Matrix multiplication using quantum-dot cellular automata to implement conventional microelectronics

Quantum-dot cellular automata (QCA) shows promise as a post silicon CMOS, low power computational technology. Nevertheless, to generalize QCA for next-generation digital devices, the ability to implement conventional programmable circuits based on NOR, AND, and OR gates is necessary. To this end, we devise a new QCA structure, the QCA matrix multiplier (MM), employing the standard Coulomb blocked, five quantum dot (QD) QCA cell and quasi-adiabatic switching for sequential data latching in the QCA cells. Our structure can multiply two N x M matrices, using one input and one bidirectional input/output data line. The calculation is highly parallelizable, and it is possible to achieve reduced calculation time in exchange for increasing numbers of parallel matrix multiplier units. We show convergent, ab initio simulation results using the Intercellular Hartree Approximation for one, three, and nine matrix multiplier units. The structure can generally implement any programmable logic array (PLA) or any matrix multiplication based operation.Comment: 14 pages, 9 figures, supplemental informatio

Cellular Structures for Computation in the Quantum Regime

We present a new cellular data processing scheme, a hybrid of existing cellular automata (CA) and gate array architectures, which is optimized for realization at the quantum scale. For conventional computing, the CA-like external clocking avoids the time-scale problems associated with ground-state relaxation schemes. For quantum computing, the architecture constitutes a novel paradigm whereby the algorithm is embedded in spatial, as opposed to temporal, structure. The architecture can be exploited to produce highly efficient algorithms: for example, a list of length N can be searched in time of order cube root N.Comment: 11 pages (LaTeX), 3 figure

Ground State Quantum Computation

We formulate a novel ground state quantum computation approach that requires no unitary evolution of qubits in time: the qubits are fixed in stationary states of the Hamiltonian. This formulation supplies a completely time-independent approach to realizing quantum computers. We give a concrete suggestion for a ground state quantum computer involving linked quantum dots.Comment: 4 pages, 2 figure

Flat-band ferromagnetism in quantum dot superlattices

Possibility of flat-band ferromagnetism in quantum dot arrays is theoretically discussed. By using a quantum dot as a building block, quantum dot superlattices are possible. We consider dot arrays on Lieb and kagome lattices known to exhibit flat band ferromagnetism. By performing an exact diagonalization of the Hubbard Hamiltonian, we calculate the energy difference between the ferromagnetic ground state and the paramagnetic excited state, and discuss the stability of the ferromagnetism against the second nearest neighbor transfer. We calculate the dot-size dependence of the energy difference in a dot model and estimate the transition temperature of the ferromagnetic-paramagnetic transition which is found to be accessible within the present fabrication technology. We point out advantages of semiconductor ferromagnets and suggest other interesting possibilities of electronic properties in quantum dot superlattices.Comment: 15 pages, 7 figures (low resolution). High-resolution figures are available at http://www.brl.ntt.co.jp/people/tamura/Research/PublicationPapers.htm

An Integrated Computer Architecture Experience

This paper presents a collaborative effort to combine a computer architecture lecture course wish a computer topics laboratory. This integrated course provided the students with an opportunity To apply VHDL modeling to semester-long projects that illustrated many of the points learned in the lecture course. It also gave the students an opportunity to see the same material from two different perspectives, and increased teamwork skills of both the students and the faculty members involved

Stray Charge in Quantum-dot Cellular Automata: A Validation of the Intercellular Hartree Approximation

The authors analyze the effect of stray charges near a line of quantum-dot cellular automata (QCA) cells. Considering both the ground-state polarization and the excitation energy of the system, it is determined that there is a 129-nm-wide region surrounding a QCA wire where a stray charge will cause the wire to fail. This calculation is the result of a full-basis-set simulation of a four-cell line. A comparison is made between cells with parallel-spin electrons and those with antiparallel spin electrons, showing that they yield essentially identical results. Therefore, the added complexity of accounting for antiparallel spins does not yield superior simulation results. Finally, a comparison is made between the full-basis calculations and the results of the same calculation using the intercellular Hartree approximation (ICHA). The similarity of these two results demonstrates that the ICHA method is a valid tool for studying the effect of stray charges in larger systems