Quantum control by von Neumann measurements

A general scheme is presented for controlling quantum systems using evolution driven by non-selective von Neumann measurements, with or without an additional tailored electromagnetic field. As an example, a 2-level quantum system controlled by non-selective quantum measurements is considered. The control goal is to find optimal system observables such that consecutive non-selective measurement of these observables transforms the system from a given initial state into a state which maximizes the expected value of a target operator (the objective). A complete analytical solution is found including explicit expressions for the optimal measured observables and for the maximal objective value given any target operator, any initial system density matrix, and any number of measurements. As an illustration, upper bounds on measurement-induced population transfer between the ground and the excited states for any number of measurements are found. The anti-Zeno effect is recovered in the limit of an infinite number of measurements. In this limit the system becomes completely controllable. The results establish the degree of control attainable by a finite number of measurements

Experimental determination of the energy efficiency of rotors of vertical-axis wind turbines for autonomous power supply on land and at sea

For the first time, experimental studies have been performed to assess the effect of flaps with triangular elements on the operation of the N-Darrieus and Savonius rotors. It has been established that the rotational speed of the original N-Darrieus and Savonius rotors having blades with flaps is greater than the rotation frequency of the N-Darrieus and Savonius rotors of the known construction by 18%, and the power factors of the N-Darrieus and Savonius rotors are for 17% and 19% more. Optimization of the geometrical parameters of the blades can lead to an increase in the power factor of the N-Darrieus rotor up to a value of 0.72, which is higher than the maximum possible value of 0.45 for the horizontal axis wind turbine. It is advisable to aggregate N-Darrieus rotors with Savonius rotors having a large starting torque. The upgraded N-Darrieus and Savonius rotors, as well as the combined rotors based on them, can be used in power supply systems for various objects on land and at sea

Experimental determination of the energy efficiency of rotors of vertical-axis wind turbines for autonomous power supply on land and at sea

For the first time, experimental studies have been performed to assess the effect of flaps with triangular elements on the operation of the N-Darrieus and Savonius rotors. It has been established that the rotational speed of the original N-Darrieus and Savonius rotors having blades with flaps is greater than the rotation frequency of the N-Darrieus and Savonius rotors of the known construction by 18%, and the power factors of the N-Darrieus and Savonius rotors are for 17% and 19% more. Optimization of the geometrical parameters of the blades can lead to an increase in the power factor of the N-Darrieus rotor up to a value of 0.72, which is higher than the maximum possible value of 0.45 for the horizontal axis wind turbine. It is advisable to aggregate N-Darrieus rotors with Savonius rotors having a large starting torque. The upgraded N-Darrieus and Savonius rotors, as well as the combined rotors based on them, can be used in power supply systems for various objects on land and at sea