173 research outputs found
Strong quantitative benchmarking of quantum optical devices
Quantum communication devices, such as quantum repeaters, quantum memories,
or quantum channels, are unavoidably exposed to imperfections. However, the
presence of imperfections can be tolerated, as long as we can verify such
devices retain their quantum advantages. Benchmarks based on witnessing
entanglement have proven useful for verifying the true quantum nature of these
devices. The next challenge is to characterize how strongly a device is within
the quantum domain. We present a method, based on entanglement measures and
rigorous state truncation, which allows us to characterize the degree of
quantumness of optical devices. This method serves as a quantitative extension
to a large class of previously-known quantum benchmarks, requiring no
additional information beyond what is already used for the non-quantitative
benchmarks.Comment: 11 pages, 7 figures. Comments are welcome. ver 2: Improved figures,
no changes to main tex
Evaluation of the analytical potential of auger electron spectrometry in atmospheric analyses
The scope of this study into the analytical potential of
gas phase Auger electron spectrometry (AES) is defined, and its
relation to the work previously conducted at the University of
Technology, Loughborough on this topic is shown.
The vacuum generators AFM2 gas phase Auger electron
spectrometer is described in detail, this includes a discussion
of maintenance and fault-finding. Detailed operating instructions
based on the manufacturer's manual and the author's experience,
are included. The theoretical and experimental aspects of the
operational parameters of the electron gun, analyser, detector,
sample introduction system, and the recording system are given.
The choice of parameter values for the optimal performance of the
instrument are discussed. [Abstract.
Coherent control of quantum systems as a resource theory
Control at the interface between the classical and the quantum world is
fundamental in quantum physics. In particular, how classical control is
enhanced by coherence effects is an important question both from a theoretical
as well as from a technological point of view. In this work, we establish a
resource theory describing this setting and explore relations to the theory of
coherence, entanglement and information processing. Specifically, for the
coherent control of quantum systems the relevant resources of entanglement and
coherence are found to be equivalent and closely related to a measure of
discord. The results are then applied to the DQC1 protocol and the precision of
the final measurement is expressed in terms of the available resources.Comment: 9 pages, 4 figures, final version. Discussions were improved and some
points were clarified. The title was slightly changed to agree with the
published versio
Quantum benchmarking with realistic states of light
The goal of quantum benchmarking is to certify that imperfect quantum
communication devices (e.g., quantum channels, quantum memories, quantum key
distribution systems) can still be used for meaningful quantum communication.
However, the test states used in quantum benchmarking experiments may be
imperfect as well. Many quantum benchmarks are only valid for states which
match some ideal form, such as pure states or Gaussian states. We outline how
to perform quantum benchmarking using arbitrary states of light. We demonstrate
these results using real data taken from a continuous-variable quantum memory.Comment: 14 pages, 3 figures. Updated to more closely match the published
versio
Einstein-Podolsky-Rosen-like correlation on a coherent-state basis and inseparability of two-mode Gaussian states
The strange property of the Einstein-Podolsky-Rosen (EPR) correlation between
two remote physical systems is a primitive object on the study of quantum
entanglement. In order to understand the entanglement in canonical
continuous-variable systems, a pair of the EPR-like uncertainties is an
essential tool. Here, we consider a normalized pair of the EPR-like
uncertainties and introduce a state-overlap to a classically correlated mixture
of coherent states. The separable condition associated with this state-overlap
determines the strength of the EPR-like correlation on a coherent-state basis
in order that the state is entangled. We show that the coherent-state-based
condition is capable of detecting the class of two-mode Gaussian entangled
states. We also present an experimental measurement scheme for estimation of
the state-overlap by a heterodyne measurement and a photon detection with a
feedforward operation.Comment: 9 pages, 5 figures. A part of the materials in Sec. VI B of previous
versions was moved into another paper: Journal of Atomic, Molecular, and
Optical Physics, 2012, 854693 (2012).
http://www.hindawi.com/journals/jamop/2012/854693
Relative concentration and structure of native defects in GaP
The native defects in the compound semiconductor GaP have been studied using a pseudopotential density functional theory method in order to determine their relative concentrations and the most stable charge states. The electronic and atomic structures are presented and the defect concentrations are estimated using calculated formation energies. Relaxation effects are taken into account fully and produce negative-U charge transfer levels for VP and PGa. The concentration of VGa is in good agreement with the results of positron annihilation experiments. The charge transfer levels presented compare qualitatively well with experiments where available. The effect of stoichiometry on the defect concentrations is also described and is shown to be considerable. The lowest formation energies are found for PGa +2 in p-type and VGa −3 in n-type GaP under P-rich conditions, and for GaP −2 in n-type GaP under Ga-rich conditions. Finally, the finite size errors arising from the use of supercells with periodic boundary conditions are examined
Sized Types for low-level Quantum Metaprogramming
One of the most fundamental aspects of quantum circuit design is the concept
of families of circuits parametrized by an instance size. As in classical
programming, metaprogramming allows the programmer to write entire families of
circuits simultaneously, an ability which is of particular importance in the
context of quantum computing as algorithms frequently use arithmetic over
non-standard word lengths. In this work, we introduce metaQASM, a typed
extension of the openQASM language supporting the metaprogramming of circuit
families. Our language and type system, built around a lightweight
implementation of sized types, supports subtyping over register sizes and is
moreover type-safe. In particular, we prove that our system is strongly
normalizing, and as such any well-typed metaQASM program can be statically
unrolled into a finite circuit.Comment: Presented at Reversible Computation 2019. Final authenticated
publication is available online at
https://doi.org/10.1007/978-3-030-21500-2_
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