2,870 research outputs found
Preparation of n-qubit Greenberger-Horne-Zeilinger entangled states in cavity QED: An approach with tolerance to nonidentical qubit-cavity coupling constants
We propose a way for generating -qubit Greenberger-Horne-Zeilinger (GHZ)
entangled states with a three-level qubit system and (n-1) four-level qubit
systems in a cavity. This proposal does not require identical qubit-cavity
coupling constants, and thus is tolerant to qubit-system parameter
nonuniformity and nonexact placement of qubits in a cavity. The proposal does
not require adjustment of the qubit-system level spacings during the entire
operation. Moreover, it is shown that entanglement can be deterministically
generated using this method and the operation time is independent of the number
of qubits. The present proposal is quite general, which can be applied to
physical systems such as various types of superconducting devices coupled to a
resonator or atoms trapped in a cavity.Comment: 3 figures, accepted by Phys. Rev.
Generation of GHZ entangled states of photons in multiple cavities via a superconducting qutrit or an atom through resonant interaction
We propose an efficient method to generate a GHZ entangled state of n photons
in n microwave cavities (or resonators) via resonant interaction to a single
superconducting qutrit. The deployment of a qutrit, instead of a qubit, as the
coupler enables us to use resonant interactions exclusively for all
qutrit-cavity and qutrit-pulse operations. This unique approach significantly
shortens the time of operation which is advantageous to reducing the adverse
effects of qutrit decoherence and cavity decay on fidelity of the protocol.
Furthermore, the protocol involves no measurement on either the state of qutrit
or cavity photons. We also show that the protocol can be generalized to other
systems by replacing the superconducting qutrit coupler with different types of
physical qutrit, such as an atom in the case of cavity QED, to accomplish the
same task.Comment: 11 pages, 5 figures, accepted by Phys. Rev.
Feedback cooling of a cantilever's fundamental mode below 5 mK
We cool the fundamental mechanical mode of an ultrasoft silicon cantilever
from a base temperature of 2.2 K to 2.9 +/- 0.3 mK using active optomechanical
feedback. The lowest observed mode temperature is consistent with limits
determined by the properties of the cantilever and by the measurement noise.
For high feedback gain, the driven cantilever motion is found to suppress or
"squash" the optical interferometer intensity noise below the shot noise level.Comment: 4 pages, 6 figure
Nuclear spin relaxation induced by a mechanical resonator
We report on measurements of the spin lifetime of nuclear spins strongly
coupled to a micromechanical cantilever as used in magnetic resonance force
microscopy. We find that the rotating-frame correlation time of the statistical
nuclear polarization is set by the magneto-mechanical noise originating from
the thermal motion of the cantilever. Evidence is based on the effect of three
parameters: (1) the magnetic field gradient (the coupling strength), (2) the
Rabi frequency of the spins (the transition energy), and (3) the temperature of
the low-frequency mechanical modes. Experimental results are compared to
relaxation rates calculated from the spectral density of the magneto-mechanical
noise.Comment: 4 pages, 4 figure
Phase separation and vortex states in binary mixture of Bose-Einstein condensates in the trapping potentials with displaced centers
The system of two simultaneously trapped codensates consisting of
atoms in two different hyperfine states is investigated theoretically in the
case when the minima of the trapping potentials are displaced with respect to
each other. It is shown that the small shift of the minima of the trapping
potentials leads to the considerable displacement of the centers of mass of the
condensates, in agreement with the experiment. It is also shown that the
critical angular velocities of the vortex states of the system drastically
depend on the shift and the relative number of particles in the condensates,
and there is a possibility to exchange the vortex states between condensates by
shifting the centers of the trapping potentials.Comment: 4 pages, 2 figure
Magnetic Field Induced Insulating Phases at Large
Exploring a backgated low density two-dimensional hole sample in the large
regime we found a surprisingly rich phase diagram. At the highest
densities, beside the , 2/3, and 2/5 fractional quantum Hall states,
we observe both of the previously reported high field insulating and reentrant
insulating phases. As the density is lowered, the reentrant insulating phase
initially strengthens, then it unexpectedly starts weakening until it
completely dissapears. At the lowest densities the terminal quantum Hall state
moves from to . The intricate behavior of the insulating
phases can be explained by a non-monotonic melting line in the -
phase space
Symmetric-Asymmetric transition in mixtures of Bose-Einstein condensates
We propose a new kind of quantum phase transition in phase separated mixtures
of Bose-Einstein condensates. In this transition, the distribution of the two
components changes from a symmetric to an asymmetric shape. We discuss the
nature of the phase transition, the role of interface tension and the phase
diagram. The symmetric to asymmetric transition is the simplest quantum phase
transition that one can imagine. Careful study of this problem should provide
us new insight into this burgeoning field of discovery.Comment: 6 pages, 3 eps figure
Wigner crystallization and metal-insulator transition of two-dimensional holes in GaAs/AlGaAs at B=0
We report the transport properties of a low disorder two-dimensional hole
system (2DHS) in the GaAs/AlGaAs heterostructure, which has an unprecedentedly
high peak mobility of , with hole density of in the temperature range of
. From their T, p, and electric field dependences, we find that
the metal-insulator transition in zero magnetic field in this exceptionally
clean 2DHS occurs at , which is in good agreement with the
critical for Wigner crystallization , predicted by
Tanatar and Ceperley for an ideally clean 2D system.Comment: 4 pages, 4 Postscript figure
Trajectories of Depressive Symptoms in Old Age: Integrating Age-, Pathology-, and Mortality-Related Changes.
yesLate life involves a variety of different challenges to well-being. This study extends and qualifies
propositions drawn from the paradox of well-being in aging using 15-year longitudinal data on depressive symptoms from old and very old participants in the Australian Longitudinal Study of Ageing (Baseline N 2,087; Mage 78.69 years; range: 65–103 years; 49.40% women). We first examined age-related trajectories in depressive symptoms from young-old to oldest-old, taking into account (changes in) relevant correlates, pathology, and mortality; and, second, we investigated gender differences in these trajectories. Results revealed that age-related trajectories of depressive symptoms were predictive of
mortality hazards. The unique predictive effects of both level of, and change in, depressive symptoms were independent of one another and held after taking into account education as well as changes in marital status, living arrangements, cognitive function, and illness burden. In addition, results indicated that depressive symptoms were elevated among participants suffering from arthritis, and increased with
age more markedly in men than in women. In particular, the significant Age Gender interaction
indicated that the gender gap in depressive symptoms reduced from young-old to old-old and reversed in very old age when men showed more depressive symptoms than women. Qualifying the paradox of well-being in aging, findings demonstrated that depressive symptoms increased from young-old to oldest-old and suggest that age-, pathology-, and mortality-related changes should be examined in concert to advance our understanding of individual differences in depressive symptom trajectories in late life
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