Hasil untuk "quant-ph"

Menampilkan 20 dari ~2354503 hasil · dari DOAJ, CrossRef, Semantic Scholar

JSON API
S2 Open Access 2021
A Portrait of the Collaboration Network in Quantum Information

S. Brito, Rute Oliveira, R. Oliveira et al.

From its inception at the beginning of the eighties, with milestone results and ideas such as quantum simulation, the no-cloning theorem, and quantum computers, quantum information has established itself over the next decades, being nowadays a fast-developing field at the interface between fundamental science and a variety of promising technologies. In this work we aim to offer a portrait of this dynamic field, analyzing the statistical properties of the network of collaborations among its researchers. Using the quant-ph section from the arXiv as our database, we draw several conclusions on its properties. In particular, we show that the quantum information network of collaborations displays the small-world property, is very aggregated and assortative, being also in line with Newman's findings as for the presence of hubs and the Lotka's law regarding the average number of publications per author.

1 sitasi en Physics
S2 Open Access 2020
Combinations of quantum observables and instruments

S. Gudder

This article points out that observables and instruments can be combined in many ways that have natural and physical interpretations. We shall mainly concentrate on the mathematical properties of these combinations. After an introduction in section , section reviews the basic definitions and observables are considered in section . We study parts of observables, post-processing, generalized convex combinations, sequential products and tensor products. These combinations are extended to instruments in section . We consider properties of observables measured by combinations of instruments. We introduce four special types of instruments, namely Kraus, Lüders, trivial and semitrivial instruments. We study when these types are closed under various combinations. In this work, we only consider finite-dimensional quantum systems. A few of the results presented here have appeared in the author’s previous articles Gudder (2020 arXiv:2005.08117 [quant-ph], arXiv:2005.13642 [quant-ph], arXiv:2009.07371 [quant-ph]).

6 sitasi en Physics, Mathematics
S2 Open Access 2020
Caractérisation du sol du site dégradé de Sakey koira Tegui au Niger pour un meilleur reboisement avecAcacia senegal

Djabri Hassimiou Halidou, Maman Manssour Abdou, Z. Mayaki

La degradation des sols resultants des facteurs climatiques et anthropiques constitue l’un des problemes majeurs de l’agriculture au Niger. En reponse a ce phenomene, les agroecosystemes s’adaptent a travers la mise en oeuvre des techniques de gestion integree des eaux et des sols dont notamment le reboisement des terres degradees. C’est ainsi que cette etude a ete menee avec pour objectif de caracteriser le sol degrade du site de Sakey koira Tegui en vue d’un meilleur reboisement avec Acacia senegal. A cet effet, des profils pedologiques ont ete ouverts et decrits suivant la topo-sequence du site. Des echantillons de sol ont ete preleves au niveau de chaque profil et analyses au laboratoire. Les resultats ont montre que la texture de sols est de type sableuse (72,32%) et limoneuse (45%). Quant aux caracteristiques chimiques des sols, le pH est acide variant de 5,1 a 5,53 sur l’ensemble des horizons avec une conductivite electrique de l’ordre de 13, 00 a 33, 00 μs/cm. Ces resultats montrent que ce sol de faible fertilite chimique, avec une predominance sableuse pourrait etre recupere et reboise avec Acacia senegal, sol de predilection de cette espece. Mots cles : caracteristiques chimiques, textures, terres degradees, Acacia senegal, Niger.   English Title: Soil characterization of the degraded site of Sakey koira Tegui in Niger for better reforestation with Acacia senegalSoil degradation resulting from climatic and anthropogenic factors is one of the major problems of agriculture in Niger. In response to this phenomenon, agro-ecosystems are adapting through the implementation of integrated water and soil management techniques, including reforestation of degraded land. Thus, this study was conducted with the objective of characterizing the degraded soil of the Sakey koira Tegui site for better reforestation with Acacia senegal. To this end, soil profiles were opened and described according to the topo-sequence of the site. Soil samples were taken from each profile and analysed in the laboratory. The results showed that the soil texture is sandy (72.32%) and silty (45%). As for the chemical characteristics of the soils, the pH is acidic ranging from 5.1 to 5.53 over all horizons with an electrical conductivity of 13.00 to 33.00 μs/cm. These results show that this soil of low chemical fertility, with a sandy predominance, could be recovered and reforested with Acacia senegal, the soil of predilection of this species.Keywords: Chemical characteristics, textures, degraded soils, Acacia senegal, Niger.

5 sitasi en Environmental Science
S2 Open Access 2020
Entropic time–energy uncertainty relations: an algebraic approach

C. Bertoni, Yuxiang Yang, J. Renes

We address entropic uncertainty relations between time and energy or, more precisely, between measurements of an observable G and the displacement r of the G-generated evolution e−irG. We derive lower bounds on the entropic uncertainty in two frequently considered scenarios, which can be illustrated as two different guessing games in which the role of the guessers are fixed or not. In particular, our bound for the first game improves the previous result by Coles et al [Phys. Rev. Lett. 122 100401 (2019)]. To derive our bounds, we extend a recently proposed novel algebraic method by Gao et al [arXiv:1710.10038 [quant-ph]] which was used to derive both strong subadditivity and entropic uncertainty relations for measurements.

3 sitasi en Physics, Mathematics
S2 Open Access 2019
Square-integrable eigenfunctions in quantizing the Bateman oscillator model.

S. Deguchi, Yuki Fujiwara

In a recent paper [Phys. Lett. A 383 (2019) 2836; arXiv:1906.05121 [quant-ph]], Bagarello, Gargano, and Roccati have claimed that no square-integrable vacuum exists in quantizing the Bateman oscillator model. In this paper, we rebut their claim by actually deriving the square-integrable vacuum eigenfunction using a common procedure. We see that no problems occur in quantizing the Bateman oscillator model.

5 sitasi en Physics, Mathematics
S2 Open Access 2019
Two variations on (A3 × A1 × A1)(1) type discrete Painlevé equations

Yang Shi

By considering the normalizers of reflection subgroups of types A(1)1 and A(1)3 in W~(D5(1)), two subgroups: W~(A3×A1)(1)⋉W(A1(1)) and W~(A1×A1)(1)⋉W(A3(1)) can be constructed from a (A3 × A1 × A1)(1) type subroot system. These two symmetries arose in the studies of discrete Painlevé equations (Kajiwara K, Noumi M, Yamada Y. 2002 q-Painlevé systems arising from q-KP hierarchy. Lett. Math. Phys. 62, 259–268; Takenawa T. 2003 Weyl group symmetry of type D(1)5 in the q-Painlevé V equation. Funkcial. Ekvac. 46, 173–186; Okubo N, Suzuki T. 2018 Generalized q-Painlevé VI systems of type (A2n+1 + A1 + A1)(1) arising from cluster algebra. (http://arxiv.org/abs/quant-ph/1810.03252)), where certain non-translational elements of infinite order were shown to give rise to discrete Painlevé equations. We clarify the nature of these elements in terms of Brink-Howlett theory of normalizers of Coxeter groups (Howlett RB. 1980 Normalizers of parabolic subgroups of reflection groups. J. London Math. Soc. (2) 21, 62–80; Brink B, Howlett RB. 1999 Normalizers of parabolic subgroups in Coxeter groups. Invent. Math. 136, 323–351). This is the first of a series of studies which investigates the properties of discrete integrable equations via the theory of normalizers.

5 sitasi en Physics, Mathematics
S2 Open Access 2018
Quantum field theory with classical sources—linearized quantum gravity

B. Skagerstam, K. Eriksson, P. Rekdal

In a previous work (Skagerstam 2018 arXiv:1801.09947v1 [quant-ph]) and in terms of an exact quantum-mechanical framework, -independent causal and retarded expectation values of the second-quantized electro-magnetic fields in the Coulomb gauge were derived in the presence of a conserved classical electric current. The classical -independent Maxwell’s equations then naturally emerged. In the present work, we extend these considerations to linear gravitational quantum deviations around a flat Minkowski space-time in a Coulomb-like gauge. The emergence of the classical, causal, and properly retarded linearized classical theory of general relativity with a conserved classical energy–momentum tensor is then outlined. The quantum-mechanical framework also provides for a simple approach to classical quadrupole gravitational radiation of Einstein and microscopic spontaneous graviton emission and/or absorption processes.

9 sitasi en Physics
S2 Open Access 2014
Tunable negative permeability in a quantum plasmonic metamaterial

K. McEnery, M. Tame, S. Maier et al.

School of Chemistry and Physics, University of KwaZulu-Natal, Durban 4001, South Africa(Dated: January 22, 2014)We consider the integration of quantum emitters into a negative permeability metamaterial design in order tointroduce tunability as well as nonlinear behavior. The unit cell of our metamaterial is a ring of metamolecules,each consisting of a metal nanoparticle and a two-level semiconductor quantum dot (QD). Without the QDs, thering of the unit cell is known to act as an artificial optical magnetic resonator. By adding the QDs we show that aFano interference profile is introduced into the magnetic field scattered from the ring. This induced interferenceis shown to cause an appreciable earXiv:1401.5402v1 [quant-ph] 21 Jan 2014 ect in the collective magnetic resonance of the unit cell. We find that theinterference provides a means to tune the response of the negative permeability metamaterial. The exploitationof the QD’s inherent nonlinearity is proposed to modulate the metamaterial’s magnetic response with a separatecontrol field.I. INTRODUCTION

22 sitasi en Physics
S2 Open Access 2013
Disproving Heisenberg's error-disturbance relation

M. Ozawa

Recently, Busch, Lahti, and Werner (arXiv:1306.1565v1 [quant-ph]) claimed that Heisenberg's error-disturbance relation can be proved in its original form with new formulations of error and disturbance, in contrast to the theory proposed by the present author and confirmed by recent experiments. Despite their claim, it is shown here that a class of solvable models of position measurement with explicit interaction Hamiltonians escape the Busch-Lahti-Werner relation. It is also made clear where their proof fails. Those models have unambiguously defined zero root-mean-square error and finite root-mean-square disturbance in every input state and are naturally considered to violate Heisenberg's error-disturbance relation in any conceivable formulation.

30 sitasi en Mathematics, Physics
S2 Open Access 2007
Precise protein quantification based on peptide quantification using iTRAQ™

Andreas M. Boehm, Stephanie M Pütz, Daniela Altenhöfer et al.

BackgroundMass spectrometry based quantification of peptides can be performed using the iTRAQ™ reagent in conjunction with mass spectrometry. This technology yields information about the relative abundance of single peptides. A method for the calculation of reliable quantification information is required in order to obtain biologically relevant data at the protein expression level.ResultsA method comprising sound error estimation and statistical methods is presented that allows precise abundance analysis plus error calculation at the peptide as well as at the protein level. This yields the relevant information that is required for quantitative proteomics. Comparing the performance of our method named Quant with existing approaches the error estimation is reliable and offers information for precise bioinformatic models. Quant is shown to generate results that are consistent with those produced by ProQuant™, thus validating both systems. Moreover, the results are consistent with that of Mascot™ 2.2. The MATLAB® scripts of Quant are freely available via http://www.protein-ms.de and http://sourceforge.net/projects/protms/, each under the GNU Lesser General Public License.ConclusionThe software Quant demonstrates improvements in protein quantification using iTRAQ™. Precise quantification data can be obtained at the protein level when using error propagation and adequate visualization. Quant integrates both and additionally provides the possibility to obtain more reliable results by calculation of wise quality measures. Peak area integration has been replaced by sum of intensities, yielding more reliable quantification results. Additionally, Quant allows the combination of quantitative information obtained by iTRAQ™ with peptide and protein identifications from popular tandem MS identification tools. Hence Quant is a useful tool for the proteomics community and may help improving analysis of proteomic experimental data. In addition, we have shown that a lognormal distribution fits the data of mass spectrometry based relative peptide quantification.

115 sitasi en Chemistry, Computer Science
S2 Open Access 2000
Speed of ion-trap quantum-information processors

Andrew Steane, C. F. Roos, D. Stevens et al.

We investigate theoretically the speed limit of quantum gate operations for ion trap quantum information processors. The proposed methods use laser pulses for quantum gates which entangle the electronic and vibrational degrees of freedom of the trapped ions. Two of these methods are studied in detail and for both of them the speed is limited by a combination of the recoil frequency of the relevant electronic transition, and the vibrational frequency in the trap. We have experimentally studied the gate operations below and above this speed limit. In the latter case, the fidelity is reduced, in agreement with our theoretical findings. // Changes: a) error in equ. 24 and table III repaired b) reference Jonathan et al, quant-ph/ 0002092, added (proposes fast quantum gates using the AC-Stark effect)

91 sitasi en Physics
S2 Open Access 2002
Local vs. joint measurements for the entanglement of assistance

T. Laustsen, F. Verstraete, S. J. Enk

We consider a variant of the entanglement of assistance, as independently introduced by D.P. DiVincenzo et al. (quant-ph/9803033) and O. Cohen (Phys. Rev. Lett. 80, 2493 (1998)). Instead of considering three-party states in which one of the parties, the assistant, performs a measurement such that the remaining two parties are left with on average as much entanglement as possible, we consider four-party states where two parties play the role of assistants. We answer several questions that arise naturally in this scenario, such as (i) how much more entanglement can be produced when the assistants are allowed to perform joint measurements, (ii) for what type of states are local measurements sufficient, (iii) is it necessary for the second assistant to know the measurement outcome of the first, and (iv) are projective measurements sufficient or are more general POVMs needed?

90 sitasi en Computer Science, Mathematics
S2 Open Access 2002
The generalized partial transposition criterion for separability of multipartite quantum states

Kai Chen, Ling-An Wu

Abstract We present a generalized partial transposition separability criterion for the density matrix of a multipartite quantum system. This criterion comprises as special cases the famous Peres–Horodecki criterion and the recent realignment criterion in [O. Rudolph, quant-ph/0202121 ] and [K. Chen, L.A. Wu, quant-ph/0205017 ]. It involves only straightforward matrix manipulations and is easy to apply. A quantitative measure of entanglement based on this criterion is also obtained.

89 sitasi en Physics
S2 Open Access 2006
Merlin-Arthur Games and Stoquastic Complexity

S. Bravyi, A. Bessen, B. Terhal

MA is a class of decision problems for which `yes'-instances have a proof that can be efficiently checked by a classical randomized algorithm. We prove that MA has a natural complete problem which we call the stoquastic k-SAT problem. This is a matrix-valued analogue of the satisfiability problem in which clauses are k-qubit projectors with non-negative matrix elements, while a satisfying assignment is a vector that belongs to the space spanned by these projectors. Stoquastic k-SAT is the first non-trivial example of a MA-complete problem. We also study the minimum eigenvalue problem for local stoquastic Hamiltonians that was introduced in quant-ph/0606140, stoquastic LH-MIN. A new complexity class StoqMA is introduced so that stoquastic LH-MIN is StoqMA-complete. Lastly, we consider the average LH-MIN problem for local stoquastic Hamiltonians that depend on a random or `quenched disorder' parameter, stoquastic AV-LH-MIN. We prove that stoquastic AV-LH-MIN is contained in the complexity class \AM, the class of decision problems for which yes-instances have a randomized interactive proof with two-way communication between prover and verifier.

64 sitasi en Computer Science, Mathematics

Halaman 7 dari 117726