We discuss some seemingly paradoxical yet valid effects of quantum physics in informationprocessing. Firstly, we argue that the act of "doing nothing" on part of an entangled quantum system is a highly non-...
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(纸本)354065514X
We discuss some seemingly paradoxical yet valid effects of quantum physics in informationprocessing. Firstly, we argue that the act of "doing nothing" on part of an entangled quantum system is a highly non-trivial operation and that it is the essential ingredient underlying the computational speedup in the known quantumalgorithms. Secondly, we show that the watched pot effect of quantum measurement theory gives the following novel computational possibility: suppose that we have a quantum computer with an on/off switch, programmed ready to solve a decision problem. Then (in certain circumstances) the mere fact that the computer would have given the answer if it were run, is enough for us to learn the answer, even though the computer is in fact not run.
Introduced by Fuji Photo Film Japan in the early 1980s, computed radiography (CR) technology has developed considerably since then to become the mature widely installed technology it is today (about 7500 systems world...
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Introduced by Fuji Photo Film Japan in the early 1980s, computed radiography (CR) technology has developed considerably since then to become the mature widely installed technology it is today (about 7500 systems worldwide). Various mammographic examinations require high performance results to which CR complies on demand or following some procedures such as geometrical magnification carried out during the examination. The basic CR principles and digital image processing as well as technical improvements are detailed in this study, which also includes a synthesis of the articles on CR mammographic applications referenced in the bibliography, focusing on strong points, limits and current methods of surpassing these limits. New CR technology development perspectives in mammography and computed assisted diagnosis (CAD) algorithms will allow wider use of this method in the near future. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.
When the 4-state or the 6-state protocol of quantum cryptography is carried out on a noisy quantum channel, then the raw key has to be processed to reduce the information of a spy down to an arbitrarily low value, pro...
When the 4-state or the 6-state protocol of quantum cryptography is carried out on a noisy quantum channel, then the raw key has to be processed to reduce the information of a spy down to an arbitrarily low value, providing Alice and Bob with a secret key. In principle, quantumalgorithms as well as classical algorithms can be used for this processing. A natural question is: Up to which error rate on the raw key is a secret-key agreement at all possible? Under the assumption of incoherent eavesdropping, we find that the quantum and classical limits are precisely the same: As long as Alice and Bob share some entanglement, both quantum and classical protocols provide secret keys.
quantum networks are created to implement fundamental quantum communication protocols and for distributed quantum computation. Beyond quantuminformationprocessing with internal atomic states and photons serving as q...
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quantum networks are created to implement fundamental quantum communication protocols and for distributed quantum computation. Beyond quantuminformationprocessing with internal atomic states and photons serving as qubits, an algorithms for continuous quantum variables are also investigated. A recent example is the realization of quantum teleportation for the quadrature amplitudes of a beam of light. It utilizes squeezed-state entanglement to achieve unconditional quantum teleportation.
Summary form only given. quantum mechanics offers the information scientist a new rich resource, which is only recently being tapped to allow for secure communication in the form of quantum cryptography, and for treme...
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Summary form only given. quantum mechanics offers the information scientist a new rich resource, which is only recently being tapped to allow for secure communication in the form of quantum cryptography, and for tremendous parallelism in quantuminformationprocessing and computing. I will describe developments and prospects for each. quantum cryptography has already advanced beyond the research laboratory to become a realizable technology with proven secret key distribution for encryption. quantum computing, although at an earlier stage of development has been recognized as a major new development in physics, enables us (if a quantum computer is realizable) to attack problems previously thought to be too complex for normal computation in a reasonable time. Examples of quantumalgorithms involving this kind of advantage are Shor's for fast factorization (in itself a threat to secure communication) and Grover's for database searching. I will discuss the ways quantum mechanics allow such a speed-up, stressing how quantum entanglement is the key resource being exploited, and how quantum gates, networks, and the processors may be implemented in a realistically noisy environment. Simple demonstrators have already been built, and I will discuss prospects for future realization of large-scale processors.
The paper presents a general model for estimating access times of serpentine tape drives. The model is used to schedule I/O requests in order to minimize the total access time. We propose a new scheduling algorithm, M...
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The paper presents a general model for estimating access times of serpentine tape drives. The model is used to schedule I/O requests in order to minimize the total access time. We propose a new scheduling algorithm, Multi-Pass Scan Star (MPScan*), which makes good utilization of the streaming capability of the tape drive and avoids the pitfalls of naive multi-pass scan algorithms and greedy algorithms like Shortest Locate Time First. The performance of several scheduling algorithms have been simulated for problem sizes up to 2048 concurrent I/O requests. For scheduling of two to 1000 I/O requests, MPScan* gives equal or better results than any other algorithm, and provides up to 85 percent reduction of the total access time. All results have been validated by extensive experiments on Tandberg MLRI and quantum DLT2000 drives.
In this paper, we introduce a SPICE compatibile SET transient model. The basic recipe of our model is similar to CAMSET but we have adopted a much simpler way for the truncation of the number of charge states required...
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In this paper, we introduce a SPICE compatibile SET transient model. The basic recipe of our model is similar to CAMSET but we have adopted a much simpler way for the truncation of the number of charge states required in the calculation. The validity of our model has been checked by comparing our transient calculation with the result of the steady-state master equation method.
Summary form only given. Real-time characterization of ultrashort optical pulses is critical for a number of important emerging applications: adaptive phase control for oscillator and amplifier optimization, quantum c...
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Summary form only given. Real-time characterization of ultrashort optical pulses is critical for a number of important emerging applications: adaptive phase control for oscillator and amplifier optimization, quantum control with learning feedback, laser diagnostics, nonlinear pulse propagation and ultrafast spectroscopy. To date, however, most techniques that return quantitative, high resolution information about the pulse shapes do so at a sub-Hertz repetition rate. It is possible to increase the acquisition rate in certain cases by using a reduced resolution spectrogram and dedicated signal processing hardware, as has been demonstrated by Kane (1998). We present a real-time pulse measurement-device that has no moving components, requires only one-dimensional data collection, and uses a noniterative inversion algorithm. Our technique, spectral phase interferometry for direct electric-field reconstruction (SPIDER), retrieves the spectral phase of the input pulses at an update rate of greater than 15 Hz using an inexpensive linear CCD array and standard data acquisition hardware in a desktop computer that implements the simple and rapid inversion algorithm in LabView.
In 1982 Feynman(1) observed that quantum-mechanical systems have an information-processing capability much greater than that of corresponding classical systems, and could thus potentially be used to implement a new ty...
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In 1982 Feynman(1) observed that quantum-mechanical systems have an information-processing capability much greater than that of corresponding classical systems, and could thus potentially be used to implement a new type of powerful computer. Three years later Deutsch(2) described a quantum-mechanical Turing machine, showing that quantum computers could indeed be constructed. Since then there has been extensive research in this field, but although the theory is fairly well understood, actually building a quantum computer has proved extremely difficult. Only two methods have been used to demonstrate quantum logic gates: ion traps(3,4) and nuclear magnetic resonance (NMR)(5,6). NMR quantum computers have recently been used to solve a simple [GRAPHICS] quantum algorithm-the two-bit Deutsch problem(7,8). Here we show experimentally that such a computer can be used to implement a non-trivial fast quantum search algorithm initially developed by Grover(9,10), which can be conducted faster than a comparable search on a classical computer.
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