https://youtu.be/JfJWOgJF_KA?si=3o_CTTQyb-kGjvs_

What are quantum sensors? And how do they enable precision measurements of gravity, inertial forces, and magnetic fields?

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This lecture was recorded at the Ri on 29 November 2023, in partnership with The National Physical Laboratory.

Discover how atomic magnetometry is used to monitor the spin of atoms in external magnetic fields and how NPL is supporting the development of portable magnetometers for instance for non-destructive imaging of structural defects. Learn about atom interferometry and how it is being used to measure gravity, linear accelerations, and rotations.

Find out about NPL's leading-edge research in this area, including their work on the measurement behind gravity gradiometers and absolute gravimeters based on a double rubidium atomic fountain, which has advantages over classical devices.

Take advantage of this opportunity to delve into the exciting world of quantum sensors and their applications in precision measurement.

Prof Jan-Theodoor (JT) Janssen FREng FinstP FIET is the Chief Scientist at NPL and a member of the executive team. JT joined NPL in 1998 and is distinguished for the application of quantum technologies and an NPL Fellow in Quantum Electrical Metrology. His research involves a wide range of topics in solid-state physics applied to metrology applications. JT launched the National Graphene Metrology Centre (NGMC), the role of which is to develop metrology and standardisation for the nascent graphene industry. He is also a Scientific Co-Director of the Quantum Metrology Institute (QMI), which covers all of NPL's leading-edge quantum science and metrology research and provides the expertise and facilities needed for academia and industry to test, validate, and ultimately commercialise new quantum research and technologies.

Since 2017, JT has been a member of the NPL Executive team, first as the Research Director, and now as the Chief Scientist. In this role he is responsible for the external scientific engagements with academia and other government organisations and recently also our international activities. He responsible for the Science & Technology Advisory Council (STAC) and Post Graduate Institute (PGI) which NPL jointly runs with the Universities of Strathclyde and Surrey. Internally, he is responsible for the quality and benchmarking of the research outputs of the laboratory and its knowledge management. JT is also the UK delegate for EURAMET the European Association of National Metrology Institutes. JT is the executive sponsor for NPL’s Juno committee, which aims to address gender equality in physics and to encourage better practice for all staff and sponsor of the disability working group. JT is passionate about diversity and inclusion at the laboratory and in STEM more generally.

JT is a Chartered Physicist and Chartered Engineer and a Fellow of NPL, the Institute of Physics (IOP) and the Institute of Engineering and Technology (IET). He is also the NPL Head of Science and Engineering Profession for the Government Science and Engineering Profession (GSE) and a visiting professor at the University of Lancaster. He is the UK representative on EURAMET (European Metrology Organisation) and a member of its Board of Directors. In 2021 JT was elected a Fellow of the Royal Academy of Engineering.



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The future of measurement with quantum sensors - with The National Physical Laboratory - YouTube

https://www.youtube.com/watch?v=JfJWOgJF_KA

Here’s a summary of the transcript in five bullet points:

1. **Importance of Measurement**: The talk emphasizes that measurement is critical in various aspects of life, from consumer goods to aviation and healthcare. Accurate measurement is essential for precision and reproducibility, supporting industries and technologies globally.

2. **Role of Quantum Sensors**: Quantum sensors open new possibilities in measurement, offering unprecedented precision and enabling advancements in science and technology. This includes redefining measurement standards based on quantum mechanics.

3. **Quantum Mechanics in Action**: The lecture explains key concepts of quantum mechanics, including the dual slit experiment and entanglement. These phenomena reveal the strange and counterintuitive nature of quantum mechanics but also its incredible accuracy and potential for technological applications.

4. **Applications of Quantum Technology**: Quantum technologies have already revolutionized areas like atomic clocks, GPS, and financial trading. Future applications include quantum computers, superconductivity, and advanced sensors for detecting dark matter and improving gravimetry.

5. **The Future of Quantum Sensors**: Advancements in quantum sensors could lead to transformative applications, including more accurate brain scanners, enhanced navigation systems, and even the ability to look around corners or observe interactions that are currently undetectable.

Transcript:

(00:12) Thank you Lisa for that introduction and uh first of all I'd like to say it's an incredible honor to be able to give a lecture here in this very uh historic location where lots of uh Great Signs has uh happened in the in the past so today we will be talking about uh Quantum sensors and measurement and maybe uh before we we dive into that topic we should talk about uh measurement why is measurement important why do we do uh measurement at all and really measurement affects everything in our life from the from the goods we buy

(00:47) to uh the airplanes we re build to uh treatments in hospital everything around us relies on measurement and it relies on very accurate measurement so that these things are precise and we can be done they can be done in a reproducible way and we can improve things by measurement Lord Kelvin uh said that if you if you can't measure it you can't improve it you can't make it better and really that's sort of the um uh the the the important point of this talk we look at making measurements more and more

(01:25) accurate and thereby opening a window into new science new understanding and new applications and that's really where we're going with uh Quantum sensing it allows us to create new opportunities and new measurements Lord Kelvin will return a few more times in this talk it's it's a little bit downhill from here for him but this was a a very good statement which we which we use all the time so confidence and measurement uh the laboratory where I work the national physical laboratory uh at MPL is

(01:57) specialized in precise and accurate measurement and not just any measurement but measurement which is reproducible and stable across the world so we hold the the national standards for for measurement for time for mass and we we create these standards and we disseminate these standards and that means we we calibrate other Laboratories who maybe uh calibrate factories who then create products and that's how measurement appears in your in your everyday life and an important role of the of the laboratory is to compare our

(02:32) measurements around the world so we compare ourselves with other labs around the world every lab in in the world has got a laboratory uh like MPL and we we compare our measurement standards with them so that measurements are are stable around the world we can trade we can we can build uh components in in one country and move them to another one and they they fit together uh there's no waste we can uh for instance your your mobile phone it works all across the world where you go all of that is underpinned by by accurate uh

(03:11) measurements and standards and that's one of the thing about measurement you you don't really notice it if it's if if if it's working fine that means we we are doing our job really well you do notice it when it's not working for instance when uh there are glitches in the stock market or when uh a Luna Lander crashes on uh on mars or something like that that's examples of where where measurement has gone wrong and it's the it's the the role of a lab like MPL to make sure that that

(03:42) never happens so you should normally not not hear about us if if we're doing our job uh if we're doing our job correctly but we do much more than than comparing measurements we we develop new measurement standards and um these new measurement standards are driven by the need to to address new challenges for instance in in climate and energy in health and life sciences and a lot of these new measurement standards are based on quantum physics quantum mechanics and that's the uh the topic of the of the lecture today so here we

(04:17) start with the first question uh how much do you know about quantum mechanics so a little a lot nothing at all oh okay interesting I know everything can went up and down there some some people less confident as we as we've gone along okay so most of us know a little bit and like to know a little bit more then you're absolutely in the right place um so let's get started um can we have the the next slide please okay so when we talk I think I went a little bit too quickly there um so we're going to talk about quantum mechanics

(05:10) what it is a very uh short introduction uh on on on quantum mechanics then we'll talk about uh uh what applications are already there on on Quantum Technologies and then we move on to Quantum Technologies of the future and I'll I'll I'll give a number of uh examples around that so before we start with uh quantum mechanics we maybe have to remind ourselves what came before uh quantum mechanics and that of course was classical mechanics or or Newtonian physics um very successful uh theories developed by by Newton which described

(05:49) the world around us um he did his famous work on on on gravity and acceleration uh this is a picture of uh Newton's Apple Tree which we got at MPL uh it's uh is grown of a uh of a graft of the original Newton Apple Tree in his uh in his garden in linkshire and MPL has got regularly open days and you can come and visit us and you can see the historic Place uh where MPL started 125 years ago and you can on these open days walk around uh Newton's Apple Tree ah here we go there of course there are about many more uh uh um great minds

(06:33) in uh In classical uh mechanics a couple uh names here uh kler L Grange Oiler and of course let not forget uh Michael Faraday who did a lot of interesting work on uh electricity and magnetism right here in this laboratory downstairs I just had a look at it it's very impressive uh What uh what's down at the bottom here and Lord Calvin back again he stated that in the beginning of the 19th century all of physics is done there's nothing more to discover we just need to make some more accurate measurements of course he was a little

(07:12) bit wrong with that around the the turn of the century there were a number of experiments which really were very hard to explain uh with uh classical uh mechanics uh a couple of examples here on the on the slide for instance the the radiation coming out of a black body a very hot body couldn't be described by by classical mechanics um the photo electric effect if you shine light on a uh on a metal it can liberate electrons and again it's is something which is not not being able to explain with with with classical

(07:51) mechanics and the last one there the the spectr of a hydrogen atom the simplest atom in our periodic table the spectral lines of this uh of this atom it's it's impossible to explain that by uh by classical classical physics and that's really where uh quantum mechanics started to develop there was this understanding that uh matter behaved in a different way as what we classically know and that matter has got wavelike properties and this is a quite a weird concept uh to get your head around and these are the sort of

(08:27) founders of uh of quantum mechanics uh Unfortunately they all men uh diversity wasn't very good at the beginning of the 19th century um so these these people developed this the first theories of of quantum mechanics and um they uh proposed how nature should be described in terms of uh the wave matter and next year or in in in uh 2025 there will be Centenary of quantum mechanics and there will be quite a few celebrations and uh lectures on uh quantum mechanics so let's have a look at some of these strange uh effects in in in

(09:11) quantum mechanics so the first one I mentioned is this uh wave matter nature of matter so that everything is described by uh a wavelength and this is called the the Broly wavelength which is given by this little equation here where H is the plank constant and P is momentum and one of the things you have to remember from this equation is that H the plank constant is a very very very small number 10 to Theus 34 this incredibly small and that means that the wavelength of matter is also incredibly small it means that if you have

(09:47) something which is macroscopic like a a cannonball it doesn't behave in a quantum mechanical way it really behaves classical but if you have an atomic uh particle like an electron or an atom then the wavelength of this particle starts to matter and that's why quantum mechanics they often say is is the is the is the physics of of small particles the other important aspect of of quantum mechanics is quantization it means that uh lots of parameters can only have certain values it's a bit like if you have a guitar the strings on a

(10:23) guitar can only play certain nodes and not other ones and this is this happens when you put a Quantum particle in a very tiny box say of the of the same order of the of this broccoli wavelength then its energy becomes quantized the next one is superposition the fact that particles can be in two states at the same time and I will explain superposition in a little bit uh bit more in more detail and the last effect is entanglement this is the property that if you have two particles uh in in one Quantum state and you pull

(11:00) them apart these particles remain entangled attached to each other so if you if you measure the properties of one particle the properties of the other particle are instantly uh determined and this is also a really weird concept of which there is no classical analog so let's start by looking at uh this famous uh Young's double slit experiment this is an experiment which goes right to the part of quantum mechanics and really shows us how uh conceptually strange some of these effects are so we first do the

(11:38) experiment with uh bullets so we got a machine gun and it fires bullets at a wall with two openings in the wall and then behind this wall is another wall where we detect the bullets with this uh red detector on there we can move that up and down and we can count the number of bullets which which hits the wall so this is a completely classical experiment so if we close one split and we we start shooting our bullets from our machine gun we can measure the probability of these bullets hitting the hitting the screen at the back and we

(12:12) get this curve P1 there where we have uh a large number of bullets right behind the opening in in the wall and then we can close one of the slits and open the other one and do the experiment again and we get the the other picture P2 now if we open both slits and we you shoot the bullets we get the sum of the two uh probabilities which is given by the one P1 plus P2 this is completely classical and completely understood so this is uh an experiment with hard classical particles so next we do the experiment with waves like water

(12:48) waves and we we close one of our slits we we we send the waves through the the the slit and measure the probability in the of the of the Waves going through first the one and then the other one and if we open them both we get interference because the maxima and Minima of this wave will interfere with each other and we get this nice interference pattern which is uh uh completely classical understood uh as the properties of of waves so next we do the experiment with electrons Quantum particles if we open one split we get

(13:27) the same experiment as with the uh classical particles and with the other one again the same now we open both slits and we shoot our electrons onto this wall this is actually a really difficult experiment to do in real life but it has been done and it has been demonstrated and if we shoot uh uh electrons through both splits onto the screen we get an interference pattern so this means that the electrons have behaved like waves so how how does this work do the electrons interact with each other so we can turn the intensity of

(14:01) the electron Source down so that there's only always one electron in the instrument we still get the interference pattern so does the electron split itself into two and go through both slits so we can do another experiment whereby we try to be clever and we set up a detection method which can determine through which slit the electron goes as it uh goes through the screen and if we do that we measure again the classical pattern with one split the other one again the classical pattern if we have both slits open and

(14:35) we try to measure through which slit the electron goes the different the interference pattern disappears so this means that if we start to interact with the experiment and try to measure what goes on we change the experiment so the Observer is an integral part of the experiment and this is really really weird so this must mean that the the electron went through both splits at the same time it's the electron was in the superposition of both possibilities it didn't go through one or the other when you measure it it

(15:10) goes through one or the other and this is one of the things of the weird sort of concepts of s of quantum mechanics which you cannot explain in any sort of classical way you just have to accept that the that that nature is like that and that this is the way it behaves I explained this in some detail because there are a number of quantum senses which really rely on this interferometric uh property of of quantum particles so we understand quantum mechanics now so we we we can summarize things things can be in two states at

(15:44) the same time things can be described things have to be described by probabilities a measurement has got a profound exper uh effect on the experiment particles can interact in a non-local way and it's impossible to know everything so quantum mechanics sounds like a really uncomfortable Theory yet quantum mechanics is the most successful Theory we've got in physics it describes what happens in incredible detail very un unprecedented precision and really there are there are people like for instance Einstein who felt

(16:21) really uncomfortable with this uh concept of quantum mechanics they thought maybe there is something about the theory which we don't know maybe there are some hidden variables in the quantum particles which we can't measure but which are there but it's been proven time and time again that this is not the case you can demonstrate that there are no hidden variables quantum mechanics is really like this so quantum mechanics is all around us already there are many applications which have shaped our lives uh in the

(16:54) last sort of 50 years and there's a couple of them on the on the screen here for instance NMR nuclear magnetic resonance it's uh relies on uh uh the quantum properties of uh of atoms and it's transformed uh the way we do medicine same with x-rays a Quantum property which has changed the way we we work lasers lasers are all around us lasers are in in lots of applications uh they they've been really transformative semiconductors semiconductors wouldn't work without Quantum prop is like tunneling and well

(17:31) semiconductors computers iPhones everything relies on that sort of Technology we've got it all around us nuclear power of course is not application of quantum mechanics and atomic clocks what we worked on for a long time at npl atomic clocks work on the the principles of uh Atomic transitions in in an atom and atomic clocks underpin many Technologies like GPS Google Maps Financial trading you name it uh time time is all around us and the lecture a few weeks ago was all about that topic so quantum mechanics

(18:03) has really shaped our our lives in a in a very significant way and it will do so in the future as well with these new Quantum senses which are uh coming around so why did it take from 1900 to now to realize these quantum mechanics well there were a number of really uh important enabling Technologies to make to make Quantum happen and the first one is is is nanotechnology I said that the the broccoli wavelength which is uh plung constant in it is very small and that means that we need to make uh devices very small to see Quantum effects and

(18:43) really therefore you need lithography and semiconductor growth Technologies which allows us to go to those dimensions and that's largely been driven by the semiconductor industry we want ever faster computers uh and process processors with more and more transistors on there and this technology of shrinking uh materials has really Advanced very significantly we can now grow uh devices with atomic Precision we can we can put at atoms uh where we want using microscopy and various techniques and we've got really good control of of

(19:21) how we do that and then the next really important uh technology has been uh cryogenics the way to cool things down at room temperature uh atoms and electrons really move around very fast they got lots of energy and that destroys their Quantum behavior and for that we need to uh cool them down they slow down and we can start to observe uh Quantum effects so here are a number of uh uh temperatures of uh liquid cryogens as you go from liquid oxygen or the coldest place on Earth uh somewhere in Siberia I guess to all the way to absolute zero

(20:02) minus 270° Kelvin and a person who was very uh instrumental in this uh cryogenics was a guy called Carling onus who was the first person to um create liquid helium at his laboratory at the University of Leiden in in the Netherlands and uh this this is quite a dangerous thing to do at that time because there there wasn't much helium around uh so they had to do very carefully do precooling stages and they used uh liquid oxygen a liquid hydrogen and as you guess where liquid oxygen liid liquid hydrogen in one lap together

(20:40) is it's it's quite a dangerous thing to do and if you go to Leiden and then ens to the original Laboratories you can still see the holes in the ceiling of where of where it went wrong but eventually Carling onus uh succeeded in uh creating uh liquid helium and he started to look at what the resistance of of metals is uh is doing at those low temperatures and uh Lord Kelvin there he is again he predicted that the uh the resistance of metals would go to Infinity as the electrons stopped moving so that's what they they wanted to

(21:14) investigate and when uh Carling onus uh cool down uh Mercury uh exactly the opposite happened uh as you can see here at a temperature of uh 4.2 Kelvin the resist of uh of mercury dropped to zero so the material became superconducting and that's really one of the first demonstrations of a of a Quantum uh of a Quantum effect and super conductivity is really uh uh a macroscopic manifestation of of the way the electrons uh the electrons uh behave in a metal it took 50 years to actually explain that with with quantum mechanics how this process

(21:58) actually happens I'm not going to explain that but we're going to demonstrate it so my colleague here from npl Nick Fletcher is going to uh demonstrate some of the weird and wonderful properties of um of a superconductor now this is not uh an ultra low temperature superconductor this is u a material uh which is a high temperature superconductor uh itum barium copper oxide which was discovered in the uh in the 1980s and and this is a material which becomes uh superconducting at uh temperatures below liquid nitrogen so we got a little bit

(22:36) of liquid nitrogen here and we we cool the material down and it will become it will become superc conducting and one of the things we want to demonstrate here is another property of a of a superconductor and that's the Meer effect superconductors don't want to have a uh magnetic field in their interior and so they uh they set up a current in their on their on their surface which expels uh the magnetic field and that uh results in uh a field of the opposite direction which then makes it uh levitate if everything goes

(23:13) well it still cooling it down yeah all right let's see if it works it worked in practice this m effect we'll come back to that later it's an import there we go so this is a track of magnets and the the uh superconductor will levitate as long as it's superc conducting and will be moving frictionless over this uh over this track as it expells the the magnetic field from its interior hey and in Japan they've actually used this technique to make levitating trains which can uh I think went on U they can

(24:06) go for 600 kilometers per hour they broke the uh the speed so this may be an idea for hs2 so as long as you keep it superc conducting it will float without any resistance sorry I could hear that there we are and superconductor is a perfect diam magnet uh and that's the demonstration of that and diamagnetism was developed uh was discovered by uh Faraday here at the at the Royal Institution thank you Nick so today we don't we don't play with liquid nitrogen uh although we do like it um oh yeah put a LD on

(25:08) uh today we've got we've got instruments where we can create ultra low temperatures uh almost at Absolute Zero by the push of a button these things are called dilution refrigerators and whenever you see uh uh things in the news about quantum computers you'll always see a picture of a dilution refriger Ator with this gold shiny sh candelabra of uh of cables and plates uh where the bottom bit uh can be kept cold at this uh ultra low temperature almost indefinitely and that's where we do a lot of our uh

(25:46) experiments there's another way of cooling things down uh rather than uh using cryogenics and that's with lasers uh so normally you think if you shine a laser onto something you'll make it hot uh but there is uh a technique to cool atoms individual atoms down with laser light and uh I'll I'll try to explain this very shortly here so we've got this little dot here is a is an atom and we shine uh laser light onto this uh atom but the laser light is not really exactly resonant with the transition of

(26:19) this this atom you can see that this uh this green arrow is just not high enough to get to the first excited level and that means that this this atom can't absorb this uh this laser beam if the if the atom is moving away from the laser beam we get something like the Doppler effect this is the effect of where you say have a an ambulance coming towards you if it comes towards you it sounds very uh high pitched and when it goes past you it sounds uh low pitched so if you're moving away from a source the frequency

(26:53) goes down and so if the atom moves away from the laser you can see the red arrow there is even lower and again it can't transition but when the atom moves towards the laser beam the the frequency is double shifted to the blue to a higher frequency and the atom can absorb this uh this Photon and it becomes excited and it gets a little little momentum kick uh from this Photon and then it mits it in a in a random Direction uh uh as it uh as it decays back down and on average this means that atoms which move towards the laser beam

(27:32) get slowed down and atoms which move away from the laser beam not and if you shine lasers from all directions onto this uh cloud of atoms you can cool them down very very efficiently uh to very low temperatures much colder than cryogenic temperatures you can cool atoms down to nanokelvin temperatures almost absolute uh zero it's a bit analogous uh analogous to uh slowing an airplane down by firing tennis balls at it um it works as long as you got enough tennis balls going towards the towards the airplane and of course the laser is

(28:07) is exactly the right tool to do this the laser fires billions and billions of photons uh at this atom and and thereby can uh can slow it down so laser cooling you'll see in lots of uh Quantum sensing applications they will lie on on laser Cooling and if you can if you can laser cool uh the these atoms then you can also trap them you can hold them uh for a little while and do all sorts of interesting uh experiments uh with them so next I want to talk about another application of quantum which is my old in my own field of uh electrical

(28:44) Metrology because quantum mechanics has been really transformational uh for for that area of uh of Metrology and the first Quantum effect I want to show you is the uh Quantum hall effect this discovered by Claus V klitzing in the uh in the 1980s and he was working on on measuring the uh the properties of semiconductors in very high magnetic fields at ultra low temperatures now classically you would expect the um uh the resistance of this material to be a straight line but as you can see here from the picture it

(29:19) looks completely different there are plateaus the resistance only want to have certain values of of resistance and not others and what from found out is that these values of resistance are uh given by this simple equation which is plank constant over the elementary charge squared so plank constants comes back here and the elementary charge and the really unique thing about this property is that there are no material properties in this equation so it doesn't matter what this material is made from it doesn't matter what kind of

(29:53) size it is the resistance of this material is always the same it's this equation of planks constant over the electron charge squared and so nature or quantum mechanics has given us a natural standard for resistance we can recreate this anywhere on Earth and actually anywhere in the universe because these fundamental constants are constant everywhere and the same everywhere and so since this discovery this effect has been used as the international standard for uh for resistance ever since and we're building instruments on

(30:28) these uh so that other countries other nmis can use this this effect as well the next effect I want to uh mention is the joseon effect this was discovered by Brian Josephson in the uh the 1960s uh Cambridge University he was uh he was looking at the um the resistance of uh two pieces of semiconductor with an insulator in between now classically electrons can't go through an insulating barrier classically that's forbidden they have to the the the resistance would be would be infinite but in the quantum world where electrons

(31:12) behave like waves they can penetrate through this barrier and that that can be uh a current through such a junction and the really unique thing of this type of Junction is that if you radiate it with microwaves the same as you got in your in your uh kitchen home then it generates a voltage across this Junction and this voltage is again given by a very simple equation of Plank's constant and the electron charge multiplied by the by the frequency which we irradiated with so again Quantum quantum physics and nature has given us a natural

(31:47) standard of uh of voltage and since it's Discovery this was used everywhere in the world as a as a standard the last one I want to measure is the mention is the uh uh transport of single electrons to make a Quantum standard of current and here we try to make devices where we can manipulate uh the electrons at a very uh accurate uh way so that we transport electrons one by one through an electrical circuit and the current is then given by the number of electrons uh times their charge times their frequency and uh this is a way of

(32:27) making very very precise electrical currents and so we got the three Quantum standards for voltage resistance and current all realized by uh by Quantum effects and it was a very nice um Exhibition at the the Royal Society summer exhibition uh over the summer where uh one of my colleagues uh uh John Fletcher and Messiah ker demonstrated all the interesting things you can do with these uh with these individual electons you can make little uh little uh colliders of electrons and study the properties of of electrons in

(33:04) these circuits this is like a a mini a mini hydrogen hydron collider as opposed to a large hydron collider this is a very nice piece of work but the importance of these Quantum effects is that um it allows us to uh redefine one of the last artifacts which was left in the SI system and that was the kilogram the kilogram is historically defined as the the mass the weight of a uh of a liter of water in a in a cube 10 x 10 x 10 cm um that's how the uh Mass was linked to uh uh two dimensional constants and for 150 years people have compared uh

(33:51) masses using a balance whereby there was one kilogram which was kept in a in a volt in Paris uh which was the the original kilogram L gr and every kilogram in the world was compared uh with that kilogram through through weighing measurements and this of course is a was a very unsatisfactory situation because if something happened to this kilogram in Paris the whole uh traceability of mass would be lost and every measurement of mass Force pressure in the world would change and so for a long time people have been thinking about a way of

(34:30) redefining this kilogram in a way which is not relying on on an artifact and uh Brian kibble a scientist uh at npl came up with an ingenious way of of doing this experiment by replacing one half of this balance with a coil and uh a magnet and a bit like your uh your your bathroom scales at home basically when you uh uh put a a current through this coil you can make you can make the uh the balance uh balance and by using our two Quantum effects which I just discussed the the quantum hall effect and the Jos effect you can express this

(35:12) current in terms of the fundamental constants of nature H and E and through uh very simple equation from Einstein es is MC squ you can link uh Mass to Plank's con and that's really uh been a massive change for for Metrology we could take the kilogram away and realize uh Mass based on a fundamental constant of Nature and so pre 2019 we had all these artifact standards like uh for for the Kelvin and for uh Mass uh and for electron uh for the ampare after 1919 the 2019 the SSI system was redefined in terms of

(36:00) fundamental constants of Nature and so now the system is fixed forever and everybody can uh realize these units independently to the highest level of uh of accuracy and that's been work which took 50 60 years to uh to complete but it's been a major achievement of of both quantum mechanics and Precision Metrology so maybe it's time for another quiz question if we can bring it up the next one so which of the SI units is not related to a fundamental concept of nature which one is it is it the Kelvin the meter the amp the second the mole

(36:48) the kilogram or the Candela oh pretty evenly spread okay are we done I think so well most of you got a right is the Candela the Candela is is uh the the unit of luminous intensity and it's uh it's how humans perceive perceive light and so it's got a factor in there this K candila which is the response of the eye and that's uh that's sort of experimentally determined that's not

(37:52) really uh a fundamental concept of nature whereas all the other ones yes they are that's most of you got it right so okay okay so we've we've talked about uh Quantum so far and uh all the applications which are here why is there so much talk about this uh second uh Quantum Revolution and really that is the the fact that uh people want to use uh people have been able to use uh the more non-trivial uh Quantum properties like superposition an entanglement uh to uh create really new applications uh of

(38:34) of quantum technology and uh the UK uh has been very much at the Forefront of this development uh only this year the government announced two and a half billion pound uh investment in Quantum strategy to realize the opportunities of this uh of this new technology and there are lots of other countries who are doing the same it's uh it's become uh a bit of an arms race of who gets there first because some of these uh applications will really give you quite a significant uh advantage over your over your competitors and if you're if

(39:08) you're first to Market with your with your Quantum Technologies this is incredibly uh incredibly beneficial and U the UK Quantum uh Technologies are can be S grouped in these uh four major categories uh Quantum Computing Quantum comps Quantum sensing and and Quantum Imaging now most of the uh sort of attention and hype is on Quantum Computing and and Quantum Quantum Communications because that's that's where uh potentially uh the biggest uh promise uh and application uh might lie but Quantum sensing and

(39:46) Quantum enaging are the ones which are much further developed and are are already applications around these Technologies in the in the market and that's why we are focusing focusing on those at the at the moment and at MPL we've we've built a new laboratory uh our Advanced Quantum Metrology laboratory uh to specifically uh look at these uh Quantum properties this is a labor this is a laboratory which has got uh very very uh good uh environmental conditions it's ultra low noise Ultra stable temperature uh really

(40:23) we can do some of the most uh sensitive uh experiment ments which we which we want to do and we build it around Newton's Apple Tree which is a nice a nice feature there as well it was opened earlier this year by by the Secretary of State okay so let's look at some of these uh new uh Quantum sensing uh Technologies and the first one I want to discuss is uh is the one based on superconductivity so we've seen superc conductivity in action here with uh a little puck of uh superc conducting material which expels uh the magnetic

(40:56) field field through the marer effect now if you make a ring of superc conducting material the flux which penetrates through this ring is also quantized and again it's quantized in those two fundamental constants of nature H and E and uh if you if you put this in a magnetic field and you keep it cold this flux would be in there forever but the next step is to to make a squid and a squit is not uh an animal which lives in the sea but a squit is a superconducting Quantum interference device and basically you take a super conducting

(41:29) ring and you put two of these Jose in Junctions in there so two two uh insulating barriers very thin insulating barriers and basically what you've what you've created here is an interferometer for superc conducting current and if you think back on the uh Young's Double Split experim slit experiment the current can go two ways and it will interfere with itself and that's a way of making a very very sensitive uh sensor for magnetic field so sensitive that you can see uh you can measure differences of 10 F to Tesla now what's

(42:04) 10 fular if you look at this uh magnetic field scale here you've got uh a neutron star which is probably the highest magnetic field in the universe which is about a a million Tesla down to uh your fridge magnet which is maybe five millit Tesla 5,000 of Tesla to the Earth magnetic field 30 micro Tesla or the magnetic field produced by by your brain there's there's there's uh electrical currents flowing through your brain and again uh through Faraday flowing electrical currents make a magnetic

(42:40) field and those fields are of the order of uh picotesla and so this quit is pro uh is is capable of detecting these signals in the in the brain and you can uh develop technology here you can see this this this man here with this enormous cryostat on his head and there are a few hundred squit sensors in there and through that measurement they can they can see the activity of the brain in in real time and this is really important to uh study things like uh epilepsy dementia schizophrenia or or head trauma uh these are very important

(43:20) uh uh conditions for which there is not necessarily a cure and so research in that field is really important and this is an example where where new measurement technology more sensitive measurements opens up the opportunity for for new treatments and understanding and here are some examples from my colleague uh Ling how and John gallab where they're making very specific squits for uh particular uh applications for instance for detecting uh single photons or the the the magnetization of tiny particles uh or

(43:57) uh tiny movements of of M's resonators and these types of scits are being used for some really big science experiments for instance uh the search of Dark Matter uh may may be detected through these Ultra sensitive uh devices or another experiment is the is the gravity Pro B mission where they are looking at testing some of Einstein's theories these effects are very very small and so they've got a number of gyroscopes superc conducting gyroscopes in space and they measure the magnetic field created by these gyroscopes with uh with

(44:32) squids and they can see the very very small uh effects of this on these uh on these gyroscopes and thereby prove some of the basic principles of Einstein's theories so you can do both some really interesting useful applications but also understand big signs and big physics experiments the next one I want to do to uh discuss is an atomic magnetometer so we just seen a superc conducting uh magnetometer you can also uh build a magnetometer from uh from atoms and Nick I need you I need you again for this one

(45:10) um so you can see these uh Quantum effects at uh at room temperature if you put uh a number of uh Alkali atoms in a in a vapor cell these are atoms like cesium or rubidium and they've got one unpaired electron in their in their outer shell and this electron behaves a little bit like a little gyroscope and so with one laser beam you can you can direct this um uh this pin and then these these pins are sensitive to magnetic field and that's what you see when they start rotating it's uh it pushes the uh uh the the gyroscope out

(45:52) and it starts to oscillate around this position and you can measure that with with uh a second uh laser beam and thereby have a very very sensitive uh measurement of of magnetic field in this way and of course like in real life these atoms they they bounce off each other and so they start to lose their their coherence and at that point you have to start the experiment Again by aligning the spins putting in the magnetic field and measuring the uh uh what's called the lour uh frequency of these of these atoms and this can be

(46:27) done at uh at room temperature and it's an incredibly sensitive technique the more atoms you put in there the more signal you get but then also of course H you get uh um you get collisions which destroy uh the the yeah it's fine thank you Nick that worked well thank you and so this type of magnetometry can can be used for uh non-destructive testing uh if you for instance have materials which you don't really want to cut open if they see if they're broken but by moving such an atomic sensor over

(47:07) the surface you can see what's going on underneath the surface you can see whether there are cracks there or any sort of damage uh which is very important to maintain to maintain infrastructure uh you can configure these types of atomic magnetometers to also be sensitive to inertia and use them for for positioning or navigation uh applications and uh the one at the bottom there you can also make brain scanners out of these devices and you get a a device which is a lot easier to operate than the cryogenic one uh with

(47:41) the squitch you don't have this big cry St on your head but you just get this little helmet with tiny little uh Atomic uh magnetometer sensors in there and so a lot of the development is are making these these sensors smaller uh uh lower power more usable in in the field and this is a really interesting uh field of development another important area is gravimetry uh we've been measuring uh gravity for for a very long time but there are lots of um uh properties which which affect uh gravity and there are a

(48:19) few examples there the the the the sphericity of the earth gravity is not the same everywhere on the poles and on the equator gravity is is different whether there are mountains nearby that changes gravity but also what happens under the surface so if there's there's oil or gas that changes uh gravity uh the tides and all sorts of infrastructure so measurements of gravity become really uh important because people uh want to know uh what's going on uh belong there so the traditional way of measuring gravity of

(48:53) course uh Newton where with his Apple Under The Apple Tree um at school we used the a pendulum using Galileo's method of measuring Gravity by looking at the periodicity of a pendulum and and getting gravity out of that equation uh usually to a few per if you're lucky uh the most accurate way of measuring gravity is with uh a falling Corner Cube so you have a laser beam which shines up and you you drop a prism into this laser beam and you count the interference fringes and that's a way of measuring

(49:29) gravity to to Parts in 10 to the N it's very very accurate uh way of doing it but it's not very transportable you need to set it up you need to average for a long time and so people have been looking for ways of making gravity measurements much more easier uh and the way of doing that is with uh Atomic uh gravimeters so really we're moving from from apples to to atoms and the way it works is uh um so shortly explained in this uh little animation so we start with a bunch of uh hot atoms and we we cool

(50:04) them down with laser cooling to a low temperature and then we drop them in a vacuum tube and at some point we give a uh a laser pulse and put this uh uh sample of atoms in a super position of two uh different uh Atomic States and they start to move uh with split the uh the atom Cloud into two and they move into do two different ways then we give another pulse and we bring them back together again and we interfere them and then we uh measure the the states of the of the atoms as they come through the interferometer and so what we've done is

(50:41) basically we've created an interferometer in space and the there's two different arms of the interferometer and this this type of device is incredibly sensitive to changes uh to to to gravity and again if you make the interaction time longer or you uh increase the amount of uh atoms in the cloud you can improve the sensitivity and this technique has been demonstrated to be at least a thousand times more accurate than a falling uh Corner Cube Cube for absolute measurements of gravity and even for making relative

(51:18) measurements of gravity it can be made much more accurate in the field and so this there are a number of uh groups in the UK particularly birmingam University have been very advanced in developing these types of atom gravimeters which you can take out in the field you can use for surveying and you can see what's what's on the ground and that has lots of applications the other one is uh for example atomic clocks uh atomic clocks are are incredibly accurate but you have to isolate them from from everything

(51:51) because lots of things affect an atomic clock so you can turn that around and you can use an atomic clock as a sensor so Einstein's general uh principle of Relativity says that the um uh time flows slower in higher uh gravitational uh potentials so that's why your your head goes gray first because that that bit of your body ages ages first um you can calculate that the uh the core of the earth is 2 and a half years younger than the crust because of uh gravitational gravitational red shift but this really allows uh atomic

(52:33) clocks to be incredibly sensitive uh measurements of uh of gravity and that's why we at MPL we we're building clocks which can go onto uh onto satellites so that we can do some really interesting uh interesting science experiments with those with those clocks and once you once you can make uh called atom clouds you can do lots of different things with it so we made lots of different uh types of devices at npl for measuring for measuring different uh different properties like gravimetry magnetometry or or or inertia uh senses

(53:13) and so having said all these things um it won't surprise you that we're working on many many different uh Quantum Senses at at MPL uh this one is an example from my colleague gray Ma on using Quantum effect to make uh measurements of of temperature um in in in a in a very accurate way and by linking this to fundamental concepts of nature like we saw we saw earlier you can make sensors which you never have to calibrate so you can basically put them in a place uh they measure the temperature and because

(53:46) they're linked to a fundamental constant they always give you the the right answer and this can be very interesting for applications where you can't get to a sensor anymore for inance when you you put it into a nuclear power plant where you can't really go in and calibrate your sensor and that's why where these kind of things are really important the last uh Quantum uh effect I want to I want to me uh mention is is Quantum Imaging and this is a uh this is a sensing technique which is based on uh

(54:16) entanglement so basically the property of two two particles being in this shared Quantum state if you measure one it determines the properties of the other one and Quantum Imaging is something which has become uh really uh quite of an interesting topic in in recent years now the way to create entangled photons is by uh a technique called parametric down conversion you you use one laser beam the one here in blue and you you shine it onto a very special uh nonlinear Crystal and it generates these two uh photons coming

(54:51) out in this entangled State and so these two photons are of different color then the original color you shine into the uh into the uh into the crystal uh there can be uh the same color these two uh photons or or different color um both both are possible and then when you've got these two different photons in in a different uh uh you can send them to a different location and they remain sort of attached to each other and that's a technique you can you can build uh to to do something which is called ghost

(55:23) Imaging so you can you can build uh an interferometer by sending these two photons into different ways one Photon when will interact with an object in one arm of the interferometer the other Photon goes the other way and then you detect the photon which is not interacted with the object and you can see the object which was in the other arm where the photon interacted and this is really uh something which of course there's absolutely no classical explanation for this but it has some very interesting applications because

(55:54) for instance you can you can look around the corner uh by by this technique or you can you can look at um uh effects where for instance uh if you if you look at a u um a biological uh cell where certain interactions happen at a certain frequency where there are no detectors you can you can do that with one Photon but detect the the the the interaction of the photon with the other one where there are really good detectors available and that way you can stud the uh biological processes which would not be possible uh with normal light and

(56:30) that's for instance something where my colleagues Alex Jones at npl is uh is working on we got another uh question which of these techniques magnetometry gravimetry or Quantum Imaging will be the most exciting application in the future I mean there's no right or wrong answer it's just what you think would be wow oh you over Quantum Imaging interesting well it was the Nobel Prize for physics last year uh interesting I wasn't expecting that

(57:36) that was good lots of opportunity there I guess looking around corners is is quite cool okay can we have the slides back right we're come to the end now so I hope I've given you a glimpse into the world of uh of uh of quantum sensing we've looked at interference of uh of of electrons atoms superc conducting current but there are many many more ways of to uh to make Quantum sensors many more I uh I can discuss um and we also of course don't know what what the interesting applications of of quantum

(58:20) sensors uh will be uh when Lou Essen developed the first season clock at MPL in the 1960s he didn't he didn't Envision uh Google Maps or GPS or or or gravimetry he just wanted to make a better clock and all these applications uh really came came later I mean most of the value of of quantum sensing will be in the in the applications and so it's really important that we we take these Quantum Technologies out of the lab and into the hands of of Engineers and companies and innovators who can who can use them for

(58:57) all sorts of U cases which we in in in in the world of Metrology and science haven't even think F about and that's really the uh the aim of the UK Quantum program is to stimulate that connection between research and application to really create the uh the benefits of of of quantum sensing and that's really what what the exciting thing is we we don't know yet what what's going to come come out of quantum sensing but one thing is for sure I think it will be it will be very very interesting so I thank

(59:29) you all for your attention and happy to answer [Applause] questions