Optical Flip-Flops and Shift Registers from populations and coherences in multi-level systems using stimulated Raman adiabatic passage

In digital circuits, a Flip-Flop (FF) is a circuit element that has two stable states which can be used to store and remember state information. The state of the circuit can be changed by applying signals to the control input. FFs are the basic building blocks of sequential logic circuits, as logic gates AND,OR, NOT are the basic building block for combinational logic circuits, and are therefore necessary for any computations involving memory. Consequently, the design and implementation of FFs can be considered as a pre-requisite for memory machine design. Here we present the design of an optical FFs in an atomic multi-level system, based on the optical manipulation of populations and coherences using stimulated Raman adiabatic passage. We first demonstrate that both populations and coherences can be transferred over multistate systems. We then propose the design of toggle-FFs, Delay-FFs, and Serial-in Serial-Out (SISO) shift registers using such systems. For the design of the filp-flops we use a three level $\Lambda$-type system. In order to design SISO shift registers we concatenate two $\Lambda$-type systems and construct an "M"-type scheme, and similarly concatenating three $\Lambda$-type system we are able to obtain a seven level system. By concatenating we are able to use output of one three level $\Lambda$-type system serve as input of another three level $\Lambda$-type system. On top of using populations for design of logic gates, we uniquely exploit the coherences for logic machine, which provides an additional degree of freedom which can be used for the design of computing elements.