IA Scholar Query: Groups Presented by Certain Classes of Finite Length-Reducing String-Rewriting Systems.
https://scholar.archive.org/
Internet Archive Scholar query results feedeninfo@archive.orgFri, 30 Sep 2022 00:00:00 GMTfatcat-scholarhttps://scholar.archive.org/help1440Runtime Complexity Bounds Using Squeezers
https://scholar.archive.org/work/rl374t3unrghnc7chpb4a65oie
Determining upper bounds on the time complexity of a program is a fundamental problem with a variety of applications, such as performance debugging, resource certification, and compile-time optimizations. Automated techniques for cost analysis excel at bounding the resource complexity of programs that use integer values and linear arithmetic. Unfortunately, they fall short when the complexity depends more intricately on the evolution of data during execution. In such cases, state-of-the-art analyzers have shown to produce loose bounds, or even no bound at all. We propose a novel technique that generalizes the common notion of recurrence relations based on ranking functions. Existing methods usually unfold one loop iteration and examine the resulting arithmetic relations between variables. These relations assist in establishing a recurrence that bounds the number of loop iterations. We propose a different approach, where we derive recurrences by comparing whole traces with whole traces of a lower rank, avoiding the need to analyze the complexity of intermediate states. We offer a set of global properties, defined with respect to whole traces, that facilitate such a comparison and show that these properties can be checked efficiently using a handful of local conditions. To this end, we adapt state squeezers , an induction mechanism previously used for verifying safety properties. We demonstrate that this technique encompasses the reasoning power of bounded unfolding, and more. We present some seemingly innocuous, yet intricate, examples that previous tools based on cost relations and control flow analysis fail to solve, and that our squeezer-powered approach succeeds.Oren Ish-Shalom, Shachar Itzhaky, Noam Rinetzky, Sharon Shohamwork_rl374t3unrghnc7chpb4a65oieFri, 30 Sep 2022 00:00:00 GMT6d SCFTs, Center-Flavor Symmetries, and Stiefel–Whitney Compactifications
https://scholar.archive.org/work/pppjl7wvgjcb7mkh2emb7s647q
The center-flavor symmetry of a gauge theory specifies the global form of consistent gauge and flavor bundle background field configurations. For 6d gauge theories which arise from a tensor branch deformation of a superconformal field theory (SCFT), we determine the global structure of such background field configurations, including possible continuous Abelian symmetry and R-symmetry bundles. Proceeding to the conformal fixed point, this provides a prescription for reading off the global form of the continuous factors of the zero-form symmetry, including possible non-trivial mixing between flavor and R-symmetry. As an application, we show that this global structure leads to a large class of 4d 𝒩 = 2 SCFTs obtained by compactifying on a T^2 in the presence of a topologically non-trivial flat flavor bundle characterized by a 't Hooft magnetic flux. The resulting "Stiefel–Whitney twisted" compactifications realize several new infinite families of 4d 𝒩 = 2 SCFTs, and also furnish a 6d origin for a number of recently discovered rank one and two 4d 𝒩 = 2 SCFTs.Jonathan J. Heckman, Craig Lawrie, Ling Lin, Hao Y. Zhang, Gianluca Zoccaratowork_pppjl7wvgjcb7mkh2emb7s647qWed, 14 Sep 2022 00:00:00 GMTLattice Quantum Gravity: EDT and CDT
https://scholar.archive.org/work/5pjoltdlrjadfpm2i4dkjhyaxe
This article is an overview of the use of so-called Euclidean Dynamical Triangulations (EDT) and Causal Dynamical Triangulations (CDT) as lattice regularizations of quantum gravity. The lattice regularizations have been very successful in the case of two-dimensional quantum gravity, where the lattice theories indeed provide regularizations of continuum well defined quantum gravity theories. In four-dimensional spacetime the Einstein-Hilbert action leads to a theory of gravity which is not renormalizable as a perturbative quantum theory around flat spacetime. It is discussed how lattice gravity in the form of EDT or CDT can be used to search for a non-perturbative UV fixed point of the lattice renormalization group in the spirit of asymptotic safety. In this way it might be possible to define a quantum theory of gravity also at lengthscales smaller than the Planck length.Jan Ambjornwork_5pjoltdlrjadfpm2i4dkjhyaxeWed, 14 Sep 2022 00:00:00 GMTHow the Higgs potential got its shape
https://scholar.archive.org/work/b356glqgkvgwfewtqjonldnaea
String-localized quantum field theory allows renormalizable couplings involving massive vector bosons, without invoking negative-norm states and compensating ghosts. We analyze the most general coupling of a massive vector boson to a scalar field, and find that the scalar field necessarily comes with a quartic potential which has the precise shape of the shifted Higgs potential. In other words: the shape of the Higgs potential has not to be assumed, but arises as a consistency condition. We derive this result as a consequence of the "Principle of String-Independence" (PSI) for renormalized perturbation theory with string-localized interactions: While the renormalizable interaction density may be localized along an auxiliary "string", the S-matrix (and also the local observables of the theory) must not depend on it. Along the way, we develop a model-independent scheme how the PSI is implemented in string-localized perturbation theory, and how it can be used as a tool to "renormalize the non-renormalizable".Jens Mund, Karl-Henning Rehren, Bert Schroerwork_b356glqgkvgwfewtqjonldnaeaTue, 13 Sep 2022 00:00:00 GMTTachyon-dependent Chern-Simons terms and the V-QCD Baryon
https://scholar.archive.org/work/3w3uxxp3pjgjvigesdhngaf2qq
The structure of the five-dimensional Tachyon-Chern-Simons action and its relevance to single-baryon states in the context of the V-QCD models for holographic QCD with backreacting flavor are analyzed. The most general form of the Tachyon-Chern-Simons 5-form, compatible with symmetries and flavor anomalies is determined. It is the sum of a non-trivial gauge-invariant 5-dimensional form and a non-invariant closed 5-form that reproduces the flavor anomalies. Single-baryon solutions of the gravity theory, arising from the DBI plus Tachyon-Chern-Simons actions are considered. The baryon is realised as a bulk axial instanton. The baryon ansatz and the field equations are derived and the boundary conditions are determined, which ensure that the solution has finite boundary energy and unit baryon charge. The boundary baryon number, which is computed from the universal (closed) part of the Tachyon-Chern-Simons action, is shown to coincide with the bulk axial instanton number.M. Järvinen, E. Kiritsis, F. Nitti, E. Préauwork_3w3uxxp3pjgjvigesdhngaf2qqTue, 13 Sep 2022 00:00:00 GMTGeometry and analysis of contact instantons and entanglement of Legendrian links I
https://scholar.archive.org/work/uebt2r7sovh6ppe4k37pjuon5m
We introduce the class of tame contact manifolds (M,λ), which includes compact ones but not necessarily compact, and establish uniform a priori C^0-estimates for the nonlinear elliptic boundary value problem of Hamiltonian-perturbed contact instantons with the Legendrian boundary condition introduced in [Oh21b]. We study the problem of estimating the untangling energy of one Legendrian submanifold from the Reeb flow trace of another, and formulate a particularly designed parameterized moduli space for the study of the problem. We establish the Gromov-Floer-Hofer type convergence result for Hamiltonian-perturbed contact instantons of finite energy and construct its compactification of the moduli space, first by defining the correct energy and then by proving a uniform a priori energy bounds in terms of the oscillation of the relevant contact Hamiltonian. Using this, we prove that the self Reeb-untangling energy of a compact Legendrian submanifold R in any tame contact manifold (M,λ) is greater than that of the period gap T_λ(M,R) of the Reeb chords of R. Then applying the operation of the Legendrianization of contactomorphisms we study a conjecture of Sandon and Shelukhin which is a contact anolog to the Arnold conjecture type: there exists a translated point for any contactomorphism isotopic to the identity whose oscillation norm is smaller than the period gap of the contact manifold (M,λ), and at least dim H_*(M,ℤ_2) translated points if the contactomorphism is nondegenerate in addition. This is 1/2 of the conjectured size of the oscillation norm in Shelukhi's conjecture.Yong-Geun Ohwork_uebt2r7sovh6ppe4k37pjuon5mTue, 13 Sep 2022 00:00:00 GMTSoftware-Hardware Codesign for Efficient In-Memory Regular Pattern Matching
https://scholar.archive.org/work/yevofpvxwvawdefyut7rbtoavq
Regular pattern matching is used in numerous application domains, including text processing, bioinformatics, and network security. Patterns are typically expressed with an extended syntax of regular expressions that include the computationally challenging construct of bounded iteration or counting, which describes the repetition of a pattern a fixed number of times. We develop a design for a specialized in-memory hardware architecture for NFA execution that integrates counter and bit vector elements. The design is inspired by the theoretical model of nondeterministic counter automata (NCA). A key feature of our approach is that we statically analyze regular expressions to determine bounds on the amount of memory needed for the occurrences of counting. The results of this analysis are used by a regex-to-hardware compiler in order to make an appropriate selection of counter or bit vector elements. We evaluate the performance of our hardware implementation on a simulator based on circuit parameters collected by SPICE simulation using a TSMC 28nm process. We find the usage of counter and bit vector quickly outperforms unfolding solutions by orders of magnitude with small counting quantifiers. Experiments concerning realistic workloads show up to 76% energy reduction and 58% area reduction in comparison to traditional in-memory NFA processors.Lingkun Kong, Qixuan Yu, Agnishom Chattopadhyay, Alexis Le Glaunec, Yi Huang, Konstantinos Mamouras, Kaiyuan Yangwork_yevofpvxwvawdefyut7rbtoavqTue, 13 Sep 2022 00:00:00 GMTSpace-Efficient Representations of Graphs
https://scholar.archive.org/work/vjtulzxmxnaunai4oh7eybsmkq
Computer science is no more about computers than astronomy is about telescopes. -Edsger Dijkstra To my sister, Tamara. . . Completing a Ph.D. is a long and arduous journey, and would have been neither possible nor worth doing without all the people that helped me along the way. I am immensely thankful to all those who have contributed either to my work or to my life during these past five years. First and foremost, I would like to express my gratitude to my advisor, Michael Kapralov, for his continued guidance, encouragement, and motivation throughout my time at EPFL. One could not ask for a better mentor. His apparent love of research, and his limitless energy made him a truly inspiring person to work with. It never ceased to amaze me how many projects he could juggle simultaneously while still being able to meet regularly on each of them, and come up with brilliant insights and helpful suggestions. I'm also grateful to the culture of collaboration he cultivated, always encouraging us to share, discuss, and work together on projects; this I think is one of the biggest reasons I found my work at EPFL so enjoyable. I would also like to thank my other jury members, Mika Göös, Sanjeev Khanna, Ola Svensson, and Luca Trevisan for their time and effort in reading this thesis, as well as their insightful questions and comments during the defense. Research is not a solo endeavor, and I could never have produced the quality and quantity of work that this thesis represents without my many collaborators. It is no accident that this is the only page of my thesis written in the singular first person. Both for directly contributing to the works contained in the following chapters, and perhaps more importantly, for shaping me as a researcher through our many discussions, I am indebted to my collaborators. For this reason, I would like to express my immense gratitude to MarwaJakab Tardoswork_vjtulzxmxnaunai4oh7eybsmkqMon, 12 Sep 2022 00:00:00 GMTDiscovering Noncritical Organization: Statistical Mechanical, Information Theoretic, and Computational Views of Patterns in One-Dimensional Spin Systems
https://scholar.archive.org/work/g7rl3fzr45fdpmjrscfazyta3u
We compare and contrast three different, but complementary views of "structure" and "pattern" in spatial processes. For definiteness and analytical clarity, we apply all three approaches to the simplest class of spatial processes: one-dimensional Ising spin systems with finite-range interactions. These noncritical systems are well-suited for this study since the change in structure as a function of system parameters is more subtle than that found in critical systems where, at a phase transition, many observables diverge, thereby making the detection of change in structure obvious. This survey demonstrates that the measures of pattern from information theory and computational mechanics differ from known thermodynamic and statistical mechanical functions. Moreover, they capture important structural features that are otherwise missed. In particular, a type of mutual information called the excess entropy—an information theoretic measure of memory—serves to detect ordered, low entropy density patterns. It is superior in several respects to other functions used to probe structure, such as magnetization and structure factors. ϵ-Machines—the main objects of computational mechanics—are seen to be the most direct approach to revealing the (group and semigroup) symmetries possessed by the spatial patterns and to estimating the minimum amount of memory required to reproduce the configuration ensemble, a quantity known as the statistical complexity. Finally, we argue that the information theoretic and computational mechanical analyses of spatial patterns capture the intrinsic computational capabilities embedded in spin systems—how they store, transmit, and manipulate configurational information to produce spatial structure.David P. Feldman, James P. Crutchfieldwork_g7rl3fzr45fdpmjrscfazyta3uSun, 11 Sep 2022 00:00:00 GMTOn the M2-Brane Index on Noncommutative Crepant Resolutions
https://scholar.archive.org/work/ctts5nlb5vho5jsa7cct4tlqlm
On certain M-theory backgrounds which are a circle fibration over a smooth Calabi-Yau, the quantum theory of M2 branes can be studied in terms of the K-theoretic Donaldson-Thomas theory on the threefold. We extend this relation to noncommutative crepant resolutions. In this case the threefold develops a singularity and classical smooth geometry is replaced by the algebra of paths of a certain quiver. K-theoretic quantities on the quiver representation moduli space can be computed via toric localization and result in certain rational functions of the toric parameters. We discuss in particular the case of the conifold and certain orbifold singularities.Michele Ciraficiwork_ctts5nlb5vho5jsa7cct4tlqlmSun, 11 Sep 2022 00:00:00 GMTQuantum Complexity and Holography
https://scholar.archive.org/work/o3u4ezis6va7tgdwkqorjtxyu4
This thesis develops recent work on the so called Volume-Complexity and Action-Complexity conjectures. According to this family of proposals, geometric quantities can be defined in some holographic gravitational theories that can be mapped with the concept of quantum complexity for states in a dual quantum-mechanical theory. In this work, we review the original motivations for the use of quantum-information theory in the search of a theory of quantum gravity, and argue in favour of holographic complexity as a promising new tool that could play a key role in the elucidation of the properties of black holes. After this introduction, we devote some time to the study of 'exotic' thermodynamical systems of diverse origin, confronting the conjectures with expectations and seeking for new behaviours of holographic complexity that could help us understand or refine the existing proposals. Next, we turn our attention to the study of holographic complexity for singular spacetimes, defining slightly modified versions of the conjecture that are well adapted to singularities and searching for universal behaviours of complexity dynamics within these setups. Finally, we finish with some speculations about the relation between holographic complexity and older characterization criteria for singularities in general relativity.Javier Martin-Garciawork_o3u4ezis6va7tgdwkqorjtxyu4Sat, 10 Sep 2022 00:00:00 GMTFinding Collisions against 4-Round SHA-3-384 in Practical Time
https://scholar.archive.org/work/klfpbt63drd6njnmn5mdfohism
The Keccak sponge function family, designed by Bertoni et al. in 2007, was selected by the U.S. National Institute of Standards and Technology (NIST) in 2012 as the next generation of Secure Hash Algorithm (SHA-3). Due to its theoretical and practical importance, cryptanalysis of SHA-3 has attracted a lot of attention. Currently, the most powerful collision attack on SHA-3 is Jian Guo et al.'s linearisation technique. However, this technique is infeasible for variants with asmaller input space, such as SHA-3-384.In this work we improve upon previous results by utilising three ideas which were not used in previous works on collision attacks against SHA-3. First, we use 2-block messages instead of 1-block messages, to reduce constraints and increase flexibility in our solutions. Second, we reduce the connectivity problem into a satisfiability (SAT) problem, instead of applying the linearisation technique. Finally, we propose an efficient deduce-and-sieve algorithm on the basis of two new non-random propertiesof the Keccak non-linear layer.The resulting collision-finding algorithm on 4-round SHA-3-384 has a practical time complexity of 259.64 (and a memory complexity of 245.94). This greatly improves upon the best known collision attack so far: Dinur et al. achieved an impractical 2147 time complexity. Our attack does not threaten the security margin of the SHA-3 hash function. However, the tools developed in this paper could be used to analyse other cryptographic primitives as well as to develop new and faster SAT solvers.Senyang Huang, Orna Agmon Ben-Yehuda, Orr Dunkelman, Alexander Maximovwork_klfpbt63drd6njnmn5mdfohismFri, 09 Sep 2022 00:00:00 GMTSelf-force in hyperbolic black hole encounters
https://scholar.archive.org/work/optuxvb2czhffkimyz4za3w52m
Self-force methods can be applied in calculations of the scatter angle in two-body hyperbolic encounters, working order by order in the mass ratio (assumed small) but with no recourse to a weak-field approximation. This, in turn, can inform ongoing efforts to construct an accurate description of the general-relativistic binary dynamics via an effective-one-body description or other approaches. Existing self-force methods are to a large extent specialised to bound, inspiral orbits. Here we derive the first-order conservative self-force correction to the scattering angle, show its agreement with recent post-Minkowsian results, and develop a technique for (numerical) self-force calculations that can efficiently tackle scatter orbits. In the method, the metric perturbation is reconstructed from a Hertz potential that satisfies (mode-by-mode) a certain inhomogeneous version of the Teukolsky equation. The crucial ingredient in this formulation are certain jump conditions that the (multipole modes of the) Hertz potential must satisfy along the worldline of the small body's orbit. We present a closed-form expression for these jumps, for an arbitrary geodesic orbit in Schwarzschild spacetime. To begin developing the numerical infrastructure, a scalar-field evolution code on a Schwarzschild background (in 1+1D) is developed. Following this, results for the conservative scalar self-force corrections to the scatter angle are calculated. We continue by constructing a Teukolsky evolution code on a Schwarzschild background. This produces numerically unstable solutions due to unphysical homogeneous solutions of the Teukolsky equation at the horizon and null infinity being seeded by numerical error. This can be resolved by a change of variables to a Regge-Wheeler-like field. We then present a full numerical implementation of this method for circular and scatter orbits in Schwarzschild.Oliver Longwork_optuxvb2czhffkimyz4za3w52mThu, 08 Sep 2022 00:00:00 GMTQuantum Field Theory Anomalies in Condensed Matter Physics
https://scholar.archive.org/work/kguxl4rcqzfsllo2shl4isq2em
We give a pedagogical introduction to quantum anomalies, how they are calculated using various methods, and why they are important in condensed matter theory. We discuss axial, chiral, and gravitational anomalies as well as global anomalies. We illustrate the theory with examples such as quantum Hall liquids, Fermi liquids, Weyl semi-metals, topological insulators and topological superconductors. The required background is basic knowledge of quantum field theory, including fermions and gauge fields, and some familiarity with path integral and functional methods. Some knowledge of topological phases of matter is helpful, but not necessary.Rodrigo Arouca, Andrea Cappelli, Hans Hanssonwork_kguxl4rcqzfsllo2shl4isq2emThu, 08 Sep 2022 00:00:00 GMTMatrix Product Operator Algebras II: Phases of Matter for 1D Mixed States
https://scholar.archive.org/work/whacq6iupzci7oqqpvxmqnsply
The classification of topological phases of matter is fundamental to understand and characterize the properties of quantum materials. In this paper we study phases of matter in one-dimensional open quantum systems. We define two mixed states to be in the same phase if both states can be transformed into the other by a shallow circuit of local quantum channels. We aim to understand the phase diagram of matrix product density operators that are renormalization fixed points. These states arise, for example, as boundaries of two-dimensional topologically ordered states. We first construct families of such states based on C*-weak Hopf algebras, the algebras whose representations form a fusion category. More concretely, we provide explicit local fine-graining and local coarse-graining quantum channels for the renormalization procedure of these states. Finally, we prove that those arising from C*-Hopf algebras are in the trivial phase.Alberto Ruiz-de-Alarcón, José Garre-Rubio, András Molnár, David Pérez-Garcíawork_whacq6iupzci7oqqpvxmqnsplyThu, 08 Sep 2022 00:00:00 GMTDepth-efficient proofs of quantumness
https://scholar.archive.org/work/egtwdz5oi5cszme4dopnvm6zre
A proof of quantumness is a type of challenge-response protocol in which a classical verifier can efficiently certify the quantum advantage of an untrusted prover. That is, a quantum prover can correctly answer the verifier's challenges and be accepted, while any polynomial-time classical prover will be rejected with high probability, based on plausible computational assumptions. To answer the verifier's challenges, existing proofs of quantumness typically require the quantum prover to perform a combination of polynomial-size quantum circuits and measurements. In this paper, we give two proof of quantumness constructions in which the prover need only perform constant-depth quantum circuits (and measurements) together with log-depth classical computation. Our first construction is a generic compiler that allows us to translate all existing proofs of quantumness into constant quantum depth versions. Our second construction is based around the learning with rounding problem, and yields circuits with shorter depth and requiring fewer qubits than the generic construction. In addition, the second construction also has some robustness against noise.Zhenning Liu, Alexandru Gheorghiuwork_egtwdz5oi5cszme4dopnvm6zreWed, 07 Sep 2022 00:00:00 GMTAverage Symmetry-Protected Topological Phases
https://scholar.archive.org/work/riopjfm4ynfnnmvczkque4fvre
Symmetry-protected topological (SPT) phases are many-body quantum states that are topologically nontrivial as long as the relevant symmetries are unbroken. In this work we show that SPT phases are also well defined for average symmetries, where quenched disorders locally break the symmetries, but restore the symmetries upon disorder averaging. An example would be crystalline SPT phases with imperfect lattices. Specifically, we define the notion of average SPT for disordered ensembles of quantum states. We then classify and characterize a large class of average SPT phases using a decorated domain wall approach, in which domain walls (and more general defects) of the average symmetries are decorated with lower dimensional topological states. We then show that if the decorated domain walls have dimension higher than (0+1)d, then the boundary states of such average SPT will almost certainly be long-range entangled, with probability approaching 1 as the system size approaches infinity. This generalizes the notion of t'Hooft anomaly to average symmetries, which we dub "average anomaly". The average anomaly can also manifest as constraints on lattice systems similar to the Lieb-Schultz-Mattis (LSM) theorems, but with only average lattice symmetries. We also generalize our problem to "quantum disorders" that can admit short-range entanglement on their own, and develop a theory of such generalized average SPTs purely based on density matrices and quantum channels. Our results indicate that topological quantum phenomena associated with average symmetries can be at least as rich as those with ordinary exact symmetries.Ruochen Ma, Chong Wangwork_riopjfm4ynfnnmvczkque4fvreTue, 06 Sep 2022 00:00:00 GMTQuantum cryptography with classical communication: parallel remote state preparation for copy-protection, verification, and more
https://scholar.archive.org/work/n2gcpkczwjgedgucslq7ulj3d4
Quantum mechanical effects have enabled the construction of cryptographic primitives that are impossible classically. For example, quantum copy-protection allows for a program to be encoded in a quantum state in such a way that the program can be evaluated, but not copied. Many of these cryptographic primitives are two-party protocols, where one party, Bob, has full quantum computational capabilities, and the other party, Alice, is only required to send random BB84 states to Bob. In this work, we show how such protocols can generically be converted to ones where Alice is fully classical, assuming that Bob cannot efficiently solve the LWE problem. In particular, this means that all communication between (classical) Alice and (quantum) Bob is classical, yet they can still make use of cryptographic primitives that would be impossible if both parties were classical. We apply this conversion procedure to obtain quantum cryptographic protocols with classical communication for unclonable encryption, copy-protection, computing on encrypted data, and verifiable blind delegated computation. The key technical ingredient for our result is a protocol for classically-instructed parallel remote state preparation of BB84 states. This is a multi-round protocol between (classical) Alice and (quantum polynomial-time) Bob that allows Alice to certify that Bob must have prepared n uniformly random BB84 states (up to a change of basis on his space). Furthermore, Alice knows which specific BB84 states Bob has prepared, while Bob himself does not. Hence, the situation at the end of this protocol is (almost) equivalent to one where Alice sent n random BB84 states to Bob. This allows us to replace the step of preparing and sending BB84 states in existing protocols by our remote-state preparation protocol in a generic and modular way.Alexandru Gheorghiu, Tony Metger, Alexander Porembawork_n2gcpkczwjgedgucslq7ulj3d4Tue, 06 Sep 2022 00:00:00 GMTMassless Scalars and Higher-Spin BMS in Any Dimension
https://scholar.archive.org/work/vszoyfrnpndn7gsp5io5qinaaq
Starting from the asymptotic kinematics of massless scalar fields near null infinity in any spacetime dimension, we build two higher-spin extensions of the Carrollian definition of the BMS group and its generalisations. The first extension exhibits conformal properties reminiscent of the singleton in Anti-de Sitter space. The second acts on the space of radiative solutions of the d'Alembert equation, i.e. on Sachs's representation of BMS, which we relate to the scalar massless Poincare representation and extend to any Carrollian manifold. The corresponding enveloping algebra is a higher-spin extension of BMS that can be interpreted as the asymptotic symmetry of a putative exotic higher-spin gravity theory around Minkowski spacetime. Along the way, we provide a pedagogical introduction to Carrollian geometry and its relation to BMS.Xavier Bekaert, Blagoje Oblakwork_vszoyfrnpndn7gsp5io5qinaaqTue, 06 Sep 2022 00:00:00 GMTSilicide-based Josephson field effect transistors for superconducting qubits
https://scholar.archive.org/work/h2nn6wi5srbrnd7caz3gbsbly4
Scalability in the fabrication and operation of quantum computers is key to move beyond the NISQ era. So far, superconducting transmon qubits based on aluminum Josephson tunnel junctions have demonstrated the most advanced results, though this technology is difficult to implement with large-scale facilities. An alternative "gatemon" qubit has recently appeared, which uses hybrid superconducting/semiconducting (S/Sm) devices as gate-tuned Josephson junctions. Current implementations of these use nanowires however, of which the large-scale fabrication has not yet matured either. A scalable gatemon design could be made with CMOS Josephson Field-Effect Transistors as tunable weak link, where an ideal device has leads with a large superconducting gap that contact a short channel through high-transparency interfaces. High transparency, or low contact resistance, is achieved in the microelectronics industry with silicides, of which some turn out to be superconducting. The first part of the experimental work in this thesis covers material studies on two such materials: V_3Si and PtSi, which are interesting for their high T_c, and mature integration, respectively. The second part covers experimental results on 50 nm gate length PtSi transistors, where the transparency of the S/Sm interfaces is modulated by the gate voltage. At low voltages, the transport shows no conductance at low energy, and well-defined features at the superconducting gap. The barrier height at the S/Sm interface is reduced by increasing the gate voltage, until a zero-bias peak appears around zero drain voltage, which reveals the appearance of an Andreev current. The successful gate modulation of Andreev current in a silicon-based transistor represents a step towards fully CMOS-integrated superconducting quantum computers.Tom Doekle Vethaakwork_h2nn6wi5srbrnd7caz3gbsbly4Tue, 06 Sep 2022 00:00:00 GMT