TRACA- a new way to track axion
Noboru Sasao
RIIS, Okayama U.
(work with M. Yoshimura)2017/12/20-21

Axion Workshop @ Osaka

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ContentsIntroduction

TRACA




Macro-coherence and its experimental proof
Principle of a new experimental method
Experimental setup
Counting rateSummary

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Amplification by coherence
among atoms
Super-Radiance a la Dicke
De-excitation via single photon emission

NT

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R   Exp ik xm M ( xm )  NT2m0l M ( xm )  M (0), | target size | l 

Macroscopic coherent amplification
NT

De-excitation via multi-particle emission:

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

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e  g   M ( xm )  M (0), k  k  k  0 Axion Workshop @ Osaka

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Effects of Spatial Phase Memory
General conditions of amplification;

NT



2R   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
Laser field: E0 e  i (t  k  x )Spatial phase Peg can be controlled; Raman excitation:

Peg  k1  k2
Ladder excitation:

Peg  k1  k2 (co-propagating)Peg  k1  k2 (counter-propagating)2017/12/20-21

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

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

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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)2017/12/20-21

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

Experimental setup(gas)2017/12/20-21

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

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Features of adiabatic
Raman process

Why we use Raman process?


Creation of coherence among two levels |e> and |g>
Generation of higher side-bands

Eigenstates:

Density matrix r|y>y|2017/12/20-21

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Coherence estimated by simulation:

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

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Comparison with spontaneous emission# of observed photons=6 x 10^11/pulse# of expected photons due to spontaneous emission

EExpected photons=R0   w Ln0  A t  10 7 / pulseE20


Huge amplification factor of >10^(18).
Experimental confirmation of macroscopic coherent
amplification mechanism.

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Y. Miyamoto, et al., “Vibrational Two-Photon Emission from Coherently Excited SolidParahydrogen'', J. Phys. Chem. A, vol. 121, 3943 (2017)

Solid instead of gas target
Gas pH2 (78K,60kPa)

Solid pH2 (4K)

Density~5.6x1019/cm3~2.6x1022/cm3

De-coherence time~1 nsec

~10 nsec

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Summary for PSR experiments

PSR experimentTwo-photon decay process from pH2 v=1 -> v=0.
Confirmed the principle of macro-coherent amplification.

Conditions of macro-coherence.
Energy-momentum conservation.

Eeg  (a  b  c )Peg  (ka  kb  kc )
Peg : controlled by excitation schemeLong de-coherence time for atoms/molecules.

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Contents

Introduction

TRACA




Macro-coherence and its experimental proof
Experimental principle
Experimental setup
Counting rate

Summary

2017/12/20-21

Axion Workshop @ Osaka

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TRACA experimentBasic process of interest:i  ma  f   t   sPrepare excited states |i>, which are macro-coherent with theground state |f>.
Inject trigger laser to stimulate axion decay into two photons: a   t  " "One of the photons hits the atom to induce de-exicitation.

TRACA (Triggered Radiative Absorption of Cosmic Axion)(TRACk Axion)

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How to exploit macro-coherence ?
PSR vs TRACA|i>

Eif  ma  s  t
Pif  k s  k t|f>Principle of experiments
Prepare coherently-excited states |i> by Raman excitation scheme.
Inject trigger laser (t) with angle w.r.t. pump lasers.
Detect signal photon (s).
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Experimental Layout

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Eif  ma  s  t

Kinematics of TRACA

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P if  k s  k t

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Counting rate

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Finite target size effects(acceptance)

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TRACA events with efficiency/acceptance
TRACA Phase-1

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Experimental challenges


Laser system
High power pump lasers
1064nm+738nm (for Raman excitation)
 ~400 mJ/pulse at 10kHz
High power trigger laser
CO2 laser; new to us ~1 J/pulse at 10kHz


Solid pH2 target

10cm-long target

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Infrared single-photon detector

Detect infrared photonSingle photonUp-conversion methodNon-liner crystal

PPLN (Periodically Poled LithiumNiobate)

Carrier laser injection
Detect frequency-summed photonwith APD (Avalanche Photo-Diode)
Conversion efficiency:  cnv  0.94 at 2 m

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Axion search

TRACA
Phase-1Helioscope (M. Giannotti)
Suzaku/XIS (R. Yamamoto)Light-shining-through a wall(A.Spector)
2017/12/20-21

NMR (D. Budker)
XMASS (K. Abe)
Clock (P. MOrzynski)
Radio burst (A. Iwazaki)

Haloscope (Y. Semertzidis)Axion Workshop @ Osaka

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Summary for TRACA experiment

TRACA experimentA new way to track axions
Exploits macro-coherence of atoms/molecules
Different systematics from others

Challenges for TRACA experiment.
High-power pump laser system.
Long solid pH2 target
Low-noise and high-efficiency single-photon IR detector
Control of PSR backgrounds (under examination)

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“invisible axion”

Theoreticalbackground of axion


Why we need it?
To solve “Strong-CP” problemQCD (Quantum Chromo-Dynamics) describes strong interaction
Contains a CP-violating term in its Lagrangian: 10 [ eV]  a  1050 [sec] maContradicts with experiments, e.g. neutron EDM measurements

Axion solves the “Strong CP problem” in an elegant way.

PropertiesInteracts with electro-magnetic fields extremely weaklyGcL  Ga aE  Baa fa
Mass and coupling strength has definite relation
1012 [GeV]m a  6 [ eV]
fa

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