Improving the detection sensitivity of dark-matter axion search with a Rydberg-atom single-photon detector M.Saeed For newCARRACK Collaboration Kyoto FPUA2010

T. Arai, A. Fukuda, A. Matsubara, T. Mizusaki, A. Sawada,M.Saeed: S. Ikeda, K. Imai, T. Nakanishi, Y. Takahashi: Y. Isozumi, T. Kato, D. Ohsawa, M. Tosaki: K. Yamamoto: H. Funahashi,J.Uda: Y. Kido, T. Nishimura, S. Matsuki: Research Center for Low Temperature and Materials Sciences, Kyoto University Department of Physics, Kyoto University Radioisotope Center, Kyoto University Department of Nuclear Engineering, Kyoto University Institute for the promotion of excellence in higher education Kyoto University Department of Physics, Ritsumeikan University T. Arai, A. Fukuda, A. Matsubara, T. Mizusaki, A. Sawada,M.Saeed: S. Ikeda, K. Imai, T. Nakanishi, Y. Takahashi: Y. Isozumi, T. Kato, D. Ohsawa, M. Tosaki: K. Yamamoto: H. Funahashi,J.Uda: Y. Kido, T. Nishimura, S. Matsuki: Research Center for Low Temperature and Materials Sciences, Kyoto University Department of Physics, Kyoto University Radioisotope Center, Kyoto University Department of Nuclear Engineering, Kyoto University Institute for the promotion of excellence in higher education, Kyoto University Department of Physics, Ritsumeikan University newCARRACK Collaboration

(1) Principle of Rydberg-atom single-photon detector (2) Performance of detector : measurements of blackbody radiations in a cavity at low temperature (3) Sensitivity limit: effect of stray electric field (4) Practical design for improving the sensitivity Contents

Ａｘｉｏ ｎ A hypothetical particle postulated by Peccei-Quinn in 1977 to resolve the so called strong CP problem in QCD. is a well-motivated candidate for the Dark Matter Dark Matter Rotation-velocity distribution of a typical spiral galaxy A: expected B: observed Dark Matter Rotation curve of a typical spiral galaxy, i.e. rotating velocity of the galaxy versus distance from the center of the galaxy, cannot be explained only by the visible matter. Existence of a roughly spherically symmetric and centrally-concentrated matter called galaxy halo explains the rotation curve. Non-visible form of matter which would provide the enough mass and gravity is called “Dark Matter” [eV] < m a < [eV] 240[MHz] < f < 240 [GHz]

4s 1/2 Axion B0B0 ns 1/2 np 1/2 Diode laser 766.7nm 4p 3/2 Diode laser 455nm γ Primakoff effectRydberg atom ｜ｇ 〉｜ｇ 〉 ｜ e 〉 Ｌｏｗｅｒ ｓｔａｔｅ ｜ｇ＞Ｕｐｐｅｒ ｓｔａｔｅ |e ＞ Principle of the Kyoto Rydberg-atom single-photon detector 39 K Axion is resonantly converted to a single microwave photon by a Primakoff interaction,enabling us to develop an effective axion detection by counting axion converted photons indirectly Schematic

Laser Electron multiplier Dilution fridge electron Field ionization electrodes Atomic beamMetal posts for tuning mirror 7T magnet Whole System Liquid Helium

Dilution fridge and selective field ionization detector Electron multiplier Selective Field ionization region Laser set up Top view of the Dilution Fridge

Noise source Blackbody radiation in the cavity Cavity temperature must be kept as low as possible

Stray electric field limited the Sensitivity Reduction of absorption probability of photon in the resonant cavity (Resonance broadening) Degradation of the selectivity in the field ionization process (SFI) (Rotational effect of electric field)

Actual pulsed-field ionization scheme Lower state Upper state P 111S 111P 111S

M. Tada et al., Phys. Lett. A 349(2006)488 Measurement of blackbody radiations in a resonant microwave cavity SQL Limit 2527 MHz p stst sasa p p stst stst sasa sasa

Improvements 1.Instead of Rb,Potassium Rydberg atoms will be used (reduce the effect of Stark broadening in the microwave absorption Process) 2.Guiding field method to avoid the rotation of the electric field 3.A spatially collimated bunched packets of Rydberg atomic beam (by laser cooling) time varying electric field will be applied to compensate the stray electric field.

Improvements 1.Instead of Rb,Potassium Rydberg atoms will be used (reduce the effect of Stark broadening in the microwave absorption Process) 2.Guiding field method to avoid the rotation of the electric field 3.A spatially collimated bunched packets of Rydberg atomic beam (by laser cooling) time varying electric field will be applied to compensate the stray electric field.

Improvements (1): Use of 39 K Rydberg atoms instead of 85 Rb H.Haseyama et al J.Low Temp Phys (2008) 39 K 85 Rb

Electric field [mV/cm] K:n =102 Experimental data of Stark shift in 39 K for n=102 More Precise measurements are in Progress s-p energy difference [MHz] Red solid circles : Preliminary experimental data for the s 1/2 to p 3/2 transitions open circles : those for the s 1/2 to p 1/2 transitions.

Improvements 1.Instead of Rb,Potassium Rydberg atoms will be used (reduce the effect of Stark broadening in the microwave absorption Process) 2.Guiding field method to avoid the rotation of the electric field 3.A spatially collimated bunched packets of Rydberg atomic beam (by laser cooling) time varying electric field will be applied to compensate the stray electric field.

Guiding electric field Improvements(2): Cavity and electrodes cavity Stark electrode SFI electrodes electrodes for field rotation atomic beam y z field direction Stark field direction Cavity electro-magnetic field: TM 010 E M.Shibata et al J.Low Temp Phys (2008)

Cavity and electrodes structure i.d. 90, length 958 cylindrical TM 010 mode

A distinctive step to overcome the stray electric field dynamically Instead of continuous beam a spatially collimated bunched packets of Rydberg atomic beam will be used by laser cooling technique and by applying time varying field to compensate the stray field Increasing absorption probability and state selectivity

Improvements 1.Instead of Rb,Potassium Rydberg atoms will be used (reduce the effect of Stark broadening in the microwave absorption Process) 2.Guiding field method to avoid the rotation of the electric field 3.A spatially collimated bunched packets of Rydberg atomic beam (by laser cooling) time varying electric field will be applied to compensate the stray electric field.

Time to reach the bunched beam from trap to Resonant Cavity S=1.365 m V=350 m/s t = 3.9 ms Spatial Spread of 39 K at the position of the Resonant Cavity V = 350m/s t 1(time taken for accelerated motion)=1.4 ms S1(Distance Traveled to attain V ) = 0.24 m S2(Distance to Resonant Cavity)=1.365m t2(Time to reach the Cavity)=3.9 ms Velocity spread after acceleration=2m/s Spatial spread after acceleration is about 2mm at the position of cavity spatial spread increase Improvements(3): Laser cooled bunched beam T=145mK

Summary Obtained preliminary data of Stark Shift of 39 K Constructed the Guiding Field system in the cavity. More precise measurement of Stark Shifts of 39 K Experimental testing of Guiding electric field and sensitivity up to 10 mK Designing and construction of laser cooling apparatus for collimated bunched beam of 39 K Rydberg atoms Improvements in Progress Present Status

Thank you For your kind Attention

Room Temp 39 K source Ion Pump Anti Helmotz coils Laser Beams s+s+ s-s- s-s- - C.Monroe et all Phy.Rev.Lett,65,1571(1990) Omit this slide

B=m o nIr 2 /2(r 2 +z 2 ) 3/2 If separation is twice of the Radius of the coil B= (4/5) 3/2 m o nI/r Coil Radius (r) = 30mm Separation (z) = 60mm Number of turns (n)=25 Current=3A Required Field Gradient=0.20T/m Anti -Helmholtz coils z x y I I s-s- s+s+ s+s+ s-s- s-s- s+s+

n=10n=100n=1000 Mean radius n253A00.53 micro meter 53 micro meter Binding energy 1/n21100cm-111cm-10.1m-1c Period of electronic motion n30.15pico second 0.15ns0.1micro second Polarizebi lity n x1070.2x1014 Spacing between adjacent level n-3200cm-10.2cm-12x10- 4cm-1 Ionization field n v/cm 3.3 v/cm 3.3x10-4 v/cm

Some parameters regarding axion-photon-atom system Initial average quantum state occupation number of axion=5.7x1025 Spread in the axion energies= eV/h Axion- photon- photon coupling constant=4x eV/h Collective coupling constant between the resonant photons and the N Rydberg atoms=1x eV/h Cavity length=20cm V=350m/s Ma=10 - 5ev Q=2x10 - 4

Loading Rate Coefficient also depends upon the beam diameter and the Total intensity of the trapping laser as shown in fig.3 Fig. 3.Loading rate coefficient l as a function of (a) beam diameter d and of (b) intensity Itot

Some Parameters dependence of 39 K Trap 1.Number of Trapped atoms(N) 2.Loading Rate Coefficient(l) 3.Trapped atoms density(n) 4.Loss Rate I tot =220mW/cm 2 and beam diameter is 1.2cm Williamson III JOSA B Vol 12,1393(1995)

Kitagawa, Yamamoto, and Matsuki, 2000.

From Kitagawa,Yamamoto, and Matsuki, 1999.

33 Shibata et al., Rev.Sci.Inst. 74(2003)3317. atomic beam e-e- 0.15kV 1kV CEM Cross Sectional View 20K