Novel microwave isolator points the way to new radio cameras, quantum computers | Hacker News Reader

Novel microwave isolator points the way to new radio cameras, quantum computers

phys.org

63 pointswglb13 comments

Abstract:We propose a nonreciprocal microwave isolator realized using an electrical circuit with two frequency mixers. A phase shift between the mixers at the same frequency as the local oscillator (LO) frequency is $\pi /4 + m\pi /2$ , and the powers of LO applied to each mixer have a phase difference of $\pi /4+ n\pi /2$ (where $n$ and $m$ are the arbitrary integers). The up-converted signals in the upper and lower sidebands at the first mixer are combined at the subsequent mixer, even if they have phase differences. Because each sideband is in-phase for one direction and out-of-phase for the other direction, the circuit principally functions as an isolator with broadband from near dc to LO frequency. An isolator using commercially available microwave components successfully demonstrated more than 17 dB of isolation across the 0.01–1.50-GHz band at an LO frequency of 2.30 GHz. An on-chip broadband isolator with positive gain can be realized using superconductor–insulator–superconductor mixers.

17 dB is not bad for an isolator, but it's not good either. But this kind of just begs the question by using frequency mixers as the non-reciprocal element because frequency mixers are such lower power devices. I guess this helps for really lower power science stuff, but not so much communications.

Still, very cool! The only other non-magnetic non-reciprocal RF elements I can think of used angular-momentum bias.

What does this mean in simple terms?

Imagine you have a special device that can control the flow of microwaves. This device is like a gate that only lets the waves pass through in one direction and blocks them from going the other way.

To make this device, we use a special circuit with two parts. These parts are like mixers that combine different waves together. When we put the waves into these mixers, they change a little bit and become different from how they were before.

The waves that come out of the mixers are then combined together again. Even if they changed a little bit, we can still put them together. It's like putting puzzle pieces together even if they don't match perfectly.

The cool thing is that when the waves go through this device, they behave differently depending on which direction they're going. It's like a one-way street. If the waves go in one direction, they can pass through the device without any problems. But if they try to go in the other direction, they get blocked and can't pass through.

The device that was described in the abstract was made using parts that are easily available. It worked really well and blocked the waves from going in the unwanted direction, giving us more than 17 times less of those waves.

The abstract also mentions the possibility of making an even better device using a different kind of part that can make the waves stronger. It's like giving the waves a little boost. This new device could be made very small and fit on a tiny chip.

So, in simple terms, the abstract is talking about a device that can control the flow of microwaves and only let them go in one direction

Tesla valve for microwaves then?

is this your summary or chatGPT? Serious question, no judgment

I can't say I've often seen GPT use phrases like "the cool thing about this.."

That's trivial, by asking it to respond with a certain "personality". Something like "respond as a space cowboy from Silicon Valley, who was an elementary school science teacher."

A 17dB reduction in power is not 17 times less! It is a reduction by a factor of 10^(17/10) or about 50 times.

So the basic problem to overcome is, microwaves are a kind of light, and if I can see you, you can see me, no matter what ordinary fancy optics are in between. If a light ray gets from you to me, then the reverse path is physically exactly the same as time-reversing the original light ray (and time reversal is a symmetry of electromagnetism).

I read the above explanation and I still don't get where it overcomes reciprocity. (Didn't try to read the paper itself.) Can you point to where the asymmetry is introduced? Or how I'm thinking about this all wrong?

The mixers in the device are designed to combine different frequencies of waves together. By carefully adjusting the phase shift between the mixers and the powers of the local oscillator (LO) applied to each mixer, a specific phase relationship is created for the up-converted signals (upper and lower sidebands) produced by the mixers.

When these signals are combined again in a subsequent mixer, they interact in a way that results in different phase relationships for waves traveling in different directions. This means that the waves are in-phase (in sync) for one direction but out-of-phase (out of sync) for the opposite direction.

This phase relationship difference causes an asymmetry in how the waves propagate through the device. Waves traveling in the desired direction experience constructive interference, meaning they reinforce each other and can pass through the device. On the other hand, waves traveling in the opposite direction experience destructive interference, meaning they cancel each other out and are blocked from passing through.

Boiled down to the simplest terms? Microwave diode.

That was might first thought as well but "diode" might make people think about polarity.

I would rather describe it as unidirectional valve for microwaves instead.

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