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Contrary to fermions and bosons, anyons are quasiparticles that keep a robust memory of particle exchanges via a braiding phase factor. This provides them with unique dynamical properties so far unexplored. When an anyon excitation is emitted toward a quantum point contact (QPC) in a fractional quantum Hall (FQH) fluid, this memory translates into tunneling events that may occur long after the anyon excitation has exited the QPC. Here, we use triggered anyon pulses incident on a QPC in a $\nu= 1/3$ FQH fluid to investigate anyon tunneling in the time domain. We observe that braiding increases the tunneling timescale, which is set by the temperature and the anyon scaling dimension that characterizes the edge state dynamics. This contrasts with the electron behavior where braiding is absent and the tunneling timescale is set by the temporal width of the generated electron pulses. Our experiment introduces time-domain measurements for characterizing the braiding phase and scaling dimension of anyons.

We propose a source of purely electronic energy-entangled states implemented in a solid-state system with potential applications in quantum information protocols based on electron flying qubits. The proposed device relies on the standard tools of Electron Quantum Optics (EQO) and exploits entanglement of the Cooper pairs of a BCS superconductor. The latter is coupled via an adjustable quantum point contact to two opposite spin polarized electron wave-guides, which are driven by trains of Lorentzian pulses. This specific choice for the drive is crucial to inject purely electronic entangled-states devoid of spurious electron-hole pairs. In the Andreev regime, a perturbative calculation in the tunnel coupling confirms that entangled electrons states (EES) are generated at the output of the normal side. We introduce a quantity related to charge current cross-correlations which allows one to verify experimentally the entangled nature of the emitted state., Comment: 18 pages, 5 figures, comments are welcomed !

Deep learning models are crucial for autonomous vehicle perception, but their reliability is challenged by algorithmic limitations and hardware faults. We address the latter by examining fault-tolerance in semantic segmentation models. Using established hardware fault models, we evaluate existing hardening techniques both in terms of accuracy and uncertainty and introduce ReLUMax, a novel simple activation function designed to enhance resilience against transient faults. ReLUMax integrates seamlessly into existing architectures without time overhead. Our experiments demonstrate that ReLUMax effectively improves robustness, preserving performance and boosting prediction confidence, thus contributing to the development of reliable autonomous driving systems., Comment: Accepted ECCV 2024 UnCV Workshop - https://github.com/iurada/neutron-segmentation

Quantum Computing (QC) offers the potential to enhance traditional High-Performance Computing (HPC) workloads by leveraging the unique properties of quantum computers, leading to the emergence of a new paradigm: HPC-QC. While this integration presents new opportunities, it also brings novel challenges, particularly in ensuring the dependability of such hybrid systems. This paper aims to identify integration challenges, anticipate failures, and foster a diverse co-design for HPC-QC systems by bringing together QC, cloud computing, HPC, and network security. The focus of this emerging inter-disciplinary effort is to develop engineering principles that ensure the dependability of hybrid systems, aiming for a more prescriptive co-design cycle. Our framework will help to prevent design pitfalls and accelerate the maturation of the QC technology ecosystem. Key aspects include building resilient HPC-QC systems, analyzing the applicability of conventional techniques to the quantum domain, and exploring the complexity of scaling in such hybrid systems. This underscores the need for performance-reliability metrics specific to this new computational paradigm.

Reliability is fundamental for developing large-scale quantum computers. Since the benefit of technological advancements to the qubit's stability is saturating, algorithmic solutions, such as quantum error correction (QEC) codes, are needed to bridge the gap to reliable computation. Unfortunately, the deployment of the first quantum computers has identified faults induced by natural radiation as an additional threat to qubits reliability. The high sensitivity of qubits to radiation hinders the large-scale adoption of quantum computers, since the persistence and area-of-effect of the fault can potentially undermine the efficacy of the most advanced QEC. In this paper, we investigate the resilience of various implementations of state-of-the-art QEC codes to radiation-induced faults. We report data from over 400 million fault injections and correlate hardware faults with the logical error observed after decoding the code output, extrapolating physical-to-logical error rates. We compare the code's radiation-induced logical error rate over the code distance, the number and role in the QEC of physical qubits, the underlying quantum computer topology, and particle energy spread in the chip. We show that, by simply selecting and tuning properly the surface code, thus without introducing any overhead, the probability of correcting a radiation-induced fault is increased by up to 10\%. Finally, we provide indications and guidelines for the design of future QEC codes to further increase their effectiveness against radiation-induced events., Comment: 10 pages, 8 figures

We present a fault-tolerant by-design RISC-V SoC and experimentally assess it under atmospheric neutrons and 200 MeV protons. The dedicated ECC and Triple-Core Lockstep countermeasures correct most errors, guaranteeing a device cross-section lower than $5.36 \times 10^{-12}$ cm$^2$., Comment: 4 pages (excluding title page), accepted at RADECS 2024

Conversational AI (CAI) systems which encompass voice- and text-based assistants are on the rise and have been largely integrated into people's everyday lives. Despite their widespread adoption, users voice concerns regarding privacy, security and trust in these systems. However, the composition of these perceptions, their impact on technology adoption and usage and the relationship between privacy, security and trust perceptions in the CAI context remain open research challenges. This study contributes to the field by conducting a Systematic Literature Review and offers insights into the current state of research on privacy, security and trust perceptions in the context of CAI systems. The review covers application fields and user groups and sheds light on empirical methods and tools used for assessment. Moreover, it provides insights into the reliability and validity of privacy, security and trust scales, as well as extensively investigating the subconstructs of each item as well as additional concepts which are concurrently collected. We point out that the perceptions of trust, privacy and security overlap based on the subconstructs we identified. While the majority of studies investigate one of these concepts, only a few studies were found exploring privacy, security and trust perceptions jointly. Our research aims to inform on directions to develop and use reliable scales for users' privacy, security and trust perceptions and contribute to the development of trustworthy CAI systems., Comment: 39 pages, 4 figures

in nanoscale systems in the presence of single-electron excitations generated by Lorentzian voltage drives, termed \textit{Levitons}. These excitations allow to realize the analog of quantum optics experiments using electrons instead of photons. Importantly, electrons in condensed matter systems are strongly affected by the presence of different types of non-trivial correlations, with no counterpart in the domain of photonic quantum optics. After providing a short introduction about Levitons in non-interacting systems, we focus on how they operate in the presence of two types of strong electronic correlations in nanoscale systems, such as those arising in the fractional quantum Hall effect or in superconducting systems. Specifically, we consider Levitons in a quantum Hall bar of the fractional quantum Hall effect, pinched by a quantum point contact, where anyons with fractional charge and statistics tunnel between opposite edges. In this case, a Leviton-Leviton interaction can be induced by the strongly correlated background. Concerning the effect of superconducting correlations on Levitons, we show that, in a normal metal system coupled to BCS superconductors, half integer Levitons minimize the excess noise in the Andreev regime. Interestingly, energy-entangled electron states can be realized on-demand in this type of hybrid setups by exploiting crossed Andreev reflection. The results exposed in this review have potential applications in the context of quantum information and computation with single-electron flying qubits., Comment: 19 pages, 9 figures, Special issue in honor of the 80th birthday of D.K. Campbell

The frontier of quantum computing (QC) simulation on classical hardware is quickly reaching the hard scalability limits for computational feasibility. Nonetheless, there is still a need to simulate large quantum systems classically, as the Noisy Intermediate Scale Quantum (NISQ) devices are yet to be considered fault tolerant and performant enough in terms of operations per second. Each of the two main exact simulation techniques, state vector and tensor network simulators, boasts specific limitations. The exponential memory requirement of state vector simulation, when compared to the qubit register sizes of currently available quantum computers, quickly saturates the capacity of the top HPC machines currently available. Tensor network contraction approaches, which encode quantum circuits into tensor networks and then contract them over an output bit string to obtain its probability amplitude, still fall short of the inherent complexity of finding an optimal contraction path, which maps to a max-cut problem on a dense mesh, a notably NP-hard problem. This article aims at investigating the limits of current state-of-the-art simulation techniques on a test bench made of eight widely used quantum subroutines, each in 31 different configurations, with special emphasis on performance. We then correlate the performance measures of the simulators with the metrics that characterise the benchmark circuits, identifying the main reasons behind the observed performance trend. From our observations, given the structure of a quantum circuit and the number of qubits, we highlight how to select the best simulation strategy, obtaining a speedup of up to an order of magnitude., Comment: 13 pages, 10 figures, 1 table

The technical limitations of the intelligent reflecting surface (IRS) (re)configurations in terms of both communication overhead and energy efficiency must be considered when IRSs are used in cellular networks. In this paper, we investigate the downlink time-frequency scheduling of an IRS-assisted multi-user system in the orthogonal frequency-division multiple access (OFDMA) framework wherein both the set of possible IRS configurations and the number of IRS reconfigurations within a time frame are limited. We formulate the sum rate maximization problem as a non-polynomial (NP)-complete generalized multi-knapsack problem. A heuristic greedy algorithm for the joint IRS configuration and time-frequency scheduling is also proposed. Numerical simulations prove the effectiveness of our greedy solution., Comment: 6 pages, 5 figures, journal paper

Andreev reflection is a fundamental transport process occurring at the junction between a normal metal and a superconductor (a N-S junction), when an incident electron from the normal side can only be transmitted in the superconductor as a Cooper pair, with the reflection of a hole in the normal metal. As a consequence of the spin singlet nature of the BCS Cooper pairs, the current due to Andreev reflection at a N-S junction is always symmetric in spin. Using a Keldysh Nambu Floquet approach, combining analytical and numerical calculations, we study in details the AC transport at a N-S junction, when the two spin components in the normal metal are driven by different periodic drives. We show that, in the Andreev regime, i.e. when the superconducting gap is much larger than the frequency of the drives, the spin-resolved photo-assisted currents are always equal even if the two drives are different. In addition, we show that in this regime the excess noise depends only on the sum of the periodic drives, and we consider in particular the case of Lorentzian pulses (Levitons). We also show how these properties get modified when going beyond the Andreev regime. Finally we give a simple analytical proof of the special properties of the Andreev regime using an exact mapping to a particular N-N junction., Comment: 13 pages, 4 figures

Anyons are particles intermediate between fermions and bosons, characterized by a nontrivial exchange phase, yielding remarkable braiding statistics. Recent experiments have shown that anyonic braiding has observable consequences on edge transport in the fractional quantum Hall effect (FQHE). Here, we study transport signatures of anyonic braiding when the anyons have a finite width. We show that the width of the anyons, even extremely small, can have a tremendous impact on transport properties and braiding signatures. In particular, we find that taking the finite width into account allows us to explain recent experimental results on FQHE at filling factor $2/5$ [Ruelle et al., Phys. Rev. X \textbf{13}, 011031 (2023)]. Our work shows that the finite width of anyons crucially influences setups involving anyonic braiding, especially when the exchange phase is larger than $\pi/2$., Comment: 5 pages + supplemental material

Andreev reflection occurs in a normal metal-superconductor junction, when an electron on the normal side can only be transmitted as a Cooper pair in the superconductor, with the reflection of a hole on the normal side. A similar phenomenon can occur in strongly correlated systems, in particular in the fractional quantum Hall effect (FQHE), as the system quasiparticles have a charge $e/m$ different from the electron charge. We study theoretically a setup involving two quantum point contacts (QPC) in the FQHE where Andreev reflection occurs, as charges $e/m$ impinging on the second QPC can only be transmitted as charges $e$, with the reflection of holes of charge $e (1-m)/m $. Using the bosonization formalism, and out-of-equilibrium Keldysh Green function techniques, we provide a full analytical calculation of the current correlations at the outputs of the QPC, both at zero and finite temperature. The ratio between the auto- and cross-correlations of the output currents is a direct manifestation of Andreev reflection. Our results agree with recent experimental observations, and give precious information on the temperature dependence of this ratio.

Partial-information multiple access (PIMA) is an orthogonal multiple access (OMA) uplink scheme where time is divided into frames, each composed of two parts. The first part is used to count the number of users with packets to transmit, while the second has a variable number of allocated slots, each assigned to multiple users to uplink data transmission. We investigate the case of correlated user activations, wherein the correlation is due to the retransmissions of the collided packets, modeling PIMA as a partially observable-Markov decision process. The assignment of users to slots is optimized based on the knowledge of both the number of active users and past successful transmissions and collisions. The scheduling turns out to be a mixed integer nonlinear programming problem, with a complexity exponentially growing with the number of users. Thus, sub-optimal greedy solutions are proposed and evaluated. Our solutions show substantial performance improvements with respect to both traditional OMA schemes and conventional PIMA., Comment: Conference paper, 6 pages, 4 figures

We consider a two-dimensional electron system in the Laughlin sequence of the fractional quantum Hall regime to investigate the effect of strong correlations on the mutual interaction between two Levitons, single-electron excitations generated by trains of quantized Lorentzian pulses. We focus on two-Leviton states injected in a single period with a time separation $\Delta t$. In the presence of a quantum point contact operating in the weak-backscattering regime, we compute the backscattered charge by means of the Keldysh technique. In the limit of an infinite period and zero temperature, we show that the backscattered charge for a two-Leviton state is not equal to twice the backscattered charge for a single Leviton. We present an interpretation for this result in terms of the wave-packet formalism for Levitons, thus proposing that an effective interaction between the two Levitons is induced by the strongly-correlated background. Finally, we perform numerical calculations in the periodic case by using the Floquet formalism for photo-assisted transport. By varying the system parameters such as pulse width, filling factor and temperature we show that the value of the backscattered charge for two-Leviton states is strongly dependent on the pulse separation, thus opening scenarios where the effective interaction between Levitons can be controllably tuned., Comment: 12 pages, 7 figures, all comments are welcome!

We study charge transport in voltage-biased single-channel junctions involving helical superconductors with finite Cooper pair momentum. For a Josephson junction, the equilibrium current-phase relation shows a superconducting diode effect: the critical current depends on the propagation direction. We formulate a scattering theory for voltage-biased Josephson diodes and show that multiple Andreev reflection processes cause a rich subharmonic structure in the DC current-voltage curve at low temperatures and small voltages due to Doppler shifts of the spectral gap. In the current-biased case, the diode efficiency has maximal rectification efficiency $\eta_0\approx 0.4$ for this model. In the voltage-biased case, however, the rectification efficiency can reach the ideal value $\eta=1$. We also discuss charge transport for NS junctions between a normal metal and a helical superconductor and comment on related models with spin-orbit interactions and magnetic Zeeman fields., Comment: 21 pages, 9 figures. arXiv admin note: text overlap with arXiv:2307.14698

Next-generation internet-of-things (IoT) networks require extremely low latency, complexity, and collision probability. We introduce the novel partial-information multiple access (PIMA) scheme, a semi-grant-free (GF) coordinated random access (RA) protocol for short packet transmission, with the aim of reducing the latency and packet loss of traditional multiple access schemes, as well as more recent preamble-based schemes. With PIMA, the base station (BS) acquires partial information on instantaneous traffic conditions in the partial information acquisition (PIA) sub-frame, estimating the number of active devices, i.e., having packets waiting for transmission in their queue. Based on this estimate, the BS chooses both the total number of slots to be allocated in the data transmission (DT) sub-frame and the respective user-to-slot assignment. Although collisions may still occur due to multiple users assigned to the same slot, they are drastically reduced with respect to the slotted ALOHA (SALOHA) scheme, while achieving lower latency than both time-division multiple-access (TDMA) and preamble-based protocols, due to the extremely reduced overhead of the PIA sub-frame. Finally, we analyze and assess the performance of PIMA under various activation statistics, proving the robustness of the proposed solution to the intensity of traffic, also with burst traffic., Comment: Journal paper, 11 pages, 8 figures. arXiv admin note: text overlap with arXiv:2304.12057

We analyze the rectification properties of voltage-biased Josephson junctions exhibiting the superconducting diode effect. Taking into account multiple Andreev reflection (MAR) processes in our scattering theory, we consider a short weak link of arbitrary transparency between two superconductors with finite Cooper pair momentum $2q$. In equilibrium, the diode efficiency is bounded from above in this model, with maximal efficiency $\eta_0\approx 0.4$. Out of equilibrium, we find a rich subharmonic structure in the current-voltage curve. For high transparency and low bias voltage $V$, the rectification efficiency $\eta(V)$ approaches the ideal value $\eta=1$ for $q\xi\to 1$ (with coherence length $\xi$)., Comment: 7 pages, 3 figures. All material now contained in Phys. Rev. B 109, 024504 (2024)

We study theoretically the effect of electronic interactions in 1d systems on electron injection using periodic Lorentzian pulses, known as Levitons. We consider specifically a system composed of a metallic single-wall carbon nanotube, described with the Luttinger liquid formalism, a scanning tunneling microscope (STM) tip, and metallic leads. Using the out-of-equilibrium Keldysh Green function formalism, we compute the current and current noise in the system. We prove that the excess noise vanishes when each Leviton injects an integer number of electrons from the STM tip into the nanotube. This extends the concept of minimal injection with Levitons to strongly correlated, uni-dimensional non-chiral systems. We also study the time-dependent current profile, and show how it is the result of interferences between pulses non-trivially reflected at the nanotube-lead interface., Comment: 14 pages, 6 figures

Biasing a three-terminal Josephson junction (TTJ) with symmetrical voltages $0,V,-V$ leads to new kinds of DC currents, namely quartet Josephson currents and phase-dependent multiple Andreev reflection (MAR) currents. We study these currents in a system where a normal diffusive metallic node $N$ is connected to three terminals $S_{0,1,2}$ by barriers of arbitrary transparency. We use the quantum circuit theory to calculate the current in each terminal, including decoherence. In addition to the stationary combination $\varphi_Q=\varphi_1+\varphi_2-2\varphi_0$ of the terminal phases $\varphi_i$, the bias voltage $V$ appears as a new and unusual control variable for a DC Josephson current. A general feature is the sign changes of the current-phase characteristics, manifesting in minima of the quartet ``critical current". Those sign changes can be triggered by the voltage, by the junction transparency or by decoherence. We study the possible separation of quartet currents from MAR currents in different regimes of parameters, including an "funnel" regime with very asymmetric couplings to $S_{0,1,2}$. In the regime of low transparency and asymetric couplings, we provide an analytic perturbative expression for the currents which shows an excellent agreement with the full numerical results.

Photons are emitted or absorbed by a nano-circuit under both equilibrium and non-equilibrium situations. Here, we focus on the non-equilibrium situation arising due to a temperature difference between the leads of a quantum point contact, and study the finite frequency (colored) noise. We explore this delta-$T$ noise in the finite frequency regime for two systems: conventional conductors described by Fermi liquid scattering theory and the fractional quantum Hall system at Laughlin filling fractions, described by the chiral Luttinger liquid formalism. We study the emission noise, its expansion in the temperature difference (focusing on the quadratic component) as well as the excess emission noise defined with respect to a properly chosen equilibrium situation. The behavior of these quantities are markedly different for the fractional quantum Hall system compared to Fermi liquids, signalling the role of strong correlations. We briefly treat the strong backscattering regime of the fractional quantum Hall liquid, where a behavior closer to the Fermi liquid case is observed.