1,830 research outputs found
Natural three-qubit interactions in one-way quantum computing
We address the effects of natural three-qubit interactions on the
computational power of one-way quantum computation (\QC). A benefit of using
more sophisticated entanglement structures is the ability to construct compact
and economic simulations of quantum algorithms with limited resources. We show
that the features of our study are embodied by suitably prepared optical
lattices, where effective three-spin interactions have been theoretically
demonstrated. We use this to provide a compact construction for the Toffoli
gate. Information flow and two-qubit interactions are also outlined, together
with a brief analysis of relevant sources of imperfection.Comment: 4 pages, 3 figures, RevTeX
Tunable negative permeability in a quantum plasmonic metamaterial
We consider the integration of quantum emitters into a negative permeability
metamaterial design in order to introduce tunability as well as nonlinear
behavior. The unit cell of our metamaterial is a ring of metamolecules, each
consisting of a metal nanoparticle and a two-level semiconductor quantum dot
(QD). Without the QDs, the ring of the unit cell is known to act as an
artificial optical magnetic resonator. By adding the QDs we show that a Fano
interference profile is introduced into the magnetic field scattered from the
ring. This induced interference is shown to cause an appreciable effect in the
collective magnetic resonance of the unit cell. We find that the interference
provides a means to tune the response of the negative permeability
metamaterial. The exploitation of the QD's inherent nonlinearity is proposed to
modulate the metamaterial's magnetic response with a separate control field.Comment: 11 pages, 6 figure
Quantum information processing with noisy cluster states
We provide an analysis of basic quantum information processing protocols
under the effect of intrinsic non-idealities in cluster states. These
non-idealities are based on the introduction of randomness in the entangling
steps that create the cluster state and are motivated by the unavoidable
imperfections faced in creating entanglement using condensed-matter systems.
Aided by the use of an alternative and very efficient method to construct
cluster state configurations, which relies on the concatenation of fundamental
cluster structures, we address quantum state transfer and various fundamental
gate simulations through noisy cluster states. We find that a winning strategy
to limit the effects of noise, is the management of small clusters processed
via just a few measurements. Our study also reinforces recent ideas related to
the optical implementation of a one-way quantum computer.Comment: 13 pages, 13 figures, RevTe
Toward a more economical cluster state quantum computation
We assess the effects of an intrinsic model for imperfections in cluster
states by introducing {\it noisy cluster states} and characterizing their role
in the one-way model for quantum computation. The action of individual
dephasing channels on cluster qubits is also studied. We show that the effect
of non-idealities is limited by using small clusters, which requires compact
schemes for computation. In light of this, we address an experimentally
realizable four-qubit linear cluster which simulates a controlled-{\sf NOT}
({\sf CNOT}).Comment: 4 pages, 2 figures, RevTeX4; proposal for experimental setup include
Experimental verification of entanglement generated in a plasmonic system
A core process in many quantum tasks is the generation of entanglement. It is
being actively studied in a variety of physical settings - from simple
bipartite systems to complex multipartite systems. In this work we
experimentally study the generation of bipartite entanglement in a nanophotonic
system. Entanglement is generated via the quantum interference of two surface
plasmon polaritons in a beamsplitter structure, i.e. utilising the
Hong-Ou-Mandel (HOM) effect, and its presence is verified using quantum state
tomography. The amount of entanglement is quantified by the concurrence and we
find values of up to 0.77 +/- 0.04. Verifying entanglement in the output state
from HOM interference is a nontrivial task and cannot be inferred from the
visibility alone. The techniques we use to verify entanglement could be applied
to other types of photonic system and therefore may be useful for the
characterisation of a range of different nanophotonic quantum devices.Comment: 7 pages, 4 figure
Experimental demonstration of a measurement-based realisation of a quantum channel
We introduce and experimentally demonstrate a method for realising a quantum
channel using the measurement-based model. Using a photonic setup and modifying
the bases of single-qubit measurements on a four-qubit entangled cluster state,
representative channels are realised for the case of a single qubit in the form
of amplitude and phase damping channels. The experimental results match the
theoretical model well, demonstrating the successful performance of the
channels. We also show how other types of quantum channels can be realised
using our approach. This work highlights the potential of the measurement-based
model for realising quantum channels which may serve as building blocks for
simulations of realistic open quantum systems.Comment: 8 pages, 4 figure
Experimental Demonstration of Decoherence-Free One-Way Information Transfer
We report the experimental demonstration of a one-way quantum protocol
reliably operating in the presence of decoherence. Information is protected by
designing an appropriate decoherence-free subspace for a cluster state
resource. We demonstrate our scheme in an all-optical setup, encoding the
information into the polarization states of four photons. A measurement-based
one-way information-transfer protocol is performed with the photons exposed to
severe symmetric phase-damping noise. Remarkable protection of information is
accomplished, delivering nearly ideal outcomes.Comment: 5 pages, 3 figures, RevTeX
Experimental realization of Dicke states of up to six qubits for multiparty quantum networking
We report the first experimental generation and characterization of a
six-photon Dicke state. The produced state shows a fidelity of F=0.56+/-0.02
with respect to an ideal Dicke state and violates a witness detecting genuine
six-qubit entanglement by four standard deviations. We confirm characteristic
Dicke properties of our resource and demonstrate its versatility by projecting
out four- and five-photon Dicke states, as well as four-photon GHZ and W
states. We also show that Dicke states have interesting applications in
multiparty quantum networking protocols such as open-destination teleportation,
telecloning and quantum secret sharing.Comment: 4 pages, 4 figures, RevTeX
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