LOSSLESS LOGIC DESIGN IN NANO-SCALE USING QCA Tanay Chattopadhyay1 and Tamal Sarkar2* Mechanical Operation (stage-II), Kolaghat Thermal power station, WBPDCL, Mecheda, Purbamedinipur, 721137, West Bengal, India. 2 University Science Instrumentation Centre, University of North Bengal, Siliguri 734013, West Bengal, India. Email: [email protected] and [email protected] 1

Quantum-dot cellular automata (QCA) have been widely considered as a replacement for CMOS technology circuits. In nano-scale, QCA design fabrication is low cost and consumes low power. Hence it will make the revolution in future computing [1]. We all know that computer works with binary logic (0 and 1). It is possible to encode Binary Information using two possible polarization states of typical Quantum dot cellular automata. Here logic states are not stored as voltage level, but rather the potion of individual electrons. Electrons being quantum mechanical particles and hence are cable to tunnel between the dots in a cell. The cell will switch from polarization state P=-1 (logic ‘0’) to P=+1 (logic ‘1’) when the electrons quantum mechanically tunnel from one set of dots to the other. Using an array of QCA, it is possible to make a wire that may able to transmit information from one end to another. This is possible because the electron in cells placed adjacent to each other has power to interact. As a result, the polarization of one cell will be directly affected by the polarization of its neighboring cells. This interaction forces neighboring cells to synchronize their polarization. Traditional Boolean logic has two inputs and one output. Hence one data is lost every time which is the loss of energy at least KBTln2. This problem can be solved by reversible computing [2] but, if we combine two irreversible logic gates together then data can be conserved. ‘AND’ and ‘OR’ are two well known irreversible logic operation. In this proposal a combined AND–OR logic gate with QCA is proposed, which has two inputs (A, B) and two outputs (AB, A+B) (Fig-1a). Hence no data loss happens during the operation. This can be easily seen from the truth table (Fig-1b). The performance of the circuit has been done by computer simulation (Fig-1c). Keywords: quantum-dot cellular automata, lossless logic, logic circuit

Fig-1: Lossless AND-OR logic gate with QCA. (a) circuit, (b) truth table, (c) simulation result. References: [1] C.S.Lent and P.D.Tougaw, “A device architecture for computing with Quantum dots”, Proc. IEEE, 85(4), 1997, 541-557. [2] T.Chattopadhyay, “All-optical modified Fredkin gate”, IEEE Journal of Selected Topics in Quantum Electronics, (In press), DOI: 10.1109/JSTQE.2011.2106111.