61,622 research outputs found
Coherent Imaging Spectroscopy of a Quantum Many-Body Spin System
Quantum simulators, in which well controlled quantum systems are used to
reproduce the dynamics of less understood ones, have the potential to explore
physics that is inaccessible to modeling with classical computers. However,
checking the results of such simulations will also become classically
intractable as system sizes increase. In this work, we introduce and implement
a coherent imaging spectroscopic technique to validate a quantum simulation,
much as magnetic resonance imaging exposes structure in condensed matter. We
use this method to determine the energy levels and interaction strengths of a
fully-connected quantum many-body system. Additionally, we directly measure the
size of the critical energy gap near a quantum phase transition. We expect this
general technique to become an important verification tool for quantum
simulators once experiments advance beyond proof-of-principle demonstrations
and exceed the resources of conventional computers
Highly frustrated spin-lattice models of magnetism and their quantum phase transitions: A microscopic treatment via the coupled cluster method
We outline how the coupled cluster method of microscopic quantum many-body
theory can be utilized in practice to give highly accurate results for the
ground-state properties of a wide variety of highly frustrated and strongly
correlated spin-lattice models of interest in quantum magnetism, including
their quantum phase transitions. The method itself is described, and it is
shown how it may be implemented in practice to high orders in a systematically
improvable hierarchy of (so-called LSUB) approximations, by the use of
computer-algebraic techniques. The method works from the outset in the
thermodynamic limit of an infinite lattice at all levels of approximation, and
it is shown both how the "raw" LSUB results are themselves generally
excellent in the sense that they converge rapidly, and how they may accurately
be extrapolated to the exact limit, , of the truncation
index , which denotes the {\it only} approximation made. All of this is
illustrated via a specific application to a two-dimensional, frustrated,
spin-half -- model on a honeycomb lattice with
nearest-neighbor and next-nearest-neighbor interactions with exchange couplings
and , respectively, where both
interactions are of the same anisotropic type. We show how the method can
be used to determine the entire zero-temperature ground-state phase diagram of
the model in the range of the frustration parameter and
of the spin-space anisotropy parameter. In particular,
we identify a candidate quantum spin-liquid region in the phase space
Dynamics in the Sherrington-Kirkpatrick Ising spin glass at and above Tg
A detailed numerical study is made of relaxation at equilibrium in the
Sherrington-Kirkpatrick Ising spin glass model, at and above the critical
temperature Tg. The data show a long time stretched exponential relaxation q(t)
~ exp[-(t/tau(T))^beta(T)] with an exponent beta(T) tending to ~ 1/3 at Tg. The
results are compared to those which were observed by Ogielski in the 3d ISG
model, and are discussed in terms of a phase space percolation transition
scenario.Comment: 6 pages, 7 figure
Spin-1/2 - Heisenberg model on a cross-striped square lattice
Using the coupled cluster method (CCM) we study the full (zero-temperature)
ground-state (GS) phase diagram of a spin-half () -
Heisenberg model on a cross-striped square lattice. Each site of the square
lattice has 4 nearest-neighbour exchange bonds of strength and 2
next-nearest-neighbour (diagonal) bonds of strength . The bonds
are arranged so that the basic square plaquettes in alternating columns have
either both or no bonds included. The classical () version of the model has 4 collinear phases when and
can take either sign. Three phases are antiferromagnetic (AFM), showing
so-called N\'{e}el, double N\'{e}el and double columnar striped order
respectively, while the fourth is ferromagnetic. For the quantum model
we use the 3 classical AFM phases as CCM reference states, on top of which the
multispin-flip configurations arising from quantum fluctuations are
incorporated in a systematic truncation hierarchy. Calculations of the
corresponding GS energy, magnetic order parameter and the susceptibilities of
the states to various forms of valence-bond crystalline (VBC) order are thus
carried out numerically to high orders of approximation and then extrapolated
to the (exact) physical limit. We find that the model has 5 phases,
which correspond to the four classical phases plus a new quantum phase with
plaquette VBC order. The positions of the 5 quantum critical points are
determined with high accuracy. While all 4 phase transitions in the classical
model are first order, we find strong evidence that 3 of the 5 quantum phase
transitions in the model are of continuous deconfined type
A frustrated spin-1/2 Heisenberg antiferromagnet on a chevron-square lattice
The coupled cluster method (CCM) is used to study the zero-temperature
properties of a frustrated spin-half () -- Heisenberg
antiferromagnet (HAF) on a 2D chevron-square lattice. Each site on an
underlying square lattice has 4 nearest-neighbor exchange bonds of strength
and 2 next-nearest-neighbor (diagonal) bonds of strength , with each square plaquette having only one diagonal bond.
The diagonal bonds form a chevron pattern, and the model thus interpolates
smoothly between 2D HAFs on the square () and triangular () lattices,
and also extrapolates to disconnected 1D HAF chains (). The
classical () version of the model has N\'{e}el order for and a form of spiral order for , where
. For the model we use both these classical
states, as well as other collinear states not realized as classical
ground-state (GS) phases, as CCM reference states, on top of which the
multispin-flip configurations resulting from quantum fluctuations are
incorporated in a systematic truncation scheme, which we carry out to high
orders and extrapolate to the physical limit. We calculate the GS energy, GS
magnetic order parameter, and the susceptibilities of the states to various
forms of valence-bond crystalline (VBC) order, including plaquette and two
different dimer forms. We find that the model has two quantum
critical points, at and ,
with N\'{e}el order for , a form of spiral order for
that includes the correct three-sublattice
spin ordering for the triangular-lattice HAF at , and
parallel-dimer VBC order for
Bethe ansatz solution of an integrable, non-Abelian anyon chain with D(D_3) symmetry
The exact solution for the energy spectrum of a one-dimensional Hamiltonian
with local two-site interactions and periodic boundary conditions is
determined. The two-site Hamiltonians commute with the symmetry algebra given
by the Drinfeld double D(D_3) of the dihedral group D_3. As such the model
describes local interactions between non-Abelian anyons, with fusion rules
given by the tensor product decompositions of the irreducible representations
of D(D_3). The Bethe ansatz equations which characterise the exact solution are
found through the use of functional relations satisfied by a set of mutually
commuting transfer matrices.Comment: 19 page
Time- and frequency-domain polariton interference
We present experimental observations of interference between an atomic spin
coherence and an optical field in a {\Lambda}-type gradient echo memory. The
interference is mediated by a strong classical field that couples a weak probe
field to the atomic coherence through a resonant Raman transition. Interference
can be observed between a prepared spin coherence and another propagating
optical field, or between multiple {\Lambda} transitions driving a single spin
coherence. In principle, the interference in each scheme can yield a near unity
visibility.Comment: 11 pages, 5 figure
Three field tests of a gas filter correlation radiometer
Test flights to remotely measure nonurban carbon monoxide (CO) concentrations by gas filter correlation radiometry are discussed. The inferred CO concentrations obtained through use of the Gas Filter Correlation Radiometer (GFCR) agreed with independent measurements obtained by gas chromatography air sample bottle analysis to within 20 percent. The equipment flown on board the aircraft, the flight test procedure, the gas chromatograph direct air sampling procedure, and the GFCR data analysis procedure are reported
Computer and photogrammetric general land use study of central north Alabama
The object of this report is to acquaint potential users with two computer programs, developed at NASA, Marshall Space Flight Center. They were used in producing a land use survey and maps of central north Alabama from Earth Resources Technology Satellite (ERTS) digital data. The report describes in detail the thought processes and analysis procedures used from the initiation of the land use study to its completion, as well as a photogrammetric study that was used in conjunction with the computer analysis to produce similar land use maps. The results of the land use demonstration indicate that, with respect to computer time and cost, such a study may be economically and realistically feasible on a statewide basis
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