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Observation of Quantum Coherence for Gaseous Molecules

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）

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Observation of Quantum Coherence for Gaseous Molecules

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  1. Observation of Quantum Coherencefor Gaseous Molecules Jian Tang　（唐　健） Natural Science and Technology (Chemistry) Okayama University FPUA2010Aug. 7-9, Osaka Univ.

  2. 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）

  3. 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)

  4. Coherent transient effects • Relaxation time: T1≳T2 (homo T2' and inhomo T2*) • Absorption and coherent emission t<T2transient 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

  5. 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'

  6. Observations in 1970s • With cw-CO2 laser (~6 W/cm2) in the 10μm region photon echo FID optical nutation NH2D 13CH3F 13CH3F “superradiance” 13CH3F R. G. Brewer et al., PRL&PRA (1971-1979)

  7. Present experiment • CH3F n4 vibrational band @3mm weaker (~1/2) than n3 vibrational band @10mm • Observation first with the OPO laser in Okayama ~14 mW, Dn<100 kHz, f ~ 5 mmw/o focusing ~ 0.14 W/cm2« 6 W/cm2 no observationNutation and FID for pP3(4): J, K = 3, 2  4, 3observed with focusing

  8. Vacuum CH3F inlet With focusing Polarization DM=±1 DC Amp 0-450 MHz M Detector VIGO PVI-5 <15 ns Stark cell Limit 2.5 W/cm2 Lens 25 cm FID observed OPO laser, D ~ 0.5 mm, 6 W/cm2 CO2 laser, D = 2.7 mm, 6.3 W/cm2 OPO IR laser

  9. Vacuum CH3F inlet With collimation Polarization DM=±1 DC Amp 0-450 MHz M Detector VIGO PVI-5 <15 ns Stark cell Lens 5 cm Limit 2.5 W/cm2 FID Stronger! OPO laser, D ~ 0.7 mm, 3 W/cm2 Lens 25 cm CO2 laser, D = 2.7 mm, 6.3 W/cm2 OPO IR laser

  10. Pressure dependence 1 mTorr 3.0 mTorr 0 mTorr 1.5 mTorr 2.5 mTorr 4.0 mTorr 6.0 mTorr 11 mTorr 15 mTorr 19 mTorr 24 mTorr 32 mTorr 37 mTorr Average: 2000 times

  11. Stark field dependence ±30 V/cm ±15 V/cm 0-30 V/cm

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

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

  14. Simulation for FID and Nutation

  15. Simulation: 4 mTorr T2 = 2.0 μs  = 2 MHz

  16. Simulation: 11 mTorr T2 = 0.73 μs  = 2 MHz

  17. Discussion • T2·p = 7.96 ms·mTorr　（ from ref.）p = 4 mTorr, T2 = 2.0 msp = 11 mTorr, T2 = 0.73 ms • c = 2 MHz,c = m·E/h,I = 0E2/(2c)m= 0.086 D ⇒ I = 3 W/cm2 • Threshold of power density for FID & nutation 30％ of 3 W/cm2  1 W/cm2 （with linewidth <100 kHz）

  18. 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 rR0(0): J, K = 1, 1  0, 0nutation and FID: simple beat photon echo: observed weakly • Potential problem high power density > detector limit 2.5 W/cm2 partially damaged?! ⇒ new detetor

  19. Expanding & focusing Vacuum CH3F inlet Polarization DM=±1 AC Amp -150 MHz M Detector VIGO PVI-5 <15 ns Stark cell Limit 2.5 W/cm2 Photo echo observed Lens 100 cm OPO laser, D ~ 1 mm, 20 W/cm2 Compared with 5cm/25cm lens collimation D ~ 2 mm, 5 W/cm2 CO2 laser, D = 2.7 mm, 6.3 W/cm2 OPO IR laser 200 mW

  20. Nutation and FID for rR0(0)

  21. FID beat vs. Stark field

  22. Observation of photon echo for rR0(0)

  23. Echo timing v.s. interval between two pulses

  24. Photon echo with different Stark field

  25. Summary & Future work • We have observed optical nutation, FID, and photon echo for the n4 band of CH3F by cw-OPO lasers with Stark switching. • With lens expanding, focusing, and collimating, a power density larger than 3 W/cm2 has been reached for the 14 mW cw-OPO laser, and ~20 W/cm2 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, .

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