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Okay. Good afternoon, everybody,

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and welcome to scarily what is the last physics Friday afternoon colloquium this academic year which seems to have gone in a flash.

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It's a great pleasure today to welcome our old friends for lunch on the patio, who is a very distinguished accelerator physicist.

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So Swapan has had his finger in most of the big accelerators which have been built over the last 30, 30 years.

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In one way or another, he's been associated with those.

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He's held a number of senior senior positions at just one lab at Lawrence Berkeley in 2007 eight,

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he moved to he moved to become the first director of the Cockcroft Institute in Liverpool.

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And where he was has been responsible for pulling together a large part of the UK's accelerated science efforts.

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And of course the other part of that is here at the John Adams Institute, part of the John Adams Institute.

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And so following his retirement from from the Cockroft Institute,

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he's now a distinguished scientist at Fermi National Accelerator Laboratory, and he is a visiting professor here.

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So it's a great pleasure to welcome him today as he's keen to talk to us about quantum sensors.

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So forget. And you'll hear me, you know.

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Okay. So I give my top ten accelerators last week, so today is not going to be anything to do.

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It actually is because I can afford and I think after 40 years of being in that field,

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we are kind of hitting the wall and maybe you should think a little bit differently to address

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the same questions with the same expertise that one needs for particle beams and lasers,

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but slightly time differently so that you can do something in a reasonable length of time with a finite amount of money.

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But that means a bit more thinking in a slightly different way.

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So Quantum Sensors is a topic today. So I simply introduce you to that idea which is not new to many of you UK and very strong quantum

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technologies activity and I'll talk about that a little bit on the roundtable that I chaired very recently,

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which may lead to a new initiative in the American side about how to compliment particle accelerator based particle physics astrophysics,

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cosmology by quantum sensor based particle physics,

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astrophysics and things like that give you a I don't have time to go through all the examples, but to give you a couple of examples,

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one from a particle physics, cosmology, dark matter, dark universe sector,

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one from gravitational wave sector, which also connects with inflationary cosmology a little bit.

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The just hint that we can also existing for many, many other things like, you know, neuroscience, material science, geoscience and bioscience.

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And so I probably would not have time to talk about quantum computing, but the whole idea is that countries like UK, USA,

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Canada, they're spending a lot of money in quantum information science, hoping someday they will have a quantum cryptography.

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From my perspective, that's probably 100 years from now.

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But on the way as you go there, you can actually pluck some of the fruits of the scientific R&D that can benefit basic and applied science.

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So okay, so I just want the whole bunch of people you can see is a very mixed bag of people,

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not all particle physicists, not all affiliated people, but people of different mix that have helped me.

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I also want to thank Andre for sitting here.

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Ian is missing and John who introduced me for for giving me the extended offer to come here every year I enjoyed last year.

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This is my second year and I hope to continue next year. Okay.

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So I will start with this slide that says I am a builder of instruments and I

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believe in this philosophy that if you just if you build a new instrument,

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you have to understand what is being built for the science.

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You do not have to be an expert in the science because you have to interpret it and understand it enough

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that you can give the scientist you are into that they are science the best tool that they can have.

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And then you can advance the science and it gives the feedback, just like Galileo and his telescope, right?

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So Quantum Sensors is actually a new tool that's like particle accelerators with drives.

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Quality beams are tools is a new tool,

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a new instrument that actually fundamentally depend on a quantum phenomena or quantum entanglement at the very core of it.

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And it has a promise for very weak to to detect very weak processes.

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So it can give you very precise and high resolution information about very weak

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with processes that can enhance this very good start for fundamental science,

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quantum information, science and computing. So what is actually a quantum sensor?

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Everything that you sense ultimately is classical is giving you a charge or a electric current or voltage,

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which is all classical, of course, and measure with some real instruments.

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However, if the source of that signal is fundamentally related to a quantum system,

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and in particular if it relies on superposition of quantum states which are entangled,

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then in principle it seems to us the instrument that you been with on that principle tend to give you higher position or higher, higher resolution.

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So hence the new initiative on how you can have fundamental and information science based through quantum limited macroscopic sensors,

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or you can actually have macroscopic computers based on Quantum Limited or performance.

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So I'll give you some examples of quantum.

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So, for example, here is a squid invented by Professor John Farquhar actually from Cambridge originally, but then I started from him at Berkeley.

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He was there for a long time, is still there. And nowadays he could have squid that can grow up to 20 miles 16.

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That's the pursuit of Hertz type of sensitivity in magnetic fields, power spectrum.

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You can have accelerometers, which uses atomic beams of some sort,

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that can give you a ten to the -13 g of go to the earth giving that field of acceleration.

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These are incredible numbers. You can have superconducting cavities, microwave cavity that had a few factor of ten to the ten.

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And using quantum information technology, you can actually put a qubit inside a cavity and measure a single photon,

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which is not a noise photon from the amplifier.

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You can, after the couple come out of this cavity and make gravitational distortion of the space time metric,

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and you can look to the electromagnetic field of the superconducting cavities and measure strain at the level

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of 20 -18 people that are talking about superconducting follow metre photon to their superconducting circuits.

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Of course, if you look at the quantum optics of the circles, they actually deal with a fluctuating electromagnetic field which is still coherent,

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but due to the very small number of photons, like five or ten or one that microscopically correlated.

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Here's an example of a coupling of mechanical motion with optics.

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You have transducers, and if you if you look at the space and from KG to central brands to Hertz to ten gigahertz,

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you can actually have all kinds of opto of two mechanical actuators that can operate in the nano micro macro domain,

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fantastic sensors that one can build. And finally, people have used, of course, atoms, molecules and trapped audience, and they've actually can.

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So yes, these are actually if you look at starting from a centimetre all the way to an angstrom,

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which is the atomic level with MRI, nothing like squids.

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I'll quote now, this is nitrogen vacant diamond.

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Well, actually, you get down to very, very small resolutions indeed.

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So all these sensors, all they are actually they are either they exploit quantum effects,

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including the entanglement aspect of it, either in solids or in atomic systems or in some kind of a cavities geometry.

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And you actually use all these things to actually help the field of quantum information science.

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But as I said along the way,

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you probably can pluck the low hanging fruit and some of the areas where you could find applications are like you can sense new particles.

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They're everywhere. They don't have to be just created in a collider.

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If you are sensitive enough, have a very good hearing aid, you can hear a particle without being created in a collision.

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New types of interactions with gravitational waves can be used to probe the very, very, very early universe before even the event horizon.

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During inflationary phase, if there was some kind of some kind of inflation nature of the dark universe,

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biological signals of extremely weak signal from the brain, neuroscience, geosciences, all so.

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So that's quite a bit. So the whole idea is that the funding agents in my field,

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which is accelerators and some other fields like atomic physics, laser physics, defence theory, they work together.

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I think that people are, you know, pursuing different disciplines in different areas.

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But at least in my field where everything is driven by very large scale science,

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either you do space borne experiments or you do a certain base experiments.

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They're expensive because you have to create energy density in a laboratory to actually get the effect.

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But the whole idea is that experiments have been done already and somebody did it and we already have all the things around us.

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We just have to be smart enough to search for, like in archaeology, rather than trying to recreate all the stuff to find the easy way out.

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The easy way is not easy anymore. The laws are expensive and so we have to think a bit differently.

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That means things we have been. Investing in for the last 50 years.

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Maybe we have to think a little bit differently, and that's the whole idea.

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And with this idea in mind, there was a roundtable that was held at Department of Energy.

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I was asked to chair co-chair it together with two others.

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I guess I was there because I'm coming from the traditional laser beams physics side of it that have benefited particle physics for the last 56 years.

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There was also two more people.

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One come from the photon side, Roger from Tony from Berkeley on one come from that really quantum sense aside from Harvard.

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And we were supposed to have a one day roundtable and we actually had it.

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And this was supported by the entire complex of various agencies,

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high energy physics and mass computing B And basically the sciences that funds all the light sources in America National Science Foundation,

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which governs metrology of things. It's kind of similar, but quite different from the ones.

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And you had a one or two year long quantum technology hub discussion?

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I was part of it in the in a very painful way.

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And that also, you know, brought out a few roadmaps for quantum technologies that stressed the technologies of various things like atomic clocks,

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new materials and stuff. And the main difference here is that we had a whole bunch of particle physicists, computer scientists,

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basically energy scientists who actually want to use the sensors to do basic science.

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And so that's that's the major difference. Eventually, the composition of this people, the very hand-selected people, about 14 or 15.

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And there are some people who could not participate but give us contribution in a

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remotely in a whole bunch of agency people that you can see them the top heavy,

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all the funding agency. And then there are some international people you see and want to hear it, you hear in audience.

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Is he supposed to be so good at that?

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Oh, yeah. Uh huh. I've been trying to catch him.

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Oh. So we included him. Of course. He was very busy, did not have enough time to contribute.

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But we are getting contributions from all these people. And the whole idea to come up with a blueprint and a short report for duty and then

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then interact with the international body of people to see what we can do with it.

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So some of the things I'll tell you that came out of it before I give you some examples of that stuff which are really fascinating,

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is that we came up with the thing that if we did it right,

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we probably should be able to, by design, put effort into quantum systems of five, ten, 15, 20 years that are not only for the technology of it.

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We should definitely spend a lot of benefit to society,

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but we probably can make a big leap through in physics of processes at very high or very low energies, either very high meaning rather than TV.

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I've never done to the precise measurements we go beyond what we know about systems today.

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It could also help us explore the understanding of the so-called Dark Universe gravitational wave,

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which cannot be saved by lasers very long remnant low frequency gravitational wave,

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which controls all of the cosmic history, quantum materials, all kinds of new materials,

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quantum simulation of chemistry, which is very, very difficult. But our bio sensing, geo sensing and also quantum computers themselves,

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meaning networks and machines that can be engineered and truly put in programming if I put a little one

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line are almost everything and also the reason that we can be involved in this kind of an activity.

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And of course there were some observations that in order to do this, you have to think differently.

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You have to probably follow the appropriate interdisciplinary community for them to talk to each other.

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You have to kind of deliberately pump prime so things can be advanced,

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actively continue and sustained effort not yet to year effort, which America does every year to change our budget.

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Five years of year, 5 to 10 years sustained effort to a bunch of teams that can more progress identify impact on other areas.

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Importance of you know collaborate with with international partners like UK Quantum Technology Hub and so on, optimising resources.

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We don't necessarily have to have more resources, but obviously analyse the same metrics,

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but the diagonal to be out of a different axis, meaning the precision probing then high energy radiation of high, high density.

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Okay. So now let me give you a few examples. I cannot give you very many, but let me just give you a few examples of how exciting this would be.

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One is the cavity electrodynamics coupled with quantum information science algorithm

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that can actually make probably make a big dent in understanding dark matter,

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we believe, without really going through a collider or space.

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And the second one is actually this technology of atomic beams instead sort of lasers,

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which have to be reflected by mirrors and mirrors, inertial objects that are subject to all kinds of vibrations.

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If you are free falling atoms which do not have any vibrations in their fall,

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but they simply sense fluctuation on the metric which is the space it is vibrating.

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A space is undulating that way. You should be able to sense it by that on the wave function, by the phase factor of the quantum information.

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So those two are very good examples.

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I skip this too, and then maybe they are brain mapping, not the details, but people are looking into functional mapping of the brain.

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They will map the brain in terms of neurones and axons and all the networks through very complicated,

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coherent synchrotron radiation and terahertz imaging. But that physical mapping, what I'm talking about now,

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the functional mapping of different functionalities through magnetic and electromagnetic activity of the brain.

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Very, very small magnetic fields. Many of them occupy responsible point about the list you have, which is Google.

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Certainly you can do dark energy tests using that laboratory scale.

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It's worth remembering that that's not correct.

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Not that I'm familiar with the artificial waves. Definitely yet.

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So intense dark energy that is large. Well, it's always there's a very nice result in the place where I can talk to you about it later on.

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I think the gravitational wave test must connect somehow to dark energy in a very conceptual.

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I do not know how to do that. We can talk about it. Okay.

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So let me just quickly, those of you guys from students that I know if got not do something for those of you who know all this already,

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I'm also a student but but basically the standard model of amateur, inquisitive, incomplete, completely normal people.

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I've seen classically, if you look at the the rotational velocity and look at the mass inside this,

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then we know that it doesn't quite match to obviously there's some kind of a matter which is not visible,

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but still interacting in a major way, gravitationally and through for lack of imagination.

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We call it dark matter. So that's there.

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And then also standard model of cosmology is incomplete because we have discovered by the

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expansion of the universe through supernovae that probably there is acceleration of this,

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of this, of this expansion and probably there is some kind of a field or dark energy.

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And so we do not really know what it is. And that, again, basically very simplistic model of that.

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For those of you that know that there is this model of field manipulation based on the size of a typical universe

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and you try to balance out of gravitational force with the pressure of of the system and you try to balance it out.

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But actually, when you observe the actual motion of this of this galaxy, they don't quite match up.

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And they have to you have to introduce a little number here to actually match numerically the

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field of the supernova expansion and the actual thing to try to measure this object very,

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very precisely. And it's not going away. And so it is.

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And so this object either is a fundamental object or there's some physics behind it.

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And the whole idea that I'm talking about is without questioning whether it's real or not,

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we are telling my take on it that is their way of testing anything that is associated with this extra term physics behind it.

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Okay. So let me now, so this this whole thing, then this to today's pie chart, you've seen this for many talking.

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We talk about this thing, which is our ignorance of most of the world, except for 4%,

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which is a baryonic matter, which I have been working on for 45 years, three accelerators.

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So this is not provocative. After all these years, we have not really been touching this 96% of the thing.

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So it's probably time for us to think about we can probably never get there by

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particle accelerators because it's just impossible to take because there were.

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So maybe we should think slightly differently to sense phenomena that are in the laboratory already, but very, very weak.

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So and if you just put some numbers in there,

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I'll just put some numbers for for undergraduate and graduate who actually know this energy density of expansion.

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You know, if you if you imagine how much is the dark energy density that actually corresponds to this number?

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And if you imagine this is not actually electromagnetic, but if it were,

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then Maxwell's would be square and the electric field that corresponds to that actually corresponds to 12 square metre dark matter,

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of course, is even more much, much denser. Right. Dark matter, if you look at it, is actually ten kilovolt, familiar kind of feet.

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So these are non-trivial numbers of the actual energy that we are talking about that

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one should not think that one come a do something in the laboratory to sense them.

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The problem is if these are fixed DC.

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As a background DC bias of some voltage or some energy or background mass.

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It's very difficult to see something without a bias or if somebody fluctuating or changing it.

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And you know, we are looking at AC effects over a DC background and in a sense everything is a fluctuation of a vacuum anyway.

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So it is actually the proper way of thinking about what level of fluctuation above these levels can we expect conceptually,

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theoretically and can measure them no matter how small are these are the quantum sensors which are actually turning out to be extremely sensitive.

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So. And in order to do this analysis, fluctuations are not sufficient unless you can measure them at two different points and correlate.

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So the whole idea is actually you have to be able to do this in space and time in a

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coordinated fashion so you can actually get a measure of the strength of the power spectrum,

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of the fluctuation and the entire thing behind it.

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So here I will just tell you my philosophy.

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Some people, some of my friends, I coming from the instrument side, I do not question the observations as much.

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Let the people who take the data make them more and more precise.

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But I'm going to say that at some point, maybe they are real effects.

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How come we actually do experiments to prove, to verify?

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I have one example from the past.

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If you look at the plants law of Blackbody radiation and the plans constant, it was simply, simply used by planning just to fit a curve,

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a bar of just a fitting power, an indefinite lambda in a fitting pattern of the expansion of the thing.

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Right. However, it is not that because pretty soon there was photoelectric effect, we saw the light come from packets and each contender.

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And then there was the spectra of the hydrogen atom which are each.

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It turns out that H was not just a fitting parameter, it was something more.

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If there is a fundamental contradiction. So far we are just too early.

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Lambda is not turning out showing up anywhere else, so it may be a constant given to us.

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Not what you can do about it. Or maybe there's something that generating it. We are.

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So we are going to leave that judgement for future. I'm not going to assume that is just a constant given to us by nature.

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So so then the question is how do we how do we measure this?

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And so if you look at the dark matter universe, it just it's all over the place then many, many theories.

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There's nothing really has been observed today. Some people thought the massive particles could be detected in Large Hadron Collider.

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There is no indication of any massive dark matter candidate.

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Some people are saying amazing light particles, maybe light photons,

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which are dark like for every particle of light as a dark particle of light of the ring for particle connections which could be generated.

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And these are all very light mass particles, but no one one can imagine to look at how do these particles couple the first couple of gravitationally,

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which we know, because that's how they got the heart of the couple.

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Even if the very feeble coupling with the standard model in some interactions, how do you measure these these couplings by their very small DC effect.

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So imagine a very shielded volume where ordinary light or matter cannot penetrate, but dark matter can penetrate.

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And then you could actually put a sensor inside this volume that can detect the very small coupling of the dark matter with ordinary matter,

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giving you a real particle of light from light. And that's the kind of detection that we are talking about.

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And here is where this clarity and superconducting qubit technology comes in.

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I give you a simple picture here. If we imagine a shielded volume and inside there's some kind of a electromagnetic circuit,

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which is a oscillator which can measure something coming in,

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something the sensor is completely shielded by ordinary electromagnetic radiation, so no ordinary matter can get in that.

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But dark matter, of course, can get in.

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And you have to detect the coupling of this very, very weakly coupled up to this internal circuit at this level.

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Okay. And if you see a single photon that is coming inside this volume that resonates with the resonance frequency,

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and that photon could not have come from anywhere else, and that photon must be a real, real photon coming from from copying from the real particle.

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And so so that so that way you can do an experiment where you just have a cavity and the flux of hidden particles or dark matter is going through.

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And you convert that flux of hidden particles with the oscillating fields into the oscillating fields of the cavity.

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And there comes a question of even not know the coupling of these two fields, how strong, how weak.

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And so we need to really know that we need to assume in the field the extremely weak so that you could actually have a chance of detecting it.

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And so and this is where we are. We are talking about electromagnetic cavities, which are superconducting.

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And so let me give you an example of even that. Up the line resonators, which are not unfortunately very high IQ.

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They don't ring for a long time. Then they have superconducting aluminium cavities, superconducting niobium cavities, a very high IQ.

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Nowadays they are going over ten to the ten.

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But there's a lot of noise inside the volume coming from amplifiers, even when they are cool to zero degree temperature.

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So we have to eliminate that noise spectrum.

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Just to illustrate for those of you why superconductivity in this particular application,

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if you look at the normal conducting RF cavity, of course you pump in some kind of power, could be any kind of religious pulse.

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And of course, because it's normal conducting it does not stay for too long.

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Losses and stuff decays and then you have the again.

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And so if you have a very strongly coupled system which does not need renewing for a long time, that's okay.

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But you've got a very weakly capital system you need for the ring for long time so you can cumulatively add up the interaction.

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Right. So this is for example, superconducting this like for all action of dark matter, such people are looking into superconductivity.

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This was kept on ringing where I tell you the ten, ten to the 11, if practically infinite, I want to talk.

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Does it? So just to illustrate that a bit more, let me give you an example of a two very simple two pendulum,

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which are very weakly coupled, and you will see the energy will be transferred from one to the other.

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So I'm would put one out and that's going to very the connected slowly over time you will see energy transfer from this one to that coupler.

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That oscillator will pick up all the energy and this one will be addressed almost.

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And then that will transfer all the energy to this one.

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Then this one will be addressed and so on and so forth. The different long time to build up information.

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This is coming up positive. See this? It's almost definitely now and most of the energy is transferred to this guy

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is almost stationary and all of that ticking again and it'll go up slowly.

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So over many, many cycles the transfer of back and forth with us weekly double thing.

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But if we have a strongly coupled thing is if.

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I was beginning to transfer to the other one. Okay.

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Let me now do this. And you will see very quickly within three or four oscillations the changes back and forth.

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Very simple demonstration for this quickly as it done now.

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So depending on the coupling of the this dark matter field,

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which is oscillating in time with the cavity feel and depending on what you have to have very high kill systems.

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And this is why most of the superconducting RF is used for dark matter.

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Such is superconducting, not room temperature.

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That is not sufficient because even if you get a signal inside the cavity at the same frequency of the cavity,

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that will mean that you have seen a particle with a mass that is equivalent to the frequency because it could be a noise photon.

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And this here comes a problem of noise that even if you cooled down classical amplifiers to very cold temperatures,

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you still have one background photon, the zero point photon left after which the amplifier lies.

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Now this noise, now it is. If quantum mechanics allows us to understand noise, and that is the tuition fees.

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And people actually have been able to have technologies that can squeeze the feed.

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Information of the knowledge is not important to us,

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but we just want to know that there's one photon which is the right fork on a lot of noise photon as the what they do,

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they simply mirror the entire phase and they have total, absolute, almost absolute certainty that that's a little photon.

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So, you know, the photon number is a concert number, so you do not kill the photon number in that.

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And so you introduce all kinds of phase kicks to distribute the phase so that you are allowed to measure the photon count.

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Precisely. And so this technology is actually being used.

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We just found out last year very successfully in quantum computing community and being funded by Department of Defence laser.

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And we have never been able to use this in the setup of a cavity that we use today, particle accelerators dealing with dark matter,

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people searching for it, but they never been able to put this kind of a cubic circuit inside it, what we can do.

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So now we have a collaboration with University of Chicago Cubit Group and a superconducting RF affiliated group

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and the Dark Matter Action Group at Fermilab to actually do the next generation cavity based search for Axion.

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If you put down the numbers, you can immediately see that so far people have been getting all these small areas.

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If you look at the mass of that's the only large logarithmic scale on the microwave scale and the coupling thing.

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Even after in one sweep,

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if you could have a major large volume of a cavity and the superconducting cavity would tend to return to the level kind of a cu.

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And if you can put the stupid circuits inside, Discovery will actually wait long enough and you can actually discriminate and

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you can actually count and see if there's a foregone that a certain mass and

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not so clearly for dark sector photon for epsilon four actually allows it becomes

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a bit more difficult because it is not sufficient to just have a cavity.

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You also have to have a magnetic field coupled to the quantum numbers of the actual and RF cavity.

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You do not like to be living inside a very high field, so this is a problem,

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but we think we definitely can address the question of hidden photon very accurately in these in this paradox,

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but it is still a little 100 times bigger face space than what we have to do.

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Epsilon requires magnetic field and we are actually looking into it.

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How to how to make that a separate problem, isolate the cavity from the field problems.

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And I just want to give you some example of that.

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This is actually a real work in progress, taking into account a collaboration of parking further people,

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detector people, quantum gravity people and dark matter.

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Such people are Fermilab to do this experiment.

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So next generation admits three or four will definitely take advantage of the quantum sensors to sense dark matter inside a superconducting cavity.

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Okay, now let me. So, therefore, Galileo told you about it.

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Really? That is a very funny collaboration. We are not used to it.

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We are learning this collaboration for the whole idea of this workshop was to bring us together

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so that we can actually do this lesson is controversial and this is atomic being part of it.

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And the whole business is you know, we just saw recently the gravitational waves, right.

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And when I was a graduate student give talk and everybody came, there was talk of black holes and stuff we saw.

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And I never thought that you would see gravitational wave like that, two black holes merging, but actually saw it.

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Right. And this was a coherent wave. That was.

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That was emitted by the merger of two black holes at a coherent rate.

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And you see it propagates. It probably here they probably give them a decent enough order.

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So that's, of course, all good and legal did it.

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But Labour had a frequency which is very high and long for a short lived and compared to what it needed for particle physics connection.

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I'll tell you what, if you look at some people have computer experts here who know better,

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that signals of gravitational wave from sources that are out there in the cosmos,

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merger of other types of binaries that exist between the mini hertz and the ten hertz.

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And what's more important to me, at least, is because I have some background in stochastic noise and feedback systems,

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is that if you believe this theory of intelligence,

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which I was just trying to understand, it is probably it's a matter of faith or not, but inflation has not been tested.

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It's a very elegant theory.

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However, if it is true that you want to probe something beyond this horizon and the inflation came to an end and then start to grow slowly,

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then no other probe than gravitational waves that are coming from that era.

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And you can imagine that having such an interesting heart and you begin to slowly extend.

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There was some tremors, felt gravitationally.

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So the metric of space was disturbed. And we must be still feeding that rumour.

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We must be still feeling that earthquake. Our empty space today coming from the crunch of inflation and people have computed what's the measure?

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What kind of what strength could that gravitational background noise could be?

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And then can we then? So this is really a demonstration that these are really actually these are fuzzy lines we

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got this will build me a new is not quite three metres is three metres plus or -227 metres.

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Right. How do I measure that, that thing.

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And so we want to use atoms because atoms are inertial objects and we don't have to hang them from something.

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And we want to measure the first shift of a falling atom over a long distance to measure whether the spacecraft is historic or not.

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And that's the whole, whole idea.

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And I think calculations show initially that you can probably get to a frequency range of 1000000 hours to ten hertz if you use atoms,

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and hence all the excitement about atomic beams. Okay,

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so here is the scenario I just borrowed from particle physics finds that out that this range of Largo and so this Largo here and

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we are talking about this range and this is basically you are trying to understand and the coupling of gravitational physics.

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To particle physics coming from the evolution of the cosmos be inflation.

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And so you need to have some kind of a probe.

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And we think that these atoms are the probes and that, of course, they had in the paper, something that some of you may be familiar.

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I'm not going to question the inflationary physics of it or the calculation of the expected distortions of the gravitational

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wave background noise coming from this tremor that might have happened and then an internal impression that might even be real,

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I don't know. But if there is some level of gravitational jitter in the space metric, we are trying to detect that by recently.

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That's the whole idea. And the other purpose of the I'll just show you what that proposal is, is basically it's not following interference.

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I'll just show you the picture first and then I'll I'll come back to that.

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Well, what it is so basically the proposal is to have two atomic interferometers, not laser interferometer,

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because they said you don't want to be diverted by the, by the vibration of of inertial mass separated by a kilometre.

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And you measure the distance fluctuation of this kilometre from the rock, from the gravitational wave background.

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And actually there are possibilities because at Fermilab we are building this huge, very high power neutrino.

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We with very heavy megawatt protons, which of course are helping them get these neutrinos of what I think I'm contributing to the traditional karma.

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However, this new thing sent it along is too big, came to five kilometre back.

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And so, you know, if people know the technology of atomic beam interferometry 1015 metres,

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if we can handle it up to a certain level of sensitivity, it should not be infrastructure.

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Why is that difficult to put two of them on the shaft and see if one can get an atomic interferometry reading of gravitational waves similar to Largo,

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which measures the infrared things coming from pre-invasion.

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And we cannot say no, we have to look into it. Right.

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And that's the whole purpose of of of doing it, not just to be very naive and explain the thing to my junior colleagues.

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So so here the atomic beam interferometry is basically this.

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We have an atomic beam.

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Did you prepare it to very close and high performance dates and then by laser you manipulate this atomic being as it falls under gravity,

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it goes to two different parts. And then you bring them together and you look at the atomic beam interferometry at the bottom.

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And so it looks kind of like this from being the wave function.

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Let the fallout go up against gravity or fall, and then they come back.

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Then the laser beam, they been together and you create a little interference level here.

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So the phase of the atom changes to the fall through the gravitational distance being changing.

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All the stuff is recorded in this thing. And of course, as I said, to do it properly, you need correlation.

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It's not enough.

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Just what you want is a fluctuation of this thing and not just so you need to know the fluctuation of whatever is fluctuating at different points.

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And so there you need to have two and hence you've got to have those up and bottom.

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And you actually, if you are naive and you just made you don't get anything out of these because these signals are so small,

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they add up in in root mean to zero.

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But if you wait long enough and if you collect the fact that there is nothing is constant in life,

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everything is changing, the metric of space is changing.

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And hopefully if you if you have proper data analysis anyway, you probably will get a zero phase between the two interferometers.

387
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And then you have to interpret this is not coming from anything other than what you are trying to look for.

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It may not be gravitational wave that is causing it. It may be something else.

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Maybe some inertial stuff happening on the on the highway and on a49 or whatever the whole task is.

390
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Then to understand the noise sources that can get an effect of that on being as it falls the gravity.

391
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But people are looking into it and like other people of course have done extensive job of lasers being affected by mirrors and stuff.

392
00:42:07,670 --> 00:42:17,130
They have created very fancy mechanical suspensions that can cancel out noises so atomic beams have their own problems.

393
00:42:17,170 --> 00:42:24,739
Again, this is a technology never, ever been pushed to this limit because in order to do this,

394
00:42:24,740 --> 00:42:30,980
you have to get a sensitivity of ten -15 G, not generally -12.

395
00:42:31,340 --> 00:42:37,160
That's a that's a three or four magnitude more. So the atomic beams people who are getting funding.

396
00:42:37,830 --> 00:42:43,830
From Defence or other agencies are doing up to 20 months, nine months, ten months, 11.

397
00:42:44,190 --> 00:42:50,610
The challenge for them is can they do it? And are the two, three or four magnitude benefit could be useful for gravitational wave search.

398
00:42:51,690 --> 00:42:54,630
The Stanford guy you look, I've done it out of the previous people. I'm doing it.

399
00:42:55,560 --> 00:42:59,340
Here is a little laboratory set up often that we can see the problem.

400
00:42:59,490 --> 00:43:03,420
These are running, being set up and it takes a lot of effort to do these.

401
00:43:03,420 --> 00:43:07,020
It's not just a simple mechanical thing. You see, the beam is going to be formed.

402
00:43:07,680 --> 00:43:10,800
It coalesces and you see it last for a certain length of time.

403
00:43:11,610 --> 00:43:15,720
And then, you know, the lifetime is not really long enough to do everything in a lifetime.

404
00:43:15,990 --> 00:43:21,270
When the beam is produced, you drop it. Initially, you know what, ten metres, nine metres.

405
00:43:21,270 --> 00:43:31,560
And then they disappear. And then and then you're not sure what are the sources of this Philae floating at them?

406
00:43:31,640 --> 00:43:37,020
They're not quite free. They're not mechanically suspended, but they're trapped by certain electromagnetic fields.

407
00:43:37,320 --> 00:43:41,490
So you have to understand those noises. And so. Okay.

408
00:43:41,490 --> 00:43:43,290
So I think I motivated that.

409
00:43:43,440 --> 00:43:51,450
And I think the reason people are optimistic is the tremendous progress in atomic physics, atomic clocks, and that is incredible.

410
00:43:51,690 --> 00:43:58,230
So there's optimism that maybe if I put some directed effort into it, we can get to it at some stage.

411
00:43:59,510 --> 00:44:03,920
Simultaneously we are looking into can you simply used to superconducting cavities?

412
00:44:04,670 --> 00:44:13,219
Just cavities are a coupled but they are gravitationally captured in the sense that gravitation introduces strain into these and then that strain

413
00:44:13,220 --> 00:44:24,620
transfers into all kinds of more transfer between these two cavities is not quite the same as the reverse cylindrical receiver of gravitational waves.

414
00:44:24,620 --> 00:44:31,099
Slightly more complicated if they had to regain circuit of two superconducting oscillators that are talking to each other.

415
00:44:31,100 --> 00:44:34,459
I'm told that some people are doing to work on it and that's a long way to go.

416
00:44:34,460 --> 00:44:39,500
But again, to measure the signal, we probably have to use cubic type of technology.

417
00:44:41,030 --> 00:44:43,370
Finally, let me close by something where I have no expertise,

418
00:44:43,370 --> 00:44:51,829
but I know some people are working on measuring very, very small magnetic fields around your your neural activity.

419
00:44:51,830 --> 00:44:55,340
So people image your brains physically,

420
00:44:55,700 --> 00:45:03,620
which give you a map of the neurones and excellent stuff and the basis of intelligence or creativity in a very complicated subject.

421
00:45:03,620 --> 00:45:07,279
We used to think you'd have to do that for your ability to do logical things.

422
00:45:07,280 --> 00:45:15,589
Mathematic is not quite true to all kinds of other things come in that creates an entire thing called some kind of intelligence or creativity,

423
00:45:15,590 --> 00:45:20,960
and people are trying to try to understand it. And of course we all know why it is important for us.

424
00:45:21,350 --> 00:45:32,750
The first thing that comes to mind, you can create new science and innovate and enter society into so the very, very primitive mapping of the.

425
00:45:32,930 --> 00:45:39,590
So people have done very detailed physical mapping of the brain and it's like protein crystallography.

426
00:45:40,310 --> 00:45:45,500
But unless you connect it to the function of the protein on the membrane, you don't quite get to the biology of it.

427
00:45:45,830 --> 00:45:53,240
So people know kind of the two hemispheres and the connectivity of different human activities and so on.

428
00:45:53,390 --> 00:46:03,190
But each one of these activities comes with a very specific set, may I say lot of the normal modes of magnetic field configuration, they don't.

429
00:46:03,200 --> 00:46:07,159
It's like when the protein folds, it does not fold arbitrarily.

430
00:46:07,160 --> 00:46:09,890
It falls to a certain set of problems.

431
00:46:10,310 --> 00:46:19,160
Similarly, when some activities are happening in the brain, these are not arbitrary magnetic field patterns acting systematically,

432
00:46:19,160 --> 00:46:23,360
the magnetic field patterns which have different modes of functionality.

433
00:46:23,630 --> 00:46:32,950
So the idea is to map out those modes magnetically numb destructively, because you could destroy them many if not destructively.

434
00:46:32,960 --> 00:46:39,530
How can you devise a magneto instead from a graphic helmet with quantum sensors in it?

435
00:46:39,530 --> 00:46:43,170
And you can actually you can actually stimulate certain activity in the brain.

436
00:46:43,180 --> 00:46:50,360
And this is a big, big field, actually. It's very, very light field, probably very, very profitable field also.

437
00:46:51,500 --> 00:46:52,819
So I just plug there.

438
00:46:52,820 --> 00:47:05,389
I think so I think I've said this and similarly, geo signals, biological signals and people are working on new types of materials, all kinds of stuff.

439
00:47:05,390 --> 00:47:13,670
I don't have time to talk about it, but here is my basic thing is that there is real potential, at least in my field,

440
00:47:14,300 --> 00:47:21,890
where we're dealing with very large scale experiments and missions to maybe to think a bit cleverly in a medium scale.

441
00:47:21,890 --> 00:47:30,500
That's a scale, even the very clever listening capability. And actually it is very exciting science and you can engage in a lot of very

442
00:47:30,500 --> 00:47:34,459
young people and getting fruitful results in three or four or five years time,

443
00:47:34,460 --> 00:47:38,930
a lot of it four, six, seven, eight, nine, ten years to get data and then get to know.

444
00:47:40,250 --> 00:47:43,460
So I think it will be very important to keep our field active.

445
00:47:43,790 --> 00:47:45,740
And yet so there's some creativity and.

446
00:47:47,680 --> 00:47:54,790
We have come back here just to tell you that the problem we have with the quantum thing is that if you have one particle,

447
00:47:55,100 --> 00:47:58,270
you can control it very well, but you don't get much signal.

448
00:47:58,270 --> 00:48:01,540
If there are many particles, you get a lot of signal of how to control.

449
00:48:01,870 --> 00:48:08,650
So how can we get quality information? And quantity of information from the quantum sensors is a term of struggle.

450
00:48:08,980 --> 00:48:16,620
And so while you can have a quantum sensors of some sort, this competition between quality and quantity is always going to be a problem.

451
00:48:17,150 --> 00:48:20,740
I'll end up with a simple analogy, which is very provocative,

452
00:48:20,740 --> 00:48:26,410
but I'm using it quite a bit because what we have been doing in our field is this thing we don't know what there is.

453
00:48:26,710 --> 00:48:30,430
That's the [INAUDIBLE] out of it. If you are never comes out, catch it.

454
00:48:30,730 --> 00:48:34,900
Hey, look, I got this and that, but maybe there's a better way of doing it.

455
00:48:34,900 --> 00:48:40,960
A lot of smart people conjecturing, theorising very good theories as to why not do this.

456
00:48:41,000 --> 00:48:45,430
Very elegant, you know, fly fishing instrument. That means that the theorists are going to tell you,

457
00:48:45,430 --> 00:48:51,160
but you have to have the ability to throw the thing in the right place, in the right position, to get the right fish.

458
00:48:51,790 --> 00:48:54,610
And I think it's time that we put some effort into that direction.

459
00:48:55,510 --> 00:49:06,520
I told him, See, that Oxford particle physics definitely cannot afford just to do colliders and and fixed target beam physics at Fermilab or Japan.

460
00:49:06,520 --> 00:49:14,259
And you guys have all the expertise in optical physics to actually do this double work for particle physics and astrophysics,

461
00:49:14,260 --> 00:49:17,410
cosmology and for material science and all of that stuff.

462
00:49:18,340 --> 00:49:19,690
Thank you for listening. Thank you.