Quantum Memory with Atomic Ensembles. Yong-Fan Chen Physics Department, Cheng Kung University

Transcription

1 Quantum Memory with Atomic Ensembles Yong-Fan Chen Physics Department, Cheng Kung University

2 Outline Laser cooling & trapping Electromagnetically Induced Transparency (EIT) Slow light & Stopped light Manipulating light with light-storage techniques Quantum applications with atomic ensemble (DLCZ( scheme)

3 The Nobel Prize in Physics 1997 "for development of methods to cool and trap atoms with laser light" Steven Chu USA 1/3 of the prize Claude Cohen- Tannoudji France 1/3 of the prize William D. Phillips USA 1/3 of the prize Stanford University Stanford, CA, USA Collège de France; École Normale Supérieure Paris, France National Institute of Standards and Technology Gaithersburg, MD, USA b b (in Constantine, Algeria) b. 1948

4 Magneto-optical optical trap (MOT) z y σ + σ - (Optical Molasses) x From ultracold atom NTHU Ultracold atoms produced by laser cooling and trapping

5 From ultracold atom NTHU 10 K ultracold atoms T = K t 1 = 10 ms x = 4 mm t 2 = 30 ms

6 Image of ultracold atoms From ultracold atom NTHU

7 --Kerry J. Vahala,, Nature 424, 839 (2003) Single Atom-Light Interaction e g ge Resonant interaction of an atom with light allows coherent manipulation of light and atomic states However, single atom absorption cross-section section ~ 2 Cavity QED : fascinating but not easy experiment!! K. Vahala (Caltech) J.Kimble (Caltech) G.Rempe (MPQ) H.Walter (MPQ) Y.Yamamoto (Stanford)

8 -- M. Fleischhauer and M. D. Lukin, Phys. Rev. Lett. 84,, 5094 (2000 Atomic Ensembles-Light Interaction Interaction of light field and many atoms is strong (collective enhancement), but incoherent (spontaneous emission) Need : techniques for coherent control of resonant optical properties rties Idea : suppress the resonant absorption & coherent control light propagating in many atom system (atomic ensembles) Electromagnetically Induced Transparency (EIT) Coupled propagation of photonic and spin wave : dark-state polaritons

9 probe laser atoms probe laser atoms coupling laser

10 Electromagnetically Induced Transparency (EIT) χ (a) e Coupling Ω c ω ) = N g 2 3 3λ 2 4π p Probe g 1 Ω p Γ 4 ( ) Ω c iγ 4 p iγ EIT ( p 2 p Normalized Re[χ(ω p )] Normalized Im[χ(ω p )] (b) (c) Probe Detuning (Γ) without coupling with coupling -- S. E. Harris, J. E. Field, and A. Imamoğlu, Phys. Rev. Lett. 64,, 1107 (1990)

11 EIT : Quantum Interference e e e e Coupling g 2 Probe g 1 = g 2 path i g 1 g 2 path ii Transition Amplitudes : A i A ii g 1 g 2 g 1 path iii... A iii... Transition probability of g 1 e = A i + A ii + A iii EIT is the destructive interference between A i, A ii, A iii The probe absorption is suppressed. iii,...

12 EIT : dark-state picture Coherent Population Trapping (CPT) 3 H 3 + D = 0 probe H coupling 3 Ω c 2 1 Ωp D B = = Ω Ω Ω 2 c Ω 2 c c + Ω p + Ω 2 p 2 p Ω Ω Ω 2 c Ω 2 c p + Ω c + Ω 2 p 2 p 2 2 Ω 2 2 c Ω p D + B 3 3 Ω c Ω p EIT Condition : Ω p << Ω c Ω c Ωp 2 D B 1

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14 EIT experiment in cold 87 Rb atoms 5P 3/2 F'=3 F'=2 F'=1 m = S 1/2 F=2 F=1 Trapping Repumping Coupling Probe C P P C P C Probe BK7 M Master DL M AOM M Block OSC ECDL DL Coupling BS BK7 EOM Block AOM M M M M M BS λ/4 M Atoms Aperture PD

15 EIT Spectrum Probe Transmission Probe Transmission 1 Experiment Theory Probe Detuning (Γ) 5 e p Coupling Probe g 2 g 1 Sweep rate = 2.5 /ms Ω c = 0.4, = = MHz V dω c = g dk dn n + ω dω -- Y. F. Chen, G. C. Pan, and I. A. Yu, Phys. Rev. A 69,, (2004).

16 Slow Light in cold Na atoms Hau group : Cover of Nature associated with

17 --Y. F. Chen, Y. M. Kao, W. H. Lin, and I. A. Yu, Phys. Rev. A 74,, (2006) Slow Light in cold 87 Rb atoms Probe Transmission Input light pulse Slow light pulse Fitting curve Delay time ~ 2 s V g ~ 500 m/s T D = ( Γ Ω 2 c ) nσl Time (µs)

18 Can we stop or trap light?

19 Dark-State Polaritons : Coupled propagation of photonic and spin wave Strong coupling field ( ( 0) : Polaritons : purely photonic wave Weak coupling field ( ( /2) : Polaritons : larger parts in spin wave

20 Light Storage and Retrieval (Experiment) Cold atoms Hot atoms C. Liu t al. Nature 409, 490 (2001) D. Phillips et al.. PRL 86, 783 (2001)

21 Experiment : Atomic ensembles Cold atoms Hot atoms Yu s s group U. Tsing Hua Kimble s s group Caltech Walsworth s group U. Harvard

22 Light Storage and Retrieval in cold 87 Rb atoms e Probe Transmittance 1 (a) 0 1 (b) Input probe pulse Slow light pulse Light storage Coupling pulse Probe Write g 1 e Coupling g 2 Read Time (µs) Storage time ~ 15 s Spin Coherence g 1 g 2

23 Recent Development : Extending storage time Solid material : Pr 3+ doped Y 2 SiO 5 Pr : Praseodymium ( ( ) Storage time ~ 1 s

24 Phase? & How to measure?

25 -- Y. F. Chen, Y. C. Liu, Z. H. Tsai, S. H. Wang, and I. A. Yu, Phys. Rev. A 72,, (2005 Beat-Note Interferometer From Laser ω a AOM E z Zeroth-Order Beam PD1 Reference Beat Note OSC Beam 1 Probe Beat Note BS Atoms PD2 Beam 2 First-Order Beam E f (t) M Reference Beat Note: E z2 + E f (t) 2 +2E z E f (t)cos(ω a t+ϕ r ) Probe Beat Note: E z2 + E f (t) 2 +2E z E f (t)cos(ω a t+ϕ p + ϕ) ϕ r and ϕ p are the phases that result from the optical paths, the AOM switching, or other factors. ϕ is the phase shift induced by the atoms. Although ϕ r and ϕ p vary from one pulse to another, their difference is always fixed.

26 Phase Coherence of Storage and Retrieval Probe Transmission (arb. units) (b) (a) Quantum Storage Beat Note (arb. units) (c) (d) (e) Time (µs)

27 Low-Light Light-Level Level Phase Measurement Phase Shift (radians) Probe Transmission (µv) (a) Probe Detuning (Γ) Time (µs) (b) Phase measurement of weak probe pulses with peak power ~ 400 pw Beat Note (mv) Time (µs)

28 Manipulating light via light-storage techniques

29 Width manipulation of stored light pulse e Probe Write g 1 e Coupling g 2 Spin Coherence Read Probe Transmission (a) (b) (c) (d) g 1 g Time (µs)

30 -- Y. F. Chen, S. H. Wang, C. Y. Wang, and I. A. Yu, Phys. Rev. A 72,, (2005 Width manipulation of stored light pulse τ' (µs) φ (radians) (1/Ω c R ) 2 (Γ -2 ) Ω c R (Γ)

31 Polarization manipulation of stored light pulse Idea! 87 Rb 5P 3/2 F'=2 m= m= (d) 0.3 5S 1/2 F=2 Probe F=1 AOM AOM Coupling 2 s-polarization AOM Coupling 1 p-polarization Coupling 1 Input Probe M PBS BS BS M P λ/4 Atoms Retrieved Probe PD1 PD4 M λ/4 Coupling 2 PD3 PBS PD2 Probe Transmission (e) (f) Time (µs) Ω c (Γ)

32 -- Y. F. Chen, P. C. Kuan,, S. H. Wang, C. Y. Wang, and I. A. Yu, Opt. Lett. 23,, 3511 (2006 Wavelength manipulation of stored light pulse 87 Rb 5P 3/2 F'=2 5S 1/2 F=2 Idea! Coupling Input Probe Coupling Retrieved Probe Probe Transmittance (a) Time (µs) (b) (c) F=1 Beat Note Time (µs) Time (µs)

33 Can we manipulate the phase of stored light pulse?

34 Cross-Phase Phase-Modulation (XPM) based on EIT Theory

35 Cross-Phase Phase-Modulation (XPM) based on EIT Experiment Phase shift ~ 7.5

36 Phase manipulation of stored light pulse Idea! 87 Rb 5P 3/2 F'=3 F'=2 F'=1 F'=0 Coupling Signal Ω c Probe Ω p Ω φ = 2 2 = Γ Ω + 4 α 2 2 Γ Ω 2 Γ + 4 τ τ 5S 1/2 F=2 F=1 (a) (b) 2 Ground-State Coherence 1 φ /α = Γ Interaction of photonic field and atomic spin state!!

37 Low-light light-level level cross-phase modulation based on stored light pulses Probe Transmission 1 0 (b) 1 (a) Time (µs)

38 -- Y. F. Chen, C. Y. Wang, S. H. Wang, and I. A. Yu, Phys. Rev. Lett. 96,, (2006 Low-light light-level level cross-phase modulation based on stored light pulses φ (radians) Energy Transmission (a) 1.0 (c) (Γ) φ (radians) Energy Transmission (b) (d) Ω (Γ) 6 photons per 2 /2π φ ~ /4 ~ ~ 0.43 φ / α = Γ ~ (Γ) Ω (Γ)

39 Cavity QED : Single-photon π-phase gate? Idea! T s : Spin coherence lifetime Cavity Atoms e phase shift Signal photon Probe photon g 1 g 2 Coupling Retrieved photon φ /α ~ 3.14 / φ / α = Γ 0.46 ~ 6.8 ~ 6. 8Γ φ = α = 2 Ω τ ~ 0.11 Γ Ω Γ τ ~ Γ Single-photon π-phase gate is possible! But still need more efforts!!!

40 Quantum applications with atomic ensemble (DLCZ scheme)

41 L.-M. Duan,, M. D. Lukin,, J. I. Cirac,, and P. Zoller,, Nature 414,, 413 (2001 DLCZ Scheme Write laser Stokes photon Click

42 Recent Development : Single-photon storage M. D. Eisaman et al., Nature (London) 438,, 837 (2005)

43 Summery and Outlook Storage and Retrieval of Photonic Information Phase coherent of light storage and retrieval Manipulating the Optical Properties of Stored Light Pulses Manipulating the retrieved width of stored light pulses Wavelength and Polarization manipulation of retrieved light pulses Light-Storage Cross-Phase Modulation (XPM) Demonstration of light-storage XPM scheme Outlook Storage & Manipulation of nonclassical photon pulse (Quantum Memory) Single-photon switching & Single-photon -phase gate (Cavity QED + Atomic Ensemble) Quantum networks and communications with atomic ensembles (DLCZ Scheme) Quantum memory and manipulation in a solid

44 Thanks to (NTHU) Collaborations : (NCUE) (IAMS) (NCKU)

45 Thank you for your attention : ; : : Group member 2 ; 2 Group meeting ) 2) 3)