30,583 research outputs found
Multimode analysis of the light emitted from a pulsed optical parametric oscillator
We present a multimode treatment of the optical parametric oscillator, which
is valid for both pulsed and continuous-wave pump fields. The two-time
correlation functions of the output field are derived, and we apply the theory
to analyze a scheme for heralded production of non-classical field states that
may be subsequently stored in an atomic quantum memory.Comment: 11 pages, 6 figure
High purity bright single photon source
Using cavity-enhanced non-degenerate parametric downconversion, we have built
a frequency tunable source of heralded single photons with a narrow bandwidth
of 8 MHz, making it compatible with atomic quantum memories. The photon state
is 70% pure single photon as characterized by a tomographic measurement and
reconstruction of the quantum state, revealing a clearly negative Wigner
function. Furthermore, it has a spectral brightness of ~1,500 photons/s per MHz
bandwidth, making it one of the brightest single photon sources available. We
also investigate the correlation function of the down-converted fields using a
combination of two very distinct detection methods; photon counting and
homodyne measurement.Comment: 9 pages, 4 figures; minor changes, added referenc
Time gating of heralded single photons for atomic memories
We demonstrate a method for time gating the standard heralded continuous-
wave (cw) spontaneous parametric down-converted (SPDC) single photon source by
using pulsed pumping of the optical parametric oscillator (OPO) below
threshold. The narrow bandwidth, high purity, high spectral brightness and the
pseudo-deterministic character make the source highly suitable for light-atom
interfaces with atomic memories.Comment: Accepted for publication in Optics Letter
Directly estimating non-classicality
We establish a method of directly measuring and estimating non-classicality -
operationally defined in terms of the distinguishability of a given state from
one with a positive Wigner function. It allows to certify non-classicality,
based on possibly much fewer measurement settings than necessary for obtaining
complete tomographic knowledge, and is at the same time equipped with a full
certificate. We find that even from measuring two conjugate variables alone,
one may infer the non-classicality of quantum mechanical modes. This method
also provides a practical tool to eventually certify such features in
mechanical degrees of freedom in opto-mechanics. The proof of the result is
based on Bochner's theorem characterizing classical and quantum characteristic
functions and on semi-definite programming. In this joint
theoretical-experimental work we present data from experimental optical Fock
state preparation, demonstrating the functioning of the approach.Comment: 4+1 pages, 2 figures, minor change
Chiral Symmetry Breaking on the Lattice: a Study of the Strongly Coupled Lattice Schwinger Model
We revisit the strong coupling limit of the Schwinger model on the lattice
using staggered fermions and the hamiltonian approach to lattice gauge
theories. Although staggered fermions have no continuous chiral symmetry, they
posses a discrete axial invari ance which forbids fermion mass and which must
be broken in order for the lattice Schwinger model to exhibit the features of
the spectrum of the continuum theory. We show that this discrete symmetry is
indeed broken spontaneously in the strong coupling li mit. Expanding around a
gauge invariant ground state and carefully considering the normal ordering of
the charge operator, we derive an improved strong coupling expansion and
compute the masses of the low lying bosonic excitations as well as the chiral
co ndensate of the model. We find very good agreement between our lattice
calculations and known continuum values for these quantities already in the
fourth order of strong coupling perturbation theory. We also find the exact
ground state of the antiferromag netic Ising spin chain with long range Coulomb
interaction, which determines the nature of the ground state in the strong
coupling limit.Comment: 24 pages, Latex, no figure
The B_{s0} meson and the B_{s0}B K coupling from QCD sum rules
We evaluate the mass of the scalar meson and the coupling constant
in the vertex in the framework of QCD sum rules. We consider the
as a tetraquark state to evaluate its mass. We get m_{B_s0}=(6.04\pm
0.08) \GeV, which is bigger than predictions supposing it as a
state or a bound state with . To evaluate the coupling we use the three point correlation functions of the vertex,
considering as a normal state. The obtained coupling
constant is: g_{B_{s0} B K} =(16.3 \pm 3.2) \GeV. This number is in agreement
with light-cone QCD sum rules calculation. We have also compared the decay
width of the \BS\to BK process considering the \BS to be a state
and a molecular state. The width obtained for the molecular state is
twice as big as the width obtained for the state. Therefore, we
conclude that with the knowledge of the mass and the decay width of the \BS
meson, one can discriminate between the different theoretical proposals for its
structure.Comment: revised version to appear in Phys. Rev.
The horizon-entropy increase law for causal and quasi-local horizons and conformal field redefinitions
We explicitly prove the horizon-entropy increase law for both causal and
quasi-locally defined horizons in scalar-tensor and gravity theories.
Contrary to causal event horizons, future outer trapping horizons are not
conformally invariant and we provide a modification of trapping horizons to
complete the proof, using the idea of generalised entropy. This modification
means they are no longer foliated by marginally outer trapped surfaces but
fixes the location of the horizon under a conformal transformation. We also
discuss the behaviour of horizons in "veiled" general relativity and show,
using this new definition, how to locate cosmological horizons in flat
Minkowski space with varying units, which is physically identified with a
spatially flat FLRW spacetime.Comment: 23 page
Decoherence window and electron-nuclear cross-relaxation in the molecular magnet V 15
Rabi oscillations in the V_15 Single Molecule Magnet (SMM) embedded in the
surfactant DODA have been studied at different microwave powers. An intense
damping peak is observed when the Rabi frequency Omega_R falls in the vicinity
of the Larmor frequency of protons w_N, while the damping time t_R of
oscillations reaches values 10 times shorter than the phase coherence time t_2
measured at the same temperature. The experiments are interpreted by the N-spin
model showing that t_R is directly associated with the decoherence via
electronic/nuclear spin cross-relaxation in the rotating reference frame. It is
shown that this decoherence is accompanied with energy dissipation in the range
of the Rabi frequencies w_N - sigma_e < Omega_R < w_N, where sigma_e is the
mean super-hyperfine field (in frequency units) induced by protons at SMMs.
Weaker damping without dissipation takes place outside this dissipation window.
Simple local field estimations suggest that this rapid cross-relaxation in
resonant microwave field observed for the first time in SMMV_15 should take
place in other SMMs like Fe_8 and Mn_12 containing protons, too
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