2,893 research outputs found
Entanglement distribution for a practical quantum-dot-based quantum processor architecture
We propose a quantum dot (QD) architecture for enabling universal quantum information processing. Quantum registers, consisting of arrays of vertically stacked self-assembled semiconductor QDs, are connected by chains of in-plane self-assembled dots. We propose an entanglement distributor, a device for producing and distributing maximally entangled qubits on demand, communicated through in-plane dot chains. This enables the transmission of entanglement to spatially separated register stacks, providing a resource for the realization of a sizeable quantum processor built from coupled register stacks of practical size. Our entanglement distributor could be integrated into many of the present proposals for self-assembled QD-based quantum computation (QC). Our device exploits the properties of simple, relatively short, spin-chains and does not require microcavities. Utilizing the properties of self-assembled QDs, after distribution the entanglement can be mapped into relatively long-lived spin qubits and purified, providing a flexible, distributed, off-line resource. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft
Phonon-Induced Rabi-Frequency Renormalization of Optically Driven Single InGaAs/GaAs Quantum Dots
The authors thank the EPSRC (U.K.) EP/G001642, and the QIPIRC U.K. for financial support. A. N. is supported by the EPSRC and B.W. L. by the Royal Society.We study optically driven Rabi rotations of a quantum dot exciton transition between 5 and 50 K, and for pulse areas of up to 14 pi. In a high driving field regime, the decay of the Rabi rotations is nonmonotonic, and the period decreases with pulse area and increases with temperature. By comparing the experiments to a weak-coupling model of the exciton-phonon interaction, we demonstrate that the observed renormalization of the Rabi frequency is induced by fluctuations in the bath of longitudinal acoustic phonons, an effect that is a phonon analogy of the Lamb shift.Peer reviewe
Measurement-based approach to entanglement generation in coupled quantum dots
Measurements provide a novel mechanism for generating the entanglement
resource necessary for performing scalable quantum computation. Recently, we
proposed a method for performing parity measurements in a coupled quantum dot
system. In this paper we generalise this scheme and perform a comprehensive
analytic and numerical study of environmental factors. We calculate the effects
of possible error sources including non-ideal photon detectors, ineffective
spin-selective excitation and dot distinguishability (both spatial and
spectral). Furthermore, we present an experimental approach for verifying the
success of the parity measurement
Freezing distributed entanglement in spin chains
We show how to freeze distributed entanglement that has been created from the
natural dynamics of spin chain systems. The technique that we propose simply
requires single-qubit operations and isolates the entanglement in specific
qubits at the ends of branches. Such frozen entanglement provides a useful
resource, for example for teleportation or distributed quantum processing. The
scheme can be applied to a wide range of systems -- including actual spin
systems and alternative qubit embodiments in strings of quantum dots, molecules
or atoms.Comment: 5 pages, to appear in Phys. Rev. A (Rapid Communication
Global Optical Control of a Quantum Spin Chain
Quantum processors which combine the long decoherence times of spin qubits
together with fast optical manipulation of excitons have recently been the
subject of several proposals. I show here that arbitrary single- and entangling
two-qubit gates can be performed in a chain of perpetually coupled spin qubits
solely by using laser pulses to excite higher lying states. It is also
demonstrated that universal quantum computing is possible even if these pulses
are applied {\it globally} to a chain; by employing a repeating pattern of four
distinct qubit units the need for individual qubit addressing is removed. Some
current experimental qubit systems would lend themselves to implementing this
idea.Comment: 5 pages, 3 figure
The Parable of Portobello: Lessons and Questions from the First Urban Acquisition Under the Scottish Community Right-to-Buy Regime
Scholars, lawyers, and activists interested in community development in the United States, Scotland, or any country seeking to expand community ownership of land will be interested, we think, in the lessons we learned in Portobello and the questions it poses for the future
Selective spin coupling through a single exciton
We present a novel scheme for performing a conditional phase gate between two
spin qubits in adjacent semiconductor quantum dots through delocalized single
exciton states, formed through the inter-dot Foerster interaction. We consider
two resonant quantum dots, each containing a single excess conduction band
electron whose spin embodies the qubit. We demonstrate that both the two-qubit
gate, and arbitrary single-qubit rotations, may be realized to a high fidelity
with current semiconductor and laser technology.Comment: 5 pages, 3 figures; published version, equation formatting improved,
references adde
Coherent state transfer between an electron- and nuclear spin in 15N@C60
Electron spin qubits in molecular systems offer high reproducibility and the
ability to self assemble into larger architectures. However, interactions
between neighbouring qubits are 'always-on' and although the electron spin
coherence times can be several hundred microseconds, these are still much
shorter than typical times for nuclear spins. Here we implement an
electron-nuclear hybrid scheme which uses coherent transfer between electron
and nuclear spin degrees of freedom in order to both controllably turn on/off
dipolar interactions between neighbouring spins and benefit from the long
nuclear spin decoherence times (T2n). We transfer qubit states between the
electron and 15N nuclear spin in 15N@C60 with a two-way process fidelity of
88%, using a series of tuned microwave and radiofrequency pulses and measure a
nuclear spin coherence lifetime of over 100 ms.Comment: 5 pages, 3 figures with supplementary material (8 pages
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