Observation of Quantum Coherence for Gaseous Molecules Jian Tang （唐 健） Natural Science and Technology (Chemistry) Okayama University FPUA2010 Aug. 7-9, Osaka Univ.

Collaborators Okayama Univ. (Chemistry) Okayama Univ. (Physics) Y. Okabayashi （岡林祐介） K. Nakajima （中 島享） Y. Miyamoto （宮本祐樹） S. Kuma （久間 晋） K. Kawaguchi （川口建太郎） A. Fukumi （福見敦） T. Taniguchi （谷口敬） Tokyo Institute of Technology I. Nakano （中野逸夫） H. Kanamori （金森英人） N. Sasao （笹尾 登） M. Yoshimura （吉村太 彦）

Motivation and Approach Searching for quantum coherence in isolated matrix: demonstrate the ability to observe the phenomenon for gaseous molecules, done or yet done Optical quantum coherence: optical nutation, free induced decay (FID ) photon echo, and superradiance Linewidth of vibration-rotation transitions for gaseous molecules (Doppler width ~100 MHz): IR cw-lasers with narrow linewidth (<1 MHz)

Coherent transient effects Relaxation time: T 1 ≳ T 2 (homo T 2 ' and inhomo T 2 *) Absorption and coherent emission  <T 2 transient nutation, optical FID, photon echo superradiance for population inverted levels Pulsed lasers or cw-lasers with either Stark (molecular) switching or frequency switching Previous studies mainly with frequency-fixed IR lasers Recent development on the tunable cw-OPO laser provides us a new tool for the observation

Stark switching R. G. Brewer et al. (IBM, 1970s) Stark pulsed field shift suddenly the absorption resonance from velocity group v to velocity group v'

Observations in 1970s With cw-CO 2 laser (~6 W/cm 2 ) in the 10μm region 13 CH 3 F NH 2 D optical nutation FID photon echo R. G. Brewer et al., PRL&PRA ( ) 13 CH 3 F “superradiance”

Present experiment CH 3 F 4 vibrational  m weaker (~1/2) than 3 vibrational  m Observation first with the OPO laser in Okayama ~14 mW,  <100 kHz,  ~ 5 mm w/o focusing ~ 0.14 W/cm 2 « 6 W/cm 2 no observation Nutation and FID for p P 3 (4): J, K = 3, 2  4, 3 observed with focusing

CH 3 F inlet Vacuum OPO IR laser Stark cell M Lens 25 cm CO 2 laser, D = 2.7 mm, 6.3 W/cm 2 OPO laser, D ~ 0.5 mm, 6 W/cm 2 FID observed With focusing DC Amp MHz Detector VIGO PVI-5 <15 ns Polarization  M=±1 Limit 2.5 W/cm 2

CH 3 F inlet Vacuum OPO IR laser Stark cell M Lens 25 cm Lens 5 cm CO 2 laser, D = 2.7 mm, 6.3 W/cm 2 OPO laser, D ~ 0.7 mm, 3 W/cm 2 FID Stronger! With collimation DC Amp MHz Detector VIGO PVI-5 <15 ns Polarization  M=±1 Limit 2.5 W/cm 2

0 mTorr1 mTorr 1.5 mTorr2.5 mTorr 3.0 mTorr 4.0 mTorr6.0 mTorr11 mTorr15 mTorr19 mTorr24 mTorr32 mTorr37 mTorr Pressure dependence Average: 2000 times

Laser power 14 mW, 100%Laser power 10.5 mW, 75% Laser power 9 mW, 65% Laser power 7 mW, 50%Laser power 3.5 mW, 25% Laser power dependence

±30 V/cm ±15 V/cm0-30 V/cm Stark field dependence

Stark splitting of transition ΔM= 0, 7 components Relative intensity ΔM= ±1, 14 components M J, K = 3, 2 J, K = 4, 3

Optical Nutation and FID Hopf & Shea, PRA 7, 2105 (1973)

Simulation for FID and Nutation

T 2 = 2.0 μs  = 2 MHz Simulation: 4 mTorr

T 2 = 0.73 μs  = 2 MHz Simulation: 11 mTorr

Discussion T 2 ·p = 7.96  s·mTorr （ from ref. ） p = 4 mTorr, T 2 = 2.0  s p = 11 mTorr, T 2 = 0.73  s  = 2 MHz,  =  ·E/h, I =  0 E 2 /(2c)  = D ⇒ I = 3 W/cm 2 Threshold of power density for FID & nutation 30 ％ of 3 W/cm 2  1 W/cm 2 （ with linewidth <100 kHz ）

Experiment with higher power OPO With the OPO laser of 200 mW (up to 600 mW) Kanamori Lab in Tokyo Inst. Tech. expanding the laser beam to ~1 inch and then focusing with lens of f = 100 cm Observation for r R 0 (0): J, K = 1, 1  0, 0 nutation and FID: simple beat photon echo: observed weakly Potential problem high power density > detector limit 2.5 W/cm 2 partially damaged?! ⇒ new detetor

CH 3 F inlet Vacuum OPO IR laser 200 mW Stark cell M Lens 100 cm CO 2 laser, D = 2.7 mm, 6.3 W/cm 2 OPO laser, D ~ 1 mm, 20 W/cm 2 Compared with 5cm/25cm lens collimation D ~ 2 mm, 5 W/cm2 Photo echo observed Expanding & focusing AC Amp -150 MHz Detector VIGO PVI-5 <15 ns Polarization  M=±1 Limit 2.5 W/cm 2

Nutation and FID for r R 0 (0)

FID beat vs. Stark field

Observation of photon echo for r R 0 (0)

Echo timing v.s. interval between two pulses

Photon echo with different Stark field

Summary & Future work We have observed optical nutation, FID, and photon echo for the 4 band of CH 3 F by cw-OPO lasers with Stark switching. With lens expanding, focusing, and collimating, a power density larger than 3 W/cm 2 has been reached for the 14 mW cw-OPO laser, and ~20 W/cm 2 for the 200 mW cw-OPO laser. The next step would be to observe superradiance with the high power cw-OPO laser for gaseous molecules. Frequency switching is another approach since Stark switching may not be applicable to the isolated matrix,.