We show that in quantum computation almost every gate that operates on two or more bits is a universal gate. We discuss various physical considerations bearing on the proper definition of universality for computational components such as logic gates.

Active networking in environments built to support link rates up to several gigabits per second poses many challenges. One such challenge is that the memory bandwidth and individual processing power of the router's microprocessors limit the total available processing power of a router. In this paper, we identify and describe three key components, which promise a high performance active network solution. This solution implements the key features typical to active networking, such as automatic protocol deployment and application specific processing, and it is suitable for a gigabit environment. First, we describe the hardware of the Active Network Node (ANN), a scalable, high performance platform based on off-the-shelf CPUs connected to a gigabit ATM switch backplane. Second, we introduce the ANN's modular, extensible and highly efficient operating system (NodeOS). Third, we describe an Execution Environment running on top of the NodeOS, which implements a novel large-scale active networ...

In this paper we describe the evolution of grid systems, identifying three generations: first generation systems which were the forerunners of the Grid as we recognise it today; second generation systems with a focus on middleware to support large scale data and computation; and third generation systems where the emphasis shifts to distributed global collaboration, a service oriented approach and information layer issues. In particular, we discuss the relationship between the Grid and the World Wide Web, and suggest that evolving web technologies will provide the basis for the next generation of the Grid. The latter aspect – which we define as the Semantic Grid – is explored in a companion paper. 1.

{ A new knapsack type public key cryptosystem is introduced. The system is based on a novel application of arithmetic in nite elds, following a construction by Bose and Chowla. By appropriately choosing the parameters, one can control the density of the resulting knapsack, which is the ratio between the number of elements in the knapsack and their size in bits. In particular, the density can be made high enough to foil \low density" attacks against our system. At the moment, no attacks capable of \breaking" this system in a reasonable amount of time are known. Research supported by NSF grant MCS{8006938. Part of this research was done while the rst author was visiting Bell Laboratories, Murray Hill, NJ. A preliminary version of this work was presented in Crypto 84 and has appeared in [8]. 1 1.

Downloading executable content, which enables principals to run programs from remote sites, is a key technology in a number of emerging applications, including collaborative systems, electronic commerce, and web information services. However, the use of downloaded executable content also presents serious security problems because it enables remote principals to execute programs on behalf of the downloading principal. Unless downloaded executable contentis properly controlled, a malicious remote principal may obtain unauthorized access to the downloading principal 's resources. Current solutions either attempt to strictly limit the capabilities of downloaded content or require complete trust in the remote principal, so applications which require intermediate amounts of sharing, such as collaborative applications, cannot be constructed over insecure networks. In this paper, we describe an architecture that #exibly controls the access rights of downloaded contentby: #1# authenticating co...

Information Commerce is a business activity carried out among several parties in which information carries value and is treated as a product. The information may be content, it may be returned usage and marketing data, and it may be representative of financial transactions. In each of these cases the information is valuable and must be kept secure and private. Traditional approaches secure the transmission of that information from one point to another; there are no persistent protections. Protection of all of these components of information commerce for all parties in a transaction value chain is necessary for a robust electronic infrastructure. A prerequisite to such an environment is a cryptographically protected container for packaging information and controls that enforce information rights. This paper describes such a container, called the DigiBox . EPR has submitted initial specifications for the DigiBox container to the ANSI IISP Electronic Publishing Task Force (EPUB) within ...

Recent theoretical results confirm that quantum theory provides the possibility of new ways of performing efficient calculations. The most striking example is the factoring problem. It has recently been shown that computers that exploit quantum features could factor large composite integers. This task is believed to be out of reach of classical computers as soon as the number of digits in the number to factor exceeds a certain limit. The additional power of quantum computers comes from the possibility of employing a superposition of states, of following many distinct computation paths and of producing a final output that depends on the interference of all of them. This “quantum parallelism” outstrips by far any parallelism that can be thought of in classical computation and is responsible for the “exponential ” speed-up of computation. Experimentally, however, it will be extremely difficult to “decouple ” a quantum computer from its environment. Noise fluctuations due to the outside world, no matter how little, are sufficient to drastically reduce the performance of these

models of information sharing, and runtime support based on those models, are by themselves incomplete for the task of constructing robust, practical collaborative applications. To be usable, we must provide a means for developers to access these facilities easily. This chapter has presented developer perspectives on the concepts introduced by Intermezzo. We have investigated a number of components of the developer support, or "toolkit," in this research, including notification, programming interfaces for accessing shared data, interfaces for accessing collaboration-specific functionality, and the use of scripting through embedded computation. Notification is one of the most important problems to be addressed in any developer support: how do applications (and, by extension, their users) become aware of changes in their environments? This problems is especially vexing in the case of coordination, where information that may be considered interesting is plentiful, change is rapid, and the...

Though the truths of logic and pure mathematics are objective and independent of any contingent facts or laws of nature, our knowledge of these truths depends entirely on our knowledge of the laws of physics. Recent progress in the quantum theory of computation has provided practical instances of this, and forces us to abandon the classical view that computation, and hence mathematical proof, are purely logical notions independent of that of computation as a physical process. Henceforward, a proof must be regarded not as an abstract object or process but as a physical process, a species of computation, whose scope and reliability depend on our knowledge of the physics of the computer concerned.

Abstract. We describe in detail a general strategy for implementing a conditional geometric phase between two spins. Combined with single-spin operations, this simple operation is a universal gate for quantum computation, in that any unitary transformation can be implemented with arbitrary precision using only single-spin operations and conditional phase shifts. Thus quantum geometrical phases can form the basis of any quantum computation. Moreover, as the induced conditional phase depends only on the geometry of the paths executed by the spins it is resilient to certain types of errors and oå ers the potential of a naturally fault-tolerant way of performing quantum computation. 1.