321 research outputs found
New 3-D gas density maps of NaI and CaII interstellar absorption within 300pc
We present new high resolution (R>50,000) absorption measurements of the NaI
doublet (5889 - 5895A) along 482 nearby sight-lines, in addition to 807 new
measurements of the CaII K (3933A) absorption line. We have combined these new
data with previously reported measurements to produce a catalog of absorptions
towards a total of 1857 early-type stars located within 800pc of the Sun. Using
these data we have determined the approximate 3-dimensional spatial
distribution of neutral and partly ionized interstellar gasdensity within a
distance-cube of 300pc from the Sun. All newly recorded spectra were analyzed
by means of a multi-component line profile-fitting program, in most cases using
simultaneous fits to the line doublets. Normalized absorption profiles were
fitted by varying the velocity, doppler width and column density for all
intervening interstellar clouds. The resulting total column densities were then
used in conjunction with the Hipparcos distances of the target stars to
construct inversion maps of the 3-D spatial density distribution of the NaI and
CaII bearing gas. A plot of the equivalent width of NaI versus distance reveals
a wall of neutral gas at ~80pc that can be associated with the boundary wall to
the central rarefied Local Cavity region. In contrast, a similar plot for the
equivalent width of CaII shows no sharply increasing absorption at 80pc, but
instead we observe a slowly increasing value of CaII equivalent width with
increasing sight-line distance sampled.Comment: A&A accepte
Parametric coupling for superconducting qubits
We propose a scheme to couple two superconducting charge or flux qubits
biased at their symmetry points with unequal energy splittings. Modulating the
coupling constant between two qubits at the sum or difference of their two
frequencies allows to bring them into resonance in the rotating frame.
Switching on and off the modulation amounts to switching on and off the
coupling which can be realized at nanosecond speed. We discuss various physical
implementations of this idea, and find that our scheme can lead to rapid
operation of a two-qubit gate.Comment: 6 page
Travelling to exotic places with cavity QED systems
Recent theoretical schemes for utilizing cavity QED models as quantum
simulators are reviewed. By considering a quadrature representation for the
fields, it is shown how Jahn-Teller models, effective Abelian or non-Abelian
gauge potentials, transverse Hall currents, and relativistic effects naturally
arise in these systems. Some of the analytical predictions are verified
numerically using realistic experimental parameters taking into account for
system losses. Thereby demonstrating their feasibility with current
experimental setups.Comment: 5 pages, 3 figure
Jaynes-Cummings Models with trapped surface-state electrons in THz cavities
An electron floating on the liquid Helium is proposed to be trapped (by a
micro-electrode set below the liquid Helium) in a high finesse cavity. Two
lowest levels of the vertical motion of the electron acts as a two-level
"atom", which could resonantly interact with the THz cavity. In the Lamb-Dicke
regime, wherein the electron's in-plane activity region is much smaller than
the wavelength of the cavity mode, the famous Jaynes-Cummings model (JCM) could
be realized. By applying an additional external classical laser beam to the
electron, a driven JCM could also be implemented. With such a driven JCM
certain quantum states, e.g., coherent states and the Schrodinger cat states,
of the THz cavity field could be prepared by one-step evolution. The numerical
results show that, for the typical parameters of the cavity and electron on
liquid Helium, a strong coupling between the artificial atom and the THz cavity
could be obtained.Comment: 11 pages, 1 figure
Quantum Search with Two-atom Collisions in Cavity QED
We propose a scheme to implement two-qubit Grover's quantum search algorithm
using Cavity Quantum Electrodynamics. Circular Rydberg atoms are used as
quantum bits (qubits). They interact with the electromagnetic field of a
non-resonant cavity . The quantum gate dynamics is provided by a
cavity-assisted collision, robust against decoherence processes. We present the
detailed procedure and analyze the experimental feasibility.Comment: 4 pages, 2 figure
Universal Quantum Cloning in Cavity QED
We propose an implementation of an universal quantum cloning machine [UQCM,
Hillery and Buzek, Phys. Rev. A {\bf 56}, 3446 (1997)] in a Cavity Quantum
Electrodynamics (CQED) experiment. This UQCM acts on the electronic states of
atoms that interact with the electromagnetic field of a high cavity. We
discuss here the specific case of the cloning process using either a
one- or a two-cavity configuration
Manipulating ionization path in a Stark map: Stringent schemes for the selective field ionization in highly excited Rb Rydberg atoms
We have developed a quite stringent method in selectivity to ionize the low
angular- momentum () states which lie below and above the adjacent
manifold in highly excited Rb Rydberg atoms. The method fully exploits the
pulsed field-ionization characteristics of the manifold states in high
slew-rate regime: Specifically the low state below (above) the adjacent
manifold is firstly transferred to the lowest (highest) state in the manifold
via the adiabatic transition at the first avoided crossing in low slew-rate
regime, and then the atoms are driven to a high electric field for ionization
in high slew-rate regime. These extreme states of the manifold are ionized at
quite different fields due to the tunneling process, resulting in thus the
stringent selectivity. Two manipulation schemes to realize this method actually
are demonstrated here experimentally.Comment: 10 pages, 4 figure
Systematic observation of tunneling field-ionization in highly excited Rb Rydberg atoms
Pulsed field ionization of high- (90 150) manifold states in
Rb Rydberg atoms has been investigated in high slew-rate regime. Two peaks in
the field ionization spectra were systematically observed for the investigated
region, where the field values at the lower peak do not almost depend on
the excitation energy in the manifold, while those at the higher peak increase
with increasing excitation energy. The fraction of the higher peak component to
the total ionization signals increases with increasing , exceeding 80% at
= 147. Characteristic behavior of the peak component and the comparison
with theoretical predictions indicate that the higher peak component is due to
the tunneling process. The obtained results show for the first time that the
tunneling process plays increasingly the dominant role at such highly excited
nonhydrogenic Rydberg atoms.Comment: 8 pages, 5 figure
Several small Josephson junctions in a Resonant Cavity: Deviation from the Dicke Model
We have studied quantum-mechanically a system of several small identical
Josephson junctions in a lossless single-mode cavity for different initial
states, under conditions such that the system is at resonance. This system is
analogous to a collection of identical atoms in a cavity, which is described
under appropriate conditions by the Dicke model. We find that our system can be
well approximated by a reduced Hamiltonian consisting of two levels per
junction. The reduced Hamiltonian is similar to the Dicke Hamiltonian, but
contains an additional term resembling a dipole-dipole interaction between the
junctions. This extra term arises when states outside the degenerate group are
included via degenerate second-order (L\"{o}wdin) perturbation theory. As in
the Dicke model, we find that, when N junctions are present in the cavity, the
oscillation frequency due to the junction-cavity interaction is enhanced by
. The corresponding decrease in the Rabi oscillation period may cause
it to be smaller than the decoherence time due to dissipation, making these
oscillations observable. Finally, we find that the frequency enhancement
survives even if the junctions differ slightly from one another, as expected in
a realistic system.Comment: 11 pages. To be published in Phys. Rev.
Quantum controlled phase gate and cluster states generation via two superconducting quantum interference devices in a cavity
A scheme for implementing 2-qubit quantum controlled phase gate (QCPG) is
proposed with two superconducting quantum interference devices (SQUIDs) in a
cavity. The gate operations are realized within the two lower flux states of
the SQUIDs by using a quantized cavity field and classical microwave pulses.
Our scheme is achieved without any type of measurement, does not use the cavity
mode as the data bus and only requires a very short resonant interaction of the
SQUID-cavity system. As an application of the QCPG operation, we also propose a
scheme for generating the cluster states of many SQUIDs.Comment: 4 pages, resumitte
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