Fault-tolerant fidelity based on few-qubit codes: Parity-check circuits for biased error channels Dawei Jiao, Ying Li Sep 22 2020 quant-ph arXiv:2009.09726v1 Scited Scite! 5 @misc{2009.09726, author = {Dawei Jiao and Ying Li}, title = {{F}ault-tolerant fidelity based on few-qubit codes: {P}arity-check circuits for biased error channels}, year = {2020}, eprint = {2009.09726}, note = {arXiv:2009.09726v1} } Copy Citation PDF In the shallow sub-threshold regime, fault-tolerant quantum computation requires a tremendous amount of qubits. In this paper, we study the error correction in the deep sub-threshold regime. We estimate the physical error rate for achieving the logical error rates of $10^{-6} - 10^{-15}$ using few-qubit codes, i.e. short repetition codes, small surface codes and the Steane code. Error correction circuits that are efficient for biased error channels are identified. Using the Steane code, when error channels are biased with a ratio of $10^{-3}$, the logical error rate of $10^{-15}$ can be achieved with the physical error rate of $10^{-5}$, which is much higher than the physical error rate of $10^{-9}$ for depolarising errors.

Quantum erasing the memory of Wigner's friend Cyril Elouard, Philippe Lewalle, Sreenath K. Manikandan, Spencer Rogers, Adam Frank, Andrew N. Jordan Sep 22 2020 quant-ph arXiv:2009.09905v1 Scited Scite! 4 @misc{2009.09905, author = {Cyril Elouard and Philippe Lewalle and Sreenath K.~Manikandan and Spencer Rogers and Adam Frank and Andrew N.~Jordan}, title = {{Q}uantum erasing the memory of {W}igner's friend}, year = {2020}, eprint = {2009.09905}, note = {arXiv:2009.09905v1} } Copy Citation PDF The Wigner's friend paradox concerns one of the most puzzling concepts of quantum mechanics: the consistent description of multiple nested observers. Recently, a variation of Wigner's gedankenexperiment, introduced by Frauchiger and Renner, has lead to new debates about the self-consistency of quantum mechanics. We propose a simple single-photon interferometric setup implementing their scenario, and use our reformulation to shed a new light on the assumptions leading to their paradox. From our description, we argue that the three apparently incompatible properties used to question the consistency of quantum mechanics correspond to two logically distinct contexts: either assuming that Wigner has full control over his friends' lab, or conversely that some part of the labs remain unaffected by Wigner's subsequent measurements. The first context may be seen as the quantum erasure of the memory of Wigner's friend. We further show these properties are associated with observables which do not commute, and therefore cannot take well-defined values simultaneously. Consequently, the three contradictory properties never hold simultaneously.

Measurement of Gravitational Coupling between Millimeter-Sized Masses Tobias Westphal, Hans Hepach, Jeremias Pfaff, Markus Aspelmeyer physics.class-ph physics.ins-det Sep 22 2020 gr-qc quant-ph arXiv:2009.09546v1 Scited Scite! 3 @misc{2009.09546, author = {Tobias Westphal and Hans Hepach and Jeremias Pfaff and Markus Aspelmeyer}, title = {{M}easurement of {G}ravitational {C}oupling between {M}illimeter-{S}ized {M}asses}, year = {2020}, eprint = {2009.09546}, note = {arXiv:2009.09546v1} } Copy Citation PDF We demonstrate gravitational coupling between two gold spheres of approximately 1mm radius and 90mg mass. By periodically modulating the source mass position at a frequency f=12.7mHz we generate a time-dependent gravitational acceleration at the location of the test mass, which is measured off resonance in a miniature torsional balance configuration. Over an integration time of 350 hours the test mass oscillator enables measurements with a systematic accuracy of 4E-11m/s^2 and a statistical precision of 4E-12m/s^2. This is sufficient to resolve the gravitational signal at a minimal surface distance of 400mum between the two masses. We observe both linear and quadratic coupling, consistent in signal strength with a time-varying 1/r gravitational potential. Contributions of non-gravitational forces could be kept to less than 10% of the observed signal. We expect further improvements to enable the isolation of gravity as a coupling force for objects well below the Planck mass. This opens the way for precision tests of gravity in a new regime of isolated microscopic source masses.

A no-go theorem for the persistent reality of Wigner's friend's perception Philippe Allard Guérin, Veronika Baumann, Flavio Del Santo, Časlav Brukner Sep 22 2020 quant-ph arXiv:2009.09499v1 Scited Scite! 3 @misc{2009.09499, author = {Philippe Allard Guérin and Veronika Baumann and Flavio Del Santo and Časlav Brukner}, title = {{A} no-go theorem for the persistent reality of {W}igner's friend's perception}, year = {2020}, eprint = {2009.09499}, note = {arXiv:2009.09499v1} } Copy Citation PDF The notorious Wigner's friend thought experiment (and modifications thereof) has in recent years received renewed interest especially due to new arguments that force us to question some of the fundamental assumptions of quantum theory. In this paper, we formulate a no-go theorem for the persistent reality of Wigner's friend's perception, which allows us to conclude that the perceptions that the friend has of her own measurement outcomes at different times cannot "share the same reality", if seemingly natural quantum mechanical assumptions are met. More formally, this means that, in a Wigner's friend scenario, there is no joint probability distribution for the friend's perceived measurement outcomes at two different times, that depends linearly on the initial state of the measured system and whose marginals reproduce the predictions of unitary quantum theory. This theorem entails that one must either (1) propose a nonlinear modification of the Born rule for two-time predictions, (2) sometimes prohibit the use of present information to predict the future --thereby reducing the predictive power of quantum theory-- or (3) deny that unitary quantum mechanics makes valid single-time predictions for all observers. We briefly discuss which of the theorem's assumptions are more likely to be dropped within various popular interpretations of quantum mechanics.

The Complexity of Constrained Min-Max Optimization Constantinos Daskalakis, Stratis Skoulakis, Manolis Zampetakis cs.LG Sep 22 2020 cs.CC math.OC arXiv:2009.09623v1 Scited Scite! 2 @misc{2009.09623, author = {Constantinos Daskalakis and Stratis Skoulakis and Manolis Zampetakis}, title = {{T}he {C}omplexity of {C}onstrained {M}in-{M}ax {O}ptimization}, year = {2020}, eprint = {2009.09623}, note = {arXiv:2009.09623v1} } Copy Citation PDF Despite its important applications in Machine Learning, min-max optimization of nonconvex-nonconcave objectives remains elusive. Not only are there no known first-order methods converging even to approximate local min-max points, but the computational complexity of identifying them is also poorly understood. In this paper, we provide a characterization of the computational complexity of the problem, as well as of the limitations of first-order methods in constrained min-max optimization problems with nonconvex-nonconcave objectives and linear constraints. As a warm-up, we show that, even when the objective is a Lipschitz and smooth differentiable function, deciding whether a min-max point exists, in fact even deciding whether an approximate min-max point exists, is NP-hard. More importantly, we show that an approximate local min-max point of large enough approximation is guaranteed to exist, but finding one such point is PPAD-complete. The same is true of computing an approximate fixed point of Gradient Descent/Ascent. An important byproduct of our proof is to establish an unconditional hardness result in the Nemirovsky-Yudin model. We show that, given oracle access to some function $f : P \to [-1, 1]$ and its gradient $

abla f$, where $P \subseteq [0, 1]^d$ is a known convex polytope, every algorithm that finds a $\varepsilon$-approximate local min-max point needs to make a number of queries that is exponential in at least one of $1/\varepsilon$, $L$, $G$, or $d$, where $L$ and $G$ are respectively the smoothness and Lipschitzness of $f$ and $d$ is the dimension. This comes in sharp contrast to minimization problems, where finding approximate local minima in the same setting can be done with Projected Gradient Descent using $O(L/\varepsilon)$ many queries. Our result is the first to show an exponential separation between these two fundamental optimization problems.

Towards quantum simulation of spin systems using continuous variable quantum devices Razieh Annabestani, Brajesh Gupt, Bhaskar Roybardhan Sep 22 2020 quant-ph arXiv:2009.09455v1 Scited Scite! 2 @misc{2009.09455, author = {Razieh Annabestani and Brajesh Gupt and Bhaskar Roybardhan}, title = {{T}owards quantum simulation of spin systems using continuous variable quantum devices}, year = {2020}, eprint = {2009.09455}, note = {arXiv:2009.09455v1} } Copy Citation PDF We study the Bosonic representation of spin Ising model with the application of simulating two level systems using continuous variable quantum processors. We decompose the time evolution of spin systems into a sequence of continuous variable logical gates and analyze their structure. We provide an estimation of quantum circuit scaling with the size of the spin lattice system. The result makes a two-way connection between discrete variable aand continuous variable models and paves the way towards building a universal quantum computer. Furthermore, we discuss the possibility of using a Gaussian Boson sampling device to estimate the ground state energy of Ising Hamiltonian. The result has application in developing hybrid classical-quantum algorithms such as continuous variable version of variational quantum eigensolver.

A Tutorial on Quantum Convolutional Neural Networks (QCNN) Seunghyeok Oh, Jaeho Choi, Joongheon Kim Sep 22 2020 quant-ph arXiv:2009.09423v1 Scited Scite! 2 @misc{2009.09423, author = {Seunghyeok Oh and Jaeho Choi and Joongheon Kim}, title = {{A} {T}utorial on {Q}uantum {C}onvolutional {N}eural {N}etworks ({QCNN})}, year = {2020}, eprint = {2009.09423}, note = {arXiv:2009.09423v1} } Copy Citation PDF Convolutional Neural Network (CNN) is a popular model in computer vision and has the advantage of making good use of the correlation information of data. However, CNN is challenging to learn efficiently if the given dimension of data or model becomes too large. Quantum Convolutional Neural Network (QCNN) provides a new solution to a problem to solve with CNN using a quantum computing environment, or a direction to improve the performance of an existing learning model. The first study to be introduced proposes a model to effectively solve the classification problem in quantum physics and chemistry by applying the structure of CNN to the quantum computing environment. The research also proposes the model that can be calculated with O(log(n)) depth using Multi-scale Entanglement Renormalization Ansatz (MERA). The second study introduces a method to improve the model's performance by adding a layer using quantum computing to the CNN learning model used in the existing computer vision. This model can also be used in small quantum computers, and a hybrid learning model can be designed by adding a quantum convolution layer to the CNN model or replacing it with a convolution layer. This paper also verifies whether the QCNN model is capable of efficient learning compared to CNN through training using the MNIST dataset through the TensorFlow Quantum platform.

Optimal Provable Robustness of Quantum Classification via Quantum Hypothesis Testing Maurice Weber, Nana Liu, Bo Li, Ce Zhang, Zhikuan Zhao cs.CR cs.LG Sep 22 2020 quant-ph stat.ML arXiv:2009.10064v1 Scited Scite! 1 @misc{2009.10064, author = {Maurice Weber and Nana Liu and Bo Li and Ce Zhang and Zhikuan Zhao}, title = {{O}ptimal {P}rovable {R}obustness of {Q}uantum {C}lassification via {Q}uantum {H}ypothesis {T}esting}, year = {2020}, eprint = {2009.10064}, note = {arXiv:2009.10064v1} } Copy Citation PDF Quantum machine learning models have the potential to offer speedups and better predictive accuracy compared to their classical counterparts. However, these quantum algorithms, like their classical counterparts, have been shown to also be vulnerable to input perturbations, in particular for classification problems. These can arise either from noisy implementations or, as a worst-case type of noise, adversarial attacks. These attacks can undermine both the reliability and security of quantum classification algorithms. In order to develop defence mechanisms and to better understand the reliability of these algorithms, it is crucial to understand their robustness properties in presence of both natural noise sources and adversarial manipulation. From the observation that, unlike in the classical setting, measurements involved in quantum classification algorithms are naturally probabilistic, we uncover and formalize a fundamental link between binary quantum hypothesis testing (QHT) and provably robust quantum classification. Then from the optimality of QHT, we prove a robustness condition, which is tight under modest assumptions, and enables us to develop a protocol to certify robustness. Since this robustness condition is a guarantee against the worst-case noise scenarios, our result naturally extends to scenarios in which the noise source is known. Thus we also provide a framework to study the reliability of quantum classification protocols under more general settings.

Embedding theorems for solvable groups Vitaly Roman'kov Sep 22 2020 math.GR arXiv:2009.09958v1 Scited Scite! 1 @misc{2009.09958, author = {Vitaly Roman'kov}, title = {{E}mbedding theorems for solvable groups}, year = {2020}, eprint = {2009.09958}, note = {arXiv:2009.09958v1} } Copy Citation PDF In this paper, we prove a series of results on group embeddings in groups with a small number of generators. We show that each finitely generated group $G$ lying in a variety ${\mathcal M}$ can be embedded in a $4$-generated group $H \in {\mathcal M}{\mathcal A}$ (${\mathcal A}$ means the variety of abelian groups). If $G$ is a finite group, then $H$ can also be found as a finite group. It follows, that any finitely generated (finite) solvable group $G$ of the derived length $l$ can be embedded in a $4$-generated (finite) solvable group $H$ of length $l+1$. Thus, we answer the question of V. H. Mikaelian and A.Yu. Olshanskii. It is also shown that any countable group $G\in {\mathcal M}$, such that the abelianization $G_{ab}$ is a free abelian group, is embeddable in a $2$-generated group $H\in {\mathcal M}{\mathcal A}$.

The Complexity Landscape of Distributed Locally Checkable Problems on Trees Yi-Jun Chang Sep 22 2020 cs.DS cs.DC arXiv:2009.09645v1 Scited Scite! 1 @misc{2009.09645, author = {Yi-Jun Chang}, title = {{T}he {C}omplexity {L}andscape of {D}istributed {L}ocally {C}heckable {P}roblems on {T}rees}, year = {2020}, eprint = {2009.09645}, note = {arXiv:2009.09645v1} } Copy Citation PDF Recent research revealed the existence of gaps in the complexity landscape of locally checkable labeling (LCL) problems in the LOCAL model of distributed computing. For example, the deterministic round complexity of any LCL problem on bounded-degree graphs is either $O(\log^\ast n)$ or $\Omega(\log n)$ [Chang, Kopelowitz, and Pettie, FOCS 2016]. The complexity landscape of LCL problems is now quite well-understood, but a few questions remain open. For bounded-degree trees, there is an LCL problem with round complexity $\Theta(n^{1/k})$ for each positive integer $k$ [Chang and Pettie, FOCS 2017]. It is conjectured that no LCL problem has round complexity $o(n^{1/(k-1)})$ and $\omega(n^{1/k})$ on bounded-degree trees. As of now, only the case of $k = 2$ has been proved [Balliu et al., DISC 2018]. In this paper, we show that for LCL problems on bounded-degree trees, there is indeed a gap between $\Theta(n^{1/(k-1)})$ and $\Theta(n^{1/k})$ for each $k \geq 2$. Our proof is constructive in the sense that it offers a sequential algorithm that decides which side of the gap a given LCL problem belongs to. We also show that it is EXPTIME-hard to distinguish between $\Theta(1)$-round and $\Theta(n)$-round LCL problems on bounded-degree trees. This improves upon a previous PSPACE-hardness result [Balliu et al., PODC 2019].

On Distributed Differential Privacy and Counting Distinct Elements Lijie Chen, Badih Ghazi, Ravi Kumar, Pasin Manurangsi cs.DS cs.LG Sep 22 2020 cs.CR stat.ML arXiv:2009.09604v1 Scited Scite! 1 @misc{2009.09604, author = {Lijie Chen and Badih Ghazi and Ravi Kumar and Pasin Manurangsi}, title = {{O}n {D}istributed {D}ifferential {P}rivacy and {C}ounting {D}istinct {E}lements}, year = {2020}, eprint = {2009.09604}, note = {arXiv:2009.09604v1} } Copy Citation PDF We study the setup where each of $n$ users holds an element from a discrete set, and the goal is to count the number of distinct elements across all users, under the constraint of $(\epsilon, \delta)$-differentially privacy: - In the non-interactive local setting, we prove that the additive error of any protocol is $\Omega(n)$ for any constant $\epsilon$ and for any $\delta$ inverse polynomial in $n$. - In the single-message shuffle setting, we prove a lower bound of $\Omega(n)$ on the error for any constant $\epsilon$ and for some $\delta$ inverse quasi-polynomial in $n$. We do so by building on the moment-matching method from the literature on distribution estimation. - In the multi-message shuffle setting, we give a protocol with at most one message per user in expectation and with an error of $\tilde{O}(\sqrt(n))$ for any constant $\epsilon$ and for any $\delta$ inverse polynomial in $n$. Our protocol is also robustly shuffle private, and our error of $\sqrt(n)$ matches a known lower bound for such protocols. Our proof technique relies on a new notion, that we call dominated protocols, and which can also be used to obtain the first non-trivial lower bounds against multi-message shuffle protocols for the well-studied problems of selection and learning parity. Our first lower bound for estimating the number of distinct elements provides the first $\omega(\sqrt(n))$ separation between global sensitivity and error in local differential privacy, thus answering an open question of Vadhan (2017). We also provide a simple construction that gives $\tilde{\Omega}(n)$ separation between global sensitivity and error in two-party differential privacy, thereby answering an open question of McGregor et al. (2011).

A General Framework for the Security Analysis of Blockchain Protocols Andrew Lewis-Pye, Tim Roughgarden cs.CR Sep 22 2020 cs.DC cs.DS arXiv:2009.09480v1 Scited Scite! 1 @misc{2009.09480, author = {Andrew Lewis-Pye and Tim Roughgarden}, title = {{A} {G}eneral {F}ramework for the {S}ecurity {A}nalysis of {B}lockchain {P}rotocols}, year = {2020}, eprint = {2009.09480}, note = {arXiv:2009.09480v1} } Copy Citation PDF Blockchain protocols differ in fundamental ways, including the mechanics of selecting users to produce blocks (e.g., proof-of-work vs. proof-of-stake) and the method to establish consensus (e.g., longest chain rules vs. Byzantine fault-tolerant (BFT) inspired protocols). These fundamental differences have hindered "apples-to-apples" comparisons between different categories of blockchain protocols and, in turn, the development of theory to formally discuss their relative merits. This paper presents a parsimonious abstraction sufficient for capturing and comparing properties of many well-known permissionless blockchain protocols, simultaneously capturing essential properties of both proof-of-work (PoW) and proof-of-stake (PoS) protocols, and of both longest-chain-type and BFT-type protocols. Our framework blackboxes the precise mechanics of the user selection process, allowing us to isolate the properties of the selection process that are significant for protocol design. We demonstrate the utility of our general framework with several concrete results: 1. We prove a CAP-type impossibility theorem asserting that liveness with an unknown level of participation rules out security in a partially synchronous setting. 2. Delving deeper into the partially synchronous setting, we prove that a necessary and sufficient condition for security is the production of "certificates," meaning stand-alone proofs of block confirmation. 3. Restricting to synchronous settings, we prove that typical protocols with a known level of participation (including longest chain-type PoS protocols) can be adapted to provide certificates, but those with an unknown level of participation cannot. 4. Finally, we use our framework to articulate a modular two-step approach to blockchain security analysis that effectively reduces the permissionless case to the permissioned case.

A Reassessment of the Evidence for Macroscopic Quantum Tunneling in a Josephson Junction James A. Blackburn Sep 22 2020 cond-mat.supr-con quant-ph arXiv:2009.09272v1 Scited Scite! 1 @misc{2009.09272, author = {James A.~Blackburn}, title = {{A} {R}eassessment of the {E}vidence for {M}acroscopic {Q}uantum {T}unneling in a {J}osephson {J}unction}, year = {2020}, eprint = {2009.09272}, note = {arXiv:2009.09272v1} } Copy Citation PDF Switching current distributions have for decades been an indispensable diagnostic tool for studying Josephson junctions. They have played a key role in testing the conjecture of a macroscopic quantum state in junctions at millikelvin temperatures. The conventional basis of the test has been the observation of temperature independence of SCD peak widths, and that led to affirmative conclusions about a crossover. A different criterion is proposed here - the distance of the SCD peak from the junction critical current - and its efficacy is demonstrated. This test has distinct advantages in terms of precision, and it is found that, for three example experiments, the evidence for a crossover to the conjectured macroscopic quantum state is unequivocally negative. The implications of this finding for superconducting qubits are considered.

Entanglement Hamiltonian Tomography in Quantum Simulation Christian Kokail, Rick van Bijnen, Andreas Elben, Benoît Vermersch, Peter Zoller Sep 22 2020 quant-ph arXiv:2009.09000v1 Scited Scite! 1 @misc{2009.09000, author = {Christian Kokail and Rick van Bijnen and Andreas Elben and Benoît Vermersch and Peter Zoller}, title = {{E}ntanglement {H}amiltonian {T}omography in {Q}uantum {S}imulation}, year = {2020}, eprint = {2009.09000}, note = {arXiv:2009.09000v1} } Copy Citation PDF Entanglement is the crucial ingredient of quantum many-body physics, and characterizing and quantifying entanglement in closed system dynamics of quantum simulators is an outstanding challenge in today's era of intermediate scale quantum devices. Here we discuss an efficient tomographic protocol for reconstructing reduced density matrices and entanglement spectra for spin systems. The key step is a parametrization of the reduced density matrix in terms of an entanglement Hamiltonian involving only quasi local few-body terms. This ansatz is fitted to, and can be independently verified from, a small number of randomised measurements. The ansatz is suggested by Conformal Field Theory in quench dynamics, and via the Bisognano-Wichmann theorem for ground states. Not only does the protocol provide a testbed for these theories in quantum simulators, it is also applicable outside these regimes. We show the validity and efficiency of the protocol for a long-range Ising model in 1D using numerical simulations. Furthermore, by analyzing data from $10$ and $20$ ion quantum simulators [Brydges \textitet al., Science, 2019], we demonstrate measurement of the evolution of the entanglement spectrum in quench dynamics.

Hierarchical Black-Hole Mergers in Multiple Systems: Constrain the Formation of GW190412, GW190814 and GW190521-like events Bin Liu, Dong Lai Sep 22 2020 astro-ph.HE gr-qc arXiv:2009.10068v1 Scited Scite! 0 @misc{2009.10068, author = {Bin Liu and Dong Lai}, title = {{H}ierarchical {B}lack-{H}ole {M}ergers in {M}ultiple {S}ystems: {C}onstrain the {F}ormation of {GW}190412, {GW}190814 and {GW}190521-like events}, year = {2020}, eprint = {2009.10068}, note = {arXiv:2009.10068v1} } Copy Citation PDF The merging black-hole (BH) binaries GW190412, GW190814 and GW190521 from the third LIGO/VIRGO observing run exhibit some extraordinary properties, including highly asymmetric masses, significant spin, and component mass in the "mass gap". These features can be explained if one or both components of the binary are the remnants of previous mergers. In this paper, we explore hierarchical mergers in multiple stellar systems, taking into account the natal kick and mass loss due to the supernova explosion (SN) on each component, as well as the merger kick received by the merger remnant. The binaries that have survived the SNe and kicks generally have too wide orbital separations to merge by themselves, but can merge with the aid of an external companion that gives rise to Lidov-Kozai oscillations. The BH binaries that consist of second-generation BHs can also be assembled in dense star clusters through binary interactions. We characterize the parameter space of these BH binaries by merger fractions in an analytical approach. Combining the distributions of the survived binaries, we further constrain the parameters of the external companion, using the analytically formulated tertiary perturbation strength. We find that to produce the three LIGO/VIRGO O3 events, the external companions must be at least a few hundreds $M_\odot$, and fall in the intermediate-mass BH and supermassive BH range. We suggest that GW190412, GW190814 and GW190521 could all be produced via hierarchical mergers in multiples, likely in a nuclear star cluster, with the final merger induced by a massive BH. Our rate estimates for such events are consistent with the LIGO/VIRGO findings.

The first shear measurements from precision weak lensing Pol Gurri, Edward N. Taylor, Christopher J. Fluke Sep 22 2020 astro-ph.GA arXiv:2009.10067v1 Scited Scite! 0 @misc{2009.10067, author = {Pol Gurri and Edward N.~Taylor and Christopher J.~Fluke}, title = {{T}he first shear measurements from precision weak lensing}, year = {2020}, eprint = {2009.10067}, doi = {10.1093/mnras/staa2893}, note = {arXiv:2009.10067v1} } Copy Citation PDF We present an end-to-end methodology to measure the effects of weak lensing on individual galaxy-galaxy systems exploiting their kinematic information. Using this methodology, we have measured a shear signal from the velocity fields of 18 weakly-lensed galaxies. We selected a sample of systems based only on the properties of the sources, requiring them to be bright (apparent $i$-band magnitude $ < 17.4$) and in the nearby Universe ($z < 0.15$). We have observed the velocity fields of the sources with WiFeS, an optical IFU on a 2.3m telescope, and fitted them using a simple circular motion model with an external shear. We have measured an average shear of $\langle \gamma \rangle = 0.020 \pm 0.008$ compared to a predicted $\langle \gamma_{pred} \rangle = 0.005$ obtained using median stellar-to-halo relationships from the literature. While still a statistical approach, our results suggest that this new weak lensing methodology can overcome some of the limitations of traditional stacking-based techniques. We describe in detail all the steps of the methodology and make publicly available all the velocity maps for the weakly-lensed sources used in this study.

Machine learning based forecasting of significant daily returns in foreign exchange markets Firuz Kamalov, Ikhlaas Gurrib Sep 22 2020 cs.LG stat.ML arXiv:2009.10065v1 Scited Scite! 0 @misc{2009.10065, author = {Firuz Kamalov and Ikhlaas Gurrib}, title = {{M}achine learning based forecasting of significant daily returns in foreign exchange markets}, year = {2020}, eprint = {2009.10065}, note = {arXiv:2009.10065v1} } Copy Citation PDF Asset value forecasting has always attracted an enormous amount of interest among researchers in quantitative analysis. The advent of modern machine learning models has introduced new tools to tackle this classical problem. In this paper, we apply machine learning algorithms to hitherto unexplored question of forecasting instances of significant fluctuations in currency exchange rates. We perform analysis of nine modern machine learning algorithms using data on four major currency pairs over a 10 year period. A key contribution is the novel use of outlier detection methods for this purpose. Numerical experiments show that outlier detection methods substantially outperform traditional machine learning and finance techniques. In addition, we show that a recently proposed new outlier detection method PKDE produces best overall results. Our findings hold across different currency pairs, significance levels, and time horizons indicating the robustness of the proposed method.

Holographic Correlators at Finite Temperature Luis F. Alday, Murat Kologlu, Alexander Zhiboedov Sep 22 2020 hep-th arXiv:2009.10062v1 Scited Scite! 0 @misc{2009.10062, author = {Luis F.~Alday and Murat Kologlu and Alexander Zhiboedov}, title = {{H}olographic {C}orrelators at {F}inite {T}emperature}, year = {2020}, eprint = {2009.10062}, note = {arXiv:2009.10062v1} } Copy Citation PDF We consider weakly-coupled QFT in AdS at finite temperature. We compute the holographic thermal two-point function of scalar operators in the boundary theory. We present analytic expressions for leading corrections due to local quartic interactions in the bulk, with an arbitrary number of derivatives and for any number of spacetime dimensions. The solutions are fixed by judiciously picking an ansatz and imposing consistency conditions. The conditions include analyticity properties, consistency with the operator product expansion, and the Kubo-Martin-Schwinger condition. For the case without any derivatives we show agreement with an explicit diagrammatic computation. The structure of the answer is suggestive of a thermal Mellin amplitude. Additionally, we derive a simple dispersion relation for thermal two-point functions which reconstructs the function from its discontinuity.

Faster Algorithms for Optimal Ex-Ante Coordinated Collusive Strategies in Extensive-Form Zero-Sum Games Gabriele Farina, Andrea Celli, Nicola Gatti, Tuomas Sandholm cs.AI cs.LG Sep 22 2020 cs.GT cs.MA arXiv:2009.10061v1 Scited Scite! 0 @misc{2009.10061, author = {Gabriele Farina and Andrea Celli and Nicola Gatti and Tuomas Sandholm}, title = {{F}aster {A}lgorithms for {O}ptimal {E}x-{A}nte {C}oordinated {C}ollusive {S}trategies in {E}xtensive-{F}orm {Z}ero-{S}um {G}ames}, year = {2020}, eprint = {2009.10061}, note = {arXiv:2009.10061v1} } Copy Citation PDF We focus on the problem of finding an optimal strategy for a team of two players that faces an opponent in an imperfect-information zero-sum extensive-form game. Team members are not allowed to communicate during play but can coordinate before the game. In that setting, it is known that the best the team can do is sample a profile of potentially randomized strategies (one per player) from a joint (a.k.a. correlated) probability distribution at the beginning of the game. In this paper, we first provide new modeling results about computing such an optimal distribution by drawing a connection to a different literature on extensive-form correlation. Second, we provide an algorithm that computes such an optimal distribution by only using profiles where only one of the team members gets to randomize in each profile. We can also cap the number of such profiles we allow in the solution. This begets an anytime algorithm by increasing the cap. We find that often a handful of well-chosen such profiles suffices to reach optimal utility for the team. This enables team members to reach coordination through a relatively simple and understandable plan. Finally, inspired by this observation and leveraging theoretical concepts that we introduce, we develop an efficient column-generation algorithm for finding an optimal distribution for the team. We evaluate it on a suite of common benchmark games. It is three orders of magnitude faster than the prior state of the art on games that the latter can solve and it can also solve several games that were previously unsolvable.

Information Signaling: A Counter-Intuitive DefenseAgainst Password Cracking Wenjie Bai, Jeremiah Blocki, Ben Harsha Sep 22 2020 cs.CR cs.GT arXiv:2009.10060v1 Scited Scite! 0 @misc{2009.10060, author = {Wenjie Bai and Jeremiah Blocki and Ben Harsha}, title = {{I}nformation {S}ignaling: {A} {C}ounter-{I}ntuitive {D}efense{A}gainst {P}assword {C}racking}, year = {2020}, eprint = {2009.10060}, note = {arXiv:2009.10060v1} } Copy Citation PDF We introduce password strength information signaling as a novel, yet counter-intuitive, defense against password cracking attacks. Recent breaches have exposed billions of user passwords to the dangerous threat of offline password cracking attacks. An offline attacker can quickly check millions (or sometimes billions/trillions) of password guesses by comparing their hash value with the stolen hash from a breached authentication server. The attacker is limited only by the resources he is willing to invest. Our key idea is to have the authentication server store a (noisy) signal about the strength of each user password for an offline attacker to find. Surprisingly, we show that the noise distribution for the signal can often be tuned so that a rational (profit-maximizing) attacker will crack \em fewer passwords. The signaling scheme exploits the fact that password cracking is not a zero-sum game i.e., the attacker's profit is given by the value of the cracked passwords \em minus the total guessing cost. Thus, a well-defined signaling strategy will encourage the attacker to reduce his guessing costs by cracking fewer passwords. We give a (heuristic) algorithm to compute the optimal signaling scheme for a defender. As a proof-of-concept, we evaluate our mechanism on several empirical password datasets and show that it can reduce the total number of cracked passwords by $\approx 10\%$ of all users.

Neutrino signatures of near-critical supernova outflows Alexander Friedland, Payel Mukhopadhyay astro-ph.SR hep-ph Sep 22 2020 astro-ph.HE nucl-th arXiv:2009.10059v1 Scited Scite! 0 @misc{2009.10059, author = {Alexander Friedland and Payel Mukhopadhyay}, title = {{N}eutrino signatures of near-critical supernova outflows}, year = {2020}, eprint = {2009.10059}, note = {arXiv:2009.10059v1} } Copy Citation PDF In a core-collapse supernova, after the explosion is launched, neutrino heating above the protoneutron star creates an outflow of matter. This outflow has been extensively investigated as a nucleosynthesis site. Here, we revisit this problem motivated by the modeling of neutrino flavor transformations. In this case, it is crucial to understand whether the outflow has a termination shock: its existence observably alters neutrino oscillations a few seconds into the explosion. We derive physical criteria for the formation of this shock, in terms of neutrino luminosity, average energy, protoneutron star radius and mass, and the postshock density. For realistic physical conditions, the system is found to be on the edge of shock formation, thus reconciling seemingly disparate numerical results in the literature. Our findings imply that neutrino signatures of modulated matter effects are a sensitive probe of the inner workings of the supernova.

Exploring Intensity Invariance in Deep Neural Networks for Brain Image Registration Hassan Mahmood, Asim Iqbal, Syed Mohammed Shamsul Islam cs.AI Sep 22 2020 cs.CV cs.LG arXiv:2009.10058v1 Scited Scite! 0 @misc{2009.10058, author = {Hassan Mahmood and Asim Iqbal and Syed Mohammed Shamsul Islam}, title = {{E}xploring {I}ntensity {I}nvariance in {D}eep {N}eural {N}etworks for {B}rain {I}mage {R}egistration}, year = {2020}, eprint = {2009.10058}, note = {arXiv:2009.10058v1} } Copy Citation PDF Image registration is a widely-used technique in analysing large scale datasets that are captured through various imaging modalities and techniques in biomedical imaging such as MRI, X-Rays, etc. These datasets are typically collected from various sites and under different imaging protocols using a variety of scanners. Such heterogeneity in the data collection process causes inhomogeneity or variation in intensity (brightness) and noise distribution. These variations play a detrimental role in the performance of image registration, segmentation and detection algorithms. Classical image registration methods are computationally expensive but are able to handle these artifacts relatively better. However, deep learning-based techniques are shown to be computationally efficient for automated brain registration but are sensitive to the intensity variations. In this study, we investigate the effect of variation in intensity distribution among input image pairs for deep learning-based image registration methods. We find a performance degradation of these models when brain image pairs with different intensity distribution are presented even with similar structures. To overcome this limitation, we incorporate a structural similarity-based loss function in a deep neural network and test its performance on the validation split separated before training as well as on a completely unseen new dataset. We report that the deep learning models trained with structure similarity-based loss seems to perform better for both datasets. This investigation highlights a possible performance limiting factor in deep learning-based registration models and suggests a potential solution to incorporate the intensity distribution variation in the input image pairs. Our code and models are available at https://github.com/hassaanmahmood/DeepIntense.

Composed Variational Natural Language Generation for Few-shot Intents Congying Xia, Caiming Xiong, Philip Yu, Richard Socher Sep 22 2020 cs.CL arXiv:2009.10056v1 Scited Scite! 0 @misc{2009.10056, author = {Congying Xia and Caiming Xiong and Philip Yu and Richard Socher}, title = {{C}omposed {V}ariational {N}atural {L}anguage {G}eneration for {F}ew-shot {I}ntents}, year = {2020}, eprint = {2009.10056}, note = {arXiv:2009.10056v1} } Copy Citation PDF In this paper, we focus on generating training examples for few-shot intents in the realistic imbalanced scenario. To build connections between existing many-shot intents and few-shot intents, we consider an intent as a combination of a domain and an action, and propose a composed variational natural language generator (CLANG), a transformer-based conditional variational autoencoder. CLANG utilizes two latent variables to represent the utterances corresponding to two different independent parts (domain and action) in the intent, and the latent variables are composed together to generate natural examples. Additionally, to improve the generator learning, we adopt the contrastive regularization loss that contrasts the in-class with the out-of-class utterance generation given the intent. To evaluate the quality of the generated utterances, experiments are conducted on the generalized few-shot intent detection task. Empirical results show that our proposed model achieves state-of-the-art performances on two real-world intent detection datasets.

Cayley Graphs of Order 6pq are Hamiltonian Farzad Maghsoudi Sep 22 2020 math.CO arXiv:2009.10055v1 Scited Scite! 0 @misc{2009.10055, author = {Farzad Maghsoudi}, title = {{C}ayley {G}raphs of {O}rder 6pq are {H}amiltonian}, year = {2020}, eprint = {2009.10055}, note = {arXiv:2009.10055v1} } Copy Citation PDF Assume G is a finite group, such that |G|= 6pq or 7pq, where p and q are distinct prime numbers, and let S be a generating set of G. We prove there is a Hamiltonian cycle in the corresponding Cayley graph Cay(G;S).

Regularizing Attention Networks for Anomaly Detection in Visual Question Answering Doyup Lee, Yeongjae Cheon, Wook-Shin Han Sep 22 2020 cs.CV cs.LG arXiv:2009.10054v1 Scited Scite! 0 @misc{2009.10054, author = {Doyup Lee and Yeongjae Cheon and Wook-Shin Han}, title = {{R}egularizing {A}ttention {N}etworks for {A}nomaly {D}etection in {V}isual {Q}uestion {A}nswering}, year = {2020}, eprint = {2009.10054}, note = {arXiv:2009.10054v1} } Copy Citation PDF For stability and reliability of real-world applications, the robustness of DNNs in unimodal tasks has been evaluated. However, few studies consider abnormal situations that a visual question answering (VQA) model might encounter at test time after deployment in the real-world. In this study, we evaluate the robustness of state-of-the-art VQA models to five different anomalies, including worst-case scenarios, the most frequent scenarios, and the current limitation of VQA models. Different from the results in unimodal tasks, the maximum confidence of answers in VQA models cannot detect anomalous inputs, and post-training of the outputs, such as outlier exposure, is ineffective for VQA models. Thus, we propose an attention-based method, which uses confidence of reasoning between input images and questions and shows much more promising results than the previous methods in unimodal tasks. In addition, we show that a maximum entropy regularization of attention networks can significantly improve the attention-based anomaly detection of the VQA models. Thanks to the simplicity, attention-based anomaly detection and the regularization are model-agnostic methods, which can be used for various cross-modal attentions in the state-of-the-art VQA models. The results imply that cross-modal attention in VQA is important to improve not only VQA accuracy, but also the robustness to various anomalies.

Latin BERT: A Contextual Language Model for Classical Philology David Bamman, Patrick J. Burns Sep 22 2020 cs.CL arXiv:2009.10053v1 Scited Scite! 0 @misc{2009.10053, author = {David Bamman and Patrick J.~Burns}, title = {{L}atin {BERT}: {A} {C}ontextual {L}anguage {M}odel for {C}lassical {P}hilology}, year = {2020}, eprint = {2009.10053}, note = {arXiv:2009.10053v1} } Copy Citation PDF We present Latin BERT, a contextual language model for the Latin language, trained on 642.7 million words from a variety of sources spanning the Classical era to the 21st century. In a series of case studies, we illustrate the affordances of this language-specific model both for work in natural language processing for Latin and in using computational methods for traditional scholarship: we show that Latin BERT achieves a new state of the art for part-of-speech tagging on all three Universal Dependency datasets for Latin and can be used for predicting missing text (including critical emendations); we create a new dataset for assessing word sense disambiguation for Latin and demonstrate that Latin BERT outperforms static word embeddings; and we show that it can be used for semantically-informed search by querying contextual nearest neighbors. We publicly release trained models to help drive future work in this space.

A McCool Whitehead type theorem for finitely generated subgroups of $\mathsf{Out}(F_n)$ Mladen Bestvina, Mark Feighn, Michael Handel Sep 22 2020 math.GR arXiv:2009.10052v1 Scited Scite! 0 @misc{2009.10052, author = {Mladen Bestvina and Mark Feighn and Michael Handel}, title = {{A} {M}c{C}ool {W}hitehead type theorem for finitely generated subgroups of $\mathsf{{O}ut}({F}_n)$}, year = {2020}, eprint = {2009.10052}, note = {arXiv:2009.10052v1} } Copy Citation PDF S. Gersten announced an algorithm that takes as input two finite sequences $\vec K=(K_1,\dots, K_N)$ and $\vec K'=(K_1',\dots, K_N')$ of conjugacy classes of finitely generated subgroups of $F_n$ and outputs: (1) $\mathsf{YES}$ or $\mathsf{NO}$ depending on whether or not there is an element $\theta\in \mathsf{Out}(F_n)$ such that $\theta(\vec K)=\vec K'$ together with one such $\theta$ if it exists and (2) a finite presentation for the subgroup of $\mathsf{Out}(F_n)$ fixing $\vec K$. S. Kalajdžievski published a verification of this algorithm. We present a different algorithm from the point of view of Culler-Vogtmann's Outer space. New results include that the subgroup of $\mathsf{Out}(F_n)$ fixing $\vec K$ is of type $\mathsf{VF}$, an equivariant version of these results, an application, and a unified approach to such questions.

Measuring justice in machine learning Alan Lundgard Sep 22 2020 cs.CY arXiv:2009.10050v1 Scited Scite! 0 @misc{2009.10050, author = {Alan Lundgard}, title = {{M}easuring justice in machine learning}, year = {2020}, eprint = {2009.10050}, doi = {10.1145/3351095.3372838}, note = {arXiv:2009.10050v1} } Copy Citation PDF How can we build more just machine learning systems? To answer this question, we need to know both what justice is and how to tell whether one system is more or less just than another. That is, we need both a definition and a measure of justice. Theories of distributive justice hold that justice can be measured (in part) in terms of the fair distribution of benefits and burdens across people in society. Recently, the field known as fair machine learning has turned to John Rawls's theory of distributive justice for inspiration and operationalization. However, philosophers known as capability theorists have long argued that Rawls's theory uses the wrong measure of justice, thereby encoding biases against people with disabilities. If these theorists are right, is it possible to operationalize Rawls's theory in machine learning systems without also encoding its biases? In this paper, I draw on examples from fair machine learning to suggest that the answer to this question is no: the capability theorists' arguments against Rawls's theory carry over into machine learning systems. But capability theorists don't only argue that Rawls's theory uses the wrong measure, they also offer an alternative measure. Which measure of justice is right? And has fair machine learning been using the wrong one?

UCD-CS at W-NUT 2020 Shared Task-3: A Text to Text Approach for COVID-19 Event Extraction on Social Media Congcong Wang, David Lillis Sep 22 2020 cs.CL arXiv:2009.10047v1 Scited Scite! 0 @misc{2009.10047, author = {Congcong Wang and David Lillis}, title = {{UCD}-{CS} at {W}-{NUT} 2020 {S}hared {T}ask-3: {A} {T}ext to {T}ext {A}pproach for {COVID}-19 {E}vent {E}xtraction on {S}ocial {M}edia}, year = {2020}, eprint = {2009.10047}, note = {arXiv:2009.10047v1} } Copy Citation PDF In this paper, we describe our approach in the shared task: COVID-19 event extraction from Twitter. The objective of this task is to extract answers from COVID-related tweets to a set of predefined slot-filling questions. Our approach treats the event extraction task as a question answering task by leveraging the transformer-based T5 text-to-text model. According to the official exact match based evaluation scores returned, namely F1, our submitted run can achieve competitive performance as compared to other participating runs (Top 3). However, we argue that this evaluation can potentially underestimate the actual performance of runs based on text-generation approaches (e.g. our run). This is due to the fact that although some predictions of such runs answer the slot questions well, they may not be an exact string match for the gold standard answers. To further measure the extent of this underestimation, we adopt a simple exact answer transformation method aiming at converting the well-answered predictions to exactly-matched predictions. The results show that after the transformation our run reaches the same level of performance as the best participating run. Our code is publicly available to aid reproducibility.

A flux-limited model for glioma patterning with hypoxia-induced angiogenesis Pawan Kumar, Christina Surulescu Sep 22 2020 q-bio.TO arXiv:2009.10046v1 Scited Scite! 0 @misc{2009.10046, author = {Pawan Kumar and Christina Surulescu}, title = {{A} flux-limited model for glioma patterning with hypoxia-induced angiogenesis}, year = {2020}, eprint = {2009.10046}, note = {arXiv:2009.10046v1} } Copy Citation PDF We propose a model for glioma patterns in a microlocal tumor environment under the influence of acidity, angiogenesis, and tissue anisotropy. The bottom-up model deduction eventually leads to a system of reaction-diffusion-taxis equations for glioma and endothelial cell population densities, of which the former infers flux limitation both in the self-diffusion and taxis terms. The model extends a recently introduced [34] description of glioma pseudopalisade formation, with the aim of studying the effect of hypoxia-induced tumor vascularization on the establishment and maintenance of these histological patterns which are typical for high grade brain cancer. Numerical simulations of the population level dynamics are performed to investigate several model scenarios containing this and further effects.

Space/time-efficient RDF stores based on circular suffix sorting Nieves R. Brisaboa, Ana Cerdeira-Pena, Guillermo de Bernardo, Antonio Fariña, Gonzalo Navarro Sep 22 2020 cs.DS arXiv:2009.10045v1 Scited Scite! 0 @misc{2009.10045, author = {Nieves R.~Brisaboa and Ana Cerdeira-Pena and Guillermo de Bernardo and Antonio Fariña and Gonzalo Navarro}, title = {{S}pace/time-efficient {RDF} stores based on circular suffix sorting}, year = {2020}, eprint = {2009.10045}, note = {arXiv:2009.10045v1} } Copy Citation PDF In recent years, RDF has gained popularity as a format for the standardized publication and exchange of information in the Web of Data. In this paper we introduce RDFCSA, a data structure that is able to self-index an RDF dataset in small space and supports efficient querying. RDFCSA regards the triples of the RDF store as short circular strings and applies suffix sorting on those strings, so that triple-pattern queries reduce to prefix searching on the string set. The RDF store is then represented compactly using a Compressed Suffix Array (CSA), a proved technology in text indexing that efficiently supports prefix searches. Our experimental evaluation shows that RDFCSA is able to answer triple-pattern queries in a few microseconds per result while using less than 60% of the space required by the raw original data. We also support join queries, which provide the basis for full SPARQL query support. Even though smaller-space solutions exist, as well as faster ones, RDFCSA is shown to provide an excellent space/time tradeoff, with fast and consistent query times within much less space than alternatives that compete in time.