1,071 research outputs found
Plasmon Injection to Compensate and Control Losses in Negative Index Metamaterials
Metamaterials have introduced a whole new world of unusual materials with
functionalities that cannot be attained in naturally occurring material systems
by mimicking and controlling the natural phenomena at subwavelength scales.
However, the inherent absorption losses pose fundamental challenge to the most
fascinating applications of metamaterials. Based on a novel plasmon injection
(PI or \Pi) scheme, we propose a coherent optical amplification technique to
compensate losses in metamaterials. Although the proof of concept device here
operates under normal incidence only, our proposed scheme can be generalized to
arbitrary form of incident waves. The \Pi-scheme is fundamentally different
than major optical amplification schemes. It does not require gain medium,
interaction with phonons, or any nonlinear medium. The \Pi-scheme allows for
loss-free metamaterials. It is ideally suited for mitigating losses in
metamaterials operating in the visible spectrum and is scalable to other
optical frequencies. These findings open the possibility of reviving the early
dreams of making 'magical' metamaterials from scratch.Comment: Main text, 8 pages with 4 figures; supplemental material, 21 pages
with 21 figure
Faithful qubit distribution assisted by one additional qubit against collective noise
We propose a distribution scheme of polarization states of a single photon
over collective-noise channel. By adding one extra photon with a fixed
polarization, we can protect the state against collective noise via a
parity-check measurement and post-selection. While the scheme succeeds only
probabilistically, it is simpler and more flexible than the schemes utilizing
decoherence-free subspace. An application to BB84 protocol through collective
noise channel, which is robust to the Trojan horse attack, is also given.Comment: 4 pages, 3 figures; published version in Phys. Rev. Let
Photonic multipartite entanglement conversion using nonlocal operations
We propose a simple setup for the conversion of multipartite entangled states
in a quantum network with restricted access. The scheme uses nonlocal
operations to enable the preparation of states that are inequivalent under
local operations and classical communication, but most importantly does not
require full access to the states. It is based on a flexible linear optical
conversion gate that uses photons, which are ideally suited for distributed
quantum computation and quantum communication in extended networks. In order to
show the basic working principles of the gate, we focus on converting a
four-qubit entangled cluster state to other locally inequivalent four-qubit
states, such as the GHZ and symmetric Dicke state. We also show how the gate
can be incorporated into extended graph state networks, and can be used to
generate variable entanglement and quantum correlations without entanglement
but nonvanishing quantum discord.Comment: 10 pages, 6 figures, correction of reference list, add Journal ref.
and DO
Experimental ancilla-assisted qubit transmission against correlated noise using quantum parity checking
We report the experimental demonstration of a transmission scheme of photonic
qubits over unstabilized optical fibers, which has the plug-and-play feature as
well as the ability to transmit any state of a qubit, regardless of whether it
is known, unknown, or entangled to other systems. A high fidelity to the
noiseless quantum channel was achieved by adding an ancilla photon after the
signal photon within the correlation time of the fiber noise and by performing
quantum parity checking. Simplicity, maintenance-free feature and robustness
against path-length mismatches among the nodes make our scheme suitable for
multi-user quantum communication networks.Comment: 8 pages, 4 figures; published in New J. Phys. and selected in IOP
Selec
Kraus representation of damped harmonic oscillator and its application
By definition, the Kraus representation of a harmonic oscillator suffering
from the environment effect, modeled as the amplitude damping or the phase
damping, is directly given by a simple operator algebra solution. As examples
and applications, we first give a Kraus representation of a single qubit whose
computational basis states are defined as bosonic vacuum and single particle
number states. We further discuss the environment effect on qubits whose
computational basis states are defined as the bosonic odd and even coherent
states. The environment effects on entangled qubits defined by two different
kinds of computational basis are compared with the use of fidelity.Comment: 9 pages, 3 figure
Magnetic resonance imaging of the quadriceps fat pad oedema pattern in relation to patellofemoral joint pathologies
Purpose: Quadriceps fat pad is located posterior to the quadriceps tendon. Increased signal intensity of this fat pad is seen on routine knee magnetic resonance imaging (MRI) examinations, but the exact mechanism and related pathologies are not clear. In this study we aimed to evaluate the relationship between MRI signal intensity and morphological features of quadriceps fat pad, as well as various pathologies of the patellofemoral joint. Material and methods: Sixty-one knees with quadriceps fat pad oedema out of 457 knee MRI examinations were included. Quadriceps fat pad signal intensity, dimensions, posterior indentation, and various parameters related to patellofemoral joint such as trochlear facet asymmetry, trochlear depth and sulcus angle, and the Insall-Salvati ratio were evaluated. Results: There was no statistically significant correlation between quadriceps fat pad oedema intensity and its dimensions, but it was significant when compared to posterior indentation. There was no correlation between fat pad oedema and each of the pathologies. However, there was a significant correlation between the presence of fat pad oedema and the presence of at least one of the pathologies related to patellofemoral joint. Conclusions: Quadriceps fat pad oedema detected in MRI examinations should warn the radiologist against the presence of various pathologies related to the patellofemoral joint
Observation of quantum interference in the plasmonic Hong-Ou-Mandel effect
We report direct evidence of the bosonic nature of surface plasmon polaritons
(SPPs) in a scattering-based beamsplitter. A parametric down-conversion source
is used to produce two indistinguishable photons, each of which is converted
into a SPP on a metal-stripe waveguide and then made to interact through a
semi-transparent Bragg mirror. In this plasmonic analog of the Hong-Ou-Mandel
experiment, we measure a coincidence dip with a visibility of 72%, a key
signature that SPPs are bosons and that quantum interference is clearly
involved.Comment: 5 pages, 3 figure
Quantum random number generation using an on-chip nanowire plasmonic waveguide
Quantum random number generators employ the inherent randomness of quantum
mechanics to generate truly unpredictable random numbers, which are essential
in cryptographic applications. While a great variety of quantum random number
generators have been realised using photonics, few exploit the high-field
confinement offered by plasmonics, which enables device footprints an order of
magnitude smaller in size. Here we integrate an on-chip nanowire plasmonic
waveguide into an optical time-of-arrival based quantum random number
generation setup. Despite loss, we achieve a random number generation rate of
14.4 Mbits/s using low light intensity, with the generated bits passing
industry standard tests without post-processing. By increasing the light
intensity, we were then able to increase the generation rate to 41.4 Mbits/s,
with the resulting bits only requiring a shuffle to pass all tests. This is an
order of magnitude increase in the generation rate and decrease in the device
size compared to previous work. Our experiment demonstrates the successful
integration of an on-chip nanoscale plasmonic component into a quantum random
number generation setup. This may lead to new opportunities in compact and
scalable quantum random number generation.Comment: 10 pages, 3 figures, appendi
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