Stimulated Raman adiabatic passage (STIRAP) is a well-studied pump-probe control scheme for manipulating the population of quantum states of atoms or molecules. By encoding the digits to be operated on as ``on'' or ``off'' laser input signals we show how STIRAP can be used to implement a finite-state logic machine. The physical conditions required for an effective STIRAP operation are related to the physical conditions expected for a logic machine. In particular, a condition is derived on the mean number of photons that represent an on pulse. A finite-state machine computes Boolean expressions that depend both on the input and on the present state of the machine. With two input signals we show how to implement a full adder where the carry-in digit is stored in the state of the machine. Furthermore, we show that it is possible to store the carry-out digit as the next state and thereby return the machine to a state ready for the next full addition. Such a machine operates as a cyclical full adder. We further show how this full adder can equally well be operated as a full subtractor. To the best of our knowledge this is the first example of a nanosized system that implements a full subtraction.
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
Λ-type system. In order to design SISO shift registers we concatenate two
Λ-type systems and construct an "M"-type scheme, and similarly concatenating three
Λ-type system we are able to obtain a seven level system. By concatenating we are able to use output of one three level
Λ-type system serve as input of another three level
Λ-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.
We report on experimental investigations of stimulated Raman adiabatic passage (STIRAP) in a
Pr3+:Y2SiO5 crystal. STIRAP drives complete, coherent population transfer between two hyperfine levels in the
Pr3+ ions. We investigate the variation of the STIRAP transfer efficiency with the experimental parameters: e.g., detunings, Rabi frequencies, and pulse delays. In addition, we also observe an alternative and efficient, adiabatic transfer process---i.e.,
b-STIRAP---which occurs for a reversed sequence of laser pulses. We compare the efficiencies and time-resolved transfer dynamics of STIRAP and
b-STIRAP. The experimental data are supported by numerical simulations, also including the effect of laser frequency jitter. Our experimental data and the numerical simulations provide a clear and convincing demonstration of adiabatic excitations in a solid medium.
The Toffoli gate is an essential logic element, which permits implementation of a reversible processor. It is of relevance both for classical as well as quantum logics. We propose and theoretically study all-optical implementations of three-bit and four-bit Toffoli gates by application of adiabatic population transfer techniques. For a three-bit Toffoli gate we use variants of stimulated Raman adiabatic passage (STIRAP) processes in a
Λ-type level scheme, driven by two laser pulses at sufficiently large detunings. For the implementation of a four-bit Toffoli gate, we apply reversible adiabatic population transfer in five-level quantum systems, interacting with three laser pulses. We demonstrate correct all-optical implementation of the truth table of three-bit and four-bit Toffoli gates. Moreover, we derive conditions for adiabatic evolution of the population dynamics and robust operation of the gates.
We experimentally demonstrate composite stimulated Raman adiabatic passage (CSTIRAP), which combines the concepts of composite pulse sequences and adiabatic passage. The technique is applied for population transfer in a rare-earth doped solid. We compare the performance of CSTIRAP with conventional single and repeated STIRAP, either in the resonant or the highly detuned regime. In the latter case, CSTIRAP improves the peak transfer efficiency and robustness, boosting the transfer efficiency substantially compared to repeated STIRAP. We also propose and demonstrate a universal version of CSTIRAP, which shows improved performance compared to the originally proposed composite version. Our findings pave the way towards new STIRAP applications, which require repeated excitation cycles, e.g., for momentum transfer in atom optics, or dynamical decoupling to invert arbitrary superposition states in quantum memories.
We introduce a method for the coherent acceleration of atoms trapped in an optical lattice, using the well-known model for stimulated Raman adiabatic passage (STIRAP). Specifically, we show that small harmonic modulations of the optical lattice amplitude, with frequencies tuned to the eigenvalue spacings of three ``unperturbed'' eigenstates, reveals a three-state STIRAP subsystem. We use this model to realize an experimentally achievable method for transferring trapped atoms from stationary to motional eigenstates.