Landauer, Rolf (1994), "Is Quantum Mechanically Coherent Computation Useful?", In Proc. of the Drexel-4 Symposium on Quantum Nonintegrability (Feng, D. H., and B-L. Hu, eds.), International Press.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....by the amplitudes of the superposition. A successful algorithm is one that uses these capabilities to arrange for a large probability of a desired result, e.g. a solution to a search problem. However, there are two major difficulties with quantum computers. First, they are difficult to implement [16]. Second, the physical restriction to unitary linear operations makes quantum computers difficult program effectively. An encouraging development with respect to the design of algorithms is a method for efficiently factoring integers [23] a problem that appears to be intractable for classical ....

....This could lead to the construction of special purpose search devices for the set manipulations used in the problem independent mapping between levels of the lattice. Second, how are the results degraded by errors and decoherence, the major difficulties for the construction of quantum computers [16] While there are some quantum approaches to error control [3, 22] and studies of decoherence in the context of factoring [6] it remains to be seen how these problems affect the framework presented here. Third, it would be useful to have a theory for asymptotic behavior for large N , even if only ....

Landauer, Rolf (1994), "Is Quantum Mechanically Coherent Computation Useful?", In Proc. of the Drexel-4 Symposium on Quantum Nonintegrability (Feng, D. H., and B-L. Hu, eds.), International Press.

.... caused by imprecision and decoherence be controlled sufficiently to allow arbitrarily complex quantum computations to take place with an arbitrarily small probability of failure A number of papers have expressed pessimism regarding the question of error accumulation in quantum computers, e.g. [30, 29, 46, 47, 12, 36]. These papers show that in the absence of error correction, the probability of error increases exponentially with both the time and space complexity of the computation, and the expected error free running time for various experimental setups has been estimated to be roughly on the order of the ....

R. Landauer. Is quantum mechanically coherent computation useful? In D. H. Feng and B-L. Hu, editors, Proceedings of the Drexel-4 Symposium on Quantum Nonintegrability---Quantum Classical Correspondence. International Press, 1995.

....of measuring the distance between a quantum robot and a particle on a 1D space lattice. Hogg [Hog96] proposes the use of distributed QC to allow small scale sensors and actuators to be controlled in a distributed manner. Further discussion of the applications of QC are given by Landauer [Lan95,Lan97] ffl Winding Up Quantum Clocks. The precision of atomic clocks are limited by the spontaneous decay lifetimes of excited atomic states. An interesting application of QC proposed by Huelga [HMP 97] and Bollinger et al. [Bol96] is to extend these lifetimes by using quantum error correcting codes ....

Landauer, R. 1997 Is quantum mechanically coherent computation useful?, In Proc. Drexel-4 Symposium on Quantum Nonintegrability-Quantum-Classical Correspondence, Philadelphia, PA, 8 September 1994 (ed. D. H. Feng and B.-L. Hu), Boston: International Press, (1997). 44

.... Some suggestions have been made as to possible designs for such computers [Teich et al. 1988, Lloyd 1993, 1994a, Cirac and Zoller 1995, DiVincenzo 1995, Sleator and Weinfurter 1995, Barenco et al. 1995b, Chuang and Yamomoto 1995] but there will be substantial difficulty in building any of these [Landauer 1995, Unruh 1995, Chuang et al. 1995, Palma et al. 1995] The most difficult obstacles appear to involve the decoherence of quantum superpositions through the interaction of the computer with the environment, and the implementation of quantum state transformations with enough precision to give ....

R. Landauer (1995) "Is quantum mechanically coherent computation useful?" in Proceedings of the Drexel-4 Symposium on Quantum Nonintegrability --- Quantum Classical Correspondence (D. H. Feng and B-L. Hu, eds.) International Press, to appear.

....for the development of the idea of quantum computers. It was assumed that quantum computers will take advantage of the superpositions that are inherent in a quantum description and thereby do more than what classical computers can achieve. For accounts of research in the quantum computing area see [2, 6, 3, 15, 17, 16, 19]. The development of the idea of a quantum mechanical computer has paralleled, more or less, the structure of a classical computer. Whether such a structure, based on local interconnections, exhausts the capabilities of quantum computing, we do not know yet. Is it possible that current quantum ....

....the system is a serial model. Parallel models have also been proposed. Lloyd [17] suggested that a quantum computer could be assembled out of organometallic polymers, where laser pulses could send the superposed states down the polymer chain analogous to electrons flowing down a wire. Landauer [15, 16] has subjected these proposals for quantum computing to a penetrating scrutiny. He wonders: Physical Hamiltonians are Hermitian; that does not mean that Hermitian operators are physically realizable. Why the specification of Hamiltonians has become accepted in this field as equivalent to a ....

[Article contains additional citation context not shown here]

R. Landauer, Is quantum mechanically coherent computation useful? Proceedings of the Drexel-4 Symposium on Quantum Nonintegrability--- Quantum-Classical Correspondence, D.H. Feng and B-L. Hu, eds., International Press (1995).

.... down there , but in the end we are at their mercy. Even as schemes for quantum computation are being vigorously developed, common sense dictates that we explore two classes of questions: ffl Aren t there any exponential costs lurking sowhere that would offset the prospected exponential benefits[16, 17] ffl What is the fraction of problems that would benefit from quantum algorithms I wouldn t be surprised if it were a set of measure zero even though this set may contain some important problems. Most problems in combinatorial optimization are of exponential complexity, if we want an exact ....

Landauer, Rolf, "Is quantum mechanically coherent computation useful?" Proc. Drexel 4th Symp. Quantum Nonintegrability--Quantum Classical Correspondence (D. H. Feng and B. L. Hu ed.), International Press, Boston, in press.

.... out a computation are very sensitive to the imperfections of the hardware, and above all, to the decoherence[6] caused by interaction with the environment (by environment we mean all the degrees of freedom which can have unwanted interactions with the computer) This fragility of a quantum computer[7, 8, 9] is closely tied to its function: it acts as a sophisticated, nonlinear interferometer. The coherent interference pattern between the multitude of superpositions is essential for taking advantage of quantum parallelism, which is the key feature allowing one to explore aspects of an exponentially ....

R. Landauer. Is Quantum Mechanically Coherent Computation Useful? In D.H.Feng and B-L. Hu, editors, Proc. of the Drexel-4 Symposium on quantum Nonintegrability -- Quantum Classical Correspondence, 1995.

....their power. 89.70. c,89.80.th,02.70. c,03.65. w Typeset using REVT E X The discovery of error correcting codes [1,2] for quantum computers has revolutionized the field of quantum information. Although quantum computing holds great promise, it is plagued by the fragility of quantum information [3 6]. Quantum error correction is a technique which enables one to encode quantum information in a robust way and therefore overcome this fragility. It is important to classify codes in order to know what is the most compact way to encode a number of qubits against a given number of errors. Various ....

R. Landauer. Is Quantum Mechanically Coherent Computation Useful? Philosophical transactions of the Royal Society of London, 353, 367, 1995.

....will also depend on details of actual implementations, such as any additional operations required for controlling errors that cannot themselves be performed in parallel with the higher level steps of the algorithm. These remain significant issues in the development of quantum computation (Landauer, 1994; Unruh, 1995; Haroche Raimond, 1996; Monroe Wineland, 1996) but at this point seem unlikely to be fundamental difficulties (Berthiaume, Deutsch, Jozsa, 1994; Shor, 1995; Knill, Laflamme, Zurek, 1998) In particular, because the algorithm requires only a single step, decoherence is likely ....

Landauer, R. (1994). Is quantum mechanically coherent computation useful?. In Feng, D. H., & Hu, B.-L. (Eds.), Proc. of the Drexel-4 Symposium on Quantum Nonintegrability Boston. International Press.

....question is the physical implementation of quantum computers in general (Barenco et al. 1995; Sleator Weinfurter, 1995; Cirac Zoller, 1995) and the requirements imposed by the algorithm described here. Any implementation of a quantum computer will need to deal with two important difficulties (Landauer, 1994). First, there will be defects in the construction of the device. Thus even if an ideal design exactly produces the desired mapping, occasional manufacturing defects and environmental noise will introduce errors. We thus need to understand the sensitivity of the algorithm s behavior to errors in ....

Landauer, R. (1994). Is quantum mechanically coherent computation useful? In Feng, D. H., & Hu, B.-L. (Eds.), Proc. of the Drexel-4 Symposium on Quantum Nonintegrability.

....nobody knows how to build a quantum computer, although it seems as though it could be possible within the laws of quantum mechanics. Some suggestions have been made as to possible designs for such computers [30, 22, 23, 12] but there will be substantial difficulty in building any of these [18, 32]. Even if it is possible to build small quantum computers, scaling up to machines large enough to do interesting computations could present fundamental difficulties. It is hoped that this paper will stimulate research on whether it is feasible to actually construct a quantum computer. Even if no ....

R. Landauer, "Is quantum mechanically coherent computation useful?" in Proceedings of the Drexel-4 Symposium on Quantum Nonintegrability --- Quantum Classical Correspondence (D. H. Feng and B-L. Hu, eds.) International Press, to appear.

....of measuring the distance between a quantum robot and a particle on a 1D space lattice. Hogg [Hog96] proposes the use of distributed QC to allow small scale sensors and actuators to be controlled in a distributed manner. Further discussion of the applications of QC are given by Landauer [Lan95,Lan97] ffl Winding Up Quantum Clocks. The precision of atomic clocks are limited by the spontaneous decay lifetimes of excited atomic states. An interesting application of QC proposed by Huelga [HMP 97] and Bollinger et al. [Bol96] is to extend these lifetimes by using quantum error correcting codes ....

Landauer, R. 1997 Is quantum mechanically coherent computation useful?, In Proc. Drexel-4 Symposium on Quantum Nonintegrability-Quantum-Classical Correspondence, Philadelphia, PA, 8 September 1994 (ed. D. H. Feng and B.-L. Hu), Boston: International Press, (1997).

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R. Landauer. Is Quantum Mechanically Coherent Computation Useful? In D.H.Feng and B-L. Hu, editors, Proc. of the Drexel-4 Symposium on quantum Nonintegrability -- Quantum Classical Correspondence, 1995.

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