58,126 research outputs found
Direct Detection of the Primordial Inflationary Gravitational Waves
Inflationary cosmology is successful in explaining a number of outstanding
cosmological issues including the flatness, the horizon and the relic issues.
More spectacular is the experimental confirmation of the structure as arose
from the inflationary quantum fluctuations. However, the physics in the
inflationary era is unclear. Polarization observations of Cosmic Microwave
Background (CMB) missions may detect the tensor mode effects of inflationary
gravitational waves (GWs) and give an energy scale of inflation. To probe the
inflationary physics, direct observation of gravitational waves generated in
the inflationary era is needed. In this essay, we advocate that the direct
observation of these GWs with sensitivity Omega-gw down to 10**(-23) is
possible using present projected technology development if foreground could be
separated.Comment: 6 pages, 1 figure, received an honorable mention in the 2009 Essay
Competition of the Gravity Research Foundatio
Conductance of a single-atom carbon chain with graphene leads
We study the conductance of an interconnect between two graphene leads formed
by a single-atom carbon chain. Its dependence on the chemical potential and the
number of atoms in the chain is qualitatively different from that in the case
of normal metal leads. Electron transport proceeds via narrow resonant states
in the wire. The latter arise due to strong reflection at the junctions between
the chain and the leads, which is caused by the small density of states in the
leads at low energy. The energy dependence of the transmission coefficient near
resonance is asymmetric and acquires a universal form at small energies. We
find that in the case of leads with the zigzag edges the dispersion of the edge
states has a significant effect on the device conductance.Comment: 9 pages, 4 figure
Effect of atmospheric turbulence on propagation properties of optical vortices formed by using coherent laser beam arrays
In this paper, we consider the effect of the atmospheric turbulence on the
propagation of optical vertex formed from the radial coherent laser beam array,
with the initially well-defined phase distribution. The propagation formula of
the radial coherent laser array passing through the turbulent atmosphere is
analytically derived by using the extended Huygens-Fresnel diffraction
integral. Based on the derived formula, the effect of the atmospheric
turbulence on the propagation properties of such laser arrays has been studied
in great detail. Our main results show that the atmospheric turbulence may
result in the prohibition of the formation of the optical vortex or the
disappearance of the formed optical vortex, which are very different from that
in the free space. The formed optical vortex with the higher topological charge
may propagate over a much longer distance in the moderate or weak turbulent
atmosphere. After the sufficient long-distance atmospheric propagation, all the
output beams (even with initially different phase distributions) finally lose
the vortex property and gradually become the Gaussian-shaped beams, and in this
case the output beams actually become incoherent light fields due to the
decoherence effect of the turbulent atmosphere.Comment: 10 pages, 5 figure
Generation of nonclassical photon states using a superconducting qubit in a microcavity
Based on the interaction between the radiation field and a superconductor, we
propose a way to engineer quantum states using a SQUID charge qubit inside a
microcavity. This device can act as a deterministic single photon source as
well as generate any Fock states and an arbitrary superposition of Fock states
for the cavity field. The controllable interaction between the cavity field and
the qubit can be realized by the tunable gate voltage and classical magnetic
field applied to the SQUID.Comment: 4 page
Magnetism and Magnetic Isomers in Free Chromium Clusters
We have used the Stern-Gerlach deflection technique to study magnetism in
chromium clusters of 20-133 atoms. Between 60 K and 100 K, we observe that
these clusters have large magnetic moments and respond superparamagnetically to
applied magnetic fields. Using superparamagnetic theory, we have determined the
moment per atom for each cluster size and find that it often far exceeds the
moment per atom present anywhere in the bulk antiferromagnetic lattice.
Remarkably, our cluster beam contains two magnetically distinguishable forms of
each cluster size with >= 34 atoms. We attribute this observation to structural
isomers
Vortex Nucleation Induced Phonon Radiation from a Moving Electron Bubble in Superfluid 4He
We construct an efficient zero-temperature semi-local density functional to
dynamically simulate an electron bubble passing through superfluid 4He under
various pressures and electric fields up to nanosecond timescale. Our simulated
drift velocity can be quantitatively compared to experiments particularly when
pressure approaches zero. We find that the high-speed bubble experiences
remarkable expansion and deformation before vortex nucleation occurs.
Accompanied by vortex-ring shedding, drastic surface vibration is generated
leading to intense phonon radiation into the liquid. The amount of energy
dissipated by these phonons is found to be greater than the amount carried away
solely by the vortex rings. These results may enrich our understanding about
the vortex nucleation induced energy dissipation in this fascinating system.Comment: 7 pages, 5 figure
High efficiency tomographic reconstruction of quantum states by quantum nondemolition measurements
We propose a high efficiency tomographic scheme to reconstruct an unknown
quantum state of the qubits by using a series of quantum nondemolition (QND)
measurements. The proposed QND measurements of the qubits are implemented by
probing the the stationary transmissions of the dispersively-coupled resonator.
It is shown that only one kind of QND measurements is sufficient to determine
all the diagonal elements of the density matrix of the detected quantum state.
The remaining non-diagonal elements of the density matrix can be determined by
other spectral measurements by beforehand transferring them to the diagonal
locations using a series of unitary operations. Compared with the pervious
tomographic reconstructions based on the usual destructively projective (DP)
measurements (wherein one kind of such measurements could only determine one
diagonal element of the density matrix), the present approach exhibits
significantly high efficiency for N-qubit (N > 1). Specifically, our generic
proposal is demonstrated by the experimental circuit-quantumelectrodynamics
(circuit-QED) systems with a few Josephson charge qubits.Comment: 9pages,4figure
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