On the generation of sequential unitary gates from continuous time Schrodinger equations driven by external fields

In all the various proposals for quantum computers, a common feature is that the quantum circuits are expected to be made of cascades of unitary transformations acting on the quantum states. A framework is proposed to express these elementary quantum gates directly in terms of the control inputs entering into the continuous time forced Schrodinger equation.Comment: 10 page

Feedback control of spin systems

The feedback stabilization problem for ensembles of coupled spin 1/2 systems is discussed from a control theoretic perspective. The noninvasive nature of the bulk measurement allows for a fully unitary and deterministic closed loop. The Lyapunov-based feedback design presented does not require spins that are selectively addressable. With this method, it is possible to obtain control inputs also for difficult tasks, like suppressing undesired couplings in identical spin systems.Comment: 16 pages, 15 figure

Reflection Symmetries for Multiqubit Density Operators

For multiqubit density operators in a suitable tensorial basis, we show that a number of nonunitary operations used in the detection and synthesis of entanglement are classifiable as reflection symmetries, i.e., orientation changing rotations. While one-qubit reflections correspond to antiunitary symmetries, as is known for example from the partial transposition criterion, reflections on the joint density of two or more qubits are not accounted for by the Wigner Theorem and are well-posed only for sufficiently mixed states. One example of such nonlocal reflections is the unconditional NOT operation on a multiparty density, i.e., an operation yelding another density and such that the sum of the two is the identity operator. This nonphysical operation is admissible only for sufficiently mixed states.Comment: 9 page

SMALL ENGINE-GENERATOR SET OPERATING ON DUAL-FUEL MODE WITH ETHANOL – CASTOR OIL BLENDS

The increase in greenhouse gas emissions and our dependence on fossil fuels have motivated researchers to seek the use of renewable fuels in internal combustion engines, which can be produced locally and have clean combustion. The blending method in diesel engines has been recognized as an effective alternative to partially or totally replace the use of diesel fuel. In this regard, this paper studied the operation of a small engine-generator set in mono-fuel mode (diesel fuel - DO) and in dual-fuel mode using hydrous ethanol (HET) and castor oil (OM) blends, indicating a total replacement of diesel fuel. Efficiency, power, specific fuel consumption and gaseous emissions were assessed in a single cylinder diesel cycle engine. The percentages in volume of the HET-OM samples were: 75% - 25%, 70% - 30%, 60% - 40%, and 50% - 50%. The exhaust gas temperature decreased with the mixtures. Carbon monoxide emission decreased 57%, carbon dioxide decreased 9.8%, and nitrogen oxides reduced 19%. It was also observed that the percentage of smoke opacity tends to decrease close to zero with addition of ethanol. Hydrocarbon emissions increased with rising of the OM concentration and the same for the specific fuel consumptions, which was 25.4% higher than diesel fuel. The best fuel conversion efficiency was achieved with the blend HET75-OM25, being 9% higher compared to diesel fuel operation. Power on diesel fuel operation showed a better result keeping stable, with the increase of the compression ratio and the delay of the start of injection. In general, the results confirmed that the performance is comparable to that of diesel fuel, indicating that renewable fuels appear as an alternative for the reduction of the environmental impacts and the reduction of fossil fuels consumption

Identification of dynamical Lie algebras for finite-level quantum control systems

The problem of identifying the dynamical Lie algebras of finite-level quantum systems subject to external control is considered, with special emphasis on systems that are not completely controllable. In particular, it is shown that the dynamical Lie algebra for an N-level system with equally spaced energy levels and uniform transition dipole moments, is a subalgebra for $so(N)$ if $N=2\ell+1$, and a subalgebra of $sp(\ell)$ if $N=2\ell$. General conditions for obtaining either $so(2\ell+1)$ or $sp(\ell)$ are established.Comment: IoP LaTeX, ca. 14 page

Convergence to equilibrium for many particle systems

The goal of this paper is to give a short review of recent results of the authors concerning classical Hamiltonian many particle systems. We hope that these results support the new possible formulation of Boltzmann's ergodicity hypothesis which sounds as follows. For almost all potentials, the minimal contact with external world, through only one particle of $N$, is sufficient for ergodicity. But only if this contact has no memory. Also new results for quantum case are presented

Degrees of controllability for quantum systems and applications to atomic systems

Precise definitions for different degrees of controllability for quantum systems are given, and necessary and sufficient conditions are discussed. The results are applied to determine the degree of controllability for various atomic systems with degenerate energy levels and transition frequencies.Comment: 20 pages, IoP LaTeX, revised and expanded versio

Employing feedback in adiabatic quantum dynamics

We study quantum adiabatic dynamics, where the slowly moving field is influenced by system's state (feedback). The information for the feedback is gained from non-disturbating measurements done on an ensemble of identical non-interacting systems. The situation without feedback is governed by the adiabatic theorem: adiabatic energy level populations stay constant, while the adiabatic eigenvectors get a specific phase contribution (Berry phase). However, under feedback the adiabatic theorem does not hold: the adiabatic populations satisfy a closed equation of motion that coincides with the replicator dynamics well-known by its applications in evolutionary game theory. The feedback generates a new gauge-invariant adiabatic phase, which is free of the constraints on the Berry phase (e.g., the new phase is non-zero even for real adiabatic eigenfunctions).Comment: 4 pages, 1 figur