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Is Single-Photon Microwave/RF the Next Big Thing?

Sometimes you read an article that really makes you stop and think. No, I am not talking about one which discusses some technology advance as potentially “faster, better, cheaper,” or a futuristic one with rampant speculation based with 1% facts and 99% “weasel-word” phrases such “may,” “could,” “might,” and similar crystal-ball terms. Instead, it’s one which looks at a well-known situation in a very different light (pun fully intended) and makes you wonder: Could this really be the case? And what if it is?”

As anyone who has studied even basic physics knows, photons are strange creatures. They are energy bundles which exist in abundance, of course, yet they don’t like to be caught, characterized, or counted; in fact, they change some of their inherent characteristics if you even try to touch them, so to speak.

Nonetheless, the entire field of single photons seems to be getting both academic and hands-on attention these days. I recently wrote about the mental dissonance that the detection of single photons was causing me (is that an analog or a digital sensor event?) in connection with NASA’s plans to use lasers for deep-space communication links, see “When a Sensor Is Truly In “The Twilight Zone””.

The article which grabbed me was in a recent issue of Microwave Journal , and entitled “Controlling Single Microwave Photons: A New Frontier in Microwave Engineering.” When I saw that headline, I had to re-read it a few times, since my brain associates photons with light, not microwaves and RF. But, of course, that’s just a matter of perspective and mental conditioning, since RF energy is also comprised of photons, although we don’t think of them in that way.

Yes, we know that photons are those smallest packages of light, defined by quantum theory, Einstein’s brilliant explanation of the photoelectric effect in 1905 (for which he was awarded the Nobel Prize, not for relativity), and that photons embody a wave/particle duality. In recent years, there’s been a lot of work done with single-photon events and detection, which has some fascinating and strange implications for data encoding, qubit computing, and much more.

For one thing, the energy of these RF photons is many magnitudes lower than that of “light” photons, as clearly defined by the well-known equation of Planck’s law, E = hf , where h is Planck’s constant. But the real issue that we already have some powerful, very amazing tools for working with light photons, yet don’t really have equivalent tools and techniques for the RF ones, Figure 1.

However, the article explains how that situation is changing. It clearly describes some of the challenges, present advances, and implications of being above to control and use RF as photons rather than as RF energy (and power) in the mode we are presently accustomed to using. While the laws of physics including Maxwell’s equations still hold for RF photons, nearly everything else in their “hands-on” world must change.

It calls for a whole new way of thinking about what you can do, and how you might try to do it. I won’t try to summarize the article here; that would be short-changing you from information in the medium-length, well-written piece which does not veer in academic-speak, Instead, it uses a straightforward style targeted at engineers with a modest physics background and some RF exposure (and that’s most EE’s, I assume).

One other take-away I from the article, in addition to the main story, is how much of technical advancement is due to activities in areas which are not directly related. This is not a new theme – it has been explored by science and engineering historians as well as James Burke’s excellent “Connections” TV series several decades ago – but it’s one with remembering again.

Figure 1

This microchip, developed at ETH Zurich, has a microwave photon source in the upper half and a beam splitter in the lower half. It generates single photons two million times per second with accuracy controlled to a few nanoseconds; the microchip also includes a highly sensitive, efficient measuring device to show that the apparatus really does generate only single photons. (Source Credit: ETH Zurich)

This microchip, developed at ETH Zurich, has a microwave photon source in the upper half and a beam splitter in the lower half. It generates single photons two million times per second with accuracy controlled to a few nanoseconds; the microchip also includes a highly sensitive, efficient measuring device to show that the apparatus really does generate only single photons. (Source Credit: ETH Zurich)

For example, due to the relatively large yet unavoidable thermal noise, most of the RF photon work is done at temperatures well below 1K, which means some serious cooling systems (cryostats)are needed. The article points out that the non-RF R&D work in single photons has spurred development of smaller, dry, cryogen-free (no liquid helium) cooling systems, which is making the RF-centered single-photon research more accessible an affordable. Many other things needed to explore the RF single-photon world– and they are both amazingly esoteric yet quite real and in use now — are also derived from all the activity and advances in quantum computing, as well.

Further, while it’s very easy to generate photons, t’s very hard to greater a fully defined, single or low-rate stream of them as needed for “single photon” experiments. Not to worry: another excellent article, this one in Photonics, “Holographic atomic memory produces photons on demand” explained some efforts and progress on this made by a Polish team. Just thinking about the meaning and challenges of deterministic generation, sorting, and retrieving of single, separated photons made my head spin, although fortunately not in a quantum “spin state” sense.

My one bit of advice (again, pun intended): if you are an EE interested in continuing education, do some refresh studying on optical photons, quantum effects, and similar. It looks like there will be additional overlap and synergy among the electrical/RF world, the optical world, and the electrooptical crossover going far beyond LEDs and fiber optics.

What do you think about the possibilities of dealing with RF frequencies via single-photon processing? Is it yet another way to appeal for research-grant money (the cynics’ view), a door to new possibilities (the optimists’’ view), or other? Do you see any applications that interest you?

References

Breakthrough for photons in the microwave frequency range

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