2,702 research outputs found
Infall, Fragmentation and Outflow in Sgr B2
Observations of HCO lines and continuum at 1.3 mm towards Sgr B2(N) and
Sgr B2(M) cores were carried out with the SMA. We imaged HCO line
absorption against the continuum cores and the surrounding line emission
clumps. The results show that the majority of the dense gas is falling into the
major cores where massive stars have been formed. The filaments and clumps of
the continuum and gas are detected outside of Sgr B2(N) and Sgr B2(M) cores.
Both the spectra and moment analysis show the presence of outflows from Sgr
B2(M) cores. The HCO gas in the red-shifted outflow of Sgr B2(M) appears
to be excited by a non-LTE process which might be related to the shocks in the
outflow.Comment: 5 pages, 3 figures, Published in J. Physics Conference Serie
Influence of an external magnetic field on the decoherence of a central spin coupled to an antiferromagnetic environment
Using the spin wave approximation, we study the decoherence dynamics of a
central spin coupled to an antiferromagnetic environment under the application
of an external global magnetic field. The external magnetic field affects the
decoherence process through its effect on the antiferromagnetic environment. It
is shown explicitly that the decoherence factor which displays a Gaussian decay
with time depends on the strength of the external magnetic field and the
crystal anisotropy field in the antiferromagnetic environment. When the values
of the external magnetic field is increased to the critical field point at
which the spin-flop transition (a first-order quantum phase transition) happens
in the antiferromagnetic environment, the decoherence of the central spin
reaches its highest point. This result is consistent with several recent
quantum phase transition witness studies. The influences of the environmental
temperature on the decoherence behavior of the central spin are also
investigated.Comment: 29 preprint pages, 4 figures, to appear in New Journal of Physic
Terahertz radiation from plasma filament generated by two-color laser gas–plasma interaction
We develop a theoretical model for terahertz (THz) radiation generation, when an intense short laser pulse (ω1, k 1) is mixed with its frequency shifted second harmonic (ω2, k 2), where ω2 = 2ω1 + ωT and ωT is in the THz range in the plasma. The lasers exert a ponderomotive force on the electrons and drive density perturbations at (2ω1, 2k 1) and (ω2 − ω1, k 2 − k 1). These density perturbations couple with the oscillatory velocities of the electron due to the lasers and produce a nonlinear current at (ω2 − 2ω1, k 2 − 2k 1). This current acts as an antenna to produce the THz radiation. The THz power depends upon the square of plasma density and , where I 1 and I 2 are the intensities of fundamental and second harmonic laser. The radiation is mainly along the forward direction. Two-dimensional particle-in-cell simulations are used to study the near-field radiation properties
Piecewise linear transformation in diffusive flux discretization
To ensure the discrete maximum principle or solution positivity in finite
volume schemes, diffusive flux is sometimes discretized as a conical
combination of finite differences. Such a combination may be impossible to
construct along material discontinuities using only cell concentration values.
This is often resolved by introducing auxiliary node, edge, or face
concentration values that are explicitly interpolated from the surrounding cell
concentrations. We propose to discretize the diffusive flux after applying a
local piecewise linear coordinate transformation that effectively removes the
discontinuities. The resulting scheme does not need any auxiliary
concentrations and is therefore remarkably simpler, while being second-order
accurate under the assumption that the structure of the domain is locally
layered.Comment: 11 pages, 1 figures, preprint submitted to Journal of Computational
Physic
Memory-built-in quantum teleportation with photonic and atomic qubits
The combination of quantum teleportation and quantum memory of photonic
qubits is essential for future implementations of large-scale quantum
communication and measurement-based quantum computation. Both steps have been
achieved separately in many proof-of-principle experiments, but the
demonstration of memory-built-in teleportation of photonic qubits remains an
experimental challenge. Here, we demonstrate teleportation between photonic
(flying) and atomic (stationary) qubits. In our experiment, an unknown
polarization state of a single photon is teleported over 7 m onto a remote
atomic qubit that also serves as a quantum memory. The teleported state can be
stored and successfully read out for up to 8 micro-second. Besides being of
fundamental interest, teleportation between photonic and atomic qubits with the
direct inclusion of a readable quantum memory represents a step towards an
efficient and scalable quantum network.Comment: 19 pages 3 figures 1 tabl
Ion Kinetics and Neutron Generation Associated with Electromagnetic Turbulence in Laboratory-scale Counter-streaming Plasmas
Electromagnetic turbulence and ion kinetics in counter-streaming plasmas hold
great significance in laboratory astrophysics, such as turbulence field
amplification and particle energization. Here, we quantitatively demonstrate
for the first time how electromagnetic turbulence affects ion kinetics under
achievable laboratory conditions (millimeter-scale interpenetrating plasmas
with initial velocity of , density of $4 \times 10^{19}\
\mathrm{cm}^{-3}100\ \mathrm{eV}$) utilizing a recently
developed high-order implicit particle-in-cell code without scaling
transformation. It is found that the electromagnetic turbulence is driven by
ion two-stream and filamentation instabilities. For the magnetized scenarios
where an applied magnetic field of tens of Tesla is perpendicular to plasma
flows, the growth rates of instabilities increase with the strengthening of
applied magnetic field, which therefore leads to a significant enhancement of
turbulence fields. Under the competition between the stochastic acceleration
due to electromagnetic turbulence and collisional thermalization, ion
distribution function shows a distinct super-Gaussian shape, and the ion
kinetics are manifested in neutron yields and spectra. Our results have well
explained the recent unmagnetized experimental observations, and the findings
of magnetized scenario can be verified by current astrophysical experiments.Comment: Accepted by Phys. Rev. Lett. on 12 Ma
Quantum Memory with Optically Trapped Atoms
We report the experimental demonstration of a quantum memory for collective
atomic states in a far-detuned optical dipole trap. Generation of the
collective atomic state is heralded by the detection of a Raman scattered
photon and accompanied by storage in the ensemble of atoms. The optical dipole
trap provides confinement for the atoms during the quantum storage while
retaining the atomic coherence. We probe the quantum storage by
cross-correlation of the photon pair arising from the Raman scattering and the
retrieval of the atomic state stored in the memory. Non-classical correlations
are observed for storage times up to 60 microseconds.Comment: 4 pages, 3 figure
Experimental demonstration of a BDCZ quantum repeater node
Quantum communication is a method that offers efficient and secure ways for
the exchange of information in a network. Large-scale quantum communication (of
the order of 100 km) has been achieved; however, serious problems occur beyond
this distance scale, mainly due to inevitable photon loss in the transmission
channel. Quantum communication eventually fails when the probability of a dark
count in the photon detectors becomes comparable to the probability that a
photon is correctly detected. To overcome this problem, Briegel, D\"{u}r, Cirac
and Zoller (BDCZ) introduced the concept of quantum repeaters, combining
entanglement swapping and quantum memory to efficiently extend the achievable
distances. Although entanglement swapping has been experimentally demonstrated,
the implementation of BDCZ quantum repeaters has proved challenging owing to
the difficulty of integrating a quantum memory. Here we realize entanglement
swapping with storage and retrieval of light, a building block of the BDCZ
quantum repeater. We follow a scheme that incorporates the strategy of BDCZ
with atomic quantum memories. Two atomic ensembles, each originally entangled
with a single emitted photon, are projected into an entangled state by
performing a joint Bell state measurement on the two single photons after they
have passed through a 300-m fibre-based communication channel. The entanglement
is stored in the atomic ensembles and later verified by converting the atomic
excitations into photons. Our method is intrinsically phase insensitive and
establishes the essential element needed to realize quantum repeaters with
stationary atomic qubits as quantum memories and flying photonic qubits as
quantum messengers.Comment: 5 pages, 4 figure
- …