2,738 research outputs found
Topology and Phases in Fermionic Systems
There can exist topological obstructions to continuously deforming a gapped
Hamiltonian for free fermions into a trivial form without closing the gap.
These topological obstructions are closely related to obstructions to the
existence of exponentially localized Wannier functions. We show that by taking
two copies of a gapped, free fermionic system with complex conjugate
Hamiltonians, it is always possible to overcome these obstructions. This allows
us to write the ground state in matrix product form using Grassman-valued bond
variables, and show insensitivity of the ground state density matrix to
boundary conditions.Comment: 4 pages, see also arxiv:0710.329
Lorentz invariance of entanglement classes in multipartite systems
We analyze multipartite entanglement in systems of spin-1/2 particles from a
relativistic perspective. General conditions which have to be met for any
classification of multipartite entanglement to be Lorentz invariant are
derived, which contributes to a physical understanding of entanglement
classification. We show that quantum information in a relativistic setting
requires the partition of the Hilbert space into particles to be taken
seriously. Furthermore, we study exemplary cases and show how the spin and
momentum entanglement transforms relativistically in a multipartite setting.Comment: v2: 5 pages, 4 figures, minor changes to main body, journal
references update
Critical component of the interplanetary magnetic field responsible for large geomagnetic effects in the polar cap
An observed influence is studied of the interplanetary magnetic sector structure on the geomagnetic variations in the polar cap which appears to be due to the component of the interplanetary magnetic field near the ecliptic perpendicular to the earth-sun direction. It is suggested that the observed effect on the ground originates in the front of the magnetosphere
Sigurðar saga fóts (The Saga of Sigurðr Foot): A Translation
This is the first English translation of the short Icelandic romance Sigurðar saga fóts, with an introduction presenting the evidence for its dating and immediate literary context. Like most Icelandic romances, Sigurðar saga is a bridal-quest story; the support of a foster-brother is key to the hero winning the bride; and the foster-brothers start out as opponents before recognising their mutual excellence and swearing foster-brotherhood. Uniquely, however, the men who become foster-brothers begin by competing for the same bride (Signý): the eponymous Sigurðr fótr wins Signý only because Ásmundr gives her to him in exchange for foster-brotherhood. Ásmundr’s decision can be read as demonstrating with unusual starkness the superior importance in much Icelandic romance of homosocial relationships over heterosexual ones, giving the saga a certain paradigmatic status. Translating the saga in an open-access forum and reconstructing its literary context will, we hope, encourage further analyses
Sigurðar saga fóts (The Saga of Sigurðr Foot): A Translation
This is the first English translation of the short Icelandic romance Sigurðar saga fóts, with an introduction presenting the evidence for its dating and immediate literary context. Like most Icelandic romances, Sigurðar saga is a bridal-quest story; the support of a foster-brother is key to the hero winning the bride; and the foster-brothers start out as opponents before recognising their mutual excellence and swearing foster-brotherhood. Uniquely, however, the men who become foster-brothers begin by competing for the same bride (Signý): the eponymous Sigurðr fótr wins Signý only because Ásmundr gives her to him in exchange for foster-brotherhood. Ásmundr’s decision can be read as demonstrating with unusual starkness the superior importance in much Icelandic romance of homosocial relationships over heterosexual ones, giving the saga a certain paradigmatic status. Translating the saga in an open-access forum and reconstructing its literary context will, we hope, encourage further analyses
The warm, the excited, and the molecular gas: GRB 121024A shining through its star-forming galaxy
We present the first reported case of the simultaneous metallicity
determination of a gamma-ray burst (GRB) host galaxy, from both afterglow
absorption lines as well as strong emission-line diagnostics. Using
spectroscopic and imaging observations of the afterglow and host of the
long-duration Swift GRB121024A at z = 2.30, we give one of the most complete
views of a GRB host/environment to date. We observe a strong damped Ly-alpha
absorber (DLA) with a hydrogen column density of log N(HI) = 21.88 +/- 0.10, H2
absorption in the Lyman-Werner bands (molecular fraction of log(f)~ -1.4;
fourth solid detection of molecular hydrogen in a GRB-DLA), the nebular
emission lines H-alpha, H-beta, [O II], [O III] and [N II], as well as metal
absorption lines. We find a GRB host galaxy that is highly star-forming (SFR ~
40 solar masses/yr ), with a dust-corrected metallicity along the line of sight
of [Zn/H]corr = -0.6 +/- 0.2 ([O/H] ~ -0.3 from emission lines), and a
depletion factor [Zn/Fe] = 0.85 +/- 0.04. The molecular gas is separated by 400
km/s (and 1-3 kpc) from the gas that is photoexcited by the GRB. This implies a
fairly massive host, in agreement with the derived stellar mass of
log(M/M_solar ) = 9.9+/- 0.2. We dissect the host galaxy by characterising its
molecular component, the excited gas, and the line-emitting star-forming
regions. The extinction curve for the line of sight is found to be unusually
flat (Rv ~15). We discuss the possibility of an anomalous grain size
distributions. We furthermore discuss the different metallicity determinations
from both absorption and emission lines, which gives consistent results for the
line of sight to GRB 121024A.Comment: 20 pages, 11 figures, accepted by MNRA
Study of inter-modal four wave mixing in two few-mode fibres with different phase matching properties
We experimentally study inter-modal four-wave mixing (FWM) in few-mode fibres with different phase matching properties. The possibility of transmitting two spatial modes without intermodal FWM cross-talk in the C-band is presented
Towards universal quantum computation through relativistic motion
We show how to use relativistic motion to generate continuous variable Gaussian cluster states within cavity modes. Our results can be demonstrated experimentally using superconducting circuits where tuneable boundary conditions correspond to mirrors moving with velocities close to the speed of light. In particular, we propose the generation of a quadripartite square cluster state as a first example that can be readily implemented in the laboratory. Since cluster states are universal resources for universal one-way quantum computation, our results pave the way for relativistic quantum computation schemes
- …