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

Resolved-sideband Raman cooling to the ground state of an optical lattice

We trap neutral Cs atoms in a two-dimensional optical lattice and cool them close to the zero-point of motion by resolved-sideband Raman cooling. Sideband cooling occurs via transitions between the vibrational manifolds associated with a pair of magnetic sublevels and the required Raman coupling is provided by the lattice potential itself. We obtain mean vibrational excitations \bar{n}_x \approx \bar{n}_y \approx 0.01, corresponding to a population \sim 98% in the vibrational ground state. Atoms in the ground state of an optical lattice provide a new system in which to explore quantum state control and subrecoil laser coolingComment: PDF file, 13 pages including 3 figure

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 $\delta-$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.

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

Sub-Poissonian statistics in order-to-chaos transition

We study the phenomena at the overlap of quantum chaos and nonclassical statistics for the time-dependent model of nonlinear oscillator. It is shown in the framework of Mandel Q-parameter and Wigner function that the statistics of oscillatory excitation number is drastically changed in order-to chaos transition. The essential improvement of sub-Poissonian statistics in comparison with an analogous one for the standard model of driven anharmonic oscillator is observed for the regular operational regime. It is shown that in the chaotic regime the system exhibits the range of sub- and super-Poissonian statistics which alternate one to other depending on time intervals. Unusual dependence of the variance of oscillatory number on the external noise level for the chaotic dynamics is observed.Comment: 9 pages, RevTeX, 14 figure

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

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

Dichotomy of Tyrosine Hydroxylase and Dopamine Regulation between Somatodendritic and Terminal Field Areas of Nigrostriatal and Mesoaccumbens Pathways

Measures of dopamine-regulating proteins in somatodendritic regions are often used only as static indicators of neuron viability, overlooking the possible impact of somatodendritic dopamine (DA) signaling on behavior and the potential autonomy of DA regulation between somatodendritic and terminal field compartments. DA reuptake capacity is less in somatodendritic regions, possibly placing a greater burden on de novo DA biosynthesis within this compartment to maintain DA signaling. Therefore, regulation of tyrosine hydroxylase (TH) activity may be particularly critical for somatodendritic DA signaling. Phosphorylation of TH at ser31 or ser40 can increase activity, but their impact on L-DOPA biosynthesis in vivo is unknown. Thus, determining their relationship with L-DOPA tissue content could reveal a mechanism by which DA signaling is normally maintained. In Brown-Norway Fischer 344 F1 hybrid rats, we quantified TH phosphorylation versus L-DOPA accumulation. After inhibition of aromatic acid decarboxylase, L-DOPA tissue content per recovered TH protein was greatest in NAc, matched by differences in ser31, but not ser40, phosphorylation. The L-DOPA per catecholamine and DA turnover ratios were significantly greater in SN and VTA, suggesting greater reliance on de novo DA biosynthesis therein. These compartmental differences reflected an overall autonomy of DA regulation, as seen by decreased DA content in SN and VTA, but not in striatum or NAc, following short-term DA biosynthesis inhibition from local infusion of the TH inhibitor α-methyl-p-tyrosine, as well as in the long-term process of aging. Such data suggest ser31 phosphorylation plays a significant role in regulating TH activity in vivo, particularly in somatodendritic regions, which may have a greater reliance on de novo DA biosynthesis. Thus, to the extent that somatodendritic DA release affects behavior, TH regulation in the midbrain may be critical for DA bioavailability to influence behavior

State-of-the-art of 3D cultures (organs-on-a-chip) in safety testing and pathophysiology.

Integrated approaches using different in vitro methods in combination with bioinformatics can (i) increase the success rate and speed of drug development; (ii) improve the accuracy of toxicological risk assessment; and (iii) increase our understanding of disease. Three-dimensional (3D) cell culture models are important building blocks of this strategy which has emerged during the last years. The majority of these models are organotypic, i.e., they aim to reproduce major functions of an organ or organ system. This implies in many cases that more than one cell type forms the 3D structure, and often matrix elements play an important role. This review summarizes the state of the art concerning commonalities of the different models. For instance, the theory of mass transport/metabolite exchange in 3D systems and the special analytical requirements for test endpoints in organotypic cultures are discussed in detail. In the next part, 3D model systems for selected organs--liver, lung, skin, brain--are presented and characterized in dedicated chapters. Also, 3D approaches to the modeling of tumors are presented and discussed. All chapters give a historical background, illustrate the large variety of approaches, and highlight up- and downsides as well as specific requirements. Moreover, they refer to the application in disease modeling, drug discovery and safety assessment. Finally, consensus recommendations indicate a roadmap for the successful implementation of 3D models in routine screening. It is expected that the use of such models will accelerate progress by reducing error rates and wrong predictions from compound testing