Controlling cavity reflectivity with a single quantum dot. v + ~ v czv d

Transcription

1 Vol 45 6 Decemer 27 doi:.38/nture6234 Controlling cvity reflectivity with single quntum dot Dirk Englund *, Andrei Fron *, Ily Fushmn *, Nick Stoltz 2, Pierre Petroff 2 & Jelen Vučković Solid-stte cvity quntum electrodynmics (QED) systems offer roust nd sclle pltform for quntum optics experiments nd the development of quntum informtion processing devices. In prticulr, systems sed on photonic crystl nnocvities nd semiconductor quntum dots hve seen rpid progress. Recent experiments hve llowed the oservtion of wek nd strong coupling 2,3 regimes of interction etween the photonic crystl cvity nd single quntum dot in photoluminescence. In the wek coupling regime, the quntum dot rditive lifetime is modified; in the strong coupling regime 3, the coupled quntum dot lso modifies the cvity spectrum. Severl proposls for sclle quntum informtion networks nd quntum computtion rely on direct proing of the cvity quntum dot coupling, y mens of resonnt light scttering from strongly or wekly coupled quntum dots 4 9. Such experiments hve recently een performed in tomic systems 2 nd superconducting circuit QED systems 3, ut not in solid-stte quntum dot cvity QED systems. Here we present experimentl evidence tht this interction cn e proed in solid-stte systems, nd show tht, s expected from theory, the quntum dot strongly modifies the cvity trnsmission nd reflection spectr. We show tht when the quntum dot is coupled to the cvity, photons tht re resonnt with its trnsition re prohiited from entering the cvity. We oserve this effect s the quntum dot is tuned through the cvity nd the coupling strength etween them chnges. At high intensity of the proe em, we oserve rpid sturtion of the trnsmission dip. These mesurements provide oth method for proing the cvity quntum dot system nd step towrds the reliztion of quntum devices sed on coherent light scttering nd lrge opticl nonlinerities from quntum dots in photonic crystl cvities. In the experiment, nrrow-ndwidth lser em is scnned through the resonnce of GAs photonic crystl cvity (Fig. c). The cvity contins strongly coupled InAs quntum dot tht splits its spectrum into two polriton sttes nd cuses the cvity trnsmission to vnish t the quntum dot frequency 4. A liner three-hole defect in the photonic crystl forms the cvity 5 with resonnt mode t l nm nd mesured qulity fctor Q (corresponding to cvity linewidth of Dl cv <. nm). We oserve polriton splitting of.5 nm. The photonic crystl ws fricted on quntum dot wfer grown y moleculr em epitxy, s descried in Methods. The principle of the mesurement is explined in Fig.. It is difficult to oserve the cvity spectrum directly, ecuse only smll frction of the incident light couples to the photonic crystl cvity owing to poor mode mtching etween the gussin proe em nd the cvity mode. For tht reson, the signl reflected y the cvity is monitored in cross-polriztion. This is nlogous to oserving trnsmission through polrizing cvity inserted etween two crossed polrizers. A GAs/AlAs distriuted Brgg reflector underneth the photonic crystl memrne effectively cretes singlesided cvity system nd enhnces the collection efficiency of the proe em. The horizontl jhæ component of the scttered proe em then crries the cvity reflectivity R, s given y eqution (2). Reflectivity is mesured y scnning the nrrow-linewidth proe lser em through the cvity resonnce (Fig., ). In this wy, we gretly exceed the.3 nm resolution of the spectrometer in order to smple the nrrow spectrl fetures of the system (tht is,.5 nm Ri splitting). To void difficulties relted to lser stility nd power normliztion, we keep the lser wvelength fixed nd insted scn the cvity nd quntum dot using our recently developed locl temperture-tuning technique 6. The technique uses lser em to het the suspended structure depicted in Fig. c, which is composed of photonic crystl cvity nd heting pd. The structure ws fricted y electron em lithogrphy nd rective ion etching. The pd is coted with Cr/Au metl lyer to increse sorption of the 95 nm heting lser, which is tuned to this wvelength to minimize the crrier excittion in GAs nd thus reduce ckground photoluminescence. The smple is mintined t n verge temperture of 27 K nd proed using the confocl microscope set-up in Fig.. The reflectivity signl from different cvity without coupled quntum dots is shown in Fig. d. Here, the cvity resonnce is swept through the tunle proe lser line using the locl heting technique. A hlf-wve plte in front of the smple corrects for non-optiml orienttion of the cvity nd mximizes its visiility in the reflected signl (Fig. ). We verified tht the visiility vnishes when the proe polriztion is orthogonl or prllel to the cvity polriztion. We otin cvity signl-to-ckground rtio of unity, which together with the imperfect extinction rtio of the polrizing em splitter, lets us estimte tht the coupling efficiency into the cvity mode is 2%. A more detiled explntion of how the mesurement ws performed is presented in Methods. We first chrcterize the quntum dot photonic crystl cvity system y photoluminescence when pumped with continuous-wve lser em t 78 nm, ove the GAs ndgp (incident power,2 nw efore the ojective). For low excittion powers, the quntum dot photoluminescence increses linerly with pump power, indicting single exciton line. As the quntum dot is temperture-tuned through the cvity, cler nticrossing etween the quntum dot nd the cvity lines is oserved: the quntum dot splits the cvity spectrum into two polriton peks (with frequencies v 6 ) when it ecomes resonnt with the cvity (Fig. 2c). This splitting is descried y v + ~ v czv d {i kzc rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi g 2 z d{i k{c 4 ð ð ÞÞ2 ðþ where v c denotes the cvity frequency, v d the quntum dot frequency, d 5 v d 2 v c the quntum dot cvity detuning, cvity field decy rte k/2p 5 6 GHz (linewidth. nm), Ri frequency g/2p 5 8GHz Ginzton Lortory, Stnford University, Stnford, Cliforni 9435, USA. 2 Deprtment of Electricl nd Computer Engineering, University of Cliforni, Snt Brr, Cliforni 936, USA. *These uthors contriuted eqully to this work. 27 Nture Pulishing Group 857

2 NATURE Vol 45 6 Decemer nm heting lser Tunle diode Oscilloscope Integrtor c Metl pd 78 nm lser diode CCD Smple Flip mirror SPCM 4 5 K Lens λ/2 plte PBS Grting set-up 2 µm PC cvity 98 nm g e g V+ H + V H tv+ H V H Input V PBS ( t ) V ( t) H Output d Reflected signl (.u.) Reflected signl Lorentzin fit, Q =, PC cvity Figure Experiment set-up., Confocl microscope set-up. A 78 nm lser diode excites photoluminescence, while 95 nm modulted Ti:spphire lser loclly hets the smple to tune cvity nd quntum dot 6. The reflectivity is mesured with nrrow-nd tunle diode lser (focl spot dimeter, mm for ll ems). A grting set-up monitors the photoluminescence nd filters the reflectivity signl from ckground noise. The filtered reflected signl is detected y single photon counting module (SPCM)., Principle of the reflectivity mesurement off photonic crystl (PC) cvity. A verticl ( Væ-polrized) proe lser is directed onto the linerly polrized cvity oriented t 45u ( V Hæ). Owing to interction with (from Ri splitting of 2g corresponding to.5 nm), nd the dipole decy rte without the cvity g/2p <. GHz. As g < k/2, the cvity quntum dot system opertes t the onset of strong coupling 4,sws lso the cse for other quntum dot photonic crystl cvity QED experiments done in photoluminescence 2,3. To ccurtely interpret the photoluminescence nd reflectivity dt, we need to know the frequency of the cvity nd strongly Cvity resonnce (nm) the cvity, the V Hæ component of the proe em is reflected with frequency-dependent coefficient 2t(v). The V 2 Hæ component reflects directly with p phse shift. The polrizing em splitter (PBS) psses Hæ, giving signl tht is proportionl to 2 t 2 on the detector (see eqution (2)). c, Suspended structure composed of heting pd nd photonic crystl cvity. The heting lser incident on the metl pd controls locl temperture 6. Inset, simulted electric field intensity of photonic crystl cvity. d, Reflectivity spectrum otined y tuning n empty cvity (no coupled quntum dot) through the proe lser, indicting Q coupled quntum dot. Direct trcking of the ltter is difficult ecuse of its modified spectrum when coupled to the cvity, nd ecuse it rpidly decreses in intensity s it exits the cvity (Fig. 2). This prolem is solved y insted trcking nery quntum dot tht precisely follows, t fixed offset, the strongly coupled quntum dot s trjectory (Fig. 2). Bsed on this, the strongly coupled quntum dot wvelength is shown in the inset of Fig. 2, together with tht of the Temperture scn count Anticrossing: Cvity individul PL c scns T L = 27K Reference trce T L = 33K Proe wvelengths B C A D E Cvity trce trce Cvity λ (nm) λ (nm) λ (nm) Figure 2 Photoluminescence of single quntum dot tuned through strong coupling to photonic crystl cvity. The dot is excited using n ove-nd pump em (78 nm wvelength, with 2 nw power incident on the smple surfce). Tuning of the quntum dot through the cvity resonnce is chieved following our erlier work 6, with heting em intensity-modulted etween 6 mw nd 3 mw to chnge locl temperture T L from 27 K to 33 K., A reference quntum dot () is used for trcing the wvelength of the strongly coupled quntum dot, s dots tht re closely spced in wvelength exhiit identicl temperture tuning ehviour. The heting em power is modulted with tringulr pttern nd shifts the Nture Pulishing Group quntum dot nerly linerly., Photoluminescence (PL) emission shows the strongly coupled quntum dot tuned in nd out of resonnce with photonic crystl cvity (Q <. 3 4 ). In the reflectivity mesurements, the ove-nd pump is switched off nd the cvity/quntum dot system proed t different detunings of the reflected lser em from the point of nticrossing (lines A E). Inset, quntum dot nd cvity trces. c, Individul photoluminescence cross-sections show nticrossing etween quntum dot nd cvity, with mesured Ri splitting of.5 nm (corresponding to 2g, where the coupling strength g/2p 5 8 GHz). As guide the eye, we show the wvelengths of the uncoupled quntum dot nd cvity (red line).

3 NATURE Vol 45 6 Decemer 27 cvity, which shifts t rte equl to.28 of the rte of the quntum dot shift. The reflectivity of the quntum dot cvity system is proed t five different spectrl detunings Dl 5 l 2 l of the proe lser from l, the nticrossing point of quntum dot nd cvity (inset Fig. 3). The incident power is in the wek excittion limit t 3 nw (mesured efore the ojective lens), corresponding to less thn one photon inside the cvity per cvity lifetime, s required for proing the vcuum Ri splitting. For ech reflectivity scn, corresponding photoluminescence scn is otined to trck quntum dot nd cvity wvelengths. Figure 3 plots the reflectivity signl s function of temperture scn. In this dt set, the temperture tuning is used to sweep the quntum dot nd cvity ck nd forth through the proe lser. These dt form the centrl mesurement of this pper: s the single quntum dot sweeps cross the cvity, it strongly modifies the reflected intensity. Insted of oserving lorentzin-shped cvity spectrum (Fig. d), drop in the reflected signl is oserved t the quntum dot wvelength, s expected in the strong coupling regime. From quntum mechnicl perspective, when the quntum dot is on resonnce with the cvity nd strongly coupled to it, the quntum dot cvity system does not hve n energy eigenstte t the re quntum dot resonnce, nd photons resonnt with the quntum dot cnnot e coupled into the cvity (Fig. ). The reflected signl from the descried cvity is derived following refs 6 nd 8. The spectrum R of the reflected proe signl fter the polrizing em splitter is then given y 2 k R~g iðv c {vþzkz g 2 ð2þ iðv d {vþzc where g ccounts for the efficiency of coupling to, nd collecting from, the cvity. We fitted this reltion to the oserved spectrum, using the ove-mentioned cvity quntum dot prmeters, together with the trcked quntum dot nd cvity wvelengths shown t the ottom of Fig. 3. The experimentl dt in the top pnel of Fig. 3 show smoother fetures thn the plot of eqution (2) sed on trcked quntum dot nd cvity lines (dshed line). We ttriute this difference to spectrl fluctutions in the quntum dot nd cvity tht re elow the resolution limit of the spectrometer, ut tht re greter thn the linewidth of the proe em. These fluctutions rise from instilities in the power of the heting lser of,.7%. When therml fluctution in the quntum dot cvity wvelength is tken into ccount s gussin rodening with full-width t hlf-mximum of.5 nm, the theoreticl model mtches the dt (lck fits). The fits yield vlues for coupling strength g nd cvity Q tht gree with photoluminescence mesurements in ove-nd pumping. The reflectivity dt for the other proe wvelengths (Fig. 3) cpture the quntum dot t vrious detunings from the cvity quntum dot intersection rnging from 2.2g (2.3 nm) to 4.5g (. nm). The reflected proe drops towrds zero precisely where the quntum dot crosses its wvelength, nd the depth nd shpe of the drop chnges with cvity detuning s predicted y theory. We note tht n lterntive model of n soring quntum dot 7 inside the cvity does not fit the reflectivity dt, nd predicts cvity spectrl linewidth tht does not gree with the mesured vlue. These mesurements lso point to one of the dvntges of the solid-stte cvity QED system: it is possile to cpture the sptilly fixed quntum dot in vrious sttes of detuning nd t constnt coupling to the cvity, wheres tomic systems re complicted y moving emitters. In Fig. 4, we explore the nonliner ehviour of nother strongly coupled quntum dot photonic crystl cvity system s function of power P in of the proe lser em. This system shows the sme coupling strength s the first, with g/2p 5 8 GHz nd Q 5 4, nd is proed here when the quntum dot is detuned y Dl 52.2 nm (corresponding to 2g/2) from the nticrossing. P in is incresed from the low-excittion limit t 5 nw efore the ojective (corresponding to n verge cvity photon numer Æn cv æ <.3 in cvity without quntum dot) to the high-excittion regime with P in < 2 mw (corresponding Æn cv æ < 7.3). Here, Æn cv æ is estimted s gp in /2k"v c, where g <.8% is the coupling efficiency into the cvity t this wvelength. Figure 4 shows the quntum-dot-induced reflectivity dip vnishing s P in is incresed y roughly three orders of mgnitude. We modelled the sturtion ehviour y stedy-stte solution of the quntum mster eqution following ref. 8, using the ovementioned mesured system prmeters. The cvity mode is represented y numer stte sis truncted to n 5 nd driven y coherent electric field with vrying mplitude E. Figure 4 lso plots the clculted normlized reflected intensity s function of the cvity nd quntum dot tuning with temperture (solid line). We see very good greement when the solution is convolved with the gussin filter ccounting for spectrl fluctutions rising from heting noise, s explined ove. The full dt re summrized in Fig. 4, where we plot the reflectivity R t the quntum dot detuning Dl 52.2 nm, normlized y the reflectivity vlue R for n empty cvity t the sme wvelength s the proe lser (tht is, for g R ). Our results gree with l (nm) Normlized intensity Dl l R (eqution (2)) Dl =.2 nm (.83g) Proe A Cvity Proe A Normlized intensity Dl =.3 nm (B) (.2g) Dl =.8 nm (C) (.72g) Dl =.58 nm (D) (2.3g) Dl =. nm (E) (4.5g) Scn count R (eqution (2)) R (extrpolted) Figure 3 Quntum dot controlled cvity reflectivity t different proe wvelengths A E, s indicted in Fig. 2., Reflectivity spectrum of proe lser s function of quntum dot nd cvity detunings, s determined from corresponding photoluminescence spectr (Fig. 2). The proe lser is detuned y Dl 5.2 nm (corresponding to Dl 5.83g) from the nticrossing point l etween quntum dot nd cvity (see inset). Idel 27 Nture Pulishing Group theoreticl plots re clculted from eqution (2). Also shown re theoreticl plots tht tke into ccount jitter (,.5 nm) of cvity nd quntum dot wvelength resulting from the heting lser power fluctution., Proe lser t vrious detunings Dl from the nticrossing point smples different quntum dot cvity detunings. Incomplete scns result from the limited rnge of temperture tuning. 859

4 NATURE Vol 45 6 Decemer 27 Normlized reflected intensity n cv =.8 n cv = 4.8 n cv =.6 n cv =.8 n cv =.6 n cv = Scn count R (empty cvity) 8 µw 3 µw µw 3 nw nw 25 nw Reflectivity rtio with nd without the theoreticl model (solid curve) nd previous mesurements in tomic systems 9. Owing to the spectrl fluctutions, the reflectivity does not pproch zero t low power, s it would in the idel system (dshed curve). Sturtion egins t, mw of incident power (mesured efore the ojective), corresponding to Æn cv æ < /2. Tking into ccount the coupling efficiency g, this implies sturtion power inside the cvity of only,2 nw, in greement with previous predictions for gint opticl nonlinerity in microcvity 2. We furthermore verified tht the quntum-dot-induced reflectivity dip vnishes controllly when excitons re (incoherently) generted y excittion with n ove-gas-ndgp lser em. In conclusion, we hve experimentlly demonstrted tht single quntum dot cn e used to drmticlly lter the reflectivity spectrum of n opticl cvity. In the low-excittion regime (intrcvity photon numer Æn cv æ = ), we oserve quntum-dot-induced chnge in reflectivity to 4% nd find very good greement with theory. The remining signl is limited y mesurement noise (tht is, quntum dot nd cvity wvelength fluctutions resulting from power instilities of the heting lser), nd should vnish with improved experimentl stility. As the resonnt em intensity is incresed, we oserve sturtion of the quntum-dot-induced dip t,2 nw of cvity-coupled power (photon numer Æn cv æ < /2), closely mtched y theory. Our mesurements rely on novel quntum dot cvity tuning nd cross-polrized reflectivity method tht permits resolution of,.5 nm (full-width t hlf-mximum) nd high cvity quntum dot visiility. The photonic crystl rchitecture is idelly suited for extending this system to greter numers of quntum dots nd cvities interconnected into quntum network 2. Such n on-chip pproch gretly increses the coupling n cv 2 R/R (mesured) R/R (theory) R/R (theory, idel) Power (nw) Figure 4 Quntum-dot-controlled cvity reflectivity versus proe em power for proe lser detuning of Dl 52.2 nm from the nticrossing point., Reflectivity scns t incresing proe power (mesured efore the ojective), rnging from low-excittion to sturtion regimes. The mesured reflectivity is fitted y numericl solution to the full mster eqution. Solutions re convolved with gussin filter with full-width t hlfmximum of.5 nm to ccount for therml fluctutions (solid curves). The scle for the clculted men photon numer Æn cv æ is lso indicted for ech scn. Also plotted is the expected reflectivity R when the quntum dot is removed (dshed curve)., Reflectivity t Dl 52.2, normlized y empty-cvity reflectivity t the sme wvelength, s function of proe lser power. Sturtion egins ner mw of input power, corresponding to Æn cv æ < /2. The dshed curve shows the reflectivity rtio if no therml fluctutions were present. At lrge power, oth curves tend to unity s the quntum dot cvity spectrum pproches the lorentzin shpe of the empty cvity Nture Pulishing Group efficiency to nd from the cvity 22, nd our recent circuits should llow efficiencies exceeding 5% while ensuring cvity Q. 4. The demonstrtion of quntum-dot-controlled cvity reflectivity hs frreching implictions for quntum informtion processing in solidstte systems, s it opens the door to high-fidelity controlled phse gtes 6, single photon detection 2, coherent trnsfer of quntum dot stte to photon stte 4, nd quntum repeters using non-destructive Bell mesurements with the ddition of third long-lived quntum dot level 8. The oserved gint opticl nonlinerity hs promising pplictions for generting non-clssicl squeezed sttes of light,23, non-destructive photon numer stte mesurements 24, nd opticl signl processing. METHODS SUMMARY Reflectivity mesurement. A cvity with coupled quntum dot showing polriton nti-crossing ws first identified in photoluminescence, using ove-nd excittion t 78 nm. The temperture of the cryostt nd the power of the heting lser were controlled so the quntum dot periodiclly swept through the cvity resonnce. Then the tunle diode lser used for reflectivity mesurements ws set to the desired wvelength using the spectrometer. After spectrl lignment, the 78 nm lser ws turned off, nd the reflectivity signl ws sent to photodetector nd optimized on n oscilloscope. Once optimized, the output ws switched to the spectrometer CCD nd the reflectivity signl ws recorded with the spectrometer tking successive spectr t.2-s-long integrtion, while the heting lser power (nd susequently quntum dot nd cvity wvelength) ws modulted t mhz. This scnning speed is slow enough to resolve the relevnt fetures, s seen y the numer of dt points smpling the quntumdot-induced dips in Fig. 3. Quntum dot wfer. The photonic crystl ws fricted on quntum dot wfer grown y moleculr em epitxy on Si n-doped GAs() sustrte with. mm uffer lyer, nd -period distriuted Brgg reflector consisting of qurter-wve AlAs/GAs lyers to improve collection efficiency into the lens 25. The distriuted Brgg reflector is seprted y 98 nm scrificil lyer of Al.8 G.2 As from the 5-nm GAs memrne tht contins centrl lyer of self-ssemled InGAs/GAs quntum dots. The quntum dot density vries throughout the wfer, ut in this experiment, we used the low-density re with, quntum dots per mm 2. Received 5 June; ccepted 4 Septemer 27.. Englund, D. et l. Controlling the spontneous emission rte of single quntum dots in two-dimensionl photonic crystl. Phys. Rev. Lett. 95, 394 (25). 2. Yoshie, T. et l. Vcuum Ri splitting with single quntum dot in photonic crystl nnocvity. Nture 432, 2 23 (24). 3. Hennessy, K. et l. Quntum nture of strongly coupled single quntum dotcvity system. Nture 445, (27). 4. Circ, J. I., Zoller, P., Kimle, H. J. & Muchi, H. Quntum stte trnsfer nd entnglement distriution mong distnt nodes in quntum network. Phys. Rev. Lett. 78, (997). 5. Immoglu, A. et l. Quntum informtion processing using quntum dot spins nd cvity QED. Phys. Rev. Lett. 83, (999). 6. Dun, L. M. & Kimle, H. J. Sclle photonic quntum computtion through cvity-ssisted interctions. Phys. Rev. Lett. 92, 2792 (24). 7. Childress, L., Tylor, J. M., Sorensen, A. S. & Lukin, M. D. Fult-tolernt quntum repeters with miniml physicl resources nd implementtions sed on singlephoton emitters. Phys. Rev. A 72, 5233 (25). 8. Wks, E. & Vučković, J. Dipole induced trnsprency in drop-filter cvitywveguide systems. Phys. Rev. Lett. 96, 536 (26). 9. Ldd, T. D., vn Loock, P. K., Nemoto, K., Munro, W. J. & Ymmoto, Y. Hyrid quntum repeter sed on dispersive CQED interctions etween mtter quits nd right coherent light. N. J. Phys. 8, 84 (26).. Birnum, K. M. et l. Photon lockde in n opticl cvity with one trpped tom. Nture 436, 87 9 (25).. Ruscheneutel, A. et l. Coherent opertion of tunle quntum phse gte in cvity QED. Phys. Rev. Lett. 83, (999). 2. Nogues, G. et l. Seeing single photon without destroying it. Nture 4, (999). 3. Schuster, D. I. et l. Resolving photon numer sttes in superconducting circuit. 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5 NATURE Vol 45 6 Decemer Gerrdot, B. D. et l. Contrst in trnsmission spectroscopy of single quntum dot. Appl. Phys. Lett. 9, 226 (27). 8. Tn, S. M. A computtionl toolox for quntum nd tomic physics. J. Opt. B, (999). 9. Hood, C. J., Chpmn, M. S., Lynn, T. W. & Kimle, H. J. Rel-time cvity QED with single toms. Phys. Rev. Lett. 8, (998). 2. Auffeves-Grnier, A., Simon, C., Gerrd, J. M. & Poizt, J.-P. Gint opticl nonlinerity induced y single two-level system intercting with cvity in the Purcell regime. Phys. Rev. A 75, (27). 2. Englund, D., Fron, A., Zhng, B., Ymmoto, Y. & Vučković, J. Genertionnd trnsfer of single photons on photonic crystl chip. Opt. Express 5, (27). 22. Fron, A., Wks, E., Englund, D., Fushmn, I. & Vučković, J. Efficient photonic crystl cvity-wveguide couplers. Appl. Phys. Lett. 9, 732 (27). 23. Reiner, J. E., Smith, W. P., Orozco, L. A., Crmichel, H. J. & Rice, P. R. Time evolution nd squeezing of the field mplitude in cvity QED. J. Opt. Soc. Am. B 8, 9 92 (2). 24. Imoto, N., Hus, H. A. & Ymmoto, Y. Quntum nondemolition mesurement of the photon numer vi the opticl Kerr effect. Phys. Rev. A 32, (985). 25. Vučković, J., Englund, D., Fttl, D., Wks, E. & Ymmoto, Y. Genertion nd mnipultion of nonclssicl light using photonic crystls. Physic E 32, (26). Acknowledgements Finncil support ws provided y the ONR Young Investigtor Awrd, the MURI Center for photonic quntum informtion systems (ARO/DTO Progrm), the Okw Foundtion Fculty Reserch Grnt, nd the CIS Seed fund. D.E. nd I.F. were lso supported y the NDSEG fellowship. Work ws performed in prt t the Stnford Nnofriction Fcility of NNIN supported y the Ntionl Science Foundtion. Author Informtion Reprints nd permissions informtion is ville t Correspondence nd requests for mterils should e ddressed to J.V. (jel@stnford.edu). 27 Nture Pulishing Group 86