical expressions for conventional and Ramsey type excitation that could in some cases be useful for data fitting.

Cluster States from Quantum Logic Gates with Trapped Ions inThermal Motion

Following the recent proposal by Briegel et al. [Phys. Rev. Lett. 86(2001) 910], a procedure is proposed for one-step realizing quantumcontrol phase gates with two trapped ions in thermal motion. It is shownthat the scheme can also be used to create a new special type ofentangled states, i.e., cluster states of many trapped ions. In thescheme the two-trapped ions are simultaneously excited by a single laserbeam and the frequency of the laser beam is slightly off resonance withthe first lower vibration sideband of the trapped ions. The distinctadvantage of the scheme is that it does not use the vibrational mode asthe data bus. Furthermore, our scheme is insensitive to both the initialmotional state and heating (or decay) as long as the system remains inthe Lamb–Dicke regime.

Generation of entangled states of multiple trapped ions in thermal motion

A scheme is presented for generating entangled states of the $\mathrm{W}$ type for trapped ions in thermal motion. In the scheme the ions are simultaneously excited by a laser. Our scheme is insensitive to both the initial motional state and heating as long as the system remains in the Lamb-Dicke regime.

Quantum Dynamics of a Single Trapped Ion Interacting with Standing Laser Pulses**The project supported by National Natural Science Foundation of China under Grant No. 10275023

A classically chaotic system consisting of a Paul trapped ion and a sequences of standing laser pulses is treated quantum-mechanically. Under the circumstance of time-dependence, we derive the transition probability from the ion's motional state to ', and find, in the first-order approximation, the classically chaotic character disappears. Theoretical analysis and numerical calculations show that by regulating the phase parameter we can control the transition probability. When reaches some specific values, the transition from the state to ' is forbidden and, for some laser periods, resonance occurs, which leads to the corresponding transitions between different motional states. The time-evolution of an initial motional state just over one period is also studied in detail.

Motional effects of trapped atomic or ionic qubits

We investigate decoherence effects due to motional degrees of freedom of trapped electronically coded atomic or ionic qubits. For universal single bit rotations implemented with dipole coupling from a near resonant running wave laser, the achievable fidelity is found to depend only on a single parameter characterized by the initial motional state. For two-qubit conditional logic operations inside a high Q optical cavity, we find the popular dark state structure survives even when atomic wave packets are not localized along transverse directions. Our quantitative results provide a useful realistic view for current experimental efforts in quantum logic and computing.

Inertial motion of a continuum

The Burgers equation ut+uux=νuxx represents pure inertial motion except for the effects of viscosity ν. If ν=0, this equation becomes u̇=0 and describes the inertial motion of a one-dimensional continuum until the time of formation of discontinuities, or ’’shocks’’. The study of pure inertial motion is extended to an arbitrary number of dimensions. Starting from some initial state of motion each parcel of the continuum may or may not have the intrinsic ability to form a shock, this property being a function of the symmetrical part of the velocity gradient matrix in the vicinity of the parcel. This study determines the conditions for which a parcel will, in fact, form a shock, the time that is required, and the temporal development of the full velocity gradient matrix and of coordinate invariants of the flow such as the divergence and the vorticity.

Response Time of Impulsively Loaded Structures

Consider a rigid, perfectly plastic structure that proceeds, in the absence of external forces, from an initial state of motion with given velocity distribution to a final state of rest.

On the general theory of contained rotating fluid motions

A general linear theory is developed to describe the manner in which rigid fluid rotation is established from a prescribed initial state of motion in a container of arbitrary shape. The container rotates with uniform angular velocity and is filled with a viscous incompressible fluid.A new mean circulation theorem is proved and used to separate the flow into geostrophic motion and inertial oscillations. The basic eigenvalue problem is studied and important properties concerning spectrum, orthogonality and completeness are deduced. The effect of viscosity on the inviscid modes is calculated in a manner that maintains the solution uniformly valid through the spin-up time. All modes decay in this time scale which characterizes the entire transition to rigid rotation in all configurations.

On the transient motion of a contained rotating fluid

This paper considers the transient motion of a viscous fluid in a container rotating with constant angular velocity. The principal objective is to study the manner in which an arbitrary initial state of motion becomes a rigid rotation. In order to concentrate on the effects of viscosity, only the spherical container is studied here in great detail. A general theory will be presented in a subsequent publication.Several sources of non-uniform behaviour make the analysis difficult and complex. In particular, there are three important time scales, viscous boundary layers, boundary-layer resonances at critical latitudes and intricate side-wall effects. The basic aproach consists of an expansion procedure by means of which the general inviscid solution is corrected for viscous effects and is made uniformly valid in time through the critical spin-up phase. Uniform validity is effected through the elimination of secular terms with unacceptable growth rates arising from the asymptotic perturbation series.The interior (inviscid) motion leads to a non-self-adjoint partial differential equation eigenvalue problem with many intriguing properties. The general expansion theorem, orthogonality relationships, and viscous decay factors are deduced and used to solve the arbitrary intial-value problem. It is shown that the depth averaged circulation about circular contours, x2 + y2 = r2, is extracted from the fluid in the spin-up time scale T = L(Ωv)½. This is accomplished by a secondary non-oscillatory convective motion produced by suction into the Ekman layer. The excess circulation not eliminated in this way excites inviscid inertial oscillations which are also caused to decay by the boundary layers in the same time scale. Some very small residual effects decay in the ordinary viscous diffusion time, but all the essential processes are concluded in the much shorter interval. All modal oscillations in a sphere are determined and several specific calculations of frequency and decay rate are made and compared with experimental data. Perhaps the most important of these concerns the mode corresponding to rigid internal motion about another axis which can be produced by impulsively changing the rotation axis of the container. Agreement between theory and experiment is very good in all cases compared thus far.