Reversible logic gate using adiabatic superconducting devices

Abstract

Reversible computing has been studied since Rolf Landauer advanced the argument that has come to be known as Landauer's principle. This principle states that there is no minimum energy dissipation for logic operations in reversible computing, because it is not accompanied by reductions in information entropy. However, until now, no practical reversible logic gates have been demonstrated. One of the problems is that reversible logic gates must be built by using extremely energy-efficient logic devices. Another difficulty is that reversible logic gates must be both logically and physically reversible. Here we propose the first practical reversible logic gate using adiabatic superconducting devices and experimentally demonstrate the logical and physical reversibility of the gate. Additionally, we estimate the energy dissipation of the gate, and discuss the minimum energy dissipation required for reversible logic operations. It is expected that the results of this study will enable reversible computing to move from the theoretical stage into practical usage.

Recent Progress on Reversible Quantum-Flux-Parametron for Superconductor Reversible Computing

“…In order to design RQFP-based circuits, we need a cell library including both RQFP cells and AQFP logic cells, as it is possible that we will combine RQFP cells with basic AQFP logic cells, such as buffers (BUFs) and inverters. In a previous study [10], we fabricated RQFP cells using the AIST 2.5 kA/cm 2 standard process (STP2) [32] and demonstrated their correct logic operations, where the RQFP cells were driven by threephase excitation currents. However, the previously designed RQFP cell is not compatible with the current AQFP logic cells due to the difference in fabrication processes and excitation schemes; the latest AQFP cells are designed and fabricated using the AIST 10 kA/cm 2 high-speed standard process (HSTP) [24], and they are driven by the four-phase excitation mode using a pair of ac excitation currents and a dc-offset current [24].…”

“…The layout of the RQFP cell was designed using an inductance extraction tool, InductEx [33], [34]. The dimension of the RQFP cell is 180 μm × 145 μm, which is only 36% of that of the original design (270 μm × 270 μm) [10]. Further miniaturization might be possible by using a three-dimensional fabrication process [35].…”

“…The outputs of RQFP are given by x = ¬ab + bc + c¬a, y = a¬b + ¬bc + ca, and z = ab + b¬c + ¬ca, where a, b, and c are the inputs. From the truth table [10], it is obvious that RQFP is bijective or logically reversible. Since the schematic of the SPL gates (Gates A through C) is the same as that of the MAJ gates (Gates X through Z), RQFP is symmetrical and can perform logic operations bi-directionally.…”

“…In a previous study [10], we proposed a superconductor reversible logic gate using adiabatic quantum-fluxparametron (AQFP) [11], which is an adiabatic superconManuscript received September 28, 2017. Manuscript revised January 9, 2018.…”

“…In Chapter 2, we explain briefly the operation principle of AQFP and adiabatic switching. In Chapters 3 and 4, based on our previous studies [10], [14], we review the difference between irreversible logic gates and RQFP in light of time evolution and energy dissipation using numerical calculation. We show that RQFP is thermodynamically, as well as logically, reversible.…”