212 research outputs found
Distance-dependent emission spectrum from two qubits in a strong-coupling regime
We study the emission spectrum of two distant qubits strongly coupled to a
waveguide by using the numerical and analytical approaches, which are beyond
the Markovian approximation and the rotating-wave approximation (RWA). The
numerical approach combines the Dirac-Frenkel time-dependent variational
principle with the multiple Davydov ansatz. A transformed RWA (TRWA)
treatment and a standard perturbation (SP) are used to analytically calculate
the emission spectrum. It is found that the variational approach and the TRWA
treatment yield accurate emission spectra of the two distant qubits in certain
strong coupling regimes while the SP breaks down. The emission spectrum is
found to be asymmetric irrespective of the two-qubit distance and exhibits a
single peak, doublet, and multipeaks depending on the two-qubit distance as
well as the initial states. In sharply contrast with the single-qubit case, the
excited-state populations of the two qubits can ultraslowly decay due to the
subradiance even in the presence of a strong qubit-waveguide coupling, which in
turn yields ultranarrow emission line. Our results provide insights into the
emission spectral features of the two distant qubits in the strong light-matter
coupling regime.Comment: 15 pages, 4 figure
Robust Formation Control for Networked Robotic Systems Using Negative Imaginary Dynamics
This paper proposes a consensus-based formation tracking scheme for multi-robot systems utilizing the Negative Imaginary (NI) theory. The proposed scheme applies to a class of networked robotic systems that can be modelled as a group of single integrator agents with stable uncertainties connected via an undirected graph. NI/SNI property of networked agents facilitates the design of a distributed Strictly Negative Imaginary (SNI) controller to achieve the desired formation tracking. A new theoretical proof of asymptotic convergence of the formation tracking trajectories is derived based on the integral controllability of a networked SNI systems. The proposed scheme is an alternative to the conventional Lyapunov-based formation tracking schemes. It offers robustness to NI/SNI-type model uncertainties and fault-tolerance to a sudden loss of robots due to hardware/communication fault. The feasibility and usefulness of the proposed formation tracking scheme were validated by lab-based real-time hardware experiments involving miniature mobile robots
Distributed Cooperative Autonomous Driving of Intelligent Vehicles Based on Spring-Damper Energy System
Distributed cooperative control of autonomous
vehicle platoons has been widely considered as a potential
solution for reducing traffic congestion, increasing road capacity
and improving traffic safety. However, in the real-world implementation, sudden communication loss will degrade cooperative
adaptive cruise control to adaptive cruise control, which may
bring negative influences on safety (i.e., increase the risk of
collisions). To overcome this limitation, this paper innovatively
applies a spring-damper energy system to construct a robust
leader-following vehicle platoon system. The special design of
the energy system ensures that the stability and safety of
the platoon system are maintained in the event of a sudden
degradation. Based on the proposed energy model, a distributed
control protocol is developed. The distributed control protocol
achieves speed synchronisation of vehicle platoon and ensures
that the following distance is safe over dynamic communication
networks. Finally, the effectiveness of the proposed control
strategy is validated by simulation experiments
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