Reversibility and irreversibility in quantum computational logics

María Luisa Dalla Chiara, Roberto Giuntini, Roberto Leporini

Naoki Takeuchi, Yuki Yamanashi, Nobuyuki Yoshikawa

Reversible computing is considered to be a key technology to achieve an extremely high energy efficiency in future computers. In this study, we investigated the relationship between reversibility and energy dissipation in adiabatic superconductor logic. We analyzed the evolution of phase differences of Josephson junctions in the reversible quantum-flux-parametron (RQFP) gate and confirmed that the phase differences can change time reversibly, which indicates that the RQFP gate is physically, as well as logically, reversible. We calculated energy dissipation required for the RQFP gate to perform a logic operation and numerically demonstrated that the energy dissipation can fall below the thermal limit, or the Landauer bound, by lowering operation frequencies. We also investigated the 1-bit-erasure gate as a logically irreversible gate and the quasi-RQFP gate as a physically irreversible gate. We calculated the energy dissipation of these irreversible gates and showed that the energy dissipation of these gate is dominated by non-adiabatic state changes, which are induced by unwanted interactions between gates due to logical or physical irreversibility. Our results show that, in reversible computing using adiabatic superconductor logic, logical and physical reversibility are required to achieve energy dissipation smaller than the Landauer bound without non-adiabatic processes caused by gate interactions.

Giuseppe Sergioli

H. R. Bhagyalakshmi, M.K. Venkatesha

The power dissipation problems which occur in the computational operations of a computer can be avoided by replacing the irreversible structures by reversible structures. The reversible logic gates are used for the construction of important arithmetic and logic units of quantum computers. This has led many researchers to take reversible logic very seriously. In this proposal a new reversible logic gate called BVMF gate is designed which is useful for the realization of multi functions required for building important computational blocks of quantum computers. General Terms Reversible logic circuits, Quantum computers

Mika Hirvensalo

Antonio Zecca A