10,041 research outputs found
Two-dimensional Lattice Gauge Theories with Superconducting Quantum Circuits
A quantum simulator of U(1) lattice gauge theories can be implemented with
superconducting circuits. This allows the investigation of confined and
deconfined phases in quantum link models, and of valence bond solid and spin
liquid phases in quantum dimer models. Fractionalized confining strings and the
real-time dynamics of quantum phase transitions are accessible as well. Here we
show how state-of-the-art superconducting technology allows us to simulate
these phenomena in relatively small circuit lattices. By exploiting the strong
non-linear couplings between quantized excitations emerging when
superconducting qubits are coupled, we show how to engineer gauge invariant
Hamiltonians, including ring-exchange and four-body Ising interactions. We
demonstrate that, despite decoherence and disorder effects, minimal circuit
instances allow us to investigate properties such as the dynamics of electric
flux strings, signaling confinement in gauge invariant field theories. The
experimental realization of these models in larger superconducting circuits
could address open questions beyond current computational capability.Comment: Published versio
Tunneling effects on impurity spectral function in coupled asymmetric quantum wires
The impurity spectral function is studied in coupled double quantum wires at
finite temperatures. Simple anisotropy in the confinement direction of the
wires leads to finite non-diagonal elements of the impurity spectral function
matrix. These non-diagonal elements are responsible for tunneling effects and
result in pronounced extra peak in the impurity spectral function up to
temperatures as high as 20 K.Comment: Accepted in Phys. Rev.
Spherical Collapse and the Halo Model in Braneworld Gravity
We present a detailed study of the collapse of a spherical perturbation in
DGP braneworld gravity for the purpose of modeling simulation results for the
halo mass function, bias and matter power spectrum. The presence of evolving
modifications to the gravitational force in form of the scalar brane-bending
mode lead to qualitative differences to the collapse in ordinary gravity. In
particular, differences in the energetics of the collapse necessitate a new,
generalized method for defining the virial radius which does not rely on strict
energy conservation. These differences and techniques apply to smooth dark
energy models with w unequal -1 as well. We also discuss the impact of the
exterior of the perturbation on collapse quantities due to the lack of a
Birkhoff theorem in DGP. The resulting predictions for the mass function, halo
bias and power spectrum are in good overall agreement with DGP N-body
simulations on both the self-accelerating and normal branch. In particular, the
impact of the Vainshtein mechanism as measured in the full simulations is
matched well. The model and techniques introduced here can serve as practical
tools for placing consistent constraints on braneworld models using
observations of large scale structure.Comment: 20 pages, 16 figures; v2: minor addition to appendix; matches
published version; v3: typos in Eqs. (20), (23) correcte
Qubits in phase space: Wigner function approach to quantum error correction and the mean king problem
We analyze and further develop a new method to represent the quantum state of
a system of qubits in a phase space grid of points (where
). The method, which was recently proposed by Wootters and co--workers
(Gibbons {\it et al.}, quant-ph/0401155), is based on the use of the elements
of the finite field to label the phase space axes. We present a
self--contained overview of the method, we give new insights on some of its
features and we apply it to investigate problems which are of interest for
quantum information theory: We analyze the phase space representation of
stabilizer states and quantum error correction codes and present a phase space
solution to the so--called ``mean king problem''.Comment: 18 pages, 16 figures; typos fixed, some minor corrections, figures of
the circuits were change
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