Papers by Bretislav Friedrich
Prompted by the centenary of Alfred Landé’s g-factor, we reconstruct Landé’s path to his discover... more Prompted by the centenary of Alfred Landé’s g-factor, we reconstruct Landé’s path to his discovery of half-integer angular momentum quantum numbers and of vector coupling of atomic angular momenta - both encapsulated in the g-factor - as well as point to reverberations of Landé’s breakthroughs in the work of other pioneers of quantum physics.
Physical Chemistry Chemical Physics
A celebration of the 90th birthday of Professor Jan Peter Toennies.
Israel Journal of Chemistry
The Journal of Physical Chemistry A
Superfluid helium nanodroplets comprised of thousands to millions of helium atoms can serve as a ... more Superfluid helium nanodroplets comprised of thousands to millions of helium atoms can serve as a reactor for the synthesis of heterogeneous molecular clusters at cryogenic conditions. The cluster synthesis occurs via consecutive pickup of the cluster building blocks by the helium droplet and their subsequent coalescence within the droplet. The effective collision cross section of the building blocks is determined by the helium droplet size and thus exceeds by orders of magnitude that of a reactive collision in the gas phase. Moreover, the cryogenic helium environment (at 0.38 K) as a host promotes the formation of metastable cluster configurations. The question arises as to the extent of the actual involvement of the helium environment in the cluster formation. The present study deals with clusters of single phthalocyanine (Pc) molecules with single water molecules. A large fluorophore such as Pc offers several sites where the water molecule can attach. The resulting isomeric variants of the Pc−H 2 O complex can be selectively identified by electronic spectroscopy. We compare the experimental electronic spectra of the Pc− H 2 O complex generated in superfluid helium nanodroplets with the results of quantum-chemical calculations on the same cluster but under gas-phase conditions. The number of isomeric variants observed in the helium droplet experiment comes out the same as that obtained from our gas-phase calculations.
The Journal of Chemical Physics
We investigate the solvent shift of phthalocyanine (Pc) doped into superfluid helium droplets and... more We investigate the solvent shift of phthalocyanine (Pc) doped into superfluid helium droplets and probed by optical spectroscopy at the electronic origin. Our present work complements extant studies and provides results that in part contradict previous conclusions. In particular, the solvent shift does not increase monotonously with droplet radius all the way up to the bulk limit, but exhibits just the reverse dependence instead. Moreover, a substructure is resolved, whose characteristics depend on the droplet size. This behavior can hardly be reconciled with that of a freely rotating Pc-helium complex.
Physical Review A
We make use of the Quantum Hamilton-Jacobi (QHJ) theory to investigate conditional quasisolvabili... more We make use of the Quantum Hamilton-Jacobi (QHJ) theory to investigate conditional quasisolvability of the quantum symmetric top subject to combined electric fields (symmetric top pendulum). We derive the conditions of quasi-solvability of the time-independent Schrödinger equation as well as the corresponding finite sets of exact analytic solutions. We do so for this prototypical trigonometric system as well as for its anti-isospectral hyperbolic counterpart. An examination of the algebraic and numerical spectra of these two systems reveals mutually closely related patterns. The QHJ approach allows to retrieve the closed-form solutions for the spherical and planar pendula and the Razavy system that had been obtained in our earlier work via Supersymmetric Quantum Mechanics as well as to find a cornucopia of additional exact analytic solutions.
Chemphyschem : a European journal of chemical physics and physical chemistry, Jan 18, 2016
We investigate several aspects of realizing quantum computation using entangled polar molecules i... more We investigate several aspects of realizing quantum computation using entangled polar molecules in pendular states. Quantum algorithms typically start from a product state |00⋯0⟩ and we show that up to a negligible error, the ground states of polar molecule arrays can be considered as the unentangled qubit basis state |00⋯0⟩ . This state can be prepared by simply allowing the system to reach thermal equilibrium at low temperature (<1 mK). We also evaluate entanglement, characterized by concurrence of pendular state qubits in dipole arrays as governed by the external electric field, dipole-dipole coupling and number N of molecules in the array. In the parameter regime that we consider for quantum computing, we find that qubit entanglement is modest, typically no greater than 10(-4) , confirming the negligible entanglement in the ground state. We discuss methods for realizing quantum computation in the gate model, measurement-based model, instantaneous quantum polynomial time circu...
Chemical Physics Letters, Apr 1, 1994
ABSTRACT
The Journal of Physical Chemistry, 1995
We report simple model treatments and quasiclassical trajectory calculations dealing with collisi... more We report simple model treatments and quasiclassical trajectory calculations dealing with collisional relaxation and alignment of molecular rotation in atom-diatom collisions. Since these models and trajectories involve single collisions, our results do not pertain directly to alignment ...
Frontiers in Physics, Jun 3, 2014
We make use of supersymmetric quantum mechanics (SUSY QM) to find three sets of conditions under ... more We make use of supersymmetric quantum mechanics (SUSY QM) to find three sets of conditions under which the problem of a planar quantum pendulum becomes analytically solvable. The analytic forms of the pendulum's eigenfuntions make it possible to find analytic expressions for observables of interest, such as the expectation values of the angular momentum squared and of the orientation and alignment cosines as well as of the eigenenergy. Furthermore, we find that the topology of the intersections of the pendulum's eigenenergy surfaces can be characterized by a single integer index whose values correspond to the sets of conditions under which the analytic solutions to the quantum pendulum problem exist.
In proposals for quantum computers using arrays of trapped ultracold polar molecules as qubits, a... more In proposals for quantum computers using arrays of trapped ultracold polar molecules as qubits, a strong external field with appreciable gradient is imposed in order to prevent quenching of the dipole moments by rotation and to distinguish among the qubit sites. That field induces the molecular dipoles to undergo pendular oscillations, which markedly affect the qubit states and the dipole-dipole interaction. We evaluate
The Journal of Chemical Physics, 2003
Chemistry in Britain, 1999
Zeitschrift Fur Physik D Atoms Molecules and Clusters, Mar 1, 1992
Strong magnetic fields can hybridize low rotational states of paramagnetic molecules or molecular... more Strong magnetic fields can hybridize low rotational states of paramagnetic molecules or molecular ions whose electronic angular momentum is coupled to the molecular axis. The hybridization creates pendular states in which the molecular axis is confined to librate over a limited angular range about the field direction. In this way substantial spatial alignment associated with large Zeeman shifts can be attained for many groundstate radicals or ions and electronically excited states of diatomic or linear molecules. The magnetic hybridization is analogous to that recently demonstrated for polar molecules in electric fields. The magnetic version can only provide ensemble alignment rather than orientation, but offers complementary chemical scope by virtue of its applicability to nonpolar molecules and ions.
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Papers by Bretislav Friedrich