Dark-matter Axion Search using
Quantum Coherence Amplification Mechanism
Particle Physics/ Cosmology(5) :M. Yoshimura, K. Yoshimura, N. Sasao,T. Masuda, T. Hiraki
Nuclear Physics(1) : H. Yoshimi.
Quantum Electronics/ Atomic Physics(4) :S. Uetake, H. Hara, K. Imamura, Y. Imai
Quantum Chemistry(1): Y. Miyamoto+students (8)Noboru Sasao (笹尾 登)

Research Institute for Interdisciplinary Science, Okayama University,Okayama, 700-8530, Japan
2019-July-06

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Recent papers

2019-July-06

Waseda2Outline• What is axion?: Physics motivation

Skip entirely!!!

• Amplification by coherence: Proof-of-principle
experiment by PSR process• Cosmic Axion search with atoms/molecules:• Conclusion

2019-July-06

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Outline• What is axion?: Physics motivation• Amplification by coherence: Proof-of-principle
experiment by PSR process• Cosmic Axion search with atoms/molecules:• Conclusion

2019-July-06

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Ba SR exp’t @ Okayama

Amplification by coherence
among atomsl• Super-Radiance a la Dicke• De-excitation via single photon emission
NT2R   Exp ik xm M ( xm )  NT2
m 1

 M ( xm )  M (0), | target size | l • Macroscopic coherent amplification• De-excitation via multi-particle emissionNT

2R   Exp i (k  k  k ) xm M ( xm )  NT2
m 1

2019-July-06

e  g  Waseda

 M ( xm )  M (0), k  k  k  0 
5Effects of Initial Spatial Phase• General conditions of amplification;
NT2

R   Exp i (k  k 1  k 2 ) xm M ( xm )  NT2m0

if M ( x m )  M (0)Exp iPeg xm

  k k k  P12eg• Spatial phase Peg can be controlled;• Raman excitation:• Ladder excitation:

Eeg  1  2 & Peg  k1  k2

Eeg  1  2 & Peg  k1  k2 (co-propagating)Eeg  1  2 & Peg  k1  k2 (counter-propagating)2019-July-06

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Experimental proof of macroscopic
coherent amplification• PSR (paired super-radiance )• QED process where -pair is replaced with a photon.
• A pair of strong light pulses (SR) will be emitted.

“Dynamics of two-photon paired superradiance”,M. Yoshimura, N. S, and M. Tanaka, PHYSICAL REVIEW A 86, 013812 (2012)2019-July-06

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“Externally triggered coherent two-photon emission from hydrogen molecules”,
Yuki Miyamoto et. al. Prog. Theor. Exp. Phys. 2015, 081C01 (2015)

PSR experiments• Para-hydrogen molecule (Spin=0)• Vibrational level (v=1) to ground level(v=0).
• E1 forbidden.
• Small 2-photon emission rate:  1/ 2  10 12 sec• Excitation scheme• Raman (co-propagating)• Ladder (counter-propagating)2019-July-06

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Driving laser: 5 mJ/pulse, ~10nsec fwhm
Tigger laser: 150 uJ/pulse, ~2nsec fwhm

Experimental setup(gas)2019-July-06

T=77K, P=60kPa
D=2cm, L=15cm
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Observation of Raman sidebands• 13 sidebands observed (λ=192 4662nm)• Evidence for large coherence

2019-July-06

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Degree of coherence• Maxwell-Bloch eq.

• Coherence estimated by simulation:

2019-July-06

Waseda11Observation of two-photon process|e> v=1
4.59μm（External trigger）
5.05μm|g> v=0

Amplification factor of >10^(18) is confirmed.
2019-July-06

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Recent developments on PSR (1)• Solid vs gas pH2
trigger laser injected after pump laser

gas target

solid target

Solid pH2 has x10 longer coherence time
2019-July-06

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Recent developments on PSR (2)• Initial spatial phase imprinted to atomic system.
Experimental proof:

Initial spatial phase
gives higher neutrino
sensitivity:
Invariant mass (Eeg,Peg)
can be controlled.

J.Phys.B: At Mol Opt. Phys
52 (2019) 045401
2019-July-06

WasedaPhys. Rev. D 96, 113005 (2017)14

Outline• What is axion?: Physics motivation• Amplification by coherence: Proof-of-principle
experiment by PSR process• Cosmic Axion search with atoms/molecules:• Conclusion

2019-July-06

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Basic process of interests• Basic process of interest:e  ma  g   t   s

Principle of experimentsPrepare coherently-excited states |e> by pump laser(s).
Axion decays into 2 in an external magnetic fields Bext.
Virtual photon is absorbed by |e>.
Inject trigger laser (t) with angle w.r.t. pump laser(s).
Detect signal photon (s).

2019-July-06

WasedaaG   v  "  "16

We use BaF as a target• Electronic structure:• 2S:Lz=0,Sz=1/2• 2P:Lz=1,Sz=1/2• Zeeman properties:• 2P1/2 : no magnetic dipole moment• 2S & 2P3/2: magnetic dipole moment ~ mB

• Rotational structure:• A~ spin-orbit interaction energy• B~ rotational energy (B<A)

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Zeeman splitting of BaF states

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Actual states to be used

• The mass of axion in search:• E(|i>)-E(|e>) under Bext
• ma~25 meV (in this example)
 6 [m eV] Forget for a moment:  ax   ma 

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Experimental Layout• 3 major components:• Laser system• BaF target in pH2 matrix• IR detector• Trigger laser• injected with angle w.r.t pump to satisfy
macro-coherent amplification conditions.

tseg~160 mrad2019-July-06Waseda~120 mrad20

Laser and BaF target

IR detector : APD withbandpass filter or spectrometer860

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eg : coherence

Signal counts

NT : number of target molecules

G : dark matter densityaB : Bohr radius
Et : tigger laser field p ( p  e, g , i, j , s, t ) : energy of p
 pq   p  q
 pq : resonace + laser widthA( s ) : geometrical acceptance

Bext=1 T eg : coherenceA( s ) : geometrical acceptance

Signal count [1/s]Blk: coherence
Blu: input laser
Red: population
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Rate enhancement factors• Large axion number densityG  0.4 GeV/cm3  1013 / cm3 (ma =40m eV)• Macro-coherent amplification.
NT=1016• Strong magnetic field
Bext =1 T• Near resonance condition at axion absorption vertex• Energy denominator:

2019-July-06

11Eei  m a ii
i

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The biggest background: black-body• Atoms absorb black-body photons.

• The second biggest background:• Dark count of APD is negligible.
• 100 Hz x edty=10-3 Hz

The sensitivity of the experimentcan be calibrated by observing
black-body spectrum.
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Velocity dispersion and wind direction• Velocity dispersion sv:• Axions have been virialized during alarge-scale formation.

2019-July-06

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Search sensitivity by this experiment2019-July-06

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Summary for axion search• New method of cosmic axion search.

• Amplification by macroscopic coherence is KEY.
• Use Zeeman-tunable molecular states• Large counting rate is expected for wide search region• Experimental sensitivity can be proved by b.b. “calibration”
photons• Road map• Pilot experiment with BaF 2P1/2 as |e>• Go to the smaller ma (~1 meV) with 2P3/2 as |e>• Need a cryostat of lower temperature (250 mK) andstronger magnet (>10T)• Better target (crystal? ) is needed to go below 1 meV.

2019-July-06

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Thank you for your attention!

• SPAN collaboration
Hideaki Hara1, Takahiro Hiraki1, Kei Imamura1, Takahiko Masuda1,
Yuki Miyamoto1, Noboru Sasao1, Yoshitarou Takaesu1,Minoru Tanaka2, Koji Tsumura3, Satoshi Uetake1,Akihiro Yoshimi1, Koji Yoshimura1, Motohiko Yoshimura1
1 Research Institute for Interdisciplinary Science, Okayama University, Okayama, 700-8530, Japan
2 Department of Physics, Osaka University, Toyonaka, Osaka 560-0043, Japan
2 Department of Physics, Kyoto University,

2019-July-06

Kyoto 606-8052, Japan

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