Recipes for spin-based quantum computing

Abstract

Technological growth in the electronics industry has historically been measured by the number of transistors that can be crammed onto a single microchip. Unfortunately, all good things must come to an end; spectacular growth in the number of transistors on a chip requires spectacular reduction of the transistor size. For electrons in semiconductors, the laws of quantum mechanics take over at the nanometre scale, and the conventional wisdom for progress (transistor cramming) must be abandoned. This realization has stimulated extensive research on ways to exploit the spin (in addition to the orbital) degree of freedom of the electron, giving birth to the field of spintronics. Perhaps the most ambitious goal of spintronics is to realize complete control over the quantum mechanical nature of the relevant spins. This prospect has motivated a race to design and build a spintronic device capable of complete control over its quantum mechanical state, and ultimately, performing computations: a quantum computer.In this tutorial we summarize past and very recent developments which point the way to spin-based quantum computing in the solid-state. After introducing a set of basic requirements for any quantum computer proposal, we offer a brief summary of some of the many theoretical proposals for solid-state quantum computers. We then focus on the Loss-DiVincenzo proposal for quantum computing with the spins of electrons confined to quantum dots. There are many obstacles to building such a quantum device. We address these, and survey recent theoretical, and then experimental progress in the field. To conclude the tutorial, we list some as-yet unrealized experiments, which would be crucial for the development of a quantumdot quantum computer.Recipes for spin-based quantum computing

Room-Temperature Electron Spin Dynamics in Free-Standing ZnO Quantum Dots

“…The Poissonian analysis allows resolution of individual g values from the data in Fig. 2(e), yielding g S 1 1:962 and g S 2 P 1 1:971. This increase is also evident from the comparison of g 1:968 at hni 4:4, where 93% of the EPR intensity derives from P configurations, with g 1:963 at hni 0:7, where 86% of the EPR intensity derives from the S 1 configuration.…”

“…Electron spins in semiconductor quantum dots (QDs) are promising candidates for information processing using quantum particles (quantum computation) [1]. An attraction of this motif is the slower spin-dephasing expected upon electron confinement.…”

Dynamics of coupled qubits interacting with an off-resonant cavity

“…(1) for qubits defined in terms of exciton states of a given spin in quantum dots or quantum shells and for superconducting qubits at the charge degeneracy point. While most quantum computing schemes for quantum dots rely on the electron spin as qubit, 20 we focus on charge-based qubits defined by the presence or absence of an exciton (see, e.g., Ref. 21), because such states couple to the cavity mode by photon emission and absorption.…”

“…(20) and (22) The energy non-conserving terms are usually neglected because of their smallness, leading to the Hamiltonian Eq. (1).…”

Quantum Computing with Spins in Solids

“…The second term, proportional to β, is the Dresselhaus (bulk-inversion-asymmetry) term, and is due to the fact that GaAs, which has a zincblende lattice, has no center of inversion symmetry. Corrections to this spin-orbit Hamiltonian of order |p| 3 are smaller than the linear-momentum terms in quantum dots by the ratio of z-confinement length to the quantum-dot Bohr radius, and are negligible in the two-dimensional limit (Cerletti et al 2005).…”