Physica E 6 (2000) 428–431 www.elsevier.nl/locate/physe Dynamic behavior of asymmetric quantum dot cells  F. Rojas a , E. Cota a ; * , S.E. Ulloa b a Centro de Ciencias de la Materia Condensada–UNAM, Apartado Postal 2681, Ensenada, B.C. 22800, Mexico b Department of Physics and Astronomy and Condensed Matter and Surface Sciences Program, Ohio University, Athens, Ohio 45701-2979, USA Abstract We study the dynamic evolution of 4- and 5-quantum dot cells in the presence of a time-dependent driver cell. We analyze the eects of imperfections, tunneling intensity and switching times on the response of the basic cell, for linear and periodic switching of the driver polarization. We nd that the eects of the imperfections have strong consequences in slowing down the response of the basic cell and that the ve-dot cell is less sensitive to these eects. Further studies show that a rapid deterioration of the response takes place as more cells are included. Eects of a time-dependent variation of the tunneling parameter as the switching takes place are also analyzed. ? 2000 Elsevier Science B.V. All rights reserved. PACS: 73.40.Gk; 73.20.Dx; 73.50.Bk Keywords: Quantum dots; Quantum computation 1. Introduction Arrays of quantum dots, quantum cellular automata (QCA), have been proposed [1] as systems for imple- menting novel logical computing elements and even quantum computing [2,3]. Each cell in the array con- tains four or ve quantum dots where two electrons are allowed to move within the cell, tunneling from one dot to the next, while interacting with each other, and with a positive neutralizing background. These elec- trons also interact with those in neighboring cells, but * Corresponding author. Tel.: +1-740-593-1729; fax: +1- 740-593-0433. E-mail address: ulloa@ohio.edu (S.E. Ulloa)  F.R. and E.C. acknowledge support from CONACYT (Grant 27702-E), and S.E.U. from US-DOE. are not allowed to tunnel from cell to cell. Typically, the cells are arranged in a square geometry (with a quantum dot in each corner), so that the ground state of an isolated cell is doubly degenerate, with two elec- trons on opposite corners of the cell. 1 Each of these ground states is characterized by a polarization num- ber (+1 and −1, as per Ref. [1]), which would allow the encoding of binary information and quantum bits. In this paper, we study the response of such a cell arrangement to a time-dependent driver cell in close proximity. The eects of such drivers have been stud- ied recently [4], including dissipative eects [5]. We 1 This statement assumes simultaneous eigenstates of polar- ization, while the ground state is a linear combination if driver=polarizing cell is not present nearby. 1386-9477/00/$ - see front matter ? 2000 Elsevier Science B.V. All rights reserved. PII:S1386-9477(99)00199-X