223 research outputs found
Mixed quantum state detection with inconclusive results
We consider the problem of designing an optimal quantum detector with a fixed
rate of inconclusive results that maximizes the probability of correct
detection, when distinguishing between a collection of mixed quantum states. We
develop a sufficient condition for the scaled inverse measurement to maximize
the probability of correct detection for the case in which the rate of
inconclusive results exceeds a certain threshold. Using this condition we
derive the optimal measurement for linearly independent pure-state sets, and
for mixed-state sets with a broad class of symmetries. Specifically, we
consider geometrically uniform (GU) state sets and compound geometrically
uniform (CGU) state sets with generators that satisfy a certain constraint.
We then show that the optimal measurements corresponding to GU and CGU state
sets with arbitrary generators are also GU and CGU respectively, with
generators that can be computed very efficiently in polynomial time within any
desired accuracy by solving a semidefinite programming problem.Comment: Submitted to Phys. Rev.
A Full Characterization of Quantum Advice
We prove the following surprising result: given any quantum state rho on n
qubits, there exists a local Hamiltonian H on poly(n) qubits (e.g., a sum of
two-qubit interactions), such that any ground state of H can be used to
simulate rho on all quantum circuits of fixed polynomial size. In terms of
complexity classes, this implies that BQP/qpoly is contained in QMA/poly, which
supersedes the previous result of Aaronson that BQP/qpoly is contained in
PP/poly. Indeed, we can exactly characterize quantum advice, as equivalent in
power to untrusted quantum advice combined with trusted classical advice.
Proving our main result requires combining a large number of previous tools --
including a result of Alon et al. on learning of real-valued concept classes, a
result of Aaronson on the learnability of quantum states, and a result of
Aharonov and Regev on "QMA+ super-verifiers" -- and also creating some new
ones. The main new tool is a so-called majority-certificates lemma, which is
closely related to boosting in machine learning, and which seems likely to find
independent applications. In its simplest version, this lemma says the
following. Given any set S of Boolean functions on n variables, any function f
in S can be expressed as the pointwise majority of m=O(n) functions f1,...,fm
in S, such that each fi is the unique function in S compatible with O(log|S|)
input/output constraints.Comment: We fixed two significant issues: 1. The definition of YQP machines
needed to be changed to preserve our results. The revised definition is more
natural and has the same intuitive interpretation. 2. We needed properties of
Local Hamiltonian reductions going beyond those proved in previous works
(whose results we'd misstated). We now prove the needed properties. See p. 6
for more on both point
Distinguishability of States and von Neumann Entropy
Consider an ensemble of pure quantum states |\psi_j>, j=1,...,n taken with
prior probabilities p_j respectively. We show that it is possible to increase
all of the pairwise overlaps || i.e. make each constituent pair
of the states more parallel (while keeping the prior probabilities the same),
in such a way that the von Neumann entropy S is increased, and dually, make all
pairs more orthogonal while decreasing S. We show that this phenomenon cannot
occur for ensembles in two dimensions but that it is a feature of almost all
ensembles of three states in three dimensions. It is known that the von Neumann
entropy characterises the classical and quantum information capacities of the
ensemble and we argue that information capacity in turn, is a manifestation of
the distinguishability of the signal states. Hence our result shows that the
notion of distinguishability within an ensemble is a global property that
cannot be reduced to considering distinguishability of each constituent pair of
states.Comment: 18 pages, Latex, 2 figure
Fast-, Light-Cured Scintillating Plastic for 3D-Printing Applications
Additive manufacturing techniques enable a wide range of possibilities for novel radiation detectors spanning simple to highly complex geometries, multi-material composites, and metamaterials that are either impossible or cost prohibitive to produce using conventional methods. The present work identifies a set of promising formulations of photocurable scintillator resins capable of neutron-gamma pulse shape discrimination (PSD) to support the additive manufacturing of fast neutron detectors. The development of these resins utilizes a step-by-step, trial-and-error approach to identify different monomer and cross-linker combinations that meet the requirements for 3D printing followed by a 2-level factorial parameter study to optimize the radiation detection performance, including light yield, PSD, optical clarity, and hardness. The formulations resulted in hard, clear, PSD-capable plastic scintillators that were cured solid within 10 s using 405 nm light. The best-performing scintillator produced a light yield 83% of EJ-276 and a PSD figure of merit equaling 1.28 at 450–550 keVee
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Development of a Robust 14 C Chronology for Lynch's Crater (North Queensland, Australia) Using Different Pretreatment Strategies
Whole-genome sequencing elucidates the species-wide diversity and evolution of fungicide resistance in the early blight pathogen Alternaria solani
Early blight of potato is caused by the fungal pathogen Alternaria solani and is an increasing problem worldwide. The primary strategy to control the disease is applying fungicides such as succinate dehydrogenase inhibitors (SDHI). SDHI-resistant strains, showing reduced sensitivity to treatments, appeared in Germany in 2013, shortly after the introduction of SDHIs. Two primary mutations in the SDH complex (SdhB-H278Y and SdhC-H134R) have been frequently found throughout Europe. How these resistances arose and spread, and whether they are linked to other genomic features, remains unknown. For this project, we performed whole-genome sequencing for 48 A. solani isolates from potato fields across Europe to better characterize the pathogen's genetic diversity in general and understand the development and spread of the genetic mutations that lead to SDHI resistance. The isolates can be grouped into seven genotypes. These genotypes do not show a geographical pattern but appear spread throughout Europe. We found clear evidence for recombination on the genome, and the observed admixtures might indicate a higher adaptive potential of the fungus than previously thought. Yet, we cannot link the observed recombination events to different Sdh mutations. The same Sdh mutations appear in different, non-admixed genetic backgrounds; therefore, we conclude they arose independently. Our research gives insights into the genetic diversity of A. solani on a genome level. The mixed occurrence of different genotypes, apparent admixture in the populations, and evidence for recombination indicate higher genomic complexity than anticipated. The conclusion that SDHI tolerance arose multiple times independently has important implications for future fungicide resistance management strategies. These should not solely focus on preventing the spread of isolates between locations but also on limiting population size and the selective pressure posed by fungicides in a given field to avoid the rise of new mutations in other genetic backgrounds
Information transfer and fidelity in quantum copiers
We find that very different quantum copying machines are optimal depending on
the indicator used to assess their performance. Several quantum copying machine
models acting on non-orthogonal input states are investigated, and assessed
according to two types of criteria: Transfer of (Shannon) information encoded
in the initial states to the copies, and fidelity between the copies and the
initial states. Transformations which optimise information transfer for
messages encoded in qubits are found. If the message is decoded one symbol
at-a-time, information is best copied by a Wootters-Zurek copier.Comment: 14 pages, 3 Figures, REVTeX. Accepted Physical Review A. Corrected
minor grammatical error
Experimental Proposal for Achieving Superadditive Communication Capacities with a Binary Quantum Alphabet
We demonstrate superadditivity in the communication capacity of a binary
alphabet consisting of two nonorthogonal quantum states. For this scheme,
collective decoding is performed two transmissions at a time. This improves
upon the previous schemes of Sasaki et al. [Phys. Rev. A 58, 146 (1998)] where
superadditivity was not achieved until a decoding of three or more
transmissions at a time. This places superadditivity within the regime of a
near-term laboratory demonstration. We propose an experimental test based upon
an alphabet of low photon-number coherent states where the signal decoding is
done with atomic state measurements on a single atom in a high-finesse optical
cavity.Comment: 7 pages, 5 figure
Radiocarbon Dating of Wood Using Different Pretreatment Procedures: Application to the Chronology of Rotoehu Ash, New Zealand
We compare radiocarbon accelerator mass spectrometry (AMS) ages of wood samples subjected to a conventional acid-base-acid pretreatment with stepped combustion (ABA-SC) with results from the same samples subjected to an acid-base-wet oxidation pretreatment with stepped combustion (ABOX-SC) and cellulose extraction with stepped combustion (CE-SC). The ABOX-SC procedure has been shown previously to lead to lower backgrounds for old charcoal samples. Analyses of relatively uncontaminated" C-14-dead" samples of wood suggest that backgrounds of 0.11 +/- 0.04 pMC are obtainable for both the ABOX-SC and ABA-SC procedures. Where wood is significantly contaminated the ABOX-SC technique provides significantly better decontamination than either the ABA-SC technique or cellulose extraction alone, although CE-SC can produce comparably low backgrounds to the ABOX-SC procedure. We also report the application of the ABOX-SC, ABA-SC and CE-SC procedures to wood samples associated with the chronologically controversial Rotoehu Ash eruption, New Zealand. New C-14-AMS dates from wood sampled from below the Rotoehu Ash span an age range of 43-50 ka BP consistent with recently presented OSL dates of 42-44, ka obtained for palaeosols beneath the ash
Entanglement-enhanced testing of multiple quantum hypotheses
Quantum hypothesis testing has been greatly advanced for the binary discrimination of two states, or two channels. In this setting, we already know that quantum entanglement can be used to enhance the discrimination of two bosonic channels. Here, we remove the restriction of binary hypotheses and show that entangled photons can remarkably boost the discrimination of multiple bosonic channels. More precisely, we formulate a general problem of channel-position finding where the goal is to determine the position of a target channel among many background channels. We prove that, using entangled photons at the input and a generalized form of conditional nulling receiver at the output, we may outperform any classical strategy. Our results can be applied to enhance a range of technological tasks, including the optical readout of sparse classical data, the spectroscopic analysis of a frequency spectrum, and the determination of the direction of a target at fixed range
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