1,303 research outputs found
Experimental demonstration of quantum state tomography and qubit-qubit interactions for rare-earth-ion based solid state qubits
We report on the implementation of quantum state tomography for an ensemble
of Eu dopant ions in a \YSO crystal. The tomography was applied to a
qubit based on one of the ion's optical transitions. The qubit was manipulated
using optical pulses and measurements were made by observing the optical free
induction in a phase sensitive manner. Fidelities of % for the combined
preparation and measurement process were achieved. Interactions between the
ions due to the change in the ions' permanent electric dipole moment when
excited optically were also measured. In light of these results, the ability to
do multi-qubit quantum computation using this system is discussed
Demonstration of conditional quantum phase shift between ions in a solid
Due to their potential for long coherence times, dopant ions have long been
considered promising candidates for scalable solid state quantum computing.
However, the demonstration of two qubit operation has proven to be problematic,
largely due to the difficulty of addressing closely spaced ions. Here we use
optically active ions and optical frequency addressing to demonstrate a
conditional phase shift between two qubits
Phase-dependent decoherence of optical transitions in Pr3+:LaF3 in the presence of a driving field
The decoherence times of orthogonally phased components of the optical
transition dipole moment in a two-level system have been observed to differ by
an order of magnitude. This phase anisotropy is observed in coherent transient
experiments where an optical driving field is present during extended periods
of decoherence. The decoherence time of the component of the dipole moment in
phase with the driving field is extended compared to T_2, obtained from
two-pulse photon echoes, in analogy with the spin locking technique of NMR.Comment: 5 pages, 2 figures; replaced with published versio
Microstructure modelling of hot deformation of Al–1%Mg alloy
This study presents the application of the finite elementmethod and intelligent systems techniques to the
prediction of microstructural mapping for aluminium alloys. Here, the material within each finite element
is defined using a hybrid model. The hybrid model is based on neuro-fuzzy and physically based components
and it has been combined with the finite element technique. The model simulates the evolution of
the internal state variables (i.e. dislocation density, subgrain size and subgrain boundary misorientation)
and their effect on the recrystallisation behaviour of the stock. This paper presents the theory behind
the model development, the integration between the numerical techniques, and the application of the
technique to a hot rolling operation using aluminium, 1 wt% magnesium alloy. Furthermore, experimental
data from plane strain compression (PSC) tests and rolling are used to validate the modelling outcome.
The results show that the recrystallisation kinetics agree well with the experimental results for different
annealing times. This hybrid approach has proved to be more accurate than conventional methods using empirical equations
Analytic treatment of controlled reversible inhomogeneous broadening quantum memories for light using two-level atoms
It has recently been discovered that the optical analog of a gradient echo, in an optically thick material, could
form the basis of an optical memory that is both completely efficient and noise-free. Here we present analytical
calculations showing that this is the case. There is close analogy between the operation of the memory and an
optical system with two beam splitters. We can use this analogy to calculate efficiencies as a function of optical
depth for a number of quantum memory schemes based on controlled inhomogeneous broadening. In particular,
we show that multiple switching leads to a net 100% retrieval efficiency for the optical gradient echo even
in the optically thin case
Photon echo without a free induction decay in a double-Lambda system
We have characterized a novel photon-echo pulse sequence for a
double- type energy level system where the input and rephasing
transitions are different to the applied -pulses. We show that despite
having imperfect -pulses (associated with large coherent emission due to
free induction decay), the noise added is only 0.0190.001 relative to the
shot noise in the spectral mode of the echo. Using this echo pulse sequence in
the `rephased amplified spontaneous emission' (RASE) scheme
\cite{Ledingham2010} will allow for generation of entangled photon pairs that
are in different frequency, temporal, and potentially spatial modes to any
bright driving fields. The coherence and efficiency properties of this sequence
were characterized in a Pr:YSO crystal
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