Vistas in Astronomy, Vol. 37, pp. 555-558, 1993 Printed in Great Britain. All rights rese~ed.

0083-6656/93 $24.00 @ 1993 Prxgamon Press Ltd

MANIPULATING PHASE OF DIGITIZED PHOTONS: AN APPLICATION TO RADIO ASTRONOMY

Tsuneaki Daishido, Kuniyuki Asuma, Kazuhiko Nishibori, Junichi Nakajima, Eiichiro Otobe, Naoki Watanabe, Yoshitaka Aramaki,

Hiromi Kobayashi, Tomohiro Saito, Naoki Tanaka and Tomoyuki Hoshikawa

Astrophysics Group, Department of Science, School of Education, Waseda University, 1-6-1 Nishiwaseda, Shinjuku-ku, Tokyo 169, Japan

...noises...became frozen on the air.

But just now, the rigours of winter being over ...,

these noises are meltig, and you can hear them.

Gargantua and Pantagruel

(Francois Rabelais /trans. by J.M.Cohen)

INTRODUCTION

We distingush detection and sampling in measurement. Sampling is a

kind of propagating stage for photons. We manipulate phase of sampled

photons for the observation in radio astronomy.

A photon behaves as a particle in emission and absorption, while it

behaves as a wave in propagation. Phase information is lost in detection

( power measurement process). But it is not lost in sampling( amplitude

measurement process). These features are true even in VLBI( Very Long

Baseline Interferometer; a kind of recording and playback interferome-

ter) or in the digital interferometer of Waseda University. A photon am-

plitude could be recorded on the two separate devices simultaneously in

a way that phase information is preserved, with the format of analogue

or digital. A recorded photon is a "frozen photon". However, one cannot

say which device does a photon pickup. A "frozen photon" could be re-

garded to be under "propagation". Palybacking the two devices melts a

photon, and it is possible to be interfered itself. Resulting fringe

pattern is the same as the one obtained by usual interferometer.

556 Z D~shidoet~.

PHOTON NUMBER UNCERTAINTY IN THE DIGITAL INTERFEROMETER

In the simple two element interferometer, it could not be determin-

ed that a photon arrives which antenna A nor B. It is valid even in the

digital interferometer of Waseda University or the recording interferom-

eter as VLBI. It is understood as follows.

Since there is an uncertainty relation of A NA ~ = 1/2 between

photon number N and phase ~ , precise measurement in phase ~ requires

large uncertaity in photon number N.

Y Y

digitising or I I digitising or recording A .recordin S B

Which a n t e n n a d o e s

a p h o t o n p i c k u p ?

I digital or

recorded dataJ A

digital or

recorded data B

f r i n g e p a t t e r n

AMPLIFIRES AND AMPLITUDE RECORDINGS OF BOSON AND FERMION

Classical waves which we observe by the radio interferometers are

discribed quantum mechanicaly as coherent states. The coherent state is

a superposition of photon number states as

[ a > = 5 , i n > ( < n > ° e . . . . / n ! ) 1 " ~

which gives the probability of Poisson distribution when one measures

Digitized Photons 5 5 7

the number of photons. This means that the simultaneous amplitude re-

cording on separate two devices is not prohibited even for the very weak

r a d i o w a v e s a s o n e p h o t o n p e r p h a s e s p a c e .

T h u s , a " f r o z e n p h o t o n " on t h e s e p a r a t e two m a g n e t i c t a p e c o u l d be

i n t e r f e r e d . T h i s i s o n l y p o s s i b l e f o r b o s o n . F o r f e r m i o n , on t h e c o n t r a -

r y , a m p l i f i e r s n o r a m p l i t u d e r e c o d i n g s d o e s n o t e x i s t a c c o r d i n g t o P a u l i

' s p r i n c i p l e , t h o u g h t h e b e a u t i f u l i n t e r f e r o m e t r i c e x p e r i m e n t by H . R a u c h

s h o w s t h e e x i s t e n c e o f p h a s e s h i f t f o r a n e u t r o n .

Interferometer

Amplifier

Amplitude Recording

Boson Fermion

possible possible

possible impossible

possible impossible

DIGITAL PHASE MANIPULATION IN WASEDA ARRAY TELESCOPE

Phase manipulation is done by multiplying the complex number in the

Digital Lens( Complex amplitude equalizer + 2D FFT processor ), and it

has capabilty of real time digital imaging .

The radio patrol camera project was started at Waseda University in

1979 using the 8 element radio interferometer, and the 1 dimentinal dig-

ital processor was developed in 1984-85. The following FFT digital im-

age was obtained in 1985 by MkI Digital Lens.

Gain Pattern by the Osbervation of the Sun

O b s e r v a t i o n b y MkI D i g i t a l I n t e r f e r o m e t e r ( 1 9 8 5 )

558 Z D~shidoetaL

Two dimentinal Radio Patrol Camera Project has been started in 1989

with the over all array size of 20m x 20m. Each element is a 2.4 m¢ an-

tenna. The process speed of the Digital Lens is 150 -200 GOPS( Giga Op-

eration Per Second), which is I00 times faster than super computer. The

present radio interferometer of 8x8=64 element watchs 64 directions si-

multaneously with the sensitivity of 20m¢ radio telescope at 10.6 GHz.

Sky survey to search radio novae will start in 1993.

Note : D i g i t a l Phase C o n t r o l e r

D i g i t a l complex m u l t i p l i e r i s a p h a s e c o n t r o l e d e v i s e .

exp(i¢ L +i¢2) = exp(i¢ ~)exp(i¢2) = (a~ + ib,)(a2 + ibm)

..... >

A/D

A/D

x X