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Moshe Shapiro

Publications and source records attributed to Moshe Shapiro.

At least 19 recordsLinked to original sources
PubMed2006

Cold atomic collisions: coherent control of penning and associative ionization.

Coherent control techniques are computationally applied to cold (1 mK<T<1 K) and ultracold (T<1 muK) Ne*(3s,3P2)+Ar(1S0) collisions. We show that by using various initial superpositions of the Ne*(3s,3P2) M={-2,-1,0,1,2} Zeeman sublevels it is possible to reduce the Penning ionization and associative ionization cross sections by as much as 4 orders of magnitude. It is also possible to drastically change the ratio of these two processes. The results are based on combining, within the "rotating atom approximation", empirical and ab initio ionization widths.

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PubMed2006

Enhanced selectivity and yield in multichannel photodissociation reactions: application to CH3I.

We develop a method to improve the population transfer and final-channel control of multichannel photodissociation reactions. The method is applied to the photodissociation of methyl iodide, CH3(v)+I*(2P1/2)<--CH3I-->CH3(v)+I(2P3/2). Our method is based on simultaneously exciting many two-photon pathways that lead to the same final outcome, each proceeding via a different intermediate bound state. The selectivity of the final product state(s) is a result of coherently controlled interference between the quantum pathways. The improvement in the population transfer yield from the ground state to the selected dissociative channel(s) is made possible by executing the process in an adiabatic fashion.

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PubMed2006

Coherent control of collision processes: Penning versus associative ionization.

Coherent control theory is applied to the control of Ne*(3s,(3)P2)+Ar((1)S0) collisions and computations are shown that display extensive control over these processes. Indeed we demonstrate that it is possible to essentially turn on and off the cross sections for both the Penning and associative ionization processes. This facility arises from the interference between matter waves induced by creating a linear superposition of the degenerate M={-2,-1,0,1,2} Zeeman sublevels of the Ne*(3s,(3)P2) target atom. The computations, conducted at collision energies in the 1-8 kcal/mole range, are based on combining, within the "rotating atom approximation," empirically derived and ab initio ionization widths.

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PubMed2006

Optimization of laser-focused deposition lines: Rydberg atoms.

Optimally narrow nanoscale lines are computationally obtained for Rb Rydberg atoms deposited on surfaces. The use of optimized polychromatic fields is shown to allow lines as narrow as 1 nm in the absence of transverse velocities and shown to counter the deleterious effects of transverse velocities in laser cooled beams. Specifically, lines as narrow as 6.5 nm wide are obtained in the presence of transverse velocities associated with a temperature of 1 mK. Using this approach it is possible to deposit a single narrow line, even when the atomic beam is bigger than the period of the focusing lens, using as few as two, relatively weak, laser fields.

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PubMed2006

EPR breakup of polyatomic molecules.

We explore the EPR experiment in the case of the breakup of a polyatomic molecule into two mutually entangled fragments. We give a derivation based on the properties of the dissociated wave function that no information is transferred, not even at a speed smaller than the speed of light, from one entangled partner to the other concerning its measurement or lack thereof. We also explain experiments that show that each separated fragment can retain coherences induced in its parent molecule by a broad band laser pulse, regardless of whether a measurement has been performed on its entangled partner.

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PubMed2006

Efficient partitioning technique for computing the dynamics of intramolecular processes: radiationless transitions in pyrazine.

An efficient QP partitioning algorithm to compute the eigenvalues, eigenvectors, and the dynamics of large molecular systems of a particular type is presented. Compared to straightforward diagonalization, the algorithm displays favorable scaling (proportional to N(T)2) as a function of N(T), the size of the Hamiltonian matrix. In addition, the algorithm is trivially parallelizable, necessitating no "cross-talk" between nodes, thus enjoying the full linear speedup of parallelization. Moreover, the method requires very modest storage space, even for extremely large matrices. The method has also been enhanced through the development of a coarse-grained approximation, enabling an increase of the basis set size to unprecedented levels (10(8)-10(10) in the current application). The QP algorithm is applied to the dynamics of electronic internal conversion in a 24 vibrational-mode model of pyrazine. A performance comparison with other dynamical methods is presented, along with results for the decay dynamics of pyrazine and a discussion of resonance line shapes.

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PubMed2006

Theory of "laser distillation" of enantiomers: purification of a racemic mixture of randomly oriented dimethylallene in a collisional environment.

Enantiomeric control of 1,3 dimethylallene in a collisional environment is examined. Specifically, our previous "laser distillation" scenario wherein three perpendicular linearly polarized light fields are applied to excite a set of vib-rotational eigenstates of a randomly oriented sample is considered. The addition of internal conversion, dissociation, decoherence, and collisional relaxation mimics experimental conditions and molecular decay processes. Of greatest relevance is internal conversion which, in the case of dimethylallene, is followed by molecular dissociation. For various rates of internal conversion, enantiomeric control is maintained in this scenario by a delicate balance between collisional relaxation of excited dimethylallene that enhances control and collisional dephasing, which diminishes control.

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PubMed2006

Nanoscale paul trapping of a single electron.

We demonstrate that a Paul trap made up of four conducting nanotubes is capable of trapping a single electron. In addition to the size, the major differences between such a nano-trap and its macroscopic analogue are that the electron is treated as a quantum object and that its effect ("back reaction") on the trapping device cannot be ignored. We computationally demonstrate focusing and trapping of an electronic wave packet, while fully accounting for the image charges induced by the electron on the nanotubes. The electron image charge interaction significantly affects the electron dynamics, and thus the trap stability. An (entangled) set of trapped electrons offers a number of advantages for quantum information processing.

Computer Simulation↗
PubMed2005

Detection and automatic repair of nucleotide base-pair mutations by coherent light.

We show that phase-coherent optical techniques allow for the detection and automatic repair of mutations in nucleotide pairs. We demonstrate computationally that there is a laser pulse sequence that can detect the occurrence of a mutation caused by a double proton transfer between hydrogen-bonded nucleotide pairs and automatically repair it by converting the mutated nucleotide pair to the nonmutated one. The specific system chosen for this demonstration is the hydrogen-bonded 2-pyridone.2-hydroxypyridine dimer at typical internucleotide distances, a well-established model for tautomeric acid base pairs.

Base Pairing↗
PubMed2005

Overlapping resonances in the coherent control of radiationless transitions: internal conversion in pyrazine.

Coherent control of radiationless transitions is developed and applied to internal conversion. Conditions for active versus passive control are described and overlapping resonances are shown necessary for the phase control of radiationless transitions in molecular systems. Applications to pyrazine show the possibility of extensive control via optimized state preparation, as well as the significant role of overlapping resonances, even in the evolution of single vibrational states in S2.

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PubMed2005

Reentrant onset of chaos in tubular image states.

We investigate the reentrant onset of chaos in "tubular image states," which are loosely bound states of electrons formed in the vicinity (20-40 nm) of conducting nanotubes. Chaos is shown to arise when an electron is placed in the vicinity of two metallic nanotubess with a magnetic field applied along the tubes. At stronger magnetic fields B approximately 10 T, we observe the formation of Landau-like states encircling the two-tube system, which wipe out the chaos. We can reinstall the chaos by charging oppositely the nanotubes, thus breaking the symmetry of the system and correspondingly the shape of the Landau-like states. Detailed analysis of the onset of chaos is done by studying the statistical properties of the eigenvalues spectrum and by investigating the spatial autocorrelation functions of individual eigenstates.

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PubMed2005

Tunable bands of electronic image states in nanowire lattices.

We demonstrate that suspended arrays of parallel nanowires support bound electron image states with rich band structures. Surprisingly, these Bloch states can be highly detached from the surfaces of the nanowires, similar to the single-tube wave functions. This is because an electron hovering in such a periodic lattice of nanowires is influenced by a Coulombic-like attraction and a centrifugal repulsion, which are both central symmetric around each wire. These novel states could be used in building of waveguides, mirrors, and storage places for Rydberg-like electrons.

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PubMed2004

Theory of the two step enantiomeric purification of 1,3 dimethylallene.

An application of a recently proposed [P. Kral et al., Phys. Rev. Lett. 90, 033001 (2003)] two step optical control scenario to the purification of a racemic mixture of 1,3 dimethylallene is presented. Both steps combine adiabatic and diabatic passage phenomena. In the first step, three laser pulses of mutually perpendicular linear polarizations, applied in a "cyclic adiabatic passage" scheme, are shown to be able to distinguish between the L and D enantiomers due to their difference in matter-radiation phase. In the second step, which immediately follows the first, a sequence of pulses is used to convert one enantiomer to its mirror-imaged form. This scenario, which only negligibly populates the first excited electronic state, proves extremely useful for systems such as dimethylallene, which can suffer losses from dissociation and internal conversion upon electronic excitation. We computationally observe conversion of a racemic mixture of dimethylallene to a sample containing approximately 95% of the enantiomer of choice.

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PubMed2004

Coherent control of resonance-mediated reactions: F+HD.

Cross sections resulting from scattering that proceeds via an intermediate resonance are shown to be exceptionally controllable using a coherent superposition of only two initial states. Full quantum computations on F+HD(v=0;j=0,1)-->H+DF, D+HF, which exhibits a resonance in one of the reactive channels, support the formal arguments, showing that control is indeed vast. In this case the ratio of reactive integral cross sections can be altered by a factor of 62 (compared to a noncoherent factor of only 3.3), while the ratio of reactive differential cross sections can be altered by a factor of over 6000 (compared to a noncoherent factor of less than 7). These results constitute the first prediction of extensive quantum control in a collisional process.

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PubMed2004

Complete control of population transfer between clusters of degenerate states.

We present an analytic solution to the "degenerate quantum control problem," which enables the transfer of any desired fraction of population between arbitrary initial and final pure wave packets, made up of nearly degenerate energy eigenstates. It consists of two two-photon adiabatic passage steps, in which the population of the initial wave packet is first transferred, via a number of nondegenerate intermediate states, to a single eigenstate and then returned to a different target superposition state. We demonstrate the approach by executing a stepwise isomerization of three Jahn-Teller states of the Al3O molecule, where a proper optical coupling can easily be established.

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PubMed2003

Two-step enantio-selective optical switch.

We present an optical "enantio-selective switch" that, in two steps, turns a ("racemic") mixture of left-handed and right-handed chiral molecules into the enantiomerically pure state of interest. The optical switch is composed of an "enantio-discriminator" and an "enantio-converter" acting in tandem. The method is robust, insensitive to decay processes, and does not require molecular preorientation. We demonstrate the method on the purification of a racemate of (transiently chiral) D2S2 molecules, performed on the nanosecond time scale.

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PubMed2002

Highly extended image states around nanotubes.

We predict that freely suspended, linear molecular conductors or dielectrics, such as carbon nanotubes, can support electronic states that are localized far from the surface. These "tubular image states" are formed in extended potential wells resulting from the tug of war between the external electron's attraction to its image charge in the nanotube, and its repulsion from the tube due to its transverse angular momentum. The displacement of these states (>10 nm) away from the surface prevents their wave functions from collapsing, resulting in long lifetimes at low temperatures. We predict that tubular image states with binding energies of 1-10 meV can be formed via radiative recombination.

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