435 research outputs found
Effect of component variations on the gate fidelity in linear optical networks
We investigate the effect of variations in beam-splitter transmissions and path-length differences in the nonlinear sign gate that is used for linear optical quantum computing. We identify two implementations of the gate and show that the sensitivity to variations in their components differs significantly between them. Therefore, circuits that require a precision implementation will generally benefit from additional circuit analysis of component variations to identify the most practical implementation. We suggest possible routes to efficient circuit analysis in terms of quantum parameter estimation
A Quantum Rosetta Stone for Interferometry
Heisenberg-limited measurement protocols can be used to gain an increase in
measurement precision over classical protocols. Such measurements can be
implemented using, e.g., optical Mach-Zehnder interferometers and Ramsey
spectroscopes. We address the formal equivalence between the Mach-Zehnder
interferometer, the Ramsey spectroscope, and the discrete Fourier transform.
Based on this equivalence we introduce the ``quantum Rosetta stone'', and we
describe a projective-measurement scheme for generating the desired
correlations between the interferometric input states in order to achieve
Heisenberg-limited sensitivity. The Rosetta stone then tells us the same method
should work in atom spectroscopy.Comment: 8 pages, 4 figure
An All Linear Optical Quantum Memory Based on Quantum Error Correction
When photons are sent through a fiber as part of a quantum communication
protocol, the error that is most difficult to correct is photon loss. Here, we
propose and analyze a two-to-four qubit encoding scheme, which can recover the
loss of one qubit in the transmission. This device acts as a repeater when it
is placed in series to cover a distance larger than the attenuation length of
the fiber, and it acts as an optical quantum memory when it is inserted in a
fiber loop. We call this dual-purpose device a ``quantum transponder.''Comment: 4 pages, 5 figure
Optical Communication Noise Rejection Using Correlated Photons
This paper describes a completely new way to perform noise rejection using a
two-photon sensitive detector and taking advantage of the properties of
correlated photons to improve an optical communications link in the presence of
uncorrelated noise. In particular, a detailed analysis is made of the case
where a classical link would be saturated by an intense background, such as
when a satellite is in front of the sun,and identifies a regime where the
quantum correlating system has superior performance.Comment: 12 pages, 1 figure, 1 tabl
An evolutionary computation approach to three- dimensional path planning for unmanned aerial vehicles with tactical and kinematic constraints
This paper presents a novel evolutionary computation approach to three-dimensional path planning for unmanned aerial vehicles (UAVs) with tactical and kinematic constraints. A genetic algorithm (GA) is modified and extended for path planning. Two GAs are seeded at the initial and final positions with a common objective to minimise their distance apart under given UAV constraints. This is accomplished by the synchronous optimisation of subsequent control vectors. The proposed evolutionary computation approach is called synchronous genetic algorithm (SGA). The sequence of control vectors generated by the SGA constitutes to a near-optimal path plan. The resulting path plan exhibits no discontinuity when transitioning from curve to straight trajectories. Experiments and results show that the paths generated by the SGA are within 2% of the optimal solution. Such a path planner when implemented on a hardware accelerator, such as field programmable gate array chips, can be used in the UAV as on-board replanner, as well as in ground station systems for assisting in high precision planning and modelling of mission scenarios
The creation of large photon-number path entanglement conditioned on photodetection
Large photon-number path entanglement is an important resource for enhanced
precision measurements and quantum imaging. We present a general constructive
protocol to create any large photon number path-entangled state based on the
conditional detection of single photons. The influence of imperfect detectors
is considered and an asymptotic scaling law is derived.Comment: 6 pages, 4 figure
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