Transcript DS_POAM

Phys Rev Letters Cover !
Detecting POAM with Arecibo
• Photon orbital angular momentum has never
been detected from an astronomical source,
but it holds great promise as a diagnostic
tool.
• We now know how to do it with radio
techniques.
• Arecibo is the right instrument for a first
detection !
Do it first at Arecibo!
• the most sensitive single dish on the planet
by a substantial margin
• the best user-accessible signal processing
instrumentation in the world
• a long tradition of phase-coherent
processing expertise: radar, ionospheric,
pulsar (Hankins, ...)
Astronomical potential of
POAM
• Martin Harwit in 2003: “POAM in
Astrophysics” (ApJ, 597, 1266)
• Well established physics (it has
revolutionized quantum optics in the last 10
years!)
• Astrophysics: wherever the orbital motion
of source particles or vorticity matters
(synchrotron radiation!) ...
Astronomical potential of
POAM ...
• Some possible detection scenarios
– Masers: interstellar, circumstellar, & megamasers
– Synchrotron emission with well-organized
source geometry
– propagation through a turbulent, ionized plasma
– pulsars, quasars, SETI, ...
How to produce (or detect) POAM
(Thide etL=0
al. 2007)
case
How to produce (or detect) POAM
L=0 case
L = 0 case
t=0
How to produce (or detect) POAM
L=0 case
L = 0 case
t=0
t=0
How to produce (or detect) POAM
L=0 case
L = 0 case
t=0
t=0
t=0
t=0
t=0
t=0
t=0
t=0
L=0 phase fronts
L=0 beam pattern
How to produce (or detect) POAM
L=1 case
L = 1 case
t=0
How to produce (or detect) POAM
L=1 case
L = 1 case
t=0
t = P/8
How to produce (or detect) POAM
L=1 case
L = 1 case
t=0
t = P/8
t = P/4
How to produce (or detect) POAM
L=1 case
L = 1 case
t=0
t = P/8
t = P/4
t = 3P/4
t = P/2
L=1 phase fronts
L=1 beam pattern
L=2 beam pattern
How to detect POAM
with a single radio telescope
(DRS point of view - active discussion going on)
• construct a focal plane array with circular
symmetry
• point the telescope off-axis by a prescribed
amount for each L value (not restricted to
integer L values)
• record the baseband signals from each of
the detectors
• look for the helical winding of the signal
characteristic of POAM
How to detect POAM
with a single radio telescope ...
MORE SPECULATIVE:
• detect the angular momentum content directly
(torque as opposed to force on charge carriers)
– in optics (Curtis & Grier, 2003, PRL) this has
been seen directly: imparting orbital motion to
colloidal particles!
– E. Purcell “curlmeter” might be a radio
technique
– or transfer the POAM to the ang. momentum of
a quantum liquid (B-E condensate) !!
Do it first at Arecibo!
• the most sensitive single dish on the planet
by a substantial margin
• the best user-accessible signal processing
instrumentation in the world
• a long tradition of phase-coherent
processing expertise: radar, ionospheric,
pulsar (Hankins, ...)