Developments toward
Photon Counting Terahertz
Interferometry
Hiroshi Matsuo
Advanced Technology Center
National Astronomical Observatory of Japan

Atacama Large Millimeter/submillimeter Array

干渉計とは？

Credit: ALMA (ESO/NAOJ/NRAO)

ALMA observed [OIII] 88mm (3.4THz)
from z=7.2 SXDF-NB1006-2

From NAOJ press release
Inoue, Tamura, Matsuo et al., Science 352, 1559 (2016)

Cosmic Reionization

From NAOJ press release
Inoue, Tamura, Matsuo et al., Science 352, 1559 (2016)

MACS1149-JD1
z=9.11 by [OIII] 88 mm (3.4 THz)

Hashimoto et al., Nature 557, 392 (2018)

Atmospheric Windows from Atacama（alt. 4800m）
1mm500um

300um

200um
z = 9.11

Matsushita, Matsuo et al. PASJ 51, 603 (1999)OIII 88um

Angular Scale of Observation
All Sky

3°10″THzGap
10 mas

10 mas

910111213
Log Frequency [Hz]14

Narrabri Stellar Intensity Interferometer

Hanbury-Brown, “The Intensity Interferometry” (1974)

AT N F D a i l y As t r o n o m y
17th of August 2015

PictureHBT Intensity Interferometry⚫ Correlate “Intensities”

from two individual telescopes⚫ Radio intensity interferometer at 125 MHz– Hanbury-Brown et al. (1952)⚫ Optical interferometer– Hanbury-Brown and Twiss (1956)

from Hanbury-Brown (1974)“The Intensity Interferometer”

Limitation of intensity interferometers⚫ High Dynamic Range is required– Intensity correlation ∝ (Amplitude correlation)2⚫ Low efficiency for optical observations– Observation of bright early type stars only

⚫ Phase information is missing– Measurement of stellar diameters only

Fluctuation of thermal radiation12n = n + n , where n =eh kT−1n : photon occupation numberA = 2

NEP = 2 P  (h + kTB ) [ WReferences

A. Einstein (1909)
J. Mather (1984)
J.M. Lamarre (1986)
J. Zmuidzinas (2003)

Hz ]T=TB / √Bt

Photon bunchingTHz photon statistics
10 cm10 mm

1 mm

kT 1 nWh 1 nW

250 Kh 10 pW

2.5 K

kT 10 pW

B = 100 GHz

Matsuo, JLTP 167, 840 (2012)

Photon Bunches fordelay time measurements⚫ Photon bunch can be a measure of delay time.
– Complex visibility can be obtained.

⚫ Large number of THz photon is expected.

100 M photons/sec from Stars and AGNs
1 Jy at 1 THz (B=100 GHz), using f10 m telescopet = 10-13 sec in 100 sec is expected.
𝛥𝑡 =THz Photons are bunched !

1𝑁 𝑁∙𝜏

N: photon ratet : integration time

Nobeyama Radioheliograph (NoRH)• Interferometer exclusively observing the Sun• 84 antennas of 80 cm diameter• 17 GHz R+L / 34 GHz• Fundamental Spacing 1.528 m

Date: April 14, 2014
Utilized:
17 GHz (17 mTHz) R+L
Central 16 elements aligned East-West

NRO 45 m14

Nobeyema Radioheliograph at 17 GHz
Shortest baselines averaged over 16 antennas

Antenna Temperature T A* [K]Amplitude
Correlation

IntensityCorrelation

System Temperature Tsys [K]delay

Correlation amplitude

Frequency  [Hz]Bandwidth  [Hz]Tsys11t = * [s]
T A  t 
 = 2t [rad]t ~ 5ps in 50 ms integration
Ezawa, Matsuo et al., JLTP 184, 244 (2016)

Experiment at 17 GHzwith Nobeyama Radioheliograph⚫ Real Part of Visibility– (Intensity Correlation)0.5⚫ Imaginary Part– Δφ = 2 π ν Δt

Van CittertZernikeBackground limited observation withSpace THz Intensity Interferometry⚫ Quantum noise of heterodyne receivers– TQL = h/k [K] = 150 K @ 3THz

10-14

– n = kTQLB/h = B [photons/s]⚫ Background limit of direct detectors

Quantum Limit– NEP = 10-19 W/Hz0.5, B =100 GHz– TRX = NEP / (2k B0.5) = 10 mK

10-16
Atmospheric Limit

10-17– Background vs. Quantum limit~ 4 orders

10-18
Cosmic Background Limit
10-19

NEP [W/√Hz](approximate value)

10-15

Intensity Interferometry⚫ Cross correlation of Intensity (E2)
– High correlation efficiency in far-infrared– Missing phase information⚫ Stable against phase fluctuation– Coherence lengths >> Wavelengths⚫ Photon counting detector can be used
– No receiver quantum limit⚫ Photon bunches enable delay measurements– Aperture synthesis imaging

Requirements to Detectors⚫ Sensitive to THz photons

Matsuo and Ezawa, JLTP 184, 718 (2016)– Photon energy ~10-21 Joule⚫ Fast response/ = 3– B = 1 GHz for 100 M photons/s⚫ NEP(Noise Equivalent Power)= 10-21 × (1 GHz)0.5~ 10-17 W/Hz0.5

OurTargetSPICA

SIS Photon Detectors

N = 2eI 0 [A/ Hz ]Photon Assisted Tunneling

IJc =300A/cm2h/eh

2I 0NEP =[W/ Hz ]eNEP  3  10−18W/ Hzfor I 0 = 1 pA  = 0.5

at 650 GHz

Low leakage SIS junctions

VLeakage current [A]eS = 
[A/W]h

10 mm × 10 mm
5 mm × 5 mm
3 mm × 3 mm

BCSBCS+leak2/e

Ezawa et al., JLTP 194, 426 (2019)

Temperature [K]Superconducting detectors in THz frequencies
An example of superconducting
detector at 10um (30THz)
Kawakami et al. (2019)

An antenna-coupled Nb-SIS photon detector
at 650 GHz fabricated in CRAVITY(AIST)

Ezawa et al. JLTP 200, 226 (2020)

Readout Electronics

SIS photon detector signal
One electron/photon with abandwidth of 1 GHz.
Assuming,

Capacitance = 10 fF
𝑒𝑉𝑠 = = 16 𝜇V
𝐶

J-PHEMT

1k

J-PHEMT400

50

FET thermal noise at 0.8K

8:1

𝑣𝑛 =SiGe amplifier

100uW

0.8K

36mW

4K

4𝑘𝐵 𝑇𝑅𝐷 = 0.2 𝑛V/ 𝐻𝑍𝑑𝑉𝑔
1𝑅𝐷 === 1 kΩ𝑔𝑚 𝑑𝐼𝑑With a bandwidth of 1 GHz,

𝑉𝑛 = 𝑣𝑛 × 𝐵 = 6 𝜇Vrms

Experimental Setup for Intensity Interferometry
Input Optics
0.8K Fridge

SIS-PC

RecorderCryogenic
Electronics
4K Cooler
Rotatable Mask

Thermal Source

The Most Transparent Atmosphere from Dome A
Ice Feature at 7 THz[NII]
1.5 THz[OIII]
5.8 THz[OIII]
3.4 THz

August 9th 12-18h UTC, 2010
Matsuo et al. Advances in Polar Science 30, 76 (2019)Antarctic THz Intensity
Interferometry

Two 30-cm THz telescopes

RecorderB > 1GHz

RecorderB > 1GHz

Calculate correlation and delay

Technologies forSpace Terahertz Interferometry• Cryogenics - AKARI, SPICA, Astro-H• VLBI technology - HALCA, Astro-G• Superconducting detectors - SMILES

Formation
FlightPhoton Counters
Atomic clock
RecorderPhoton Counters
Atomic clock
RecorderPossible Combination of OST and MSO• Large Cryogenic Telescopes in THz• Direct detectors will be installed.
• Both will situate around S-E L2

SPICA

ISAS/JAXA
https://www.millimetron.ru/

https://origins.ipac.caltech.edu/

High Angular Resolution withTHz Intensity Interferometry
Credit: EHT Collaboration• Closer to the central activities !

ALMA (ESO/NAOJ/NRAO), Imanishi et al.
Inoue, Tamura, Matsuo et al. (2016)

Credit: ALMA (ESO/NAOJ/NRAO)

Credit: ALMA/NAOJ

Angular Scale of Observation
All Sky

3°10″

10 mas

10 mas

910111213
Log Frequency [Hz]14Summary• High angular resolution THz observations• HBT intensity interferometry• Imaging technique• Merit of photon counting detectors• Possible future programs