155 research outputs found
QuOp_MPI: a framework for parallel simulation of quantum variational algorithms
QuOp_MPI is a Python package designed for parallel simulation of quantum
variational algorithms. It presents an object-orientated approach to quantum
variational algorithm design and utilises MPI-parallelised sparse-matrix
exponentiation, the fast Fourier transform and parallel gradient evaluation to
achieve the highly efficient simulation of the fundamental unitary dynamics on
massively parallel systems. In this article, we introduce QuOp_MPI and explore
its application to the simulation of quantum algorithms designed to solve
combinatorial optimisation algorithms including the Quantum Approximation
Optimisation Algorithm, the Quantum Alternating Operator Ansatz, and the
Quantum Walk-assisted Optimisation Algorithm.Comment: Software available at: https://github.com/Edric-Matwiejew/QuOp_MP
Quantum walk-based search and centrality
We study the discrete-time quantum walk-based search for a marked vertex on a
graph. By considering various structures in which not all vertices are
equivalent, we investigate the relationship between the successful search
probability and the position of the marked vertex, in particular its
centrality. We find that the maximum value of the search probability does not
necessarily increase as the marked vertex becomes more central and we
investigate an interesting relationship between the frequency of the successful
search probability and the centrality of the marked vertex.Comment: 29 pages, 17 figure
Orbital Expansion Variational Quantum Eigensolver: Enabling Efficient Simulation of Molecules with Shallow Quantum Circuit
In the noisy-intermediate-scale-quantum era, Variational Quantum Eigensolver
(VQE) is a promising method to study ground state properties in quantum
chemistry, materials science, and condensed physics. However, general quantum
eigensolvers are lack of systematical improvability, and achieve rigorous
convergence is generally hard in practice, especially in solving
strong-correlated systems. Here, we propose an Orbital Expansion VQE~(OE-VQE)
framework to construct an efficient convergence path. The path starts from a
highly correlated compact active space and rapidly expands and converges to the
ground state, enabling simulating ground states with much shallower quantum
circuits. We benchmark the OE-VQE on a series of typical molecules including
H-chain, H-ring and N, and the simulation results show that
proposed convergence paths dramatically enhance the performance of general
quantum eigensolvers.Comment: Wu et al 2023 Quantum Sci. Techno
Trainability Analysis of Quantum Optimization Algorithms from a Bayesian Lens
The Quantum Approximate Optimization Algorithm (QAOA) is an extensively
studied variational quantum algorithm utilized for solving optimization
problems on near-term quantum devices. A significant focus is placed on
determining the effectiveness of training the -qubit QAOA circuit, i.e.,
whether the optimization error can converge to a constant level as the number
of optimization iterations scales polynomially with the number of qubits. In
realistic scenarios, the landscape of the corresponding QAOA objective function
is generally non-convex and contains numerous local optima. In this work,
motivated by the favorable performance of Bayesian optimization in handling
non-convex functions, we theoretically investigate the trainability of the QAOA
circuit through the lens of the Bayesian approach. This lens considers the
corresponding QAOA objective function as a sample drawn from a specific
Gaussian process. Specifically, we focus on two scenarios: the noiseless QAOA
circuit and the noisy QAOA circuit subjected to local Pauli channels. Our first
result demonstrates that the noiseless QAOA circuit with a depth of
can be trained efficiently,
based on the widely accepted assumption that either the left or right slice of
each block in the circuit forms a local 1-design. Furthermore, we show that if
each quantum gate is affected by a -strength local Pauli channel with the
noise strength range of to 0.1, the noisy QAOA circuit with
a depth of can also be trained
efficiently. Our results offer valuable insights into the theoretical
performance of quantum optimization algorithms in the noisy intermediate-scale
quantum era
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Spectroscopic properties of colloidal indium phosphide quantum wires
Colloidal InP quantum wires are grown by the solution-liquid-solid (SLS) method, and passivated with the traditional quantum dots surfactants 1-hexadecylamine and tri-n-octylphosphine oxide. The size dependence of the band gaps in the wires are determined from the absorption spectra, and compared to other experimental results for InP quantum dots and wires, and to the predictions of theory. The photoluminescence behavior of the wires is also investigated. Efforts to enhance photoluminescence efficiencies through photochemical etching in the presence of HF result only in photochemical thinning or photo-oxidation, without a significant influence on quantum-wire photoluminescence. However, photo-oxidation produces residual dot and rod domains within the wires, which are luminescent. The results establish that the quantum-wire band gaps are weakly influenced by the nature of the surface passivation, and that colloidal quantum wires have intrinsically low photoluminescence efficiencies
Recent glitches detected in the Crab pulsar
From 2000 to 2010, monitoring of radio emission from the Crab pulsar at
Xinjiang Observatory detected a total of nine glitches. The occurrence of
glitches appears to be a random process as described by previous researches. A
persistent change in pulse frequency and pulse frequency derivative after each
glitch was found. There is no obvious correlation between glitch sizes and the
time since last glitch. For these glitches and
span two orders of magnitude. The pulsar suffered the
largest frequency jump ever seen on MJD 53067.1. The size of the glitch is
6.8 Hz, 3.5 times that of the glitch occured in
1989 glitch, with a very large permanent changes in frequency and pulse
frequency derivative and followed by a decay with time constant 21 days.
The braking index presents significant changes. We attribute this variation to
a varying particle wind strength which may be caused by glitch activities. We
discuss the properties of detected glitches in Crab pulsar and compare them
with glitches in the Vela pulsar.Comment: Accepted for publication in Astrophysics & Space Scienc
Precision orbital dynamics from interstellar scintillation arcs for PSR J0437-4715
Intensity scintillations of radio pulsars are known to originate from
interference between waves scattered by the electron density irregularities of
interstellar plasma, often leading to parabolic arcs in the two-dimensional
power spectrum of the recorded dynamic spectrum. The degree of arc curvature
depends on the distance to the scattering plasma and its transverse velocity
with respect to the line-of-sight. We report the observation of annual and
orbital variations in the curvature of scintillation arcs over a period of 16
years for the bright millisecond pulsar, PSR J0437-4715. These variations are
the signature of the relative transverse motions of the Earth, pulsar, and
scattering medium, which we model to obtain precise measurements of parameters
of the pulsar's binary orbit and the scattering medium itself. We observe two
clear scintillation arcs in most of our 5000 observations and we show that
they originate from scattering by thin screens located at distances pc and pc from Earth. The best-fit scattering model
we derive for the brightest arc yields the pulsar's orbital inclination angle
, and longitude of ascending node,
. Using scintillation arcs for precise astrometry and
orbital dynamics can be superior to modelling variations in the diffractive
scintillation timescale, because the arc curvature is independent of variations
in the level of turbulence of interstellar plasma. This technique can be used
in combination with pulsar timing to determine the full three-dimensional
orbital geometries of binary pulsars, and provides parameters essential for
testing theories of gravity and constraining neutron star masses.Comment: 19 pages, 10 figures. Accepted for publication in Ap
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