242 research outputs found

### Generalization of Quantum Error Correction via the Heisenberg Picture

We show that the theory of operator quantum error correction can be naturally
generalized by allowing constraints not only on states but also on observables.
The resulting theory describes the correction of algebras of observables (and
may therefore suitably be called ``operator algebra quantum error
correction''). In particular, the approach provides a framework for the
correction of hybrid quantum-classical information and it does not require the
state to be entirely in one of the corresponding subspaces or subsystems. We
discuss applications to quantum teleportation and to the study of information
flows in quantum interactions.Comment: 5 pages, preprint versio

### The Abundance of Kaluza-Klein Dark Matter with Coannihilation

In Universal Extra Dimension models, the lightest Kaluza-Klein (KK) particle
is generically the first KK excitation of the photon and can be stable, serving
as particle dark matter. We calculate the thermal relic abundance of the KK
photon for a general mass spectrum of KK excitations including full
coannihilation effects with all (level one) KK excitations. We find that
including coannihilation can significantly change the relic abundance when the
coannihilating particles are within about 20% of the mass of the KK photon.
Matching the relic abundance with cosmological data, we find the mass range of
the KK photon is much wider than previously found, up to about 2 TeV if the
masses of the strongly interacting level one KK particles are within five
percent of the mass of the KK photon. We also find cases where several
coannihilation channels compete (constructively and destructively) with one
another. The lower bound on the KK photon mass, about 540 GeV when just
right-handed KK leptons coannihilate with the KK photon, relaxes upward by
several hundred GeV when coannihilation with electroweak KK gauge bosons of the
same mass is included.Comment: 38 pages, 4 figure

### The Measure of a Measurement

While finite non-commutative operator systems lie at the foundation of
quantum measurement, they are also tools for understanding geometric iterations
as used in the theory of iterated function systems (IFSs) and in wavelet
analysis. Key is a certain splitting of the total Hilbert space and its
recursive iterations to further iterated subdivisions. This paper explores some
implications for associated probability measures (in the classical sense of
measure theory), specifically their fractal components.
We identify a fractal scale $s$ in a family of Borel probability measures
$\mu$ on the unit interval which arises independently in quantum information
theory and in wavelet analysis. The scales $s$ we find satisfy $s\in
\mathbb{R}_{+}$ and $s\not =1$, some $s 1$. We identify these
scales $s$ by considering the asymptotic properties of $\mu(J) /| J| ^{s}$
where $J$ are dyadic subintervals, and $| J| \to0$.Comment: 18 pages, 3 figures, and reference

### Topological Subsystem Codes

We introduce a family of 2D topological subsystem quantum error-correcting
codes. The gauge group is generated by 2-local Pauli operators, so that 2-local
measurements are enough to recover the error syndrome. We study the
computational power of code deformation in these codes, and show that
boundaries cannot be introduced in the usual way. In addition, we give a
general mapping connecting suitable classical statistical mechanical models to
optimal error correction in subsystem stabilizer codes that suffer from
depolarizing noise.Comment: 16 pages, 11 figures, explanations added, typos correcte

### Supersoft Supersymmetry is Super-Safe

We show that supersymmetric models with a large Dirac gluino mass can evade
much of the jets plus missing energy searches at LHC. Dirac gaugino masses
arise from "supersoft" operators that lead to finite one-loop suppressed
contributions to the scalar masses. A little hierarchy between the Dirac gluino
mass 5 - 10 times heavier than the squark masses is automatic and technically
natural, in stark contrast to supersymmetric models with Majorana gaugino
masses. At the LHC, colored sparticle production is suppressed not only by the
absence of gluino pair (or associated) production, but also because several of
the largest squark pair production channels are suppressed or absent. We recast
the null results from the present jets plus missing energy searches at LHC for
supersymmetry onto a supersoft supersymmetric simplified model (SSSM). Assuming
a massless LSP, we find the strongest bounds are: 748 GeV from a 2j + MET
search at ATLAS (4.7 fb^{-1}), and 684 GeV from a combined jets plus missing
energy search using $\alpha_T$ at CMS (1.1 fb^{-1}). In the absence of a future
observation, we estimate the bounds on the squark masses to improve only
modestly with increased luminosity. We also briefly consider the further
weakening in the bounds as the LSP mass is increased.Comment: 13 pages, 8 figure

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