We show that the g-factor and the spin-flip time T_{1} of a heterojunction quantum dot is very sensitive to the band-bending interface electric field even in the absence of wave function penetration into the barrier. When this electric field is of the order of 10^{5} V/cm, g and T_{1} show high sensitivity to dot radius and magnetic field arising from the interplay between Rashba and Dresselhaus spin-orbit interactions. This result opens new possibilities for the design of a quantum dot spin quantum computer where g-factor and T_{1} can be engineered by manipulating the spin-orbit coupling through external gates.Comment: To appear in Phys. Rev.

A quantum cluster expansion method is developed for the problem of localized electron spin decoherence due to dipolar fluctuations of lattice nuclear spins. At the lowest order it provides a microscopic explanation for the Lorentzian diffusion of Hahn echoes without resorting to any phenomenological Markovian assumption. Our numerical results show remarkable agreement with recent electron spin echo experiments in phosphorus doped silicon.PACS numbers: 76.60.Lz; 03.65.Yz; 03.67.Lx It was realized a long time ago that spectral diffusion due to the dipolar fluctuations of nuclear spins often dominates the coherence decay in electron spin echo experiments [1,2]. The recent advent of spin-based quantum computation in semiconductor nanostructures revived the interest in spectral diffusion, which is expected to be the dominant channel for low-temperature spin decoherence in several spin-based quantum computer architectures [3]. In spectral diffusion, the electron spin Zeeman frequency diffuses in time due to the noise produced by the nuclear spin bath. Dipolar fluctuations in the nuclear spins give rise to a temporally random effective magnetic field at the localized electron spin, leading to irreversible decoherence (i.e. a T 2 -process). All available theories to date are based on classical stochastic modeling of the nuclear field, a Markovian theoretical framework which is inevitably phenomenological since it requires an arbitrary choice for the spectrum of nuclear fluctuations. Such a classical Markovian modeling is arguably incompatible with the strict requirements of spin coherence and control in a quantum information device. In addition, recent rapid experimental progress in single spin measurements [4], which in the near future promise sensitive measurements of quantum effects in spin resonance, also warrant a quantum theory of spectral diffusion. Here we propose a quantum theoretical framework for spectral diffusion which is non-stochastic and fully microscopic. In addition, our theory produces an accurate quantitative prediction for the initial decoherence, which is the most important regime for quantum computation. To the best of our knowledge, ours is the first quantum theory for electron spin spectral diffusion.Spectral diffusion is not a limiting decoherence process for silicon or germanium based quantum computer proposals because these can, in principle, be fabricated free of nuclear spins using isotopic purification. Unfortunately this is not true for the important class of materials based on III-V compounds, where spectral diffusion has been shown to play a major role [3,5]. There is as yet no experimental measurement of localized spin decoherence (echo decay) in III-V materials, but such experimental results are anticipated in the near future.Our theory reveals that the inclusion of quantum corrections to nuclear spin fluctuation increases the degree of decoherence, as is best evidenced from our explanation of the existing factor of three discrepancy between the Markovian stochastic theory [5] and...

We unravel the magnon spectra of BiFeO3 by means of low-energy inelastic light scattering. We show the existence of two species of magnons corresponding to spin wave excitations in and out of the cycloidal plane. These excitations might be interpreted as electromagnon modes. The present observations present an unique opportunity to study the competition between ferroelectric and magnetic orders.

To face the challenges lying beyond present technologies based on complementary metal-oxide-semiconductors, new paradigms for information processing are required. Magnonics proposes to use spin waves to carry and process information, in analogy with photonics that relies on light waves, with several advantageous features such as potential operation in the terahertz range and excellent coupling to spintronics. Several magnonic analog and digital logic devices have been proposed, and some demonstrated. Just as for spintronics, a key issue for magnonics is the large power required to control/write information (conventionally achieved through magnetic fields applied by strip lines, or by spin transfer from large spin-polarized currents). Here we show that in BiFeO(3), a room-temperature magnetoelectric material, the spin-wave frequency (>600 GHz) can be tuned electrically by over 30%, in a non-volatile way and with virtually no power dissipation. Theoretical calculations indicate that this effect originates from a linear magnetoelectric effect related to spin-orbit coupling induced by the applied electric field. We argue that these properties make BiFeO(3) a promising medium for spin-wave generation, conversion and control in future magnonics architectures.

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