795 research outputs found
Conformal Field Theory on the Fermi Surface
The Fermi surface may be usefully viewed as a collection of 1+1 dimensional
chiral conformal field theories. This approach permits straightforward
calculation of many anomalous ground state properties of the Fermi gas
including entanglement entropy and number fluctuations. The 1+1 dimensional
picture also generalizes to finite temperature and the presence of
interactions. Finally, I argue that the low energy entanglement structure of
Fermi liquid theory is universal, depending only on the geometry of the
interacting Fermi surface.Comment: 4 pages + references, 2 figure
Oscillating terms in the Renyi entropy of Fermi liquids
In this work we compute subleading oscillating terms in the Renyi entropy of
Fermi gases and Fermi liquids corresponding to -like oscillations. Our
theoretical tools are the one dimensional formulation of Fermi liquid
entanglement familiar from discussions of the logarithmic violation of the area
law and quantum Monte Carlo calculations. The main result is a formula for the
oscillating term for any region geometry and a spherical Fermi surface. We
compare this term to numerical calculations of entanglement using the
correlation function method and find excellent agreement. We also compare with
quantum Monte Carlo data on interacting Fermi liquids where we also find
excellent agreement up to moderate interaction strengths.Comment: 8 pages, 2 figure
Non-Abelian statistics versus the Witten anomaly
This paper is motivated by prospects for non-Abelian statistics of deconfined
particle-like objects in 3+1 dimensions, realized as solitons with localized
Majorana zeromodes. To this end, we study the fermionic collective coordinates
of magnetic monopoles in 3+1 dimensional spontaneously-broken SU(2) gauge
theories with various spectra of fermions. We argue that a single Majorana
zeromode of the monopole is not compatible with cancellation of the Witten
SU(2) anomaly. We also compare this approach with other attempts to realize
deconfined non-Abelian objects in 3+1 dimensions.Comment: 11 pages, 3 figures; v2: added refs, minor corrections, published
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Correlated Topological Insulators and the Fractional Magnetoelectric Effect
Topological insulators are characterized by the presence of gapless surface
modes protected by time-reversal symmetry. In three space dimensions the
magnetoelectric response is described in terms of a bulk theta term for the
electromagnetic field. Here we construct theoretical examples of such phases
that cannot be smoothly connected to any band insulator. Such correlated
topological insulators admit the possibility of fractional magnetoelectric
response described by fractional theta/pi. We show that fractional theta/pi is
only possible in a gapped time reversal invariant system of bosons or fermions
if the system also has deconfined fractional excitations and associated
degenerate ground states on topologically non-trivial spaces. We illustrate
this result with a concrete example of a time reversal symmetric topological
insulator of correlated bosons with theta = pi/4. Extensions to electronic
fractional topological insulators are briefly described.Comment: 4 pages + ref
Apollo experience report guidance and control systems: Primary guidance, navigation, and control system development
The primary guidance, navigation, and control systems for both the lunar module and the command module are described. Development of the Apollo primary guidance systems is traced from adaptation of the Polaris Mark II system through evolution from Block I to Block II configurations; the discussion includes design concepts used, test and qualification programs performed, and major problems encountered. The major subsystems (inertial, computer, and optical) are covered. Separate sections on the inertial components (gyroscopes and accelerometers) are presented because these components represent a major contribution to the success of the primary guidance, navigation, and control system
Entanglement Renormalization and Holography
I show how recent progress in real space renormalization group methods can be
used to define a generalized notion of holography inspired by holographic
dualities in quantum gravity. The generalization is based upon organizing
information in a quantum state in terms of scale and defining a higher
dimensional geometry from this structure. While states with a finite
correlation length typically give simple geometries, the state at a quantum
critical point gives a discrete version of anti de Sitter space. Some finite
temperature quantum states include black hole-like objects. The gross features
of equal time correlation functions are also reproduced in this geometric
framework. The relationship between this framework and better understood
versions of holography is discussed.Comment: 15 pages, 5 figure
The Gravity Dual of a Density Matrix
For a state in a quantum field theory on some spacetime, we can associate a
density matrix to any subset of a given spacelike slice by tracing out the
remaining degrees of freedom. In the context of the AdS/CFT correspondence, if
the original state has a dual bulk spacetime with a good classical description,
it is natural to ask how much information about the bulk spacetime is carried
by the density matrix for such a subset of field theory degrees of freedom. In
this note, we provide several constraints on the largest region that can be
fully reconstructed, and discuss specific proposals for the geometric
construction of this dual region.Comment: 19 pages, LaTeX, 8 figures, v2: footnote and reference adde
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