ORC Seminars 2011

Semiconductor spintronics and quantum information

Speaker: Dr Irene D'Amico, University of York

Date:  2 Aug 2011

Time: 1.30pm

Venue: Building 46, Seminar room on Level 5

Abstract: 

In this talk I will present some of my recent work in the interconnected fields of spintronics and quantum information. First I will focus on the spin Coulomb drag effect[1], an intrinsic source of dissipation for spin currents generated by charged carriers. The effect is due to Coulomb scattering between carriers of opposite spin moving with different velocities, and is of importance in three-, two-, and one-dimensional systems. The spin Coulomb drag has various practical implications for spintronics, e.g. on spin drift-diffusion in semiconductors, and in the power loss of spin circuits. It also affects spin-optical excitations and here I will concentrate on its effects on intersubband spin plasmons in quantum wells and on related experimental signatures. Hence I will focus on entanglement in nanostructures. Entanglement is a key ingredient for quantum information technology and a very interesting fundamental property of quantum mechanics.

I will present our recent studies of the extended Hubbard model as an approximation to the local and spatial entanglement of a one-dimensional chain of nanostructures[2]. We introduce a protocol to calculate the particle-particle spatial entanglement for the Hubbard model and show that, in striking contrast with the loss of spatial degrees of freedom, the predictions are reasonably accurate. I will also show that, even for the extended Hubbard model, there remain realistic parameter regions where it fails to predict the quantitative and qualitative behaviour of the entanglement in the nanostructure system.

Thirdly I will present our investigations on the effectiveness of different dynamical decoupling protocols for storage of a single qubit in the presence of a purely dephasing bosonic bath[3]. By focusing on the realistic case of pure dephasing in an excitonic qubit confined within a quantum dot, we quantitatively assess the impact of physical constraints on achievable pulse separations, and show that little advantage of high-level decoupling schemes based on concatenated or optimal design may be expected if pulses cannot be applied sufficiently fast. In such constrained scenarios, we demonstrate how simple modifications of repeated periodic-echo protocols can significantly improve coherence preservation in realistic parameter regimes. We expect similar conclusions to be relevant to other constrained qubit devices exposed to quantum or classical phase noise. If time will allow I will also briefly present our recent work on exploring the metric-space aspects of quantum mechanics[4], and on how our findings may shed a new light on the cornerstone theorem of density functional theory -- the Hohenberg-Kohn mapping between densities and ground states.

[1]Irene D'Amico and Giovanni Vignale, Phys. Rev. B, 62, page 4853 (2000);

Review: Irene D'Amico, and Carsten A. Ullrich, Physica Status Solidi 247/2,

235 (2010) [2]J. P. Coe, V. V. Franca, and I. D'Amico, Phys. Rev. A 81,

052321 (2010);J. P. Coe, V. V. Franca and I. D'Amico, Europhys. Lett. 93,

10001 (2011) [3]T. E. Hodgson, L. Viola, and I. D'Amico, Phys. Rev. B 78,

165311 (2008); T. E. Hodgson, L. Viola, and I. D'Amico, Phys. Rev. A 81,

062321 (2010) [4]I. D'Amico, J. P. Coe, V. V. Franca and K. Capelle, Phys.

Rev. Lett. 106, 050401 (2011)

 

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