3,733 research outputs found
On the determination of near body orbits using mass concentration models
Mathematical model for near-body orbit calculation using mass concentration, perturbation theory, nonlinear equations, geopotentials, and least squares metho
Using Quantum Computers for Quantum Simulation
Numerical simulation of quantum systems is crucial to further our
understanding of natural phenomena. Many systems of key interest and
importance, in areas such as superconducting materials and quantum chemistry,
are thought to be described by models which we cannot solve with sufficient
accuracy, neither analytically nor numerically with classical computers. Using
a quantum computer to simulate such quantum systems has been viewed as a key
application of quantum computation from the very beginning of the field in the
1980s. Moreover, useful results beyond the reach of classical computation are
expected to be accessible with fewer than a hundred qubits, making quantum
simulation potentially one of the earliest practical applications of quantum
computers. In this paper we survey the theoretical and experimental development
of quantum simulation using quantum computers, from the first ideas to the
intense research efforts currently underway.Comment: 43 pages, 136 references, review article, v2 major revisions in
response to referee comments, v3 significant revisions, identical to
published version apart from format, ArXiv version has table of contents and
references in alphabetical orde
Universal quantum computation by discontinuous quantum walk
Quantum walks are the quantum-mechanical analog of random walks, in which a
quantum `walker' evolves between initial and final states by traversing the
edges of a graph, either in discrete steps from node to node or via continuous
evolution under the Hamiltonian furnished by the adjacency matrix of the graph.
We present a hybrid scheme for universal quantum computation in which a quantum
walker takes discrete steps of continuous evolution. This `discontinuous'
quantum walk employs perfect quantum state transfer between two nodes of
specific subgraphs chosen to implement a universal gate set, thereby ensuring
unitary evolution without requiring the introduction of an ancillary coin
space. The run time is linear in the number of simulated qubits and gates. The
scheme allows multiple runs of the algorithm to be executed almost
simultaneously by starting walkers one timestep apart.Comment: 7 pages, revte
A reconnaissance space sensing investigation of crustal structure for a strip from the eastern Sierra Nevada to the Colorado Plateau
There are no author-identified significant results in this report. Research progress in applications of ERTS-1 MSS imagery in study of Basin-Range tectonics is summarized. Field reconnaissance of ERTS-1 image anomalies has resulted in recognition of previously unreported fault zones and regional structural control of volcanic and plutonic activity. NIMBUS, Apollo 9, X-15, U-2, and SLAR imagery are discussed with specific applications, and methods of image enhancement and analysis employed in the research are summarized. Areas studied and methods employed in geologic field work are outlined
Distinguishing n Hamiltonians on C^n by a single measurement
If an experimentalist wants to decide which one of n possible Hamiltonians
acting on an n dimensional Hilbert space is present, he can conjugate the time
evolution by an appropriate sequence of known unitary transformations in such a
way that the different Hamiltonians result in mutual orthogonal final states.
We present a general scheme providing such a sequence.Comment: 4 pages, Revte
Noise resistance of adiabatic quantum computation using random matrix theory
Besides the traditional circuit-based model of quantum computation, several
quantum algorithms based on a continuous-time Hamiltonian evolution have
recently been introduced, including for instance continuous-time quantum walk
algorithms as well as adiabatic quantum algorithms. Unfortunately, very little
is known today on the behavior of these Hamiltonian algorithms in the presence
of noise. Here, we perform a fully analytical study of the resistance to noise
of these algorithms using perturbation theory combined with a theoretical noise
model based on random matrices drawn from the Gaussian Orthogonal Ensemble,
whose elements vary in time and form a stationary random process.Comment: 9 pages, 3 figure
Universal quantum computation using the discrete time quantum walk
A proof that continuous time quantum walks are universal for quantum
computation, using unweighted graphs of low degree, has recently been presented
by Childs [PRL 102 180501 (2009)]. We present a version based instead on the
discrete time quantum walk. We show the discrete time quantum walk is able to
implement the same universal gate set and thus both discrete and continuous
time quantum walks are computational primitives. Additionally we give a set of
components on which the discrete time quantum walk provides perfect state
transfer.Comment: 9 pages, 10 figures. Updated after referee comments - Section V
expanded and minor changes to other parts of the tex
Optimal state encoding for quantum walks and quantum communication over spin systems
Recent work has shown that a simple chain of interacting spins can be used as
a medium for high-fidelity quantum communication. We describe a scheme for
quantum communication using a spin system that conserves z-spin, but otherwise
is arbitrary. The sender and receiver are assumed to directly control several
spins each, with the sender encoding the message state onto the larger
state-space of her control spins. We show how to find the encoding that
maximises the fidelity of communication, using a simple method based on the
singular-value decomposition. Also, we show that this solution can be used to
increase communication fidelity in a rather different circumstance: where no
encoding of initial states is used, but where the sender and receiver control
exactly two spins each and vary the interactions on those spins over time. The
methods presented are computationally efficient, and numerical examples are
given for systems having up to 300 spins.Comment: 10 pages, LaTeX, 7 EPS figures. Corrected an error in the definition
and interpretation of C_B(T
Dynamic settling of particles in shear flows of shear-thinning fluids
Dynamic settling is the phenomenon whereby a relatively dense particle settles through a sheared flow of a non-Newtonian fluid at a speed that depends on the shear rate of the background flow. This means that due to the non-linear rheology, the settling velocity may vary spatially and temporally as the background shear rate of the suspending fluid varies, an effect which does not occur in Newtonian fluids. In this contribution, the consequences of this dependency are explored for a dilute suspension of particles released uniformly from a source in a sustained and externally-driven flow of shear-thinning fluid. It is shown theoretically that the concentration field does not remain uniform, but evolves downstream, allowing calculation of the runout length, settling times and distribution of the deposited particles. Flows with a velocity maximum are demonstrated to affect the concentration field very strongly as they develop a âkinematic barrierâ over which settling times are considerably lengthened. Flows with bidisperse suspensions are shown to produce deposits that vary non-monotonically in thickness and composition with distance downstream, an effect which is solely due to dynamic settling. Finally flows of viscoplastic fluids which exhibit yielded and unyielded regions may accentuate the role and effects of the kinematic barrier to settling
Decoherence and Quantum Walks: anomalous diffusion and ballistic tails
The common perception is that strong coupling to the environment will always
render the evolution of the system density matrix quasi-classical (in fact,
diffusive) in the long time limit. We present here a counter-example, in which
a particle makes quantum transitions between the sites of a d-dimensional
hypercubic lattice whilst strongly coupled to a bath of two-level systems which
'record' the transitions. The long-time evolution of an initial wave packet
is found to be most unusual: the mean square displacement of the particle
density matrix shows long-range ballitic behaviour, but simultaneously a kind
of weakly-localised behaviour near the origin. This result may have important
implications for the design of quantum computing algorithms, since it describes
a class of quantum walks.Comment: 4 pages, 1 figur
- âŠ