42,697 research outputs found
Simultaneous observation of high order multiple quantum coherences at ultralow magnetic fields
We present a method for the simultaneous observation of heteronuclear
multi-quantum coherences (up to the 3rd order), which give an additional degree
of freedom for ultralow magnetic field (ULF) MR experiments, where the chemical
shift is negligible. The nonequilibrium spin state is generated by Signal
Amplification By Reversible Exchange (SABRE) and detected at ULF with
SQUID-based NMR. We compare the results obtained by the heteronuclei Correlated
SpectroscopY (COSY) with a Flip Angle FOurier Series (FAFOS) method. COSY
allows a quantitative analysis of homo- and heteronuclei quantum coherences
Tensor Networks for Lattice Gauge Theories with continuous groups
We discuss how to formulate lattice gauge theories in the Tensor Network
language. In this way we obtain both a consistent truncation scheme of the
Kogut-Susskind lattice gauge theories and a Tensor Network variational ansatz
for gauge invariant states that can be used in actual numerical computation.
Our construction is also applied to the simplest realization of the quantum
link models/gauge magnets and provides a clear way to understand their
microscopic relation with Kogut-Susskind lattice gauge theories. We also
introduce a new set of gauge invariant operators that modify continuously
Rokshar-Kivelson wave functions and can be used to extend the phase diagram of
known models. As an example we characterize the transition between the
deconfined phase of the lattice gauge theory and the Rokshar-Kivelson
point of the U(1) gauge magnet in 2D in terms of entanglement entropy. The
topological entropy serves as an order parameter for the transition but not the
Schmidt gap.Comment: 27 pages, 25 figures, 2nd version the same as the published versio
Strings from Orientifolds
We construct models in 1+1 dimensions with chiral (0,N) supersymmetry by
taking orientifolds of type IIB on an eight-torus identified by different
numbers of reflections. The resulting models have Dirichlet strings, fivebranes
and ninebranes stretched along different directions. The cases we study in
detail have residual chiral supersymmetry (0,8), (0,4) and (0,2). The
gravitational anomaly in all cases is shown to cancel.Comment: 30 pages, Latex, v2: references added, version to appear in Nucl.
Phys.
Large-k Limit of Multi-Point Propagators in the RG Formalism
Renormalized versions of cosmological perturbation theory have been very
successful in recent years in describing the evolution of structure formation
in the weakly non-linear regime. The concept of multi-point propagators has
been introduced as a tool to quantify the relation between the initial matter
distribution and the final one and to push the validity of the approaches to
smaller scales. We generalize the n-point propagators that have been considered
until now to include a new class of multi-point propagators that are relevant
in the framework of the renormalization group formalism. The large-k results
obtained for this general class of multi-point propagators match the results
obtained earlier both in the case of Gaussian and non-Gaussian initial
conditions. We discuss how the large-k results can be used to improve on the
accuracy of the calculations of the power spectrum and bispectrum in the
presence of initial non-Gaussianities.Comment: 30 page
All point correlation functions in SYK
Large melonic theories are characterized by two-point function Feynman
diagrams built exclusively out of melons. This leads to conformal invariance at
strong coupling, four-point function diagrams that are exclusively ladders, and
higher-point functions that are built out of four-point functions joined
together. We uncover an incredibly useful property of these theories: the
six-point function, or equivalently, the three-point function of the primary
invariant bilinears, regarded as an analytic function of the operator
dimensions, fully determines all correlation functions, to leading nontrivial
order in , through simple Feynman-like rules. The result is applicable to
any theory, not necessarily melonic, in which higher-point correlators are
built out of four-point functions. We explicitly calculate the bilinear
three-point function for -body SYK, at any . This leads to the bilinear
four-point function, as well as all higher-point functions, expressed in terms
of higher-point conformal blocks, which we discuss. We find universality of
correlators of operators of large dimension, which we simplify through a saddle
point analysis. We comment on the implications for the AdS dual of SYK.Comment: 67 pages, v
Reversing quantum trajectories with analog feedback
We demonstrate the active suppression of transmon qubit dephasing induced by
dispersive measurement, using parametric amplification and analog feedback. By
real-time processing of the homodyne record, the feedback controller reverts
the stochastic quantum phase kick imparted by the measurement on the qubit. The
feedback operation matches a model of quantum trajectories with measurement
efficiency , consistent with the result obtained by
postselection. We overcome the bandwidth limitations of the amplification chain
by numerically optimizing the signal processing in the feedback loop and
provide a theoretical model explaining the optimization result.Comment: 5 pages, 4 figures, and Supplementary Information (7 figures
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