Quantum noise in the spin transfer torque effect

Describing the microscopic details of the interaction of magnets and spin-polarized currents is key to achieve control of such systems at the microscopic level. Here we discuss a description based on the Keldysh technique, casting the problem in the language of open quantum systems. We reveal the origin of noise in the presence of both field-like and damping like terms in the equation of motion arising from spin conductance

Quantum Hopfield Model

We find the free-energy in the thermodynamic limit of a one-dimensional XY model associated to a system of N qubits. The coupling among the σzi is a long range two-body random interaction. The randomness in the couplings is the typical interaction of the Hopfield model with p patterns ( ppeerReviewe

Analysis of MHD instabilities by asymptotic methods

The m = 1 resistive mode for a tokamak plasma with large aspect ratio is considered: the dynamic equations in a resistive layer are solved by means of an asymptotic expansion for values of the growth rate in a suitable range. The eigenvalues characterizing the perturbation are found by means of a series expansion and it is shown that the main contribution to the expression of the eigenvalues is given by the first and the second order of this expansion. This method is different from the one used in the paper [G. Ara et al., Ann. Phys. 112, 443 (1978)], and can be applied in more general situations

Reversibility and quantum coherence in one-dimensional quantum cellular automata

Quantum cellular automata are important tools in understanding quantum dynamics, thanks to their simple and effective list of rules. Here we consider a class of noisy, one-dimensional quantum cellular automata that allow one to shift from unitary dynamics to completely positive maps, investigating the evolution of coherence as well as the notion of reversibility in such a setting. To this aim, we associate an approximate reverse automaton to each noisy automaton, and assess its effect, and we define an irreversibility time based on the distance from the maximally mixed state, which is shown to be the only attractor of the automaton map in the presence of dephasing. Our analysis illustrates the interplay between unitary and noisy dynamics

Magnomechanics in suspended magnetic beams

Cavity optomechanical systems have become a popular playground for studies of controllable nonlinear interactions between light and motion. Owing to the large speed of light, realizing cavity optomechanics in the microwave frequency range requires cavities up to several mm in size, hence making it hard to embed several of them on the same chip. An alternative scheme with much smaller footprint is provided by magnomechanics, where the electromagnetic cavity is replaced by a magnet undergoing ferromagnetic resonance, and the optomechanical coupling originates from magnetic shape anisotropy. Here, we consider the magnomechanical interaction occurring in a suspended magnetic beam, a scheme in which both magnetic and mechanical modes physically overlap and can also be driven individually. We show that a sizable interaction can be produced if the beam has some initial static deformation, as is often the case due to unequal strains in the constituent materials. We also show how the magnetism affects the magnetomotive detection of the vibrations, and how the magnomechanics interaction can be used in microwave signal amplification. Finally, we discuss experimental progress towards realizing the scheme.peerReviewe