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  • 1
    Electronic Resource
    Electronic Resource
    Quantum grammars (2000)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 41 (2000), S. 4508-4520 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: We consider quantum (unitary) continuous time evolution of spins on a lattice together with quantum evolution of the lattice itself. In physics such evolution was discussed in connection with quantum gravity. It is also related to what is called quantum circuits, one of the incarnations of a quantum computer. We consider simpler models for which one can obtain exact mathematical results. We prove existence of the dynamics in both Schrödinger and Heisenberg pictures, construct KMS states on appropriate C*-algebras. We show (for high temperatures) that for each system where the lattice undergoes quantum evolution, there is a natural scaling leading to a quantum spin system on a fixed lattice Z, defined by a renormalized Hamiltonian. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.533357
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  • 2
    Electronic Resource
    Electronic Resource
    Absorption spectra of dipolar Frenkel excitons in two-dimensional lattices with configurational disorder: Long-range interaction and motional narrowing effects (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 3023-3030 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present results of numerical simulations of optical absorption line shape of Frenkel excitons in two-dimensional disordered lattices. Disorder is generated by Gaussian randomness in the molecular positions. The intersite interaction is considered to be of dipole origin, including coupling to far neighbors. Results of simulations are compared with those obtained in the frame of the nearest-neighbor approximation, showing remarkable differences in the absorption line shape. The motional narrowing effect is found to be essentially different from that previously reported for the case of diagonal disorder as well as for that produced by randomness in nearest-neighbor hopping integrals. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480876
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  • 3
    Electronic Resource
    Electronic Resource
    Intrinsic optical bistablility of an ultrathin film consisting of oriented linear aggregates (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 1170-1176 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A theoretical study of transmittivity of an ultrathin film (of thickness smaller than an optical wavelength) consisting of oriented linear aggregates is carried out. We show that within a certain domain of the incident field amplitude, optical transitions of a single disordered aggregate, the eigenstates of which are represented by the Frenkel exciton states, can be treated in the framework of a two-level approximation. This allows us to claim that an ensemble of linear aggregates is analogous to that comprised of inhomogeneously broadened two-level systems. Based on this analogy, we show that the transmittivity of the film can manifest a bistable behavior originating from the coupling of the aggregates via the emission (far-zone) field. This mechanism of bistability differs from that occurring in a single perfect aggregate. In the latter case, bistability results from the population-dependent resonance frequency shift of an individual aggregate, originating from the coupling of the molecules via the dipole–dipole (near-zone) field. Estimates of the driving parameters show that real candidates, to realize the type of behavior we found, are such well-studied objects as J-aggregates of polymethine dyes or thin films of thiophene oligomers. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481895
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  • 4
    Electronic Resource
    Electronic Resource
    Mirrorless optical bistability of an ultrathin glassy film built up of oriented J-aggregates: Effects of two-exciton states and exciton–exciton annihilation (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 1966-1969 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We theoretically analyze the optical response of an ultrathin film with accounting for the effects of creating two exciton states as well as their annihilation in an individual aggregate. We show that these two processes do not violate mirrorless optical bistability of the film found in the framework of the ground-to-one exciton state transitions but, contrary to that, act towards improving the conditions for bistability to occur. In particular, the killing action of inhomogeneous broadening of the one-exciton absorption spectrum may be considerably reduced due to the exciton–exciton annihilation process giving hope for creating a unit for an all-optical device based on such systems. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1344232
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  • 5
    Electronic Resource
    Electronic Resource
    Random walks in two-dimensional complexes (1991)
    Springer
    Queueing systems 9 (1991), S. 269-300 
    Details
    ISSN: 1572-9443
    Keywords: Random walks ; two-dimensional complexes ; ergodicity ; transience ; hedgehog
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract A 2-dimensional complex is a union of a finite number of quarter planes ℤ + 2 having some boundaries in common. The most interesting example is the union of all 2-dimensional faces of ℤ + N . We consider maximally homogeneous random walks on such complexes and obtain necessary and sufficient conditions for ergodicity, null recurrence and transience up to some “non-zero” assumptions which are of measure 1 in the parameter space. The problem we address in this paper is of theoretical range. However, the results can be applied to performance evaluation of some telecommunication systems (e.g. local area networks) viewed as interacting queues. To enforce this assertion, a detailed example of coupled queues in differentregimes is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01158467
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  • 6
    Electronic Resource
    Electronic Resource
    Phase transitions of classical Heisenberg ferromagnets with arbitrary parameter of anisotropy (1975)
    Springer
    Communications in mathematical physics 40 (1975), S. 75-82 
    Details
    ISSN: 1432-0916
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Notes: Abstract The existence of a phase transition of the first kind is proved for anisotropic classical Heisenberg ferromagnet in two or more dimensions and with arbitrary parameter of anisotropy α, |α|〈1; a similar fact is proved for much more general lattice spin systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01614098
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  • 7
    Electronic Resource
    Electronic Resource
    Invariant subspaces of clustering operators (1979)
    Springer
    Journal of statistical physics 21 (1979), S. 231-242 
    Details
    ISSN: 1572-9613
    Keywords: Clustering operators ; clustering estimates ; transfer matrix ; spectrum of many-body system ; one-particle space ; two-, three-, and many-particle spaces
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A class of clustering operators is defined which is a generalization of a transfer matrix of a Gibbs lattice field with an exponential decay of correlations. It is proved that for small values ofβ the clustering operator has invariant subspaces which are similar tok-particle subspaces of the Fock space. The restriction of the clustering operator onto these subspaces resembles the operator exp(-H k, whereH k is thek- particle Schrödinger Hamiltonian in nonrelativistic quantum mechanics. The spectrum of eachH k,k⩾1, is contained in the interval (C 1βk,C 2βk). These intervals do not intersect with each other.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01011467
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  • 8
    Electronic Resource
    Electronic Resource
    Spin interaction with an ideal Fermi gas (1987)
    Springer
    Journal of statistical physics 48 (1987), S. 51-68 
    Details
    ISSN: 1572-9613
    Keywords: Equilibrium dynamics ; quantum spin system ; Fermi gas ; particle in an ideal gas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We consider the equilibrium dynamics of a system consisting of a spin interacting with an ideal Fermi gas on the lattice ℤΝ, Ν⩾3. We present two examples: when this system is unitarily equivalent to an ideal Fermi gas or to a spin in an ideal Fermi gas without interaction between them.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01010399
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  • 9
    Electronic Resource
    Electronic Resource
    Inversionless superradiance of an ensemble of three-level atoms in a high-Q cavity (1999)
    Springer
    Journal of experimental and theoretical physics 88 (1999), S. 278-285 
    Details
    ISSN: 1090-6509
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We analyze the possibility of superradiance in an ensemble of three-level atoms in the absence of population inversion. We show that in the case of a Λ configuration of the active transitions this effect can occur for an initially coherent superposition of the states of the lower doublet. We also study how splitting of the lower levels influences this effect and discuss ways of creating low-frequency coherence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.558795
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  • 10
    Electronic Resource
    Electronic Resource
    Uniform cluster estimates for lattice models (1979)
    Springer
    Communications in mathematical physics 64 (1979), S. 131-157 
    Details
    ISSN: 1432-0916
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Notes: Abstract In [2] we obtained the complete cluster expansion for transfermatrix for lattice models with bounded potentials in high-temperature region. Here we obtain necessary cluster estimates for semiinvariants of functionals over Gibbs field with unbounded interaction in high-temperature region and for contour models in low-temperature region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01197510
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