Phys Rev Letters Cover !

• 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 !

Detecting POAM with 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, ...)

Do it first at Arecibo!

• 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, & mega-masers

– Synchrotron emission with well-organized source geometry

– propagation through a turbulent, ionized plasma

– pulsars, quasars, SETI, ...

Astronomical potential of POAM ...

L=0 case How to produce (or detect) POAM(Thide et al. 2007)

L=0 case How to produce (or detect) POAM

L = 0 caset = 0

L=0 case How to produce (or detect) POAM

L = 0 caset = 0

t = 0

L=0 case How to produce (or detect) POAM

L = 0 caset = 0

t = 0

t = 0

t = 0

t = 0

t = 0

t = 0

t = 0

L=0 phase fronts

L=0 beam pattern

L=1 case How to produce (or detect) POAM

L = 1 caset = 0

L=1 case How to produce (or detect) POAM

L = 1 caset = 0

t = P/8

L=1 case How to produce (or detect) POAM

L = 1 caset = 0

t = P/8

t = P/4

L=1 case How to produce (or detect) POAM

L = 1 caset = 0

t = P/8

t = P/4

t = P/2

t = 3P/4

L=1 phase fronts

L=1 beam pattern

L=2 beam pattern

• 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 POAMwith a single radio telescope

(DRS point of view - active discussion going on)

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) !!

How to detect POAMwith a single radio telescope ...

• 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, ...)

Do it first at Arecibo!