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Quantum error correction protects fragile quantum information by encoding it into a larger quantum system.sup.1,2. These extra degrees of freedom enable the detection and correction of errors, but also increase the control complexity of the encoded logical qubit. Fault-tolerant circuits contain the spread of errors while controlling the logical qubit, and are essential for realizing error suppression in practice.sup.3-6. Although fault-tolerant design works in principle, it has not previously been demonstrated in an error-corrected physical system with native noise characteristics. Here we experimentally demonstrate fault-tolerant circuits for the preparation, measurement, rotation and stabilizer measurement of a Bacon-Shor logical qubit using 13 trapped ion qubits. When we compare these fault-tolerant protocols to non-fault-tolerant protocols, we see significant reductions in the error rates of the logical primitives in the presence of noise. The result of fault-tolerant design is an average state preparation and measurement error of 0.6 per cent and a Clifford gate error of 0.3 per cent after offline error correction. In addition, we prepare magic states with fidelities that exceed the distillation threshold.sup.7, demonstrating all of the key single-qubit ingredients required for universal fault-tolerant control. These results demonstrate that fault-tolerant circuits enable highly accurate logical primitives in current quantum systems. With improved two-qubit gates and the use of intermediate measurements, a stabilized logical qubit can be achieved. Fault-tolerant circuits for the control of a logical qubit encoded in 13 trapped ion qubits through a Bacon-Shor quantum error correction code are demonstrated., Author(s): Laird Egan [sup.1] [sup.2] [sup.10] , Dripto M. Debroy [sup.4] [sup.11] , Crystal Noel [sup.1] [sup.2] , Andrew Risinger [sup.1] [sup.2] [sup.3] , Daiwei Zhu [sup.1] [sup.2] [sup.3] , [...]

Abstract. Finding a connected dominating set (CDS) in a given graph is a fundamental problem and has been studied intensively for a long time because of its application in computer [...]

Abstract. Connected dominating set (CDS) problem has been extensively studied in the literature due to its applications in many domains, including computer science and operations research. For example, CDS has [...]

This paper proposes a novel reversible logic gate, NFT. It is a parity preserving reversible logic gate, that is, the parity of the outputs matches that of the inputs. We demonstrate that the NFT gate can implement all Boolean functions. It renders a wide class of circuit faults readily detectable at the circuit's outputs. The proposed parity preserving reversible gate, allows any fault that affects no more than a single signal to be detectable at the circuit's primary outputs. The NFT gate can be used to make fault tolerant reversible logic circuits. We demonstrate how the well-known, and very useful, Toffoli gate can be synthesized from only two parity-preserving reversible gates. We show that our proposed parity-preserving Toffoli gate is much better in terms of number of reversible gates, number of garbage outputs and hardware complexity with compared to the existing counterpart. Keywords: Quantum computing, Reversible logic gate, Fault tolerant, Boolean functions, Toffoli gate, INTRODUCTION Traditional irreversible hardware computation inevitably leads to energy dissipation. This is due to the fact that the loss of each one bit of information dissipates an amount of KTln2 [...]

This paper presents a novel observer-based analytical redundancy for a steer-by-wire (SBW) system. An analytical redundancy methodology was utilized to reduce the total number of redundant road-wheel angle (RWA) sensors in a triply redundant RWA-based SBW system while maintaining a high level of reliability. A full-state observer was designed using the combined model of the vehicle and SBW system to estimate the vehicle-body sideslip angle. The steering angle was then estimated from the observed and measured states of the vehicle (body sideslip angle and yaw rate) as well as the current input to the SBW electric motor(s). A fault detection and isolation (FDI) algorithm was developed using a majority voting scheme, which was then used to detect faulty sensor(s) to maintain safe drivability. The proposed analytical redundancy-based FDI algorithms and the linearized vehicle model were modeled in SIMULINK. Simulation results show that the proposed analytical redundancy-based FDI algorithm provides the same level of fault tolerance as in an SBW system with full hardware redundancy against single-point failures. Index Terms--Analytical redundancy, fault detection and isolation (FDI), road-wheel control system, steer-by-wire (SBW) system.

The appearance of nanometer technologies has produced a significant increase of integrated circuit sensitivity to radiation, making the occurrence of soft errors much more frequent, not only in applications working in harsh environments, like aerospace circuits, but also for applications working at the earth surface. Therefore, hardened circuits are currently demanded in many applications where fault tolerance was not a concern in the very near past. To this purpose, efficient hardness evaluation solutions are required to deal with the increasing size and complexity of modern VLSI circuits. In this paper, a very fast and cost effective solution for SEU sensitivity evaluation is presented. The proposed approach uses FPGA emulation in an autonomous manner to fully exploit the FPGA emulation speed. Three different techniques to implement it are proposed and analyzed. Experimental results show that the proposed Autonomous Emulation approach can reach execution rates higher than one million faults per second, providing a performance improvement of two orders of magnitude with respect to previous approaches. These rates give way to consider very large fault injection campaigns that were not possible in the past. Index Terms--Fault emulation, fault injection, fault tolerance, FPGA, reliability testing, SEU.

This paper presents a comparative analysis involving several fault-tolerant operating strategies, applied to three-phase induction-motor drives, that intend to compensate for inverter faults. The results presented show the advantages and the inconveniences of several fault-tolerant drive structures, under different control techniques, such as the field-oriented control and the direct torque control. Experimental results concerning the performance of the three-phase induction motor, based on the analysis of some key parameters, like induction-motor efficiency, motor power factor, and harmonic distortion of both motor line currents and phase voltages, will be presented. Index Terms--AC motor drives, fault tolerance, induction-motor drives, reliability.

Abstract: Research on Grid Computing started under purely technical questions of how to realize the virtualization of distributed resources. Now, the commercial user should be attracted to use the Grid. [...]

An approach to reproduce radiation ground testing results for the study of microprocessors vulnerability to single event upset (SEU) is described in this paper. Resulting cross-sections fit very well with measured ones. Index Terms--Fault injection, microprocessor, single event upsets.

A protocol is proposed for dealing with the Global Data Computation (GDC) problem in asynchronous distributed systems.

A path-filtering mechanism is described which guards the DNS root and gTLD service against faults and attacks in network routing.

A design is described for a distributed store that integrates replication and secret sharing, meeting sequrity needs while tolerating Byzantine faults.

Properties of rollback-dependency trackability (RDT) communication-induced checkpointing protocols are investigated and reported.

Software errors are a major cause of outages and they are increasingly exploited in malicious attacks. Byzantine fault tolerance allows replicated systems to mask some software errors but it is expensive to deploy. This paper describes a replication technique, BASE, which uses abstraction to reduce the cost of Byzantine fault tolerance and to improve its ability to mask software errors. BASE reduces cost because it enables reuse of off-the-shelf service implementations. It improves availability because each replica can be repaired periodically using an abstract view of the state stored by correct replicas, and because each replica can run distinct or nondeterministic service implementations, which reduces the probability of common mode failures. We built an NFS service where each replica can run a different off-the-shelf file system implementation, and an object-oriented database where the replicas ran the same, nondeterministic implementation. These examples suggest that our technique can be used in practice--in both cases, the implementation required only a modest amount of new code, and our performance results indicate that the replicated services perform comparably to the implementations that they reuse. Categories and Subject Descriptors: C.2.0 [Computer-Communication Networks]: General--Security and protection; C.2.4 [Computer-Communication Networks]: Distributed Systems--Client/server; D.4.3 [Operating Systems]: File Systems Management; D.4.5 [Operating Systems]: Reliability--Fault tolerance; D.4.6 [Operating Systems]: Security and Protection--Access controls; authentication; cryptographic controls; D.4.8 [Operating Systems]: Performance--Measurements; H.2.0 [Database Management]: General--Security, integrity, and protection; H.2.4 [Database Management]: Systems--Object-oriented databases General Terms: Security, Reliability, Algorithms, Performance, Measurement Additional Key Words and Phrases: Byzantine fault tolerance, state machine replication, proactive recovery, asynchronous systems, N-version programming

An algorithm is described for implementing self-stabilizing group communication services in an asynchronous system.

The fault management (FM) design for the Universal Mobile Telecommunications (UMTS) terrestrial radio access network (UTRAN) radio network controller (RNC) is described and discussed.

The availability requirement for the fault management server in a high-availability communication system is investigated and discussed.

Two concerns are identified: 1) to strengthen system reliability by detecting transient errors in hardware, and 2) to reduce energy consumption by minimizing error-detection overhead.

Our growing reliance on online services accessible on the Internet demands highly available systems that provide correct service without interruptions. Software bugs, operator mistakes, and malicious attacks are a major cause of service interruptions and they can cause arbitrary behavior, that is, Byzantine faults. This article describes a new replication algorithm, BFT, that can be used to build highly available systems that tolerate Byzantine faults. BFT can be used in practice to implement real services: it performs well, it is safe in asynchronous environments such as the Internet, it incorporates mechanisms to defend against Byzantine-faulty clients, and it recovers replicas proactively. The recovery mechanism allows the algorithm to tolerate any number of faults over the lifetime of the system provided fewer than 1/3 of the replicas become faulty within a small window of vulnerability. BFT has been implemented as a generic program library with a simple interface. We used the library to implement the first Byzantine-fault-tolerant NFS file system, BFS. The BFT library and BFS perform well because the library incorporates several important optimizations, the most important of which is the use of symmetric cryptography to authenticate messages. The performance results show that BFS performs 2% faster to 24% slower than production implementations of the NFS protocol that are not replicated. This supports our claim that the BFT library can be used to build practical systems that tolerate Byzantine faults. Categories and Subject Descriptors: C.2.0 [Computer-Communication Networks]: General--Security and protection; C.2.4 [Computer-Communication Networks]: Distributed Systems--Client/server; D.4.3 [Operating Systems]: File Systems Management; D.4.5 [Operating Systems]: Reliability--Fault tolerance; D.4.6 [Operating Systems]: Security and Protection--Access controls; authentication; cryptographic controls; D.4.8 [Operating Systems]: Performance--Measurements General Terms: Security, Reliability, Algorithms, Performance, Measurement Additional Key Words and Phrases: Byzantine fault tolerance, state machine replication, proactive recovery, asynchronous systems, state transfer

COCA is a fault-tolerant and secure online certification authority that has been built and deployed both in a local area network and in the Internet. Extremely weak assumptions characterize environments in which COCA's protocols execute correctly: no assumption is made about execution speed and message delivery delays; channels are expected to exhibit only intermittent reliability; and with 3t + 1 COCA servers up to t may be faulty or compromised. COCA is the first system to integrate a Byzantine quorum system (used to achieve availability) with proactive recovery (used to defend against mobile adversaries which attack, compromise, and control one replica for a limited period of time before moving on to another). In addition to tackling problems associated with combining fault-tolerance and security, new proactive recovery protocols had to be developed. Experimental results give a quantitative evaluation for the cost and effectiveness of the protocols. Categories and Subject Descriptors: C.2.0 [Computer-Communication Networks]: General--Security and protection; C.2.4 [Computer-Communication Networks]: Distributed Systems--Client/server; D.4.5 [Operating Systems]: Reliability--Fault-tolerance; D.4.6 [Operating Systems]: Security and Protection--Authentication; cryptographic controls; E.3 [Data]: Data Encryption--Public key cryptosystems General Terms: Security, Reliability, Design, Performance, Measurement Additional Key Words and Phrases: Certification authority, public key infrastructure, Byzantine quorum systems, threshold cryptography, proactive secret-sharing, denial of service

Distributed applications that access persistent objects must maintain object state consistency even when failures are encountered during the manipulation of such objects. The basic transaction model, which has been implemented by several systems to ensure consistent executions of distributed applications, is not flexible enough to meet the requirements of many complex distributed applications. This has also been recognized for advanced database applications and, as a result, extended transaction models have been developed. We argue that distributed applications that manipulate long-lived data can benefit from such transaction models. We take an approach which views the various transaction models as policies for building robust applications. Thus, we advocate that the system implement several transaction models. A robust application can be programmed in such a system using a combination of several transaction models to meet its consistency requirements. We use applications from the domain of computer-supported cooperative work to motivate such an approach. We also develop a set of system-level mechanisms which can be used to implement multiple transaction models in a uniform manner. These mechanisms are used to implement nested, split, and cooperating transaction models. A prototype system that has been implemented is described to demonstrate the feasibility of this approach. Index Terms--Transaction models, fault tolerance, distributed object systems, operating systems, and computer-supported cooperative work.

Analysis of 162 disturbances from 1979 to 1995 reported by the North American Electric Reliability Council (NERC) indicates the importance of information systems under the regulated and competitive environment. This paper points out the major deficiencies in current communication and information systems and proposes a new power system information architecture aimed at correcting these deficiencies. The proposed architecture includes automation and control systems at all levels, from substation control system to independent system operator (ISO) operating center, taking into account the requirements of real-time data, security, availability, scalability, and appropriate Quality of Service (QoS). It uses multiple communication channels employing a wide variety of technologies to transmit real-time operating data and control signals. The real-time operating and control system is modeled with various redundancy configurations; the reliabilities of different configurations are studied and compared for practical values of component failure rates and repair rates. Index Terms--Communication technology, EMS/SCADA, failure rate, fault-tolerance, information architecture, internet, multi-protocol label switching (MPLS), power system, real-time, reliability, repair rate, virtual private network (VPN).

The problem of garbage collection in a single-failure fault-tolerant home-based lazy release consistency (HLRC) distributed shared memory (DSM) system, based on independent checkpointing and logging, is discussed. A solution is proposed that uses laziness in garbage collection and exploits consistency constraints of the HLRC memory model for low overhead and scalability.