ITAMP Workshop

A Mini-Symposium on

Coherent Control

Organizer: Moshe Shapiro

August 28-29, 2000

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 Online Talks

Participants

Abstracts

Schedule of Talks

Online Talks

Balakrishnan

Brumer

Cao

Fleischhauer

 Friedrich

Gordon

Ivanov

Kral

Krause

 

Pearson

Rice

Shapiro

Tannor

Vardi

Participants

Dr. N. Balakrishnan
ITAMP
60 Garden Street, MS 14
Cambridge, MA 02138
nbala@cfa.harvard.edu

Prof. Nicholas P. Bigelow
Department of Physics and Astronomy and
Laboratory for Laser Energetics
P. O. Box 270171
The University of Rochester
Rochester, NY 14627
nbig@lle.rochester.edu

Prof. Paul W. Brumer
Dept. of Chemistry
Univ. of Toronto
Toronto, Ontario, Canada M5S 1A1
pbrumer@tikva.chem.utoronto.ca

Prof. Jianshu Cao
MIT
Chemistry Department
Room 2-121
Cambridge, MA 02139
jianshu@mit.edu

Dr. Michael Fleischhauer
ITAMP
60 Garden Street, MS 14
Cambridge, MA 02138
mfleischhauer@cfa.harvard.edu

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Prof. Robert Gordon
Dept of Chemistry
The Univ. of Illinois at Chicago
845 West Taylor Street
Chicago, IL 60607-7061
rjgordon@uic.edu

Dr. Misha Ivanov
Steacie Institute for Molecular Sciences
NRC of Canada, 100 Sussex Drive, room 2069,
Ottawa, Ontario K1A 0R6, Canada
Misha.Ivanov@nrc.ca

Prof. Jeffrey L. Krause
Dept. of Chemistry
University of Florida
Gainsville, Fl. 32611
krause@qtp.ufl.edu

Dr. Mikhail Lukin
ITAMP
60 Garden Street, MS 14
Cambridge, MA 02138
mlukin@cfa.harvard.edu

Mr. Brett Pearson
Dept. of Physics
U. of Michigan
Ann Arbor, MI 48109
bpearson@umich.edu

Stuart A. Rice
Dept. of Chemistry
Univ. of Chicago
Chicago, IL
s-rice@uchicago.edu

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Dr. Hossein Sadeghpour
ITAMP
60 Garden Street, MS 14
Cambridge, MA 02138
hsadeghpour@cfa.harvard.edu

Prof. Moshe Shapiro
ITAMP
60 Garden Street, MS 14
Cambridge, MA 02138
mshapiro@cfa.harvard.edu

David Tannor
Chemical Physics Department
Weizmann Institute of Science
Rehovot 76100, Israel
David.Tannor@weizmann.ac.il

Dr. Ami Vardi
ITAMP
60 Garden Street, MS 14
Cambridge, MA 02138
avardi@cfa.harvard.edu

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Abstracts

Balakrishnan

Brumer

Cao

Fleischhauer  

Friedrich

Gordon

Ivanov

Kral

Krause 

Lukin

Pearson

Shapiro

Tannor

Vardi

Production of Excited Iodine and the Control of I*/I Branching Ratio in the Photodissociation of NaI


N. Balakrishnan and H. R. Sadeghpour


Harvard-Smithsonian Center for Astrophysics

60 Garden St., MS 14

Cambridge, MA 02138

 

 PDF Version


Control of the outcome of a chemical reaction has long been the cherished goal of chemists.
The advent of femtosecond laser pulses has revolutionalized this idea and femtochemistry
has become a major area of research in which realtime dynamics of chemical reactions can
be probed, understood and possibly controlled. In the simplest case of the photodissociation
of a molecule, a femtosecond laser pulse initiates the process and a subsequent 'probe' laser
pulse interrogates the dissociating molecular species. The alkali metal halides, especially
NaI has served as a prototype for such investigations for over a decade. In the case of NaI,
the dissociation yields either neutral Na + I atoms or Na+ and I- ionic species. However, all theoretical approaches so far have considered the production of Na+I products in the ground state. The spin-orbit interaction in iodine is large and results in a splitting of about 0.95 eV between the ground 2 P3/2 and the excited 2P1/2 states. The asymptote of the Na+I(2P1/2) channel lie below the ionic dissociation threshold and the corresponding potential curve has not been calculated before. Here we present explicit ab initio calculations of the adiabatic potential energy curves, transition dipole matrix elements and spin-orbit coupling matrix elements in NaI, and investigate the photodissociation dynamics on the computed electronic states using a time-dependent wave packet description. The possibility of two-photon coherent control to in uence the branching ratio between the ground and excited states of iodine is also explored.

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Controlled Nanoscale Deposition and Controlled Chaotic Quantum Diffusion

Paul Brumer

University of Toronto
Department of Chemistry
Toronto, Ontario, Canada M5S 1A1



We describe two new applications of coherent control scenarios. In the first, cold molecules in a superposition of states are incident on a surface. Passing the molecules through two related coherent electric fields allows for control over the nanoscale molecular deposition pattern on the surface. In the second application, coherent control is shown to provide an effective means of controlling chaotic quantum diffusion. A number of
experimental implementations are suggested.

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 Quantum Coherence in Nonlinear Optical Processes


Jianshu Cao

Department of Chemistry

Massachusetts Institute of Technology
Cambridge, MA 02139

 

 Abstract PDF


Phase-dependence in nonlinear optical processes reveals an intriguing inter-play between the phase-coherence of a short laser pulse and the laser-induced quantum wave-packet dynamics, which can not be observed in the linear response regime. In rst part of the talk, the intra-pulse quantum coherence is demonstrated with two examples: molecular pulses for total inversion of electron population and unexpected chirp-dependence in multi-photon absorption yield. In the second part of the talk, the relevance of phase coherence in the dynamics of anharmonic coupled molecular systems is explored in the context of vibrational relaxation and multi-dimensional optical spectroscopy.

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Coherent Control of Photon Propagation: Dark-State Polaritons and Quantum Memory for Light

Michael Fleischhauer

Institute for Theoretical Atomic and Molecular Physics
Harvard-Smithsonian CfA
60 Garden St.
Cambridge, MA 02138

Photons are the fastest, most robust and readily available carriers of quantum information. But this information is hard to store and to process. A technique for a loss-free and reversible transfer of the quantum state of photon wave-packets to collective atomic excitations based on dark-state polaritons is described. Dark-state polaritons consist of electromagnetic and atomic spin-wave components whose mixture can be externally controlled. Adiabatically changing the mixture between spin-wave and elm. components allows to decellerate or accelerate and reshape the photon wave-packet. In particular the light pulse can be brought to a full stop and its quantum state is transferred to a collective atomic excitation. Reversing the process re-generates the photon wavepacket. Limitations and applications of the adiabatic transfer technique for quantum memories and quantum information transfer are discussed.

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 Alignment Is Forever - and Orientation too: Molecules in Combined Static Electric and Pulsed Nonresonant Radiative Fields

Long Cai, Jotin Marango, and Bretislav Friedrich

Department of Chemistry and Chemical Biology

Harvard University

Cambridge, MA 02138

 Abstract PDF

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 Using the Phase of Light as a Photochemical Tool

Robert J. Gordon

Department of Chemistry

University of Illilnois at Chicago

845 West Taylor Street

Chicago, IL 60607-7061

Tamar Seideman

Steacie Institute fo Molecular Sciences

National Research Council of Canada

Ottawa K1A OR6, Canada

 Abstract PDF

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Ultrashort Pulses and Control of Molecular Rotations: from Taming Molecules to Pulse Compression

Misha Ivanov


Femtosecond Program,
Steacie Institute for Molecular Sciences
NRC of Canada
Ottawa, Ontario K1A 0R6, Canada

Femtosecond pulses offer two approaches to quantum control, based on using pulse shaping techniques and/or strong electric fields. Both are combined in strong field molecular optics to align molecules and force controlled molecular rotations up to rotational dissociation threshold.

If time permits, I also hope to speculate on how control over molecular rotations, combined with feedback learning algorithms, can be used to generate and deliver through dispersive media single intense 1-2 fs pulses.

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 Photo-Galvano-Mechanical Phenomena in Nanotubes

Petr Kral

Chemical Physics Department
The Weizmann Institute of Science
Rehovot 76100, Israel

We present different possibilities of a photo-current generation in C and BN nanotubes, an relate them to new mechanical effects. First, we show that electric current can be generated in all types of C nanotubes by their simultaneous excitation with one and two-photon laser transitions (two-beam coherent control). Then we show that the induced current can drag freely intercalated atoms in the nanotube, which can have interesting potential applications. In a certain sense opposite effect to this can result, if the nanotube is immersed in a flowing liquid, which drags phonons and electrons in the nanotube. Finally, we discuss generation of currents in heteropolar BN nanotubes by one laser beam. The generated shift current runs along the tube, on its circumference or in an angle to the tube axis, depending on the nanotube electronic structure. The effect is based on a partial shift of electrons between different atoms, during the interband photo-induced transitions. It is also accompanied by an ultrafast expansion of the nanotube length, which makes it promising for ultrafast photo-electric and photo-mechanical applications.

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 Selective Population Transfer with Intense, Chirped Laser Pulses

Jeffrey L. Krause and Vladimir S. Malinovsky

University of Florida
Quantum Theory Project
P.O. Box 118435
Gainesville, FL 32611-8435

We consider population transfer by adiabatic rapid passage with intense, chirped laser pulses. Using a dressed-state picture, we analyze the effects of the chirp rate, intensity and frequency detuning. We demonstrate that chirped pulses and transform-limited pulses differ considerably with respect to both the efficiency and robustness of the transfer they affect. Finally, two schemes for selective population transfer are presented. The first uses a single
pulse, and selectivity is achieved by optimizing the chirp rate, intensity and bandwidth. In the second, pairs of pulses are used to create, and then carefully shape, the light-induced potentials on which the population transfer occurs. In both cases, nearly perfect inversion to a desired final state can be achieved.

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 Quantum Control of Interacting Atoms and

Mesoscopic Ensembles: Towards Fast, Robust and

Scalable Quantum Logic Gates

Mikhail Lukin

ITAMP

60 Garden Street, MS 14

Cambridge, MA 02138

Deterministic entanglement of coupled quantum systems (qubits) as well as its scalability to many-qubit systems are the main challenges in experimental quantum information science. As a rule, an exceptional degree of quantum control over internal (e.g. electronic) and external (e.g. motional) degrees of freedom is required to implement the so-called quantum logic operations.

We discuss several schemes for implementing fast and robust qubit entanglement. The schemes are based on neutral atoms interacting via electric dipole-dipole coupling. We identify the main sources of decoherence and errors and discuss several approaches to mitigate their influence. Specific implementations of these ideas include optically excited single atoms (impurities) in the condensed phase and cold atoms trapped in optical lattices and excited into low lying Rydberg states. Furthermore, we show how the combination of
atom-atom interactions with dark state polaritons allows one to process quantum information stored in collective spin states of mesoscopic ensembles.

The present approach eliminates stringent requirements on precise control of atomic position and motion, and allows for entanglement of distantly separated qubits thereby facilitating
scalability.

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 Using an Adaptive Algorithm to Learn About Quantum Systems

J. L. White, B. J. Pearson, T. C. Weinacht, and P. H. Bucksbaum

Physics Department, University of Michigan
Ann Arbor, MI 48109-1120

We have constructed an adaptive learning algorithm to control quantum systems. By directing intense shaped ultrafast laser pulses into a variety of samples and using a measurement of the system as a feedback signal, we are able to reshape the laser pulses to direct the quantum system into a desired physical state. The algorithm programs a computer-controlled, acousto-optic modulator (AOM) pulse shaper. The learning algorithm generates new shaped laser pulses based on the success of previous pulses in achieving a predetermined goal. In addition, the algorithm itself evolves in order to arrive at the solution in the most efficient manner.

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Coherent Control of Asymmetric Synthesis and the Photoassociation of Ultracold Atoms

Moshe Shapiro

Chemical Physics Department
The Weizmann Institute of Science
Rehovot 76100, Israel

We present a laser-based method of increasing the enantiomeric excess of a chiral enantiomer in a racemic mixture[1]. Neither the initial reagents nor the incident light need be chiral. Both formal and computational results show that enhancement of the enantiomer of choice, controlled by laser parameters, can be extensive. Extension of the method to treating chiral molecule purification in homogeneous media and in the presence of relaxation are then discussed. Computations for specific molecules are presented.

In the second part of the talk we present a time dependent theory for photoassociation induced by strong pulses[2]. Both the pump-before-dump "intuitive" and dump-before-pump "counter-intuitive" schemes are considered. Resonantly-enhanced two-photon association of ultracold atoms is shown to be an efficient mechanism for the production of ultracold molecules. We have performed detailed calculations on the radiative recombination of cold Na atoms by short laser pulses. Our calculations show that, per pulse, it is possible for up to 97% of all head-on Na-Na colliding pairs to end up as v=0, J=0 translationally cold Na2 molecules. These predictions were recently[3] confirmed experimentally in BEC.

References

[1] M. Shapiro, E. Frishman, and P. Brumer, "Coherently Controlled Asymmetric Synthesis with Achiral Light" Phys. Rev. Lett. 84 1669 (2000).

[2] A.. Vardi, D. G. Abrashkevich, E. Frishman and M. Shapiro, "Theory of Radiative Recombination with Strong Laser Pulses and the Formation of Ultracold Molecules via Stimulated Photo-Recombination of Cold Atoms" J. Chem. Phys. 107 6166 (1997).

A. Vardi, M. Shapiro and K. Bergmann, "Complete Population Transfer to and from a Continuum and the Radiative Association of Cold Na Atoms to Produce Translationally Cold Na2 Molecules in Specific Vib-Rotational States." Optics Express 4, 91
(1999).

[3] R. Wynar, R.S. Freeland, D.J. Han, C.Ryu and D.J. Heinzen, Science 287, 1016 (2000)

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Laser Cooling of Molecules:
A Theory of Purity Increasing Transformations


David J. Tannor and Alon Bartana


Department of Chemical Physics
Weizmann Institute, Rehovot, Israel


Ronnie Kosloff


Department of Chemistry and the Fritz Haber Institute for Molecular Dynamics
The Hebrew University

Jerusalem, Israel

 

 PDF of Abstract


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Dynamics And Control Of A Two-Mode Bose-Einstein Condensate
Beyond Mean-Field Theory

Amichay Vardi and James R. Anglin


ITAMP

60 Garden Street, MS 14

Cambridge, MA 02138

The two-mode model has been widely used to describe the rich dynamics of a Bose-Einstein condensate (BEC) in a double-well potential and a BEC with two radiatively-coupled internal (typically spin) states. The vast majority of these studies employ mean-field theory (MFT), de-correlating the ensemble at the lowest level of the BBGKY hierarchy of expectation value equations of motion, by approximating second-order moments in term of first order moments. MFT is essentially a semiclassical approximation for the quantum field operators, with the inverse square root of the number N of particles playing the role of \hbar as a perturbative parameter. Since in current BEC experiments N is indeed large, MFT is generally an excellent approximation and it is difficult to observe qualitatively significant quantum corrections. However, in the vicinity of a dynamical instability of MFT, quantum corrections appear on time-scales that grow only logarithmically with N. The two-mode model has exactly such an unstable point, corresponding to the Josephson /pi state in the double-well case. Using a Bloch-sphere picture for the reduced single particle density matrix
(SPDM), we propose an experiment to detect the quantum corrections in a two-mode BEC, and present a simple theory to predict them. We show that, as the Gross-Pitaevskii classical limit of a condensate resembles single particle quantum mechanics, so the leading quantum corrections appear in the single-particle picture as decoherence.

The MFT dynamical instability has significant implications on the 'state-engineering' and control of the two-mode condensate. Conventional /pi-pulse techniques are hard to implement in the presence of interactions, since the shape of the wave function, as well as the level-energies change as population is being transferred from one level to another, making it difficult to maintain the resonance. Adiabatic passage, on the other hand, becomes highly sensitive to the direction of the sweep (from negative to positive detuning or vise-versa) since this determines whether the evolving adiabatic eigenstate would pass through the unstable state or not. Assuming repulsive interactions, we show that beyond a critical value of the interaction strength, corresponding to the formation of the instability, adiabaticity can not be maintained with a negative sweep, no matter how slowly the resonance is traversed (The same is true for attractive interactions and a positive sweep). The collapse of adiabaticity is motivated by the MFT instability as well as by the high quasi-particle production rate near that point.

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Schedule of Talks

 All sessions will be held in the Classroom in Building A, Room 101

Monday, August 28, 2000

Session I. Quantum Control

 9:00 a.m.  S. Rice: Variations on the Theme of STIRAP
 9:40 a.m. R. Gordon: Using the Phase of Light as a Photochemical Tool
10:20 a.m. Coffee

Session II. Wavepacket Control

10:40 a.m. B. Pearson: Using an Adaptive Algorithm to Learn About Quantum Systems
11:20 a.m. N. Balakrishnan: Production of Excited Iodine and the Control of I*/I Branching Ratio in the Photodissociation of NaI
12:00 noon Lunch

Session III. Photonic Control and Entanglement

1:30 p.m. M. Lukin: Quantum Control of Interacting Atoms and Mesoscopic
Ensembles: Towards Fast, Robust and Scalable Quantum
Logic Gates
2:10 p.m. M. Fleischhauer: Coherent Control of Photon Propagation: Dark-State Polaritons and Quantum Memory for Light
2:50 p.m. Refreshments

Session IV. Control in Condense Phase I

3:20 p.m. P. Brumer: Bichromatic Coherent Control: Controlled Nanoscale
Deposition and Controlled Chaotic Quantum Diffusion
4:00 p.m. J. Krause: Selective Population Transfer with Intense, Chirped Laser
Pulses

5:00 p.m. Reception in 3rd Floor Perkin Bridge

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Tuesday, August 28, 2000

Session V. Control in Condense Phase II

 9:00 a.m.  J. Cao: Quantum Coherence in Nonlinear Optical Processes
 9:40 a.m.  P. Kral: Photo-Galvano-Mechanical Phenomena in Nanotubes
 10:20 a.m. Coffee

Session VI. Coherent Cooling and Trapping I

 10:40 a.m. A. Vardi: Dynamics and Control of a Two-Mode Bose-Einstein Condensate Beyond Mean-Field Theory
 11:20 a.m. D. Tannor: Laser Cooling of Molecules: A Theory of Purity Increasing Transformations
12:00 noon Lunch

Session VII. Coherent Cooling and Trapping II

1:30 p.m. N. Bigelow: Formation of Homo- and Heteronuclear Ultracold
Molecules
2:10 p.m. M. Shapiro: Coherent Control of Asymmetric Synthesis and the Photoassociation of Ultracold Atoms
2:50 p.m. Refreshments

Session VIII. Strong Fields

3:10 p.m. M. Ivanov: Ultrashort Pulses and Control of Molecular Rotations:
From Taming Molecules to Pulse Compression
3:50 p.m. B. Friedrich: Alignment Is Forever - and Orientation too: Molecules in Combined Static Electric and Pulsed Nonresonant Radiative Fields
4:30 p.m. Summary

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