424 research outputs found
Measuring the Quantum State of a Large Angular Momentum
We demonstrate a general method to measure the quantum state of an angular
momentum of arbitrary magnitude. The (2F+1) x (2F+1) density matrix is
completely determined from a set of Stern-Gerlach measurements with (4F+1)
different orientations of the quantization axis. We implement the protocol for
laser cooled Cesium atoms in the 6S_{1/2}(F=4) hyperfine ground state and apply
it to a variety of test states prepared by optical pumping and Larmor
precession. A comparison of input and measured states shows typical
reconstruction fidelities of about 0.95.Comment: 4 pages, 6 figures, submitted to PR
Patterning the neuronal cells via inkjet printing of self-assembled peptides on silk scaffolds
The patterning of neuronal cells and guiding neurite growth are important for neuron tissue engineering and cell-based biosensors. In this paper, inkjet printing has been employed to pattern self-assembled I3QGK peptide nanofibers on silk substrates for guiding the growth of neuron-like PC12 cells. Atomic force microscopy (AFM) confirmed the dynamic self-assembly of I3QGK into nanofiber structures. The printed self-assembled peptide strongly adheres to regenerated silk fibroin (RSF) substrates through charge-charge interactions. It was observed that in the absence of I3QGK, PC12 cells exhibited poor attachment to RSF films, while for RSF surfaces coated or printed with peptide nanofibers, cellular attachment was significantly improved in terms of both cell density and morphology. AFM results revealed that peptide nanofibers can promote the generation of axons and terminal buttons of PC12 cells, indicating that I3QGK nanofibers not only promote cellular attachment but also facilitate differentiation into neuronal phenotypes. Inkjet printing allows complex patterning of peptide nanofibers onto RSF substrates, which enabled us to engineer cell alignment and provide an opportunity to direct axonal development in vitro. The live/dead assay showed that printed I3QGK patterns exhibit no cytotoxicity to PC12 cells demonstrating potential for future nerve tissue engineering applications
Phase Control of Nonadiabaticity-induced Quantum Chaos in An Optical Lattice
The qualitative nature (i.e. integrable vs. chaotic) of the translational
dynamics of a three-level atom in an optical lattice is shown to be
controllable by varying the relative laser phase of two standing wave lasers.
Control is explained in terms of the nonadiabatic transition between optical
potentials and the corresponding regular to chaotic transition in mixed
classical-quantum dynamics. The results are of interest to both areas of
coherent control and quantum chaos.Comment: 3 figures, 4 pages, to appear in Physical Review Letter
State determination in continuous measurement
The possibility of determining the state of a quantum system after a
continuous measurement of position is discussed in the framework of quantum
trajectory theory. Initial lack of knowledge of the system and external noises
are accounted for by considering the evolution of conditioned density matrices
under a stochastic master equation. It is shown that after a finite time the
state of the system is a pure state and can be inferred from the measurement
record alone. The relation to emerging possibilities for the continuous
experimental observation of single quanta, as for example in cavity quantum
electrodynamics, is discussed.Comment: 12 pages, 4 figures, Revte
Quantum-state control in optical lattices
We study the means to prepare and coherently manipulate atomic wave packets
in optical lattices, with particular emphasis on alkali atoms in the
far-detuned limit. We derive a general, basis independent expression for the
lattice operator, and show that its off-diagonal elements can be tailored to
couple the vibrational manifolds of separate magnetic sublevels. Using these
couplings one can evolve the state of a trapped atom in a quantum coherent
fashion, and prepare pure quantum states by resolved-sideband Raman cooling. We
explore the use of atoms bound in optical lattices to study quantum tunneling
and the generation of macroscopic superposition states in a double-well
potential. Far-off-resonance optical potentials lend themselves particularly
well to reservoir engineering via well controlled fluctuations in the
potential, making the atom/lattice system attractive for the study of
decoherence and the connection between classical and quantum physics.Comment: 35 pages including 8 figures. To appear in Phys. Rev. A. March 199
Phase diffusion as a model for coherent suppression of tunneling in the presence of noise
We study the stabilization of coherent suppression of tunneling in a driven
double-well system subject to random periodic function ``kicks''. We
model dissipation due to this stochastic process as a phase diffusion process
for an effective two-level system and derive a corresponding set of Bloch
equations with phase damping terms that agree with the periodically kicked
system at discrete times. We demonstrate that the ability of noise to localize
the system on either side of the double-well potenital arises from overdamping
of the phase of oscillation and not from any cooperative effect between the
noise and the driving field. The model is investigated with a square wave
drive, which has qualitatively similar features to the widely studied
cosinusoidal drive, but has the additional advantage of allowing one to derive
exact analytic expressions.Comment: 17 pages, 4 figures, submitted to Phys. Rev.
Mesoscopic quantum coherence in an optical lattice
We observe the quantum coherent dynamics of atomic spinor wavepackets in the
double well potentials of a far-off-resonance optical lattice. With appropriate
initial conditions the system Rabi oscillates between the left and right
localized states of the ground doublet, and at certain times the wavepacket
corresponds to a coherent superposition of these mesoscopically distinguishable
quantum states. The atom/optical double well potential is a flexible and
powerful system for further study of mesoscopic quantum coherence, quantum
control and the quantum/classical transition.Comment: 12 pages, 4 figures, submitted to Physical Review Letter
Multipartite Entanglement and Quantum State Exchange
We investigate multipartite entanglement in relation to the theoretical
process of quantum state exchange. In particular, we consider such entanglement
for a certain pure state involving two groups of N trapped atoms. The state,
which can be produced via quantum state exchange, is analogous to the
steady-state intracavity state of the subthreshold optical nondegenerate
parametric amplifier. We show that, first, it possesses some 2N-way
entanglement. Second, we place a lower bound on the amount of such entanglement
in the state using a novel measure called the entanglement of minimum bipartite
entropy.Comment: 12 pages, 4 figure
- …