Quantum Coherence Properties Research Articles

Coherence measurements on Rydberg wave packets kicked by a half-cycle pulse

A kick from a unipolar half-cycle pulse (HCP) can redistribute population and shift the relative phase between states in a radial Rydberg wave packet. We have measured the quantum coherence properties following the kick, and show that selected coherences can be destroyed by applying a HCP at specific times. Quantum mechanical simulations show that this is due to redistribution of the angular momentum in the presence of noise. These results have implications for the storage and retrieval of quantum information in the wave packet.

Femtosecond quantum dynamics of diatomic molecules in optically dense gaseous media

A consistent quantum theory of a two-pulse pump-probe experiment in the femto-and picosecond spectroscopy of diatomic molecules is developed. The theory aims at the use of weak quantum femtosecond light pulses to excite molecular coherence. It is suggested that the experiment be realized using a double-frequency excitation scheme that is feasible for Na2 molecules. On the basis of the theory developed, the luminescence signals are calculated at different temperatures and different optical densities of the medium for the time range from 100 fs to ~ 100 ps. The results obtained show the presence of a strong dependence of the time and frequency spectra of a luminescence signal on the optical density of the medium at temperatures from 50 to 300 K. The proposed approach makes it possible to use the quantum coherence properties of optically dense media for more detailed study of the vibronic dynamics of diatomic molecules, in particular, detection of weak optical transitions.

Tubulin dipole moment, dielectric constant and quantum behavior: computer simulations, experimental results and suggestions

We used computer simulation to calculate the electric dipole moments of the α- and β-tubulin monomers and dimer and found those to be | p α| = 552D, | p β| = 1193D and | p αβ| = 1740D, respectively. Independent surface plasmon resonance (SPR) and refractometry measurements of the high-frequency dielectric constant and polarizability strongly corroborated our previous SPR-derived results, giving Δ n/Δ c ∼ 1.800 × 10 −3 ml/mg. The refractive index of tubulin was measured to be n tub ∼ 2.90 and the high-frequency tubulin dielectric constant k tub ∼ 8.41, while the high-frequency polarizability was found to be α tub ∼ 2.1 × 10 −33 C m 2/V. Methods for the experimental determination of the low-frequency p are explored, as well as ways to test the often conjectured quantum coherence and entanglement properties of tubulin. Biobits, bioqubits and other applications to bioelectronics are discussed.

Mechanically controllable break-junctions for use as electrodes for molecular electronics

We discuss the use of mechanically controllable break-junctions (MCBs) as electrodes forcontacting individual objects such as clusters or molecules. A big advantage of MCBelectrodes is the possibility of varying the contact geometry and, accordingly, thecontact resistances and the quantum coherent transport properties between theobject under study and the electrodes. We compare the suitability of single-atomcontacts of different elements as electrode material. Finally, we present preliminaryresults on electronic transport through individual (or a few) fullerene moleculescontacted by gold MCB electrodes. The typical resistances are in the order of thequantum of conductance. The circuits sustain voltages of the order of 1 V and aremechanically more stable than single-atom contacts between the gold electrodesalone.

Coherence properties of the stochastic oscillator

An oscillator with stochastic frequency is discussed as a model for evaluating the quantum coherence properties of a physical system. It is found that the choice of jump statistics has to be considered with care if unphysical consequences are to be avoided. We investigate one such model, evaluate the damping it causes, the decoherence rate and the correlations it results in, and the properties of the state for asymptotically long times. Also the choice of initial state and its effect on the time evolution of the correlations are discussed.

Transition between quantum coherence and incoherence

We show that a transformed Caldeira-Leggett Hamltonian has two distinct families of fixed points, rather than a single unique fixed point as often conjectured based on its connection to the anisotropic Kondo model. The two families are distinguished by a sharp qualitative difference in their quantum coherence properties and we argue that this distinction is best understood as the result of a transition in the model between degeneracy and non-degeneracy in the spectral function of the ``spin-flip'' operator.

Observation of quantum coherence properties of the hot electron

Summary form only given. The authors report the quantum coherence properties of hot electrons for GaInAs/InP systems. They obtained these properties along a path length as long as 280 nm at 77 K, the longest coherent length ever reported. The device used for the observation was a hot-electron transistor. The common-base emitter current-voltage characteristic was observed at 77 K when the collector-base voltage V/sub CB/ is zero. To confirm the quantum interference effect, the authors evaluated this characteristic by the first derivative. Three obvious peaks at 0.04, 0.08, and 0.15 V were observed under 0.2 V, and oscillations with a short period were observed when the applied voltage was over 0.2 V. Forty-eight oscillations were observed between 0.2 and 0.4 V. Three peaks under 0.2 V occurred due to the quantum interference effect in the base region. The period of peaks above 0.2 V was very short in comparison with those below 0.2 V. This threshold voltage, 0.2 V, agrees with the band discontinuity of GaInAs/InP systems. Thus it was judged that the oscillation above 0.2 V occurred due to the quantum interference effect in the InP collector barrier. >

Destruction of quantum coherence in a nonlinear oscillator via attenuation and amplification.

The exact solution to the master equation of a nonlinear oscillator, subject to damping or amplification, is presented. The effect of such incoherent processes on the quantum-coherence properties and recurrences is obtained. It is shown that amplification destroys quantum coherence more rapidly than does attenuation.

Quantum coherence properties of the FEL

In this paper we discuss the quantum coherence properties of the FEL within the framework of the single electron non-relativistic Hamiltonian picture. We analyse both single and multimode problems.

New Superfluid Relativity Gyroscope

Experiments have been performed in which mechanical radiation pressure, generated by a megahertz sound field in helium II, successfully supported a metal sphere three dimensionally. Because the field's forces are spherically symmetrical and stable, and because the isothermal environment provided by the quantum coherence properties of helium II eliminates convection currents, only extremely small stray torques act on the suspended mass. It is demonstrated that stray torques less than 10−7 dyn cm were present on the early test model, consistent with the theoretical predictions. Also presented is the predicted performance, based upon these results, of a more refined superfluid gyroscope which demonstrates the feasibility of observing general relativistic gyroscopic motion with a gyroscope rigidly connected to the earth. A proposed experiment to discriminate between Einstein's theory and competing theories of gravitation by measuring the spin-spin interaction between a gyroscope and the spinning earth is also discussed.