Twelve years before the quantum no-cloning theorem

The celebrated quantum no-cloning theorem establishes the impossibility of making a perfect copy of an unknown quantum state. The discovery of this important theorem for the field of quantum information is currently dated 1982. I show here that an article published in 1970 [J. L. Park, Foundations of Physics, 1, 23-33 (1970)] contained an explicit mathematical proof of the impossibility of cloning quantum states. I analyze Park's demonstration in the light of published explanations concerning the genesis of the better-known papers on no-cloning.Comment: Some changes with respect to the previous version. This matches closely the published in AJ

Multiconfigurational pseudo-Hartree approach for the (t,t') propagator of a molecule in short laser fields

4 págs.; 3 figs.; PACS number(s): 33.80.2b, 42.50.HzA method was proposed to study the rotational dynamics of a molecule interacting with a single short laser pulse or a train of pulses. The possibility to use the arsenal of numerical methods developed for time independent systems was observed. It was stated that by diagonalizing a small configuration-interaction matrix formed from virtual Hartree-type wave functions, each Zeroth-order eigenstate can be improved. The number of time basis functions needed to obtain converged results may lead to a very large Floquet matrix. ©2004 American Physical SocietyFinancial support from the Ministerio de Ciencia y Tecnología of Spain, under Project No. BFM2001-2315 is acknowledged.Peer Reviewe

Anomalous asymmetry splittings in a molecule with internal rotation in the presence of classical chaos

4 págs.; 3 figs.; PACS number~s!: 03.65.2w, 05.45.1b, 34.50.Ez; Rapid CommunicationsRotation-torsion energy levels of acetaldehyde calculated from a spectroscopic Hamiltonian obtained from the fit of high-resolution microwave and far-infrared spectra, exhibit anomalously large splittings for some asymmetry doublets. It is shown that these anomalies are caused by chaos- enhanced quantum dynamical tunneling between classically disconnected regions of the phase space. A major consequence of this phenomenon is the magnification of intramolecular energy-transfer processes. ©1996 American Physical SocietyThis work was supported in part by the Division of Chemical Sciences, Office of Basic Energy Sciences, Office of Energy Research, U.S. Department of Energy, and by the Spanish DGICYT ~Research Project No. PB93-0138!.Peer Reviewe

Orientation of molecules with a small dipole moment using cyclic wave packets

5 págs.; 4 figs.; PACS number s : 32.80.Lg, 33.15.Kr, 33.80. bA robust and versatile method is demonstrated to maintain, for an arbitrary time, quasiconstant and strong orientation for molecules with minute dipole moments. The procedure is based on submitting molecules in cyclic wave packets to periodic trains of nonresonant pulses in an electrostatic field. We show that approximate cyclic states can be created by suddenly switching off a long laser pulse. A control scheme to remove the static field without spoiling orientation is suggested, which would permit large field-free orientation between pulses. © 2005 The American Physical Society.Financial support from the Ministerio de Educación y Ciencia of Spain, under Project No. FIS2004-02558 is acknowledgedPeer Reviewe

Torsional effects in molecular alignment

10 págs.; 11 figs.; 2 tabs.; app. ; PACS number(s): 33.57.+c, 33.15.BhA detailed theoretical formalism for the calculation of energy levels and eigenfunctions of molecules with a large amplitude coordinate in the presence of a strong laser pulse is developed based on a discrete variable representation to setup the Hamiltonian matrix. This approach is applied to nonrigid biphenyl-like molecules displaying a large amplitude motion corresponding to respective rotations of their two groups. The eigenvalues and eigenvectors obtained in several limiting cases of the hindering potential can be symmetry labeled and provide us with useful insights into the feasibility of torsional alignment. The present results support the rotation-induced breakdown of torsional alignment, under adiabatic following, previously described by Coudert, Pacios, and Ortigoso. © 2013 American Physical Society.J.O. acknowledges financial support from the Spanish Government through the MICINN (Project No. FIS2010- 18799).Peer Reviewe

Mechanism of Molecular Orientation by Single-cycle Pulses

Significant molecular orientation can be achieved by time-symmetric single-cycle pulses of zero area, in the THz region. We show that in spite of the existence of a combined time-space symmetry operation, not only large peak instantaneous orientations but also nonzero time-average orientations over a rotational period can be obtained. We show that this unexpected phenomenon is due to interferences among eigenstates of the time-evolution operator, as was described previously for transport phenomena in quantum ratchets. This mechanism also works for sequences of identical pulses, spanning a rotational period. This fact can be used to obtain a net average molecular orientation regardless of the magnitude of the rotational constant.Comment: Published version may be found at (URL:http://link.aip.org/link?/JCP/137/044303). Substantial changes with respect to previous versions, including new titl

2012 Quantum adiabatic theorem in light of the Marzlin-Sanders inconsistency Phys

A consensus that questions the perfunctory use of the quantum adiabatic theorem has emerged since Marzlin and Sanders [Phys. Rev. Lett. 93, 160408 (2004)] showed the existence of an inconsistency in the applicability of the theorem. Further analysis proved that the inconsistency may arise from the existence of resonant terms in the Hamiltonian, but recent work indicates that the debate about the full extent of the problem remains open. Here, we first show that key premises required in the standard demonstration of the theorem do not hold for a dual Hamiltonian involved in the Marzlin-Sanders inconsistency. Also, we show that two simple conditions can identify systems for which the adiabatic approximation fails, in spite of satisfying traditional quantitative conditions that were believed to guarantee its validity. Finally, we prove that the inconsistency only arises for Hamiltonians that contain resonant terms whose amplitudes go asymptotically to zero

Rotation-Induced Breakdown of Torsional Quantum Control

Control of the torsional angles of nonrigid molecules is key for the development of emerging areas like molecular electronics and nanotechnology. Based on a rigorous calculation of the rotation-torsion-Stark energy levels of nonrigid biphenyl-like molecules, we show that, unlike previously believed, instantaneous rotation-torsion-Stark eigenstates of such molecules, interacting with a strong laser field, present a large degree of delocalization in the torsional coordinate even for the lowest energy states. This is due to a strong coupling between overall rotation and torsion leading to a breakdown of the torsional alignment. Thus, adiabatic control of changes on the planarity of this kind of molecule is essentially impossible unless the temperature is on the order of a few Kelvin

Tailored particle current in an optical lattice by a weak time-symmetric harmonic potential

Quantum ratchets exhibit asymptotic currents when driven by a time-periodic potential of zero mean if the proper spatio-temporal symmetries are broken. There has been recent debate on whether directed currents may arise for potentials which do not break these symmetries. We show here that, in the presence of degeneracies in the quasienergy spectrum, long-lasting directed currents can be induced, even if the time reversal symmetry is not broken. Our model can be realized with ultracold atoms in optical lattices in the tight-binding regime, and we show that the time scale of the average current can be controlled by extremely weak fields.Comment: 4 pages, 4 figure