1. Quantum computing is more efficient than classical computing for all possible computations, meaning more results per unit work (the "something for nothing" myth).

2. Quantum computing exploits quantum parallelism in a way comparable to, but better than, classical parallelism (the "each *n*-qubit quantum state is 2 * ^{n}* classical bits" myth).

*F*: {0, 1} → {0, 1} is constant or not, meaning it takes on one or two values. However, this single query does

*not*tell us which of the four possible

*F*'s we're looking at; it just tells us if

*F*is in the class "takes only one value" or the class "takes two different values." In other words, only one question is asked, and only one is answered. In the case of the more general Deutsch-Joza algorithm, it's sometimes claimed that one of 2

*possibilities is decided with only one question asked. This is an illusion too, although seeing why it's an illusion is a little more difficult. In short, we're told at the outset that the function is one of two types, constant or balanced, and one question determines which type it is.*

^{n}*gate count*—the complexity of the machine that would actually execute the quantum algorithm.

*n*-qubits and the relation of that meaning to parallelism, arises from the notion of superposition of states. In classical statistical physics, quantities are defined and determined as averages of large ensembles of preexisting values. For example, if we say that a monatomic gas with Boltzmann distribution of energy is in equilibrium at some temperature

*T*, we're making a statement about the average (expected value) of the individual atoms' energies. We assume that the individual atoms have particular energies that exist independent of whether or not we happen to measure the temperature. In quantum physics, some of the same words are used, but their meaning changes and this difference is all-important. A superposition of

*n*-qubits is

*not*a "parallel" collection of values or an average of preexisting particular values, even though measurement of a state is called determination of the expectation value. In fact, if we assume that states do stand for preexisting values, we arrive at a contradiction of the basic mathematical properties of three-dimensional space. And if we try to get around the contradiction by restricting ourselves to rational numbers, we contradict quantum mechanics itself.

*CiSE*about the experience of the Sloan Sky Survey in moving from OODBMS to RDBMS ("Migrating a Multiterabyte Archive from Object to Relational Databases," vol. 5, no. 5, 2003, pp. 16-29). It touched on an important issue that I have been wrestling with, on and off, for the better part of the past decade.

*David McClain, Senior Scientist, Raytheon Missile Systems*

• The conceptual mismatch between scientific data and relational tables is of secondary importance to the data-mining performance and features the DBMS offers. Modern RDBMSs deliver both performance and features, whereas OODBMSs have not kept up with the demands of data-intensive science.

• The mismatch problem is not as bad as we had originally thought. As we described in our article, we were able to translate our object data to relational tables without too much trouble. We also added several stored procedures and functions to encode methods within the SQL database.

*Aniruddha R Thakar, Assoc. Research Scientist, The Sloan Digital Sky Survey*

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