41,501 research outputs found
Coherent versus measurement feedback: Linear systems theory for quantum information
To control a quantum system via feedback, we generally have two options in
choosing control scheme. One is the coherent feedback, which feeds the output
field of the system, through a fully quantum device, back to manipulate the
system without involving any measurement process. The other one is the
measurement-based feedback, which measures the output field and performs a
real-time manipulation on the system based on the measurement results. Both
schemes have advantages/disadvantages, depending on the system and the control
goal, hence their comparison in several situation is important. This paper
considers a general open linear quantum system with the following specific
control goals; back-action evasion (BAE), generation of a quantum
non-demolished (QND) variable, and generation of a decoherence-free subsystem
(DFS), all of which have important roles in quantum information science. Then
some no-go theorems are proven, clarifying that those goals cannot be achieved
by any measurement-based feedback control. On the other hand it is shown that,
for each control goal, there exists a coherent feedback controller
accomplishing the task. The key idea to obtain all the results is system
theoretic characterizations of BAE, QND, and DFS in terms of controllability
and observability properties or transfer functions of linear systems, which are
consistent with their standard definitions.Comment: 21 pages, 10 figures, to appear in Physical Review
Comparing and combining measurement-based and driven-dissipative entanglement stabilization
We demonstrate and contrast two approaches to the stabilization of qubit
entanglement by feedback. Our demonstration is built on a feedback platform
consisting of two superconducting qubits coupled to a cavity which are measured
by a nearly-quantum-limited measurement chain and controlled by high-speed
classical logic circuits. This platform is used to stabilize entanglement by
two nominally distinct schemes: a "passive" reservoir engineering method and an
"active" correction based on conditional parity measurements. In view of the
instrumental roles that these two feedback paradigms play in quantum
error-correction and quantum control, we directly compare them on the same
experimental setup. Further, we show that a second layer of feedback can be
added to each of these schemes, which heralds the presence of a high-fidelity
entangled state in realtime. This "nested" feedback brings about a marked
entanglement fidelity improvement without sacrificing success probability.Comment: 40 pages, 12 figure
Cost effective combined axial fan and throttling valve control of ventilation rate
This paper is concerned with Proportional-Integral-Plus (PIP) control of ventilation rate in mechanically ventilated agricultural buildings. In particular, it develops a unique fan and throttling valve control system for a 22m3 test chamber, representing a section of a livestock building or glasshouse, at the Katholieke Universiteit Leuven. Here, the throttling valve is employed to restrict airflow at the outlet, so generating a higher static pressure difference over the control fan. In contrast with previous approaches, however, the throttling valve is directly employed as a second control actuator, utilising airflow from either the axial fan or natural ventilation. The new combined fan/valve configuration is compared with a commercially available PID-based controller and a previously developed scheduled PIP design, yielding a reduction in power consumption in both cases of up to 45%
Direct and Indirect Couplings in Coherent Feedback Control of Linear Quantum Systems
The purpose of this paper is to study and design direct and indirect
couplings for use in coherent feedback control of a class of linear quantum
stochastic systems. A general physical model for a nominal linear quantum
system coupled directly and indirectly to external systems is presented.
Fundamental properties of stability, dissipation, passivity, and gain for this
class of linear quantum models are presented and characterized using complex
Lyapunov equations and linear matrix inequalities (LMIs). Coherent
and LQG synthesis methods are extended to accommodate direct couplings using
multistep optimization. Examples are given to illustrate the results.Comment: 33 pages, 7 figures; accepted for publication in IEEE Transactions on
Automatic Control, October 201
Fuzzy Control of Chaos
We introduce the idea of the fuzzy control of chaos: we show how fuzzy logic
can be applied to the control of chaos, and provide an example of fuzzy control
used to control chaos in Chua's circuit
Yaw Rate and Sideslip Angle Control Through Single Input Single Output Direct Yaw Moment Control
Electric vehicles with independently controlled drivetrains allow torque vectoring, which enhances active safety and handling qualities. This article proposes an approach for the concurrent control of yaw rate and sideslip angle based on a single-input single-output (SISO) yaw rate controller. With the SISO formulation, the reference yaw rate is first defined according to the vehicle handling requirements and is then corrected based on the actual sideslip angle. The sideslip angle contribution guarantees a prompt corrective action in critical situations such as incipient vehicle oversteer during limit cornering in low tire-road friction conditions. A design methodology in the frequency domain is discussed, including stability analysis based on the theory of switched linear systems. The performance of the control structure is assessed via: 1) phase-plane plots obtained with a nonlinear vehicle model; 2) simulations with an experimentally validated model, including multiple feedback control structures; and 3) experimental tests on an electric vehicle demonstrator along step steer maneuvers with purposely induced and controlled vehicle drift. Results show that the SISO controller allows constraining the sideslip angle within the predetermined thresholds and yields tire-road friction adaptation with all the considered feedback controllers
- …