1,927 research outputs found
Entanglement loss in molecular quantum-dot qubits due to interaction with the environment
We study quantum entanglement loss due to environmental interaction in a
condensed matter system with a complex geometry relevant to recent proposals
for computing with single electrons at the nanoscale. We consider a system
consisting of two qubits, each realized by an electron in a double quantum dot,
which are initially in an entangled Bell state. The qubits are widely separated
and each interacts with its own environment. The environment for each is
modeled by surrounding double quantum dots placed at random positions with
random orientations. We calculate the unitary evolution of the joint system and
environment. The global state remains pure throughout. We examine the time
dependence of the expectation value of the bipartite Clauser-Horne-Shimony-Holt
(CHSH) and Brukner-Paunkovi\'c-Rudolph-Vedral (BPRV) Bell operators and explore
the emergence of correlations consistent with local realism. Though the details
of this transition depend on the specific environmental geometry, we show how
the results can be mapped on to a universal behavior with appropriate scaling.
We determine the relevant disentanglement times based on realistic physical
parameters for molecular double-dots.Comment: 14 pages, 3 figure
Quasi-adiabatic Switching for Metal-Island Quantum-dot Cellular Automata
Recent experiments have demonstrated a working cell suitable for implementing
the Quantum-dot Cellular Automata (QCA) paradigm. These experiments have been
performed using metal island clusters. The most promising approach to QCA
operation involves quasi-adiabatically switching the cells. This has been
analyzed extensively in gated semiconductor cells. Here we present a metal
island cell structure that makes quasi-adiabatic switching possible. We show
how this permits quasi-adiabatic clocking, and enables a pipelined
architecture.Comment: 40 preprint-style double-spaced pages including 16 figure
Ratchet Cellular Automata for Colloids in Dynamic Traps
We numerically investigate the transport of kinks in a ratchet cellular
automata geometry for colloids interacting with dynamical traps. We find that
thermal effects can enhance the transport efficiency in agreement with recent
experiments. At high temperatures we observe the creation and annihilation of
thermally induced kinks that degrade the signal transmission. We consider both
the deterministic and stochastic cases and show how the trap geometry can be
adjusted to switch between these two cases. The operation of the dynamical trap
geometry can be achieved with the adjustment of fewer parameters than ratchet
cellular automata constructed using static traps.Comment: 7 pages, 5 postscript figure
Introduction to the Special Section on Nano Systems and Computing
It is with great pleasure that we introduce the special section on Nano Systems and Computing to the readership of the IEEE Transactions on Computers. This special section consists of five papers that have been selected to cover a wide spectrum of techniques which are encountered in the design of nano-scale computing systems
Quantum dynamics, dissipation, and asymmetry effects in quantum dot arrays
We study the role of dissipation and structural defects on the time evolution
of quantum dot arrays with mobile charges under external driving fields. These
structures, proposed as quantum dot cellular automata, exhibit interesting
quantum dynamics which we describe in terms of equations of motion for the
density matrix. Using an open system approach, we study the role of asymmetries
and the microscopic electron-phonon interaction on the general dynamical
behavior of the charge distribution (polarization) of such systems. We find
that the system response to the driving field is improved at low temperatures
(and/or weak phonon coupling), before deteriorating as temperature and
asymmetry increase. In addition to the study of the time evolution of
polarization, we explore the linear entropy of the system in order to gain
further insights into the competition between coherent evolution and
dissipative processes.Comment: 11pages,9 figures(eps), submitted to PR
Quantum Cellular Neural Networks
We have previously proposed a way of using coupled quantum dots to construct
digital computing elements - quantum-dot cellular automata (QCA). Here we
consider a different approach to using coupled quantum-dot cells in an
architecture which, rather that reproducing Boolean logic, uses a physical
near-neighbor connectivity to construct an analog Cellular Neural Network
(CNN).Comment: 7 pages including 3 figure
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