5,764 research outputs found
Ground-State Energy and Spin Gap of Spin-1/2 Kagome Heisenberg Antiferromagnetic Clusters: Large Scale Exact Diagonalization Results
We present a comprehensive list of ground state energies and spin gaps of
finite kagome clusters with up to 42 spins obtained using large-scale exact
diagonalization techniques. This represents the current limit of this exact
approach. For a fixed number of spins N we study several cluster shapes under
periodic boundary conditions in both directions resulting in a toroidal
geometry. The clusters are characterized by their side length and diagonal as
well as the shortest "Manhattan" diameter of the torii. A finite-size scaling
analysis of the ground state energy as well as the spin gap is then performed
in terms of the shortest toroidal diameter as well as the shortest "Manhattan"
diameter. The structure of the spin-spin correlations further supports the
importance of short loops wrapping around the torii.Comment: 4 pages, 4 figures, added one referenc
Enhancing quantum transduction via long-range waveguide mediated interactions between quantum emitters
Efficient transduction of electromagnetic signals between different frequency
scales is an essential ingredient for modern communication technologies as well
as for the emergent field of quantum information processing. Recent advances in
waveguide photonics have enabled a breakthrough in light-matter coupling, where
individual two-level emitters are strongly coupled to individual photons. Here
we propose a scheme which exploits this coupling to boost the performance of
transducers between low-frequency signals and optical fields operating at the
level of individual photons. Specifically, we demonstrate how to engineer the
interaction between quantum dots in waveguides to enable efficient transduction
of electric fields coupled to quantum dots. Owing to the scalability and
integrability of the solid-state platform, our transducer can potentially
become a key building block of a quantum internet node. To demonstrate this, we
show how it can be used as a coherent quantum interface between optical photons
and a two-level system like a superconducting qubit.Comment: The maintext has 6 pages, two column and 4 figure
Photon Scattering from a System of Multi-Level Quantum Emitters. I. Formalism
We introduce a formalism to solve the problem of photon scattering from a
system of multi-level quantum emitters. Our approach provides a direct solution
of the scattering dynamics. As such the formalism gives the scattered fields
amplitudes in the limit of a weak incident intensity. Our formalism is equipped
to treat both multi-emitter and multi-level emitter systems, and is applicable
to a plethora of photon scattering problems including conditional state
preparation by photo-detection. In this paper, we develop the general formalism
for an arbitrary geometry. In the following paper (part II), we reduce the
general photon scattering formalism to a form that is applicable to
-dimensional waveguides, and show its applicability by considering explicit
examples with various emitter configurations.Comment: This is first part of a two part series of papers. It has 11 pages,
double column, and one figur
The Generic, Incommensurate Transition in the two-dimensional Boson Hubbard Model
The generic transition in the boson Hubbard model, occurring at an
incommensurate chemical potential, is studied in the link-current
representation using the recently developed directed geometrical worm
algorithm. We find clear evidence for a multi-peak structure in the energy
distribution for finite lattices, usually indicative of a first order phase
transition. However, this multi-peak structure is shown to disappear in the
thermodynamic limit revealing that the true phase transition is second order.
These findings cast doubts over the conclusion drawn in a number of previous
works considering the relevance of disorder at this transition.Comment: 13 pages, 10 figure
Dispersion relations for stationary light in one-dimensional atomic ensembles
We investigate the dispersion relations for light coupled to one-dimensional
ensembles of atoms with different level schemes. The unifying feature of all
the considered setups is that the forward and backward propagating quantum
fields are coupled by the applied classical drives such that the group velocity
can vanish in an effect known as "stationary light". We derive the dispersion
relations for all the considered schemes, highlighting the important
differences between them. Furthermore, we show that additional control of
stationary light can be obtained by treating atoms as discrete scatterers and
placing them at well defined positions. For the latter purpose, a multi-mode
transfer matrix theory for light is developed
The primordial deuterium abundance at z = 2.504 from a high signal-to-noise spectrum of Q1009+2956
The spectrum of the quasar Q1009+2956 has been observed
extensively on the Keck telescope. The Lyman limit absorption system was previously used to measure D/H by Burles & Tytler using a
spectrum with signal to noise approximately 60 per pixel in the continuum near
Ly {\alpha} at . The larger dataset now available combines
to form an exceptionally high signal to noise spectrum, around 147 per pixel.
Several heavy element absorption lines are detected in this LLS, providing
strong constraints on the kinematic structure. We explore a suite of absorption
system models and find that the deuterium feature is likely to be contaminated
by weak interloping Ly {\alpha} absorption from a low column density H I cloud,
reducing the expected D/H precision. We find D/H =
for this system. Combining this new
measurement with others from the literature and applying the method of Least
Trimmed Squares to a statistical sample of 15 D/H measurements results in a
"reliable" sample of 13 values. This sample yields a primordial deuterium
abundance of (D/H). The
corresponding mean baryonic density of the Universe is . The quasar absorption data is of the same precision as, and
marginally inconsistent with, the 2015 CMB Planck (TT+lowP+lensing)
measurement, . Further quasar and more
precise nuclear data are required to establish whether this is a random
fluctuation.Comment: accepted by MNRAS, 18 pages, 12 figures, 6 table
Dynamics of many-body photon bound states in chiral waveguide QED
We theoretically study the few- and many-body dynamics of photons in chiral
waveguides. In particular, we examine pulse propagation through a system of
two-level systems chirally coupled to a waveguide. We show that the system
supports correlated multi-photon bound states, which have a well-defined photon
number and propagate through the system with a group delay scaling as
. This has the interesting consequence that, during propagation, an
incident coherent state pulse breaks up into different bound state components
that can become spatially separated at the output in a sufficiently long
system. For sufficiently many photons and sufficiently short systems, we show
that linear combinations of -body bound states recover the well-known
phenomenon of mean-field solitons in self-induced transparency. For longer
systems, however, the solitons break apart through quantum correlated dynamics.
Our work thus covers the entire spectrum from few-photon quantum propagation,
to genuine quantum many-body (atom and photon) phenomena, and ultimately the
quantum-to-classical transition. Finally, we demonstrate that the bound states
can undergo elastic scattering with additional photons. Together, our results
demonstrate that photon bound states are truly distinct physical objects
emerging from the most elementary light-matter interaction between photons and
two-level emitters. Our work opens the door to studying quantum many-body
physics and soliton physics with photons in chiral waveguide QED.Comment: Updated with new results. 14 pages plus supplementary materia
Entanglement in Anderson Nanoclusters
We investigate the two-particle spin entanglement in magnetic nanoclusters
described by the periodic Anderson model. An entanglement phase diagram is
obtained, providing a novel perspective on a central property of magnetic
nanoclusters, namely the temperature dependent competition between local Kondo
screening and nonlocal Ruderman-Kittel-Kasuya-Yoshida spin ordering. We find
that multiparticle entangled states are present for finite magnetic field as
well as in the mixed valence regime and away from half filling. Our results
emphasize the role of charge fluctuations.Comment: 5 pages, 3 figure
Generation and detection of a sub-Poissonian atom number distribution in a one-dimensional optical lattice
We demonstrate preparation and detection of an atom number distribution in a
one-dimensional atomic lattice with the variance dB below the Poissonian
noise level. A mesoscopic ensemble containing a few thousand atoms is trapped
in the evanescent field of a nanofiber. The atom number is measured through
dual-color homodyne interferometry with a pW-power shot noise limited probe.
Strong coupling of the evanescent probe guided by the nanofiber allows for a
real-time measurement with a precision of atoms on an ensemble of some
atoms in a one-dimensional trap. The method is very well suited for
generating collective atomic entangled or spin-squeezed states via a quantum
non-demolition measurement as well as for tomography of exotic atomic states in
a one-dimensional lattice
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