Impossible Time Crystal Breakthrough - Explained

a crystal is a material where the atoms molecules or ions are packed in a repeating three-dimensional array we see crystals throughout nature not just in things like gemstones but in many of the materials around us what we don't often see at all though are crystals that not only repeat in space but also repeat in time A Time Crystal but a scientific team has just built one that lasts for 10 million times longer than the previous record a Time Crystal that hints at unlocking a world of new possibilities in our understanding control of complex systems but what does that breakthrough actually mean and how does it work and what might it mean for our future my PhD is in Optical nanophysics and I really wanted to dive into the details to really understand what was actually happening here so prepare yourselves we're going full frontal physics let's start by taking a look at time crystals in general then try and understand exactly what happened in this experimental breakthrough although common crystals are fascinating materials to study because they have emergent properties from how the atoms within are arranged the simplest type of crystal is repeating cubic structure strangely enough though there's only one element that forms this type of Crystal polonium 210 a product of the radioactive decay of uranium 238 if the atomic spacing between atoms in a crystal repeats the same way in all directions the word for that is isotropic but if it has some structure and some direction and other repeating structures in other directions we call this and isotropic and it can lead to some really interesting effects for example sapphires conduct heat at different speeds along different axes due to the difference in the atomic spacing in different directions this can be a really useful property in things like high powerered LEDs or lasers or other high-powered applications so you can draw heat away from your equipment away from the substrate and manage the thermal performance of the device but what happens if a crystal structure isn't just repeating in the three spatial dimension ions but also repeats in the fourth dimension of time what if a crystal axis had time as one of its Dimensions here is an ordinary Square whoa whoa slow down Egghead this idea was the foundation of Nobel prizewinning physicist Frank wil's deceptively sophisticated concept A Time Crystal for will Che to qualify as a true time Crystal the material would have to repeat a behavior as a function of time maybe changing its structure or its energy levels and important it would need to continue this repeating pattern forever not just temporarily like ringing down of a tuning fork after it struck this constraint disqualifies things like chemical clock reactions which are fascinating but eventually consume their reactants and stop oscillating instead in wi's version of the time Crystal the behavior would need to repeat when the system was in equilibrium without needing further energy in or refueling in quantum mechanics this is called the lowest energy State or the ground state the challenge here was finding a system with no energy left to give up but was still constantly repeating and changing which sounds kind of impossible it also sounds suspiciously like a perpetual motion device in fact Wich felt similar stating in his seminal paper in 2012 a system with spontaneous breaking of time translation symmetry in its ground state must have some sort of motion in its ground state and therefore be perilously close to fitting the definition of a perpetual motion machine in this paper Wich considered a superconducting ring where charge carriers which let's just say electrons for all purposes were free to move the lack of resistance in a perfect superconducting material would mean that the electrons could travel around the ring forever if these charge carriers were arranged with a regular pattern then this sounds like a perfect candidate for a Time Crystal so let's talk about this idea for a minute cuz it tells us where this concept of time crystals actually stops working superconducting rings are a surprisingly old concept with their properties demonstrated nearly a 100 years ago in 1932 in a lab in Leen Garrett fim induced a current in a lead ring cooled by liquid helium fim then flew to London to present a Royal Institution lecture where he showed that 200 amps of current was still flowing in the ring as all moving electric Fields also produce an Associated magnetic field fim further demonstrated the current's presence inside the ring by placing a compass next to it the needle of the compass deflected towards the ring this is interesting and proves that the current is still there but it also shows us a problem in why these superconducting Rings cannot be perpetual motion devices and ultimately cannot be true time crystals if the charge carriers affect their environment even something as small as deflecting the needle of a compass these interactions are leaking energy from the system which even if it takes a very long time to happen will eventually cause the motion of the current in the ring to stop slightly frustratingly we'll check waves away solving this minor but really quite major problem as an exercise for the reader stating that simple variations can ameliorate this issue such as the use of multipoles in place of single charge carriers embedded the system in a cavity or simply arranging that the motion is slow unfortunately for whe Che actually solving this issue turned out to be anything but simple the debate over the possibility of a will Che style time Crystal continued until Haruki wanabi and masaki osakawa looked deeper into the mathematics behind wi's idea ultimately concluding in their noggo theorem that time crystals in equilibrium are prohibited in the universe for reasons that seem perfectly okay like you can't have perpetual motion devices in our universe superconducting Rings could not continue forever no matter what modifications were made to them so the original idea of the time Crystal was dead or was it fortunately a small modification remained that evaded the nogo theorem but raised its own kind of questions to compensate for the inevitable losses to the surrounding environment energy or order needs to be supplied into the time Crystal on an ongoing basis having to top up the systems means that this is not in equilibrium which was part of the appeal of time crystals in the first place as wanabi and oshikawa state oscillations of non-equilibrium Quantum states are well known and should not be called time crystals without further justification which in a research paper is basically as close as you get to Scientific smack talk something was needed to bring back the magic of time crystals and justify their maybe overly glorious name the first experimental signs that the time Crystal could still be something special come from University of Maryland in 2016 by suspending urbium in an ion trap Christopher Monroe showed that the ion levels could be induced to to oscillate at frequencies lower than the driving frequency supplied by a laser a phenomenon called subharmonics These are arguably pretty unintuitive and the only example I could actually find of something that was a little bit more intuitive is a niche singing technique where a lower note is produced by combining a bunch of higher notes within the material the ions essentially picked up their own frequency even though the frequency that they were being bombarded with was different and higher this was ultimately a breakthrough but it wasn't really that satisfying deriving an oscillating energy output from a system where the energy input is also oscillating that was confusing to get my head around feels kind of like cheating and doesn't feel like the time crystal is actually doing the majority of the work in 2022 just a decade after the original idea of the time Crystal was first introduced a brick break through in this approach was finally made in Hamburg Germany by coing rubidium atoms to near absolute zero a continuous time Crystal was finally demonstrated inside an optical cavity the laser that was providing the energy to this system had constant power applied to it but the atomic density of the crystal started to oscillate so in this instance although we had constant energy being put into the system we had a material change in that system that was oscillating as a function of time that sounds pretty cool in its surface there was only one downside with this Crystal it lasted only for about 10 milliseconds so again it feels a little bit underwhelming and for those of you that are shouting at the screen at the moment and saying how about just a quartz crystal being used in a watch isn't that just a Time Crystal well yes it is a crystal and we use it to tell time so you're right but it's actually being constantly driven to expand and Shrink at certain frequency using something called the piso electric effect and that's a problem because that falls into our first examples trap of using an input energy that is oscillating to ultimately produce an output of that system that is also oscillating it's just not that exciting we want something that is totally independent of its environment shaking around luckily a few hundred miles away Alex gik research team at dormant University realized that a new approach was needed an approach that would ultimately produce a Time Crystal that last for 10 million times longer than the previous approach as this breakthrough is I think as much about how they did it and what they did as the actual outcome that they got out of it and because obviously I'm an experimental physicist and this is the fun bit for me I want to talk about exactly what the experimental approach was in detail so that is your warning for frontal physics like I said incoming feel free to look away and we are about to cover a bunch of pretty hard topics but trust me I think you can handle it I wanted to run through this to see exactly how they achieve their results let's start with a regular gallium arsenide Crystal viewed along one axis it has a regular recurring pattern that we would expect from a crystal GX simulation work suggested that the complex behavior of time crystals wouldn't be possible with this latice structure alone the Symmetry had to be broken because gic's goal was to create an oscillation of the time Crystal through interactions of the nuclear Spin and electron spin within the Crystal and don't worry I'm going to explain what that means to do this he introduced indium atoms in place of some of the gallium atoms approximately 3% of them in total and that's a process called doping GIC then placed this Crystal in a cryostat at about 6° Kelvin or about minus 267 de C these indium atoms created distortions in the lattice that rippled outwards this means that the electrons now experience different fields based on how close they were to their local indium atom to to make time crystals actually work in our universe we said that we need to input energy into that system but we wanted that energy to be nice and continuous not oscillating to provide energy in and to compensate for the losses to the surroundings GC used a pump laser which just means a laser directed into a system with the explicit purpose of providing energy into that system the wavelength of the laser used to do this was 785 nanometers which used to always cause me anxiety in the lab when we used to work with lasers of that type because they're basically invisible to the human eye but they are often times powerful enough to instantly blind you if you're unlucky enough to be in the wrong place at the wrong time so there's always this fun game that happens within the laser lab of how do you work with the basically invisible near instant death laser G used this laser not just to give energy to the system but also to give it order he used circularly polarized light which is where the beam polarization appears to rotate as it moves through space the polarization is the photo Photon spin State and it means that all photons are delivering the same energy in the same order into the system as that pump laser beam hits the crystal the photons impart their spin to the electrons in the crystal which start to align the electron spins throughout the crystal this essentially serves to mostly uniformly raise electrons into a higher energy State we said already that electron movement or electric field movement can cause magnetic fields as the electrons start to have their spin aligned by the pump beam the magnetic field effects of these electrons begin transferring this spin to the nucleons through something called flip-flop processes causing a polarization of the nuclear spins nearby however for a reason I could actually find in the paper the magnetic field arising from those nuclear spins doesn't actually align perfectly parallel with that of the electron spins so that constant input laser energy is causing the electron spins to align which is exerting some force on the nucleus spins causing them to partially align which is then pushing back on those same electron spins this causes them to process essentially rotate around their axis like a gyroscope at an angle the procession of those electron spins as they start to oscillate around their axis changes how much they are pushing on those nucleus spins which changes how much those nucleus spins are pushing on the electron spins which creates this essentially complex oscillating dance back and forward or the very first inclinations that we're moving to a Time Crystal if this all sounds pretty chaotic you would be absolutely correct this was literal chaos theory in action the starting conditions of the system dramatically impact the eventual end conditions of the system which is actually a bad thing in time crystals because you want a regular oscillation coming out of your system in order to achieve this GC had to damp the chaotic emergent Behavior coming out of the system he did this by applying an additional magnetic field to the system tilted at 10 de to provide a small bias to the system's motion that magnetic field applied at a tilt of 10° moved the system out of this chaotic regime and into a self oscillating system this was the theory anyway obviously this is all happening inside the Crystal and we can't see any of it how do we actually measure and prove that a Time crystal is in front of us and vibrating and doing its thing this is harder actually than it might already sound and it already sounds pretty hard another thing that makes studying crystals difficult is that any large input of energy can accidentally destroy the delicate oscillations inside we call this melting in the context of a Time Crystal so our goal is to study the system but without disturbing it too much that it stops being a Time Crystal the answer to how we do this obviously is more lasers you could take more time to answer the question if you like more lasers a second beam called a probe beam because it probes the system to see what's happening is added into the experimental setup this laser was a longer wavelength of 800 50 nanom which was linearly polarized so all of the polarization states of the photons were either moving in the y direction or in the X Direction rather than a circularly polarized cork screwing their way through space this second laser is made to pass through the Crystal and what happens to the laser on the other side of the crystal will tell us whether this is a true time Crystal or not in order to understand how that part of the experimental approach works we need to introduce a final kind of hard concept needed for this experiment we can think of linearly polarized light as the combination of left and right circularly polarized light aligned so that it essentially cancels that circularly polarized cork through effect so that it is continuously polarized in just a single direction we saw already that inside a material circularly polarized light interacts with the electrons which in turn create their own magnetic field depending on which way the circul polarized light is spinning it will impart and as a result EXP experience different effects from those electron spins if it's spinning the same way as the pump laser is it slips through the crystal pretty easily if it's spinning the opposite way it's essentially working against the pump laser trying to flip the electron spins in the other direction which makes its Journey harder the end result is that these two different circly polarized beams travel at different speeds through the material and what this means is that when they emerge from the crystal one is slightly ahead head of the other these are still remember recombining though to produce linearly polarized light that linearly polarized light will now just be tilted at a small angle relative to the input angle so that means that two things should be happening if this is a true time Crystal one that the angle of the light as it emerges from the crystal should be slightly tilted relative to what it is when it was put into the Crystal and two because of the continuous oscillation between the electron spin and the nuclear Spin and their kind of continual interference this tilt should be slowly varying in nature but only to a very very very small margin the tricky bit as if all of the previous steps were not tricky is the experimental job to detect really accurately how much shift in polarization angle there really is there is luckily a very interesting and clever way of doing this you can split that beam of light into its linearly polarized compon components using a polarizing beam splitter in theory if you aligned this perfectly with the input polarization initially you could then measure how much light was in the original polarization and how much was tilted into a new angle and watch as that amount of light slowly oscillated due to the inner workings of the time Crystal the major problem though is this signal is a very minor oscillation of the tilting signal as a whole you probably see some level of signal coming from this system but the interesting time Crystal oscillation piece of it would probably be lost in the noise of the system as a whole coming from things like the laser or the environment the imperfect nature of the mirrors that you were using or the beam splitter basically everything so your challenge is how to remove all the noise associated with everything so you can just see the signal that you are interested in and we do this using math with light by introducing a half wave plate into the beam which rotates the polarization of light we can rotate it so that rather than a big signal in one beam and a very small signal in the other beam we have equal signals on both we can then put each of these two laser beams onto two photo diodes and subtract the output of one from the output of the other this means that if we get some laser noise it will be present in both branches if it comes from something like the laser or the envirment the difference should be your time Crystal oscillations so what do we actually see this take a second to look at how strange this actually is it's a repeating pattern absolutely but it's far from maybe a sinusoidal wave but it's not a million miles away it's also incredibly slow in its nature it has a period of 6.9 seconds as an optical physicist I'm used to dealing with Optical oscillators with 80 million oscillations per second so one oscillation every 6.9 seconds is slow so what is exactly setting the time of this oscillation isn't overtly apparent asking how long it takes to flip an electron spin isn't necessarily A straightforward question but it's definitely a negligible part of this time period I'm amazed at how longterm and emergent this Behavior can be from basically instantaneous changes to electron spins so that's really interesting zooming out it's pretty clear that the time Crystal shows no sign of ceasing its oscillation during the 40-minute experimental run so although the result is hey this thing lasted for 10 million times longer than the last one actually it isn't really showing any signs of stopping in the paper they say as we observed no indication of any oscillation Decay for 40 minutes we can safely conclude that the time Crystal lifetime is at least a few hours potentially even longer which feels to me like the ultimate handwavy answer ah it lasts for somewhere between 40 minutes and the lifetime of the universe maybe longer as with any good experiment the creation of the first stable continuous time Crystal raises many questions I'm very curious why it has the characteristic m shape it might just be how the math is mathing to create that m shape and maybe something about a DC offset for the subtraction step that's I mentioned earlier but without seeing the exact experimental setup I can't really say in the paper it acknowledges the details of the observed variations are not yet fully understood which is basically hey we did a thing but exactly the nature of it we're still trying to understand what is specifically happening and why it's happening that way scientific papers often feature quite dry writing as it were such as we leave however the detailed theoretical modeling of the dependence of the continuous time Crystal periodicity on different parameters for future investigations and again this just says this is very early science we've done a thing we're trying to work out exactly how it worked cuz we aren't quite sure yet that says to me that there is still much to learn about these time crystals it's clear that this research isn't the beginning of the end for the time Crystal research but is the end of the beginning as for applications and why this thing is actually potentially useful Gus is interested in the great sensitivity it has in changes to magnetic fields as well as potentially a timing standard but honestly it feels like it is way too early to look at time crystals and ask how they will be used cuz we just don't really understand them sufficiently yet it's only been a decade since the original idea was conceived which is kind of exceptionally fast when it comes to physics especially when the idea is how do I make a crystal that repeats Its Behavior in the fourth dimension but that brings us to the end this is a cool breakthrough mostly cool cuz it's unbelievable complexity of its experimental setup and just the depth of understanding of how to build this system and how to measure it and how to control it is really interesting and absolutely at the Forefront of things that we understand I hope you enjoyed this video If You did leave a like down below if you have an idea as to what a Time Crystal could be used for that would be practical in the real world let me know in the comments section and thank you again for watching I'll see you next time goodbye

Channel: Dr Ben Miles

Views: 154,468

Keywords: science, future, breakthrough

Id: Zr8zwfm1Ub8

Length: 22min 40sec (1360 seconds)

Published: Sun Mar 03 2024