397 research outputs found
Dark State Adiabatic Passage with spin-one particles
Adiabatic transport of information is a widely invoked resource in connection
with quantum information processing and distribution. The study of adiabatic
transport via spin-half chains or clusters is standard in the literature, while
in practice the true realisation of a completely isolated two-level quantum
system is not achievable. We explore here, theoretically, the extension of
spin-half chain models to higher spins. Considering arrangements of three
spin-one particles, we show that adiabatic transport, specifically a
generalisation of the Dark State Adiabatic Passage procedure, is applicable to
spin-one systems. We thus demonstrate a qutrit state transfer protocol. We
discuss possible ways to physically implement this protocol, considering
quantum dot and nitrogen-vacancy implementations.Comment: 8 pages, 6 figures (some in colour), comments welcom
Energetics of the Quantum Graphity Universe
Quantum graphity is a background independent model for emergent geometry, in
which space is represented as a complete graph. The high-energy pre-geometric
starting point of the model is usually considered to be the complete graph,
however we also consider the empty graph as a candidate pre-geometric state.
The energetics as the graph evolves from either of these high-energy states to
a low-energy geometric state is investigated as a function of the number of
edges in the graph. Analytic results for the slope of this energy curve in the
high-energy domain are derived, and the energy curve is plotted exactly for
small number of vertices . To study the whole energy curve for larger (but
still finite) , an epitaxial approximation is used. It is hoped that this
work may open the way for future work to compare predictions from quantum
graphity with observations of the early universe, making the model falsifiable.Comment: 8 pages, 3 figure
Tuneable plasmonics enabled by capillary oscillations of liquid-metal nanodroplets
Plasmonics allows manipulating light at the nanoscale, but has limitations
due to the static nature of nanostructures and lack of tuneability. We propose
and theoretically analyse a room-temperature liquid-metal nanodroplet that
changes its shape, and therefore tunes the plasmon resonance frequency, due to
capillary oscillations. We show the possibility to tune the capillary
oscillation frequency of the nanodroplet and to drive the oscillations
electrically or mechanically. Employed as a tuneable nanoantenna, the
nanodroplet may find applications in sensors, imaging, microscopy, and
medicine
Interferometry using spatial adiabatic passage in quantum dot networks
We show that techniques of spatial adiabatic passage can be used to realise
an electron interferometer in a geometry analogous to a conventional
Aharonov-Bohm ring, with transport of the particle through the device modulated
using coherent transport adiabatic passage. This device shows an interesting
interplay between the adiabatic and non-adiabatic behaviour of the system. The
transition between non-adiabatic and adiabatic behaviour may be tuned via
system parameters and the total time over which the protocol is enacted.
Interference effects in the final state populations analogous to the
electrostatic Aharonov-Bohm effect are observed.Comment: Version accepted in Phys. Rev. B, 8 pages, 6 figure
Charge shelving and bias spectroscopy for the readout of a charge-qubit on the basis of superposition states
Charge-based qubits have been proposed as fundamental elements for quantum
computers. One commonly proposed readout device is the single-electron
transistor (SET). SETs can distinguish between localized charge states, but
lack the sensitivity to directly distinguish superposition states, which have
greatly enhanced coherence times compared with position states. We propose
introducing a third dot, and exploiting energy dependent tunnelling from the
qubit into this dot (bias spectroscopy) for pseudo-spin to charge conversion
and superposition basis readout. We introduce an adiabatic fast passage-style
charge pumping technique which enables efficient and robust readout via charge
shelving, avoiding problems due to finite SET measurement time.Comment: 4 pages, 3 figures, note slightly changed title, replaced with
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