3,053 research outputs found
Quantum walks with encrypted data
In the setting of networked computation, data security can be a significant
concern. Here we consider the problem of allowing a server to remotely
manipulate client supplied data, in such a way that both the information
obtained by the client about the server's operation and the information
obtained by the server about the client's data are significantly limited. We
present a protocol for achieving such functionality in two closely related
models of restricted quantum computation -- the Boson sampling and quantum walk
models. Due to the limited technological requirements of the Boson scattering
model, small scale implementations of this technique are feasible with
present-day technology.Comment: 4 pages, 2 figure
Critical decay index at the onset of solar eruptions
Magnetic flux ropes are topological structures consisting of twisted magnetic
field lines that globally wrap around an axis. The torus instability model
predicts that a magnetic flux rope of major radius undergoes an eruption
when its axis reaches a location where the decay index of the ambient magnetic field is larger than a critical value. In
the current-wire model, the critical value depends on the thickness and
time-evolution of the current channel. We use magneto-hydrodynamic (MHD)
simulations to investigate if the critical value of the decay index at the
onset of the eruption is affected by the magnetic flux rope's internal current
profile and/or by the particular pre-eruptive photospheric dynamics. The
evolution of an asymmetric, bipolar active region is driven by applying
different classes of photospheric motions. We find that the critical value of
the decay index at the onset of the eruption is not significantly affected by
either the pre-eruptive photospheric evolution of the active region or by the
resulting different magnetic flux ropes. As in the case of the current-wire
model, we find that there is a `critical range' , rather than a
`critical value' for the onset of the torus instability. This range is in good
agreement with the predictions of the current-wire model, despite the inclusion
of line-tying effects and the occurrence of tether-cutting magnetic
reconnection.Comment: 15 pages, 9 figures. To appear in The Astrophysical Journa
Optimal tracking for pairs of qubit states
In classical control theory, tracking refers to the ability to perform
measurements and feedback on a classical system in order to enforce some
desired dynamics. In this paper we investigate a simple version of quantum
tracking, namely, we look at how to optimally transform the state of a single
qubit into a given target state, when the system can be prepared in two
different ways, and the target state depends on the choice of preparation. We
propose a tracking strategy that is proved to be optimal for any input and
target states. Applications in the context of state discrimination, state
purification, state stabilization and state-dependent quantum cloning are
presented, where existing optimality results are recovered and extended.Comment: 15 pages, 8 figures. Extensive revision of text, optimality results
extended, other physical applications include
Efficient Parity Encoded Optical Quantum Computing
We present a linear optics quantum computation scheme with a greatly reduced
cost in resources compared to KLM. The scheme makes use of elements from
cluster state computation and achieves comparable resource usage to those
schemes while retaining the circuit based approach of KLM
Loss Tolerant Optical Qubits
We present a linear optics quantum computation scheme that employs a new
encoding approach that incrementally adds qubits and is tolerant to photon loss
errors. The scheme employs a circuit model but uses techniques from cluster
state computation and achieves comparable resource usage. To illustrate our
techniques we describe a quantum memory which is fault tolerant to photon loss
Loss-tolerant operations in parity-code linear optics quantum computing
A heavy focus for optical quantum computing is the introduction of
error-correction, and the minimisation of resource requirements. We detail a
complete encoding and manipulation scheme designed for linear optics quantum
computing, incorporating scalable operations and loss-tolerant architecture.Comment: 8 pages, 6 figure
The impact of dental caries on children and young people: What they have to say?
Background: Dental caries affects 60-90% of children across the world and is associated with a variety of negative impacts. Despite its ubiquity, there has been surprisingly little exploration of these impacts from the child's perspective.
Aim: The aim was to allow children to describe the impact of dental caries on their daily lives and to describe the terminology they used.
Design: Children, aged 5-15 years, with caries experience were purposively sampled from primary and secondary care dental clinics. Focus groups (n = 5) and in-depth interviews (n = 16) were recorded and transcribed verbatim. Data analysis took a narrative approach, and themes were derived from the data using framework analysis.
Results: Pain was the main theme to emerge. Within this, three subthemes were identified: impacts related to pain, strategies adopted to reduce pain, and emotional aspects resulting from pain. A second theme was also identified relating to the aesthetic aspects of caries.
Conclusion: Children as young as 5 years of age were able to competently discuss their experiences of dental caries. Participants reported a number of impacts affecting various aspects of their lives. These will be incorporated into the future development of a caries-specific measure of oral health-related quality of life
Quantum process tomography of a controlled-NOT gate
We demonstrate complete characterization of a two-qubit entangling process -
a linear optics controlled-NOT gate operating with coincident detection - by
quantum process tomography. We use maximum-likelihood estimation to convert the
experimental data into a physical process matrix. The process matrix allows
accurate prediction of the operation of the gate for arbitrary input states,
and calculation of gate performance measures such as the average gate fidelity,
average purity and entangling capability of our gate, which are 0.90, 0.83 and
0.73, respectively.Comment: 4 pages, 2 figures. v2 contains new data corresponding to improved
gate operation. Figure quality slightly reduced for arXi
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