Search

We investigate the spin Hall conductivity σ of a clean 2D electron gas formed in a two-subband well. We determine σ as arising from the inter-subband induced spin–orbit (SO) coupling η (Calsaverini et al., Phys. Rev. B 78:155313, ) via a linear-response approach due to Rashba. By self-consistently calculating η for realistic wells, we find that σ presents a non-monotonic (and non-universal) behavior and a sign change as the Fermi energy varies between the subband edges. Although our σ is very small (i.e., ≪ `` e/4 π″), it is non-zero as opposed to linear-in- k SO models. [ABSTRACT FROM AUTHOR]

We propose to use optical detection of magnetic resonance (ODMR) to measure the decoherence time T 2 of a single-electron spin in a semiconductor quantum dot. The electron is in one of the spin 1/2 states and a circularly polarized laser can only create an optical excitation for one of the electron spin states due to Pauli blocking. An applied electron spin resonance (ESR) field leads to Rabi spin flips and thus to a modulation of the photoluminescence or, alternatively, of the photocurrent. This allows one to measure the ESR linewidth and the coherent Rabi oscillations, from which the electron spin decoherence can be determined. We study different possible schemes for such an ODMR setup, including cw or pulsed laser excitation. [ABSTRACT FROM AUTHOR]

We review our recent work towards quantum communication in a solid-state environment with qubits carried by electron spins. We propose three schemes to produce spin-entangled electrons, where the required separation of the partner electrons is achieved via Coulomb interaction. The non-product spin-states originate either from the Cooper pairs found in a superconductor, or in the ground state of a quantum dot with an even number of electrons. In a second stage, we show how spin-entanglement carried by a singlet can be detected in a beam-splitter geometry by an increased (bunching) or decreased (antibunching) noise signal. We also 'discuss how a local spin-orbit interaction can be used to provide a continuous modulation of the noise as a signature of entanglement. Finally, we review how one can use a quantum dot as a spin-filter, a spin-memory read-out, a probe for single-spin decoherence and, ultimately, a single-spin measurement apparatus. [ABSTRACT FROM AUTHOR]

We have recently calculated shot noise for entangled and spin-polarized electrons in novel beam-splitter geometries with a local Rashba orbit–spin (s-o) interaction in the incoming leads. This interaction allows for a gate-controlled rotation of the incoming electron spins. Here we present an alternate simpler route to the shot noise calculation in the above work and focus on only electron pairs. Shot noise for these shows continuous bunching and antibunching behaviors. In addition, entangled and unentangled triplets yield distinctive shot noise oscillations. Besides allowing for a direct way to identify triplet and singlet states, these oscillations can be used to extract s-o coupling constants through noise measurements. Incoming leads with spin–orbit interband mixing give rise to an additional modulation of the current noise. This extra rotation allows the design of a spin transistor with enhanced spin control. [ABSTRACT FROM AUTHOR]

An electronic beam splitter with a local Rashba spin–orbit coupling can serve as a detector for spin-polarized currents. The spin–orbit coupling plays the role of a tunable spin rotator and can be controlled via a gate electrode on top of the conductor. We use spin-resolved scattering theory to calculate the zero-temperature current fluctuations (shot noise) for such a four-terminal device and show that the shot noise is proportional to the spin polarization of the source. Moreover, we analyze the effect of spin–orbit-induced intersubband coupling, leading to an additional spin rotation. [ABSTRACT FROM AUTHOR]

We study the dynamics of a single electron spin in an isolated quantum dot induced by hyperfine interaction with nuclei. The decoherence is caused by the spatial variation of the electron wave function within the dot, leading to a nonuniform hyperfine coupling A. We evaluate the spin correlation function and find that the decay is not exponential but rather power (inverse logarithm) law-like. For polarized nuclei we find an exact solution and show that the precession amplitude and the decay behavior can be tuned by the magnetic field. The decay time is given by ℏ N/ A, where N is the number of nuclei inside the dot, and the amplitude of precession decays to a finite value. We show that there is a striking difference between the decoherence time for a single dot and the dephasing time for an ensemble of dots. [ABSTRACT FROM AUTHOR]

We present detailed calculations of low-energy spin dynamics in the “ferric wheel” systems Na:Fe6 and Cs:Fe8 in a magnetic field. We compute by exact diagonalisation the low-energy spectra and matrix elements for total-spin and Néel-vector components, and thus the time-dependent correlation functions of these operators. Comparison of our results with the semiclassical theory of coherent quantum tunnelling of the Néel vector demonstrates the validity of a two-state description for the low-energy dynamics of ferric wheels. We discuss the implications of our results for mesoscopic quantum coherent phenomena, and for the experimental techniques to observe them, in molecular magnetic rings. [ABSTRACT FROM AUTHOR]

Presented is a new complex valued radial basis function (RBF) neural network with phase transmittance between the input nodes and output, which makes it suitable for channel equalisation on quadrature digital modulation systems. [ABSTRACT FROM AUTHOR]

Single-spin qubits in semiconductor quantum dots hold promise for universal quantum computation with demonstrations of a high single-qubit gate fidelity above 99.9% and two-qubit gates in conjunction with a long coherence time. However, initialization and readout of a qubit is orders of magnitude slower than control, which is detrimental for implementing measurement-based protocols such as error-correcting codes. In contrast, a singlet-triplet qubit, encoded in a two-spin subspace, has the virtue of fast readout with high fidelity. Here, we present a hybrid system which benefits from the different advantages of these two distinct spin-qubit implementations. A quantum interface between the two codes is realized by electrically tunable inter-qubit exchange coupling. We demonstrate a controlled-phase gate that acts within 5.5 ns, much faster than the measured dephasing time of 211 ns. The presented hybrid architecture will be useful to settle remaining key problems with building scalable spin-based quantum computers. The race to produce a quantum computer has driven the development of many different qubit designs with different benefits and drawbacks. Noiri et al. demonstrate a hybrid device with two coupled semiconductor spin qubits of different designs, which should allow each qubit's advantages to be exploited. [ABSTRACT FROM AUTHOR]