DTIC ADA424420: Quantum Computing and Information Transfer by Optical Manipulation of Molecular Coherences

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QuanTUM COMPUTING & INFORMATION TRANSFFR BY OPTICAL
MANIPULATION OF MOLECULAR COHERENCES

AFOSR Grant F49620-01-1-0449

V. Aes Apkerian
Depardment af Chemistry
University of Califone, irvine CA 92697-2025

[___Accomplished Science

While fanmally quantum computation has hevorne a ralber well defined dicoretical
science, physical demonstrations aro fevr, limited to several qubits, and to several steps in
ricessing. At present, there is not a recognized, scalable physical method of implementation
thu! meeis the promise of truc computation, We have proposed noulinear spectroscopic
‘methods of eaherence manipulation, and in pattivelar, Time-Froqucney Resolved Coherent
‘Anti-Stokes Raman Seavering (TFRCARS) in die molecelar ro-vibvonie Hithet space as a
novel scheme for implementing quantum logic. ‘The method has advantages. with its
demonstrable massive parallaism, therefore well suited for jaTormalicm trunsler, wate its
sealahily retaains auesolved, both chevreieally and sith regard to physical implemeutations,
‘We ate actively following the li ler, with Ore concept of an inhiomogencously indexed arruy of
single quancun centers as the physical realization,

‘In an extended paper.' we demunstraved experimentally that the clomen‘s suffiient for
cexceuting universal quamlum logic, dammely the set of ono-qubit rotations and the two-qubic
Contralled-Not (CNOT) gute, are naturally contained in TKRCARS. The cxpeciments were
caltied out it room temaperutore mofecalur iodine, in which superpositions of 10" eigenstates
fare prepared, manipnlated and rexd-out at the uncestainty limit, trough the four-wave wicing
process of TFRCARS, We demonstrated the universal gales by consteucting logical map
between TERCARS observables and input pulses i ters of oasipulated mulc-dimensional
quantum coherences. ‘The paper conteins all of (he important original concepts regarding
nonlinear speotoscepy’ in Hilbert space at a viable approach to Q-computing. If not full
fledged contputing, thon a lens. qvanlurn communication and cneryption can be expeuied as a
neat cecm practical application of our approach

‘While defining how logie gates ean be constucted in TFRCARS is the logical starting
point, it is av useful i give concrete exaraples of how such gates can e assembled tagcther 10
fxeoule a well-defined algoritora, To this end, we illusteated how the Deutsch-Jozsa (DI)
algorithm? which has beeoms a bencltmack for expetimencal demonstrations of quanturt
computing, could be implemented ia TFRCARS.? The DJ algorithm demonstrates the
advantage of the use of qubits in superposition, as opposed lo classical definive bits, to gain
‘exphnentin! advantage in seach algorithms. Our specific example showed low up to &-qubit
searches caa he made with 99% distingvishsbility, with single projective query. he latter
impressive timit is reached only with the use of shaped pulses, to counteract anharmonicity
incod dispersion of the manipulate superposition hob in the preparation and inthe readout

‘The desiga of the DJ wlgorthin brings aut several important cansiderations, among,
which is the recognition thal 9s the data bare is increased the fli of the algoithan drops,
unless optimally tailored lasce pls art used, AlUiowgh this is not a surprise, iL useful ot
have quantitative estimates of fidelity and therefore nucoess of pulse shaping, To this ond we
have built a custom pulse shaper, using liquid erystal spaiel light mxlulatons (256 individually
addressable liquid crystal chonnel) The pulse shaper wax constructed, demonstrated, and
operuied with genetic algorithass to tilor the pulse to the desired shape. However. poe to the
implementation of he shapcr in the Qrscarch algorithm, tac studoat responsible for the prajzut
was disabled (terminal illness). ‘The project bas beon reassigned, the now student has
redeveloped the system back to full apsration, and we expect shaped pulse demonstration of
logical operations tobe excented by the end ofthis summer, supported by a new AFOSR grunt
onthe same subject

‘he above demonstrations of proat af principle were carted out in the gas phase, where
decoherence occurs on a time auch losger dan the manipulations. Practica! implementations
‘vill undoubtedly eccur in che slid state, As such, we have carted out die four-wave mixing
measurements in the solid state in rare g4s matrices doped with molecular fodine, fr the
cver of such messurements, we demanstale tha hese the elisa of ratalans, eles
dephasing acts 98 x momeninm filler enuhle w much sharper definition of vibrational
coherences." A rigorous ireatraent of the auharmonicity elec, and the potential contribution
of inbomogeneity due to lattice imperfections were developed thcorctically using sclf-
consistent field treatment of vibrations and phonons. The latter anatysis predicted the effects
observed in the relatively soft solid of At, as verified through subsequent experiments?
‘Moreover, iu the soft solid, the use of high peak power lasers to carry out the nonlinear
_manipulstions was obscrved to lead t dosirclion of tho eage and dissection af the molecule
A complete analysis of caye breuking in Ar, through noslinear optical excitation, was canied
‘ul in au experimentAleory paper:* Thene effects ave enenpletely nephigie in the hontet latice
‘of Kr, asthe four-wave mixing measuements were transfered to Kr” A rater complete map
‘of vibrational dissipation and dephasing of w= 1~19 and at''=-4K = 40 K fas boca obtained in
Ibis system, as part of the Ph.D. thesis work af M. Karavtis® and as training grounds for 6¥0
postdoctoral fellows, A manuscript summarizing the complete work on this provtypical sys
{snow in propwation."

One poste scheme of sealing, isto go heyond four-wave mixing, We have recently
‘demonstrated that in electronically resonant cases, coherent six-wave mixing can be executed
and uniquely assigncd,"* This approach alone will be rathor Limited in scalability arguments
Flowever, f-wuve mixicg Joes provite For rer unique manipalations of coherences, as such
‘can he velied upon far specific processing of information,

ecoherence is the process by which quantum systms dceay into the classical world
and cherefore provides the fundamental limitation to tho scalability of Q-operations.
molecular systems, the mochanics of decohorence is not fully understand, ant the aabjece af
intense research, ‘Ihe six-wave mixing approach was spocifcally devised to prepare and
interrogate vibratéonal coherences on the electronically excited stats of the molecule, This
‘enables a raticr unique window in the observation of vibrational decoherence a the strong
coupling Fait, a limit where system-both coherence can be expected to persist. We have given
dia explicit treatecent of Une observed vibrational dzcokerence, using seni-clasical ital aloe
reproventation appro uo exploidy simnlate a lation of 300 degrees of frcedom. The results
of the simulation ate in excellent agroement with the experimenis.” The published work
suggests that rathor goncrally, inthe limit where the systema communicates withthe bah
(atsfrs enoegy or paso, ox both) on «timo scale aster than he hath Muctuntion perieds, then
quantum cohsrert evolution of system and both wast be expected. Indeed thig cout be
demonstrned with igor luoegh 4-wave nvixing measurements, by the preparation of to
‘vibrational packets on fe exited wletranic state of a given molecule, and to obser sustained
coherence ina system undergeing extnsive dissipation "Ics possible to show hac quantum
colerent dissipation immediatly implies « eoherent bath, and to de exten thatthe activated
tich consists of uany early orthogonal degrees of freedom, quantum coherence in
rinerosuopically distinguishable states (alteraatively referred to as Scliacdinger’s cul) is
achieved. We stow that neadty 12 phono ofthe bath aro activated and resmsin simultaneously
cohereat fr the duration thatthe system can be observed (10 vibrational periods. Ia cavonee,
2 twelve qubit emaugloment is demonstrate in the experiment. This is rater impressive
achiovertear, and points athe feasbiiy of wef (2 qubic manipulations in the sold state

L__Yublications
‘side the cited references, 10 manuscripts in priac, one manuscript submitted (13), and
fone in preparation (11), material for seversl additional papers has been generated that
‘we plan fo publish in ehe near fata,

UL__Personne]

“The tn principal students that have carsied out the referenced work, Mike Kuravitis
(experimental) and Zsolt Bibary (thoorctical), have buth completed their Ph.D, theses.
Karavits is presently employed ia R&D at Intralase, while: Bitary is carrying out a
postdoctoral fellowship at Norhwestern (with Prof, M. Ruler) The vark ou deraeanstrating
Schracdinger's cat is earied out by Darren Segale, a Ph.D, student in his usiel yeur of studies.
Fe is also the lead rescarcher or the pulse shuping wplics. The shaper was originally assembted
andl operated with genelic algorithm control by Mike Sgrot, a Ph.D. student who bad to drop
‘out of the program due to illness.

atlier contributions to the experiment and theory were speathcadod by Drs, Re
Zadoyan and Daniela Kohen, respectively. We have also closely collaborated on theoretical
oneepis with Prat. Dan{ Lidar and his Ph.D. student D. R. Glens, of the University of
Tarooto.

‘Nomonlinear Optical Paranietvic Amplifiers (NOPAS) were constructed aud extensively
‘owed in the accoraplished work. These were built by students, with initial consultation with
Prof. N. Schwentner of the Froe university of Berlin whe spent the summer of 2001 at UCT.
TY, Conference Presentation

“The Hata the presented invited lectus based on this work includes:

01

200

am

402

ins

03

38

Gorton Conference on Coherent Contol of atomic and molecular dynantcs (Mt
Holyoke, Mass)

Prepavation, Manipulation, and tnerropation of totectlar coherences, ori is
ese, process and readout of the quar reginer?

Amasican Physical Society Meeting. (College Park, MD)
Tine arn Frequency Resolved Four-Wave Mixing Spectroscopy: From Quannwn
Control to Quanrs Computing

Yerevan State Univectity (Yerevaa, Annentat
Tine and Frequency Resolved Fowr-Wave Mfiving Spectroscopy: Brom Quanto.
Control to Quan Compuring

APS Cunerence (Indiznapotis, IN)
Tinefrequnnuiy Resutved Colerent Ante-Stokev Raman Scattering: Quantum
Control to Quascum Computing

University of Michigan, Amu Arbor (Ann Arbor. ML)
Cotnecting Spectroscopic Observables to Underlying Molecular Dynamics

4" nremational Coaference on Law Temperature Chemistry (Reurou, Finland
Tone Resolved Spectroscopies in Matrices

Ceye-orystaly (Munich)
Coberenrce manipulations tarangh mudtiinear spectroscopy in condensed phave

Physics of Quantum Electronics (Utah)
Quantum Information transfer atd como! through maultiineat spectroscopy

U, Wiseonsin
‘The manipulation of molecular Coherences / Decoherence: new perspectives and
prospects

U.of Oregon
Te manipulation of molecular Coherences / Decomerence: new perspectives atta
praipects

Nontusreseem (Colloguin)
‘The manipulation of molecular Coherences / Decoherence:
prospects

ew perspectives and
73 GRC, Electronic Spectroscopy (Bales College, ME)
Seulctassical reatment of nonlinear specirascopy ta condensed media -(given by
1M, Quchivutzo!

fo03° UCI
Quantum coherences, decoherence, and the emergence of cassicality

204 Thicd Iuemational Meeting on Photlynamics (Huvana, Cuba}
Quanium Coherent Dissipation ~ a glimpre of the ‘eat?

AWA Seventh Symposium yn Molecular Reaction Dynainics in Condensed Mater
¢Logana Beach, CA)
Quantum Coherent Discpaten— a glimpse ofthe ‘cas?

"guy, Keen, Cia. 8nd Apkarian. WA, Chem. Phys 768,303
‘2000,

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+ Kota, Me Zadoyan,Rpkarian. VA. 7. Chere Pye 14,4191 G00.

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" Soqale Dues, M_ Prd, and Apkevan,V. A. PRL (submaied 28),