Quantum Computing with Spins in Solids

Abstract

The ability to perform high-precision one-and two-qubit operations is sufficient for universal quantum computation. For the Loss-DiVincenzo proposal to use single electron spins confined to quantum dots as qubits, it is therefore sufficient to analyze only single-and coupled double-dot structures, since the strong Heisenberg exchange coupling between spins in this proposal falls off exponentially with distance and long-ranged dipolar coupling mechanisms can be made significantly weaker. This scalability of the Loss-DiVincenzo design is both a practical necessity for eventual applications of multi-qubit quantum computing and a great conceptual advantage, making analysis of the relevant components relatively transparent and systematic. We review the Loss-DiVincenzo proposal for quantum-dot-confined electron spin qubits, and survey the current state of experiment and theory regarding the relevant single-and double-quantum dots, with a brief look at some related alternative schemes for quantum computing.

Dynamics of Quantum Dot Nuclear Spin Polarization Controlled by a Single Electron

“…While the buildup time of DNSP (τ buildup ) is likely to be dependant on the way the nuclear spin system is addressed, the DNSP decay time (τ decay ) is an inherent property of the isolated nuclear spin system of a QD. Experimental determination of τ decay , which directly yields the correlation time of the fluctuations of the nuclear spin projection along the axis in which the nuclei are polarized [10], is crucial for understanding the limits of electron spin coherence in QDs [11].…”

“…While the buildup time of DNSP (τ buildup ) is likely to be dependant on the way the nuclear spin system is addressed, the DNSP decay time (τ decay ) is an inherent property of the isolated nuclear spin system of a QD. Experimental determination of τ decay , which directly yields the correlation time of the fluctuations of the nuclear spin projection along the axis in which the nuclei are polarized [10], is crucial for understanding the limits of electron spin coherence in QDs [11].In this work, we investigate the dynamics of DNSP in an individual, self-assembled InGaAs QD at T = 5 K. Photoluminescence (PL) of the negatively charged exciton (X −1 ) is studied under resonant excitation in one of the excited QD states. It has been shown previously that under the appropriate excitation conditions, the QD nuclear spins can be polarized to a degree of ∼ 15%.…”

Entanglement and the Kondo effect in serially coupled double quantum dots

“…It seems that these criteria for scalable qubits can be met in structures consisting of coupled quantum dots [4,5] which are therefore considered for implementation of quantum computing processes in solid state.…”

Controlling hole spins in quantum dots and wells

“…Spin-related phenomena in semiconductor nanostructures have become increasingly important in many branches of condensed matter physics, including the study of spin currents [1,2] and spin-Hall effects [3,4], the search for Majorana fermions in solidstate systems [5,6,7,8,9,10,11], topological insulators [12,13], and applications of quantum information/computation [14,15,16,17,18,19]. Improved understanding of these phenomena could lead to new technologies based on our ability to control electron spins.…”

“…The ultimate demonstration of this control would be the precise manipulation of the quantum states of independent spins as well as interactions between them. Such a level of control for spins in semiconductor quantum dots may allow for a scalable implementation of quantum computing [14,17,18,16,19]. Additionally, semiconductor 'spintronic' devices relying on spin-polarization and spin currents (rather than electric charges and charge transport) could lead to low-power high-density devices that would be unthinkable with conventional electronics [15,1,2].…”