Lent C.S., Tougaw P.D., Porod W., Bernstein G.H.: Quantum cellular automata. Nanotechnology 4 (1993) 49--57  Home/Search   Document Not in Database   Summary   Related Articles   Check

....irrespective of initial conditions. It would be interesting to see how much of this carries over to the quantum domain. There are many proposals for computation, both classical and quantum, using quantum 63 cellular automata (see, e.g. Briegel and Raussendorf [18] Fussy et al. 44] Lent et al. [77], Lloyd [84] or Meyer [88] The two main attractions of quantum cellular automata are (a) massively parallel structure, and (b) the possibility of a phase transition. We have already discussed massively parallel structure of quantum cellular automata in Section 3.4.3; here we focus our attention ....

C. Lent, P.D. Tougaw, W. Porod, and G.H. Bernstein, \Quantum cellular automata," Nanotechnology 4, 49 (1993).

....is an approach to computing with quantum dots called the quantum dot cellular automata (QCA) First proposed in 1993 by Lent, et. al and fabricated in 1997, an idealized QCA cell device can be viewed as a set of four change containers or dots , positioned at the corners of a square [7] [8]. The cells contain two extra mobile electrons which can quantum mechanically tunnel between dots but, by design, cannot tunnel between cells. The dots can be realized in several different ways electrostatically formed quantum dots in a semiconductor, small metallic islands connected by tunnel ....

C. Lent, P. Tougaw, W. Porod, and G. Bernstein. Quantum cellular automata. Nanotechnology, 4:49--57, 1993.

....the motivation for an application specific architectural approach based on regular blocks proposed further in the paper. The basic architectural model is specified and a design methodology allowing the mapping of regular problems is described. I. INTRODUCTION Since its initial proposal [1], the quantum cellular automata (QCA) model has received considerable attention in the quest for alternative technologies to CMOS mainly because of its appealing simplicity. However, several studies [5] 6] pointed out serious drawbacks in performance and manufacturability of the metallic or ....

....model that are independent of the parameters of a particular implementation. First, the model places itself into a class of computing architectures characterized by field based local interaction between elementary devices. Information is coded using physical properties as electron distribution ([1] [2] magnetic axis ( 4] or magnetic bubble presence ( 3] The nature of the basic interactions is either electrostatic ( 1] 2] or magnetic ( 3] 4] A second issue representative for the QCA model is its sensitivity to geometric positioning. As pointed in [6] very high precision is ....

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C. S. Lent, P. D. Tougaw, W. Porod, G. H. Bernstein, "Quantum Cellular Automata" Nanotechnology, no. 4, pp. 49, 1993

....current flow. In the category of QD s we include individual dots, also known as artificial atoms [28] 140] 156] as well as coupled dots ( quantum dot molecules ) 184] and a kind of composite device called a QD cell, in which four or five QDs form a single two state device. QD cells [185], the clever logic designs based upon them [18] and related composite structures that might be built from QD s [186] are beyond the scope of this overview. However, they are discussed in detail elsewhere in this issue of the Proceedings [187] 3) Single Electron Transistors: A single electron ....

....are organized in more regular structures, might be made even more dense. The problems of achieving such increases in computing power and information storage capacity still are formidable. As discussed elsewhere in this volume [88] 187] new architectures [81] 82] like cellular automata [84] [185], must be devised to reduce the amount of wire and number of interconnects on a circuit while accommodating billions or even trillions of devices in the same area now occupied by only a few million. These architectures also must compensate for the intrinsically lower reliability of very small ....

C. S. Lent et al., "Quantum cellular automata," Nanotechnol., vol. 4, p. 49, 1993.

....more heat to dissipate which may lead to limitations on the speed of operation. A detailed analysis of such effects is presented by Meindl [32] One possible solution to interconnection problems is to have a sort of wireless interaction between the devices. Proposals for Coulomb force interaction [33, 34, 35, 36], electron spin interaction [37, 38] electron photon interaction [39, 40] and Q dots interacting with an external electric field [41] are presented and each one has its own merits and disadvantages as will be discussed later. These proposals alleviate the interconnections problems and using ....

....wiring besides the primary inputs and outputs. In order to further understand this idea more details about the different wireless proposals are presented in the next section. 2.4. 5 Previously proposed wireless systems Bistable nanowires and cellular automata Lent, Tougaw, Porod and Bernstein [33, 34, 35, 36] proposed a simple scheme for implementing wireless logic. The basic cell is shown in Fig. 2.12(a) It is composed of five quantum dots with two extra free electrons (shown as dark spots) which can tunnel between the dots. The minimum energy configuration is achieved when the two electrons occupy ....

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C. S. Lent, P. D. Tougaw, W. Porod, and G. H. Bernstein, "Quantum cellular automata," Nanotechnology, vol. 4, pp. 49--57, 1993.

....introduce cell circuits suitable for large scale integration [3] Up to now, all of these cells need energy and therefore power supply. Just recently attempts have been made to build up circuitry being able to work without an external energy supply by using the energy stored in the initial state [1]. This principle can provide two major advantages. First, since no or at least not much energy is dissipated during computation, the circuit does not produce much heat. Therefore, there are no hot spots in integrated circuits, which limit integration density and operation speed. Furthermore, ....

C. S. Lent, P. D. Tougaw, W. Porod, G. H. Bernstein: "Quantum cellular automata". Nanotechnology 4 1993.

....to two dimensional systems [Ric] In this context the ergodicity of the QCA is equivalent to the state on the two dimensional system to be uniquely determined by local data, independently of boundary conditions. The term quantum cellular automaton has been used previously by some other authors [GZ,FGSS,LTPH]. In the cases we are aware of, however, it is used for a structure on the Hilbert space level, and not on the level of observables. Thus in [GZ] the classical states at each site are simply replaced by the values of the wave function at that site, and the dynamics is just a discrete Schrodinger ....

....dynamics is just a discrete Schrodinger equation with non selfadjoint Hamiltonian, made non linear by keeping the normalization fixed. There is some interest in quantum cellular automata also from the point of view of nanometer scale computers, for which quantum effects are expected to be relevant [Mai,Bia,LTPH]. The evolution of the automata considered in this paper is in general non unitary, i.e. pure states may evolve into mixed states. This might be an interesting addition to the structure of quantum computers , as studied by a number of authors recently (see [DiV] and references cited there) The ....

C. Lent, P.D. Tougaw, W. Porod, and G.H. Bernstein: "Quantum cellular automata ", Nanotechnology 4(1993) 49--57

....than t OE =t switch (probably a great deal less) we see that there are severe limits on the kind of quantum computation which these physical systems can perform. I believe that other microscopic systems which have been discussed for quantum computation, for example the Notre Dame logic gate [10] (operating by the hopping of electrons from one quantum dot to another) or the atom switch [11] operating by the hopping of a single atom from one site on a crystal surface to another) are similarly problematic; although I know of no measurements of t OE in these cases, I expect that it is ....

C. S. Lent, P. D. Tougaw, W. Porod, and G. H. Bernstein, "Quantum cellular automata ", Nanotechnology 4, 49 (1993).

....nanostructures (more specifically, quantum dots) which are arranged in locally interconnected cellular automata like arrays. We will demonstrate that suitably constructed structures may be used for computation and signal processing. Our proposal is called Quantum Dot Cellular Automata (QCA) [Lent et al. 1993]. Note that our proposal is not a quantum computer in the sense of the quantum computing community, as reviewed by Spiller [1996] QCA s do not require quantum mechanical phase coherence over the entire array; phase coherence is only required inside each cell and the cell cell interactions are ....

....10 nm, or so) the exact placement of these dots is still a problem, but progress is being made. 3. Quantum Dot Cellular Automata Based upon the emerging technology of quantumdot fabrication, the Notre Dame NanoDevices group has proposed a scheme for computing with cells of coupled quantum dots [Lent et al. 1993], which will be described below. To our knowledge, this is the first concrete proposal to utilize quantum dots for computing. There had been earlier suggestions that device device coupling might be utilized in a cellular automata scheme, but alas, these were without an accompanying proposal for a ....

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Lent, C. S., Tougaw, P. D., Porod, W. & Bernstein, G. H. [1993] "Quantum cellular automata," Nanotechnology 4, 49--57.

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Lent C.S., Tougaw P.D., Porod W., Bernstein G.H.: Quantum cellular automata. Nanotechnology 4 (1993) 49--57

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C.S. Lent et al., "Quantum Cellular Automata," Nanotechnology, Vol. 4, p. 49, 1993.

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C. S. Lent, P. D. Tougaw, W. Porod, and G. H. Bernstein, `Quantum cellular automata', Nanotechnology 4 (1993), 49--57.

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Lent, C., Tougaw, P., Porod, W., and Bernstein, G. Quantum cellular automata. Nanotechnology 4, 1 (January 1993), 49-57. 32

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