As far as I understand and I’m no expert, a parametric amplifier is just like any other amplifier in that this half a photon of noise from the vacuum arises from Heisenberg’s uncertainty principle (HUP), so there’s no getting around it.
However, with radar it’s a little different as you have control over the illuminating radiation, so potentially you can squeeze it, to reduce the phase noise, the phase error then becoming inversely proportional to the number of photons, this being a form of HUP, as opposed to shot noise from classical (unsqueezed radiation) currently used in radar where phase error is inversely proportional to root of the photon number. That’s it in my handwaving description, more than that and you’ll have to ask a quantum optics expert. Cheers, Neil From: 'Day, Peter K (US 389I)' via casper@lists.berkeley.edu <casper@lists.berkeley.edu> Sent: 25 February 2022 18:45 To: casper@lists.berkeley.edu; 'mtchen' <mtc...@asiaa.sinica.edu.tw> Subject: Re: [EXTERNAL] [casper] RE: quantum radar in astronomy One way to generate the squeezed radiation in micro/mm-wave bands would be with something like this: https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.3.023184 This is a way of replicating various non-linear optical processes in those lower frequency bands. I’m skeptical about applications for quantum radar because you will be limited to extremely low power, so any classical system will end up being more sensitive by being able to operate at higher power. A related question might be whether a parametric amplifier’s ability to almost noiselessly amplify a single quadrature of a signal (without adding the half quantum of noise that comes from the so-called standard quantum limit for a phase-preserving amplifier) can be used to improve astronomical interferometry. If anyone has any ideas about that, please let me know. Best, Peter From: "salmon.na via casper@lists.berkeley.edu <mailto:casper@lists.berkeley.edu> " <casper@lists.berkeley.edu <mailto:casper@lists.berkeley.edu> > Reply-To: "casper@lists.berkeley.edu <mailto:casper@lists.berkeley.edu> " <casper@lists.berkeley.edu <mailto:casper@lists.berkeley.edu> > Date: Friday, February 25, 2022 at 1:27 AM To: "casper@lists.berkeley.edu <mailto:casper@lists.berkeley.edu> " <casper@lists.berkeley.edu <mailto:casper@lists.berkeley.edu> >, 'mtchen' <mtc...@asiaa.sinica.edu.tw <mailto:mtc...@asiaa.sinica.edu.tw> > Subject: [EXTERNAL] [casper] RE: quantum radar in astronomy Certainly there are lots of questions surrounding just what squeezed radiation (existence only proven in 1985) can do, so a good approach is to build kit to generate and detect it and then use it in experiments. Almost all work has been in the optical, so trying this at micro/mm-wave is challenging, but while there’s good potential, it’s worth having a go. Would you have any details of the circuit and what might it cost to buy? Many thanks, Neil From: mtchen <mtc...@asiaa.sinica.edu.tw <mailto:mtc...@asiaa.sinica.edu.tw> > Sent: 24 February 2022 20:57 To: casper@lists.berkeley.edu <mailto:casper@lists.berkeley.edu> Cc: salm...@tiscali.co.uk <mailto:salm...@tiscali.co.uk> <salmon...@tiscali.co.uk <mailto:salmon...@tiscali.co.uk> > Subject: Re: quantum radar in astronomy Dear Neil, We have developed a 16 Gsps 4-bit digitizer and a strong interest in such an experiment...... On Wednesday, February 23, 2022 at 11:08:02 PM UTC-10 salm...@tiscali.co.uk <mailto:salm...@tiscali.co.uk> wrote: Dear All, Applications where background thermal radiation is low and object return reflections are weak may benefit from quantum radar. So I was curious, who if any, might be exploiting this for radioastronomy? Using a beam of entangled photons (squeezed light) to illuminate has advantage that phase error (from shot noise) is lower than that in classical coherent radar beams. This would offer greater sensitivity for detecting smaller objects and estimating their distances. I’m looking at materials and circuits to generate and detect entangled photons – eg a 20 Gsps 4-bit digitiser as part of the receiver. One potential application might be to track asteroids in the solar system, or even detect objects before they enter the solar system – a key question being achievable performance. Anyone aware of interest in this for astronomy? Many thanks, Neil -- You received this message because you are subscribed to the Google Groups "casper@lists.berkeley.edu <mailto:casper@lists.berkeley.edu> " group. To unsubscribe from this group and stop receiving emails from it, send an email to casper+unsubscr...@lists.berkeley.edu <mailto:casper+unsubscr...@lists.berkeley.edu> . 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