1,668 research outputs found
Low-noise conditional operation of singlet-triplet coupled quantum dot qubits
We theoretically study the influence of charge noise on a controlled phase
gate, implemented using two proximal double quantum dots coupled
electrostatically. Using the configuration interaction method, we present a
full description of the conditional control scheme and quantitatively calculate
the gate error arising from charge fluctuations. Our key finding is that the
existence of noise-immune sweet spots depends on not only the energy detuning
but also the device geometry. The conditions for sweet spots with minimal
charge noise are predicted analytically and verified numerically. Going beyond
the simple sweet-spot concept we demonstrate the existence of other optimal
situations for fast and low-noise singlet-triplet two-qubit gates.Comment: 4 pages, 4 figure
Topological flat band models with arbitrary Chern numbers
We report the theoretical discovery of a systematic scheme to produce
topological flat bands (TFBs) with arbitrary Chern numbers. We find that
generically a multi-orbital high Chern number TFB model can be constructed by
considering multi-layer Chern number C=1 TFB models with enhanced translational
symmetry. A series of models are presented as examples, including a two-band
model on a triangular lattice with a Chern number C=3 and an -band square
lattice model with for an arbitrary integer . In all these models, the
flatness ratio for the TFBs is larger than 30 and increases with increasing
Chern number. In the presence of appropriate inter-particle interactions, these
models are likely to lead to the formation of novel Abelian and Non-Abelian
fractional Chern insulators. As a simple example, we test the C=2 model with
hardcore bosons at 1/3 filling and an intriguing fractional quantum Hall state
is observed.Comment: 8 pages, 7 figure
Quantum theory of the charge stability diagram of semiconductor double quantum dot systems
We complete our recently introduced theoretical framework treating the double
quantum dot system with a generalized form of Hubbard model. The effects of all
quantum parameters involved in our model on the charge stability diagram are
discussed in detail. A general formulation of the microscopic theory is
presented, and truncating at one orbital per site, we study the implication of
different choices of the model confinement potential on the Hubbard parameters
as well as the charge stability diagram. We calculate the charge stability
diagram keeping three orbitals per site and find that the effect of additional
higher-lying orbitals on the subspace with lowest-energy orbitals only can be
regarded as a small renormalization of Hubbard parameters, thereby justifying
our practice of keeping only the lowest-orbital in all other calculations. The
role of the harmonic oscillator frequency in the implementation of the Gaussian
model potential is discussed, and the effect of an external magnetic field is
identified to be similar to choosing a more localized electron wave function in
microscopic calculations. The full matrix form of the Hamiltonian including all
possible exchange terms, and several peculiar charge stability diagrams due to
unphysical parameters are presented in the appendix, thus emphasizing the
critical importance of a reliable microscopic model in obtaining the system
parameters defining the Hamiltonian.Comment: 19 pages, 15 figure
Scalable High-Dimensional Multivariate Linear Regression for Feature-Distributed Data
Feature-distributed data, referred to data partitioned by features and stored
across multiple computing nodes, are increasingly common in applications with a
large number of features. This paper proposes a two-stage relaxed greedy
algorithm (TSRGA) for applying multivariate linear regression to such data. The
main advantage of TSRGA is that its communication complexity does not depend on
the feature dimension, making it highly scalable to very large data sets. In
addition, for multivariate response variables, TSRGA can be used to yield
low-rank coefficient estimates. The fast convergence of TSRGA is validated by
simulation experiments. Finally, we apply the proposed TSRGA in a financial
application that leverages unstructured data from the 10-K reports,
demonstrating its usefulness in applications with many dense large-dimensional
matrices
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