Historically, logic gates have been used as building blocks for theoretical development of deterministic computation, and the assembled logic is realized in practice over physical processes such as composition of variable voltage levels in electronic circuit elements. However, much of the logic gate theory and design has focused on forward computation only, without explicit consideration of reversible execution. Here, we consider the reversibility aspect of traditional 2-bit gates and describe the concepts behind the development of reversible gates (which happen to require gates with at least 3 bit-wide inputs and outputs), and describe popular 3-bit reversible logic gates.
Historically, logic gates have been used as building blocks for theoretical development of deterministic computation, and the assembled logic is realized in practice over physical processes such as composition of variable voltage levels in electronic circuit elements. However, much of the logic gate theory and design has focused on forward computation only, without explicit consideration of reversible execution. Here, we consider the reversibility aspect of traditional 2-bit gates and describe the concepts behind the development of reversible gates (which happen to require gates with at least 3 bit-wide inputs and outputs), and describe popular 3-bit reversible logic gates.
Logic gates with three input bits and three output bits have a privileged position within fundamental computer science: they are a sufficient building block for constructing arbitrary reversible boolean networks and therefore are the key to reversible digital computers. Such computers can, in principle, operate without heat production. As there exist as many as 8! = 40,320 different 3-bit reversible truth tables, the question arises as to which ones to choose as building blocks. Because these gates form a group with respect to the operation "cascading" , we can apply group theoretical tools, in order to make such a choice.
Abstract — Reversible logic is one of the most vital issue at present time and it has different areas for its application, those are low power CMOS, quantum computing, nanotechnology, cryptography, optical computing, DNA computing, digital signal processing (DSP), quantum dot cellular automata, communication, computer graphics. It is not possible to realize quantum computing without implementation of reversible logic. The main purposes of designing reversible logic are to decrease quantum cost, depth of the circuits and the number of garbage outputs. This paper provides the basic reversible logic gates, which in designing of more complex system having reversible circuits as a primitive component and which can execute more complicated operations using quantum computers. The reversible circuits form the basic building block of quantum computers as all quantum operations are reversible. This paper presents the data relating to the primitive reversible gates which are available in literature and helps researches in designing higher complex computing circuits using reversible gates.
Reversible circuits play an important role in quantum computation. The realization of reversible quantum circuits is required for any quantum computer to be universal. This paper1studies the realization and synthesis problem of reversible circuits. Using group theory, we present two sets of new 3-bit reversible logic gates, which included g1g2g3and nine complex gates, respectively. It is shown that any 3-bit reversible logic circuit is realizable by cascading NOT and Feynman gates, and at most one instance of our proposed gates. Given any n-bit reversible function, there are N distinct input patterns different from their corresponding outputs, where N ≤ 2n, and the other (2n- N) input patterns will be the same as their outputs. According to a synthesis example, it demonstrates that the main results are constructive and practical than others.
Nowadays, reversible computing is more fascinative research area to curtail power dissipation in comparison of conventional computing. In conventional computing, logic circuit dissipates more power by losing bits of information. Reversible computing recovers from losing bits of information through same number of output vector from same number of input vector and thus decreases the power dissipation. Since there are different cost considerations such as garbage outputs, gate count, quantum cost methods for specific cost reductions may be established.
At present days , reversible logic circuits have many applications in the field of optical information processing, digital signal processing , nano technology and quantum computing . Reversible logic plays an important role when computations with minimum energy dissipation are considered. The purpose of designing reversible logic is to decrease the number of area, power, garbage outputs , constant inputs, quantum cost, reversible gates, delay and hardware complexity . This paper reveals a review on some reversible logic gates, which is useful in designing more complex systems having reversible circuits and can do execution of more complex operations using quantum computers. In upcoming days digital technology will be using reversible logic gates in order to reduce the propagation delay and power consumption as it provides negligible loss of information in the circuit. Keywords: Reversible Gate, Garbage output, quantum cost, Reversible logic, Power dissipation
Summary form only given, as follows. With the increasing emphasis on low-power design and quantum computation, research activities in the area of reversible logic synthesis and testing have gained momentum over the last couple of decades. It is expected that reversible logic will provide us with a viable alternative to building ultra-low power circuits and systems in not too distant future. In the classical works for synthesis of reversible circuits, gate libraries comprising of standard reversible gates like NOT, CNOT, TOFFOLI, FREDKIN, etc. are considered. To evaluate the goodness of a synthesized netlist, various metrics such as gate count, quantum cost, and equivalent transistor cost have been considered by various researchers. The synthesis approaches that have been reported can be broadly categorized into three groups: (a) exact synthesis approaches which try to obtain optimal reversible gate netlists, but can be used for small circuits only, (b) heuristic based approaches which try to utilize some domain knowledge intelligently to reduce the complexity of search, and can be used for somewhat larger circuits, and (c) synthesis approaches that rely on higher level functional representations like binary decision diagram (BDD) or exclusive sum-ofproducts (ESOP). The last approach is scalable to larger circuits (with 200 inputs or more), however, the synthesized netlist is not optimal and various rule-based heuristic approaches have been proposed to minimize the cost. There have been works also that report techniques for implementing sequential circuits with reversible properties, which will be useful for building complex systems containing finite-state machines. There are various transformations that are carried out as part of cryptographic algorithms that are inherently reversible in nature. For instance, any block cipher that uses a key K to transform a plaintext P into a ciphertext C during encryption must be reversible, because decryption will be doing just the reverse (C to P). Also, in standard symmetric block ciphers like DES or AES, there is a combinational block called substitution box or S-box which is also reversible in nature. In AES, the S-box has 8 inputs and 8 outputs, and implements a one-to-one onto mapping. The same reversibility requirements hold for stream ciphers and public-key ciphers like RSA. Although not much work has been carried out in the area of reversible implementations of cryptographic algorithms, this can be a very good area for future research. Similar considerations hold for various coding and decoding techniques used in communication, which are also inherently reversible in nature. Some examples of such coding/decoding are Manchester, Differential Manchester, Bipolar AMI, 4B/5B, 8B/10B, Hamming error correcting code, etc. All these techniques can potentially be implemented using reversible logic circuits. Specific case studies of some of the areas as mentioned will be reported, with synthesis results.