Quantum Computing Expert Explains One Concept in 5 Levels of Difficulty | WIRED

hi my name is talia gershon and i'm a scientist at ibm research today i've been challenged to explain a topic with five levels of increasing complexity it's a completely different kind of computing called quantum computing quantum computers approach solving problems in a fundamentally new way and we hope that by taking this new approach to computation we'll be able to start exploring some problems that we could never solve any other way hopefully by the end of today everyone can leave this discussion understanding quantum computing at some level [Music] what's this yeah what do you think that

is fancy chandelier i think so too we jokingly call it the chandelier that's real gold you know this is a quantum computer it's a clunt it's a really special kind of computer what does it do it calculates things but in a totally different way to how your computer calculates things what do you think this is a yeah do you know what your computer thinks that is zero one this really specific combination of zeros and ones everything that your computer does showing you pink panther videos on youtube calculating things searching the internet it does all of

that with a really specific combination of zeros and ones which is crazy right that would be like saying your computer only understands these quarters for each quarter you need to tell it that you're going to use heads tails and you assign it heads or tails so i can switch between heads and tails and i can switch the zeros and ones in my computer so that it represents what i wanted to represent like an a and with quantum computers we have new rules we get to use too we can actually spin one of our quarters so

it doesn't have to choose just one or the other can computers help you with um your homework your really hard homework yeah they can especially if doing your homework involves calculating something or finding information but what if your homework was to discover something totally new a lot of those discovery questions are much harder to solve using the computers we have today so the reason we're building these kinds of computers is because we think that maybe one day they're going to do a lot of really important things like help us understand nature better maybe help us

create new medicines to help people what's your favorite kind of computer smartphone tablet regular laptop pc i've got to go with my iphone so what do you do with your iphone social media um use it for your studying have you ever run out of space on your iphone all the time me too yeah always when i'm trying to take a photo so did you know that there's certain kinds of problems that computers sort of run out of space almost like you're trying to solve the problem and just like how you run out of space on

your iphone when you're trying to take a picture if you're trying to solve the problem you just run out of space and even if you have the world's biggest supercomputer did you know that can still happen wow so my team is working on building new kinds of computers all together ones that operate by totally different set of rules so do you know what that is i have no glue it's a quantum computer a what you ever heard of a quantum computer i haven't have you ever heard of the word quantum no okay so quantum mechanics

is a branch of science just like any other branch of science it's a branch of physics it's the study of things that are either really really small really really well isolated and really really cold and this particular branch of science is something we're using to totally reimagine how computing works so we're building totally new kinds of computers based on the laws of quantum mechanics that's what a quantum computer is huh i'm going to start by telling you about something called superposition so i'm going to explain it using this giant penny wow is that like worth

100 pennies i don't know what it's worth but uh i can put it face up right in that heads i can put it face down right so at any given time point in time if i ask you is my penny heads or tails probably you could answer it right yeah okay but what if i spin the penny hmm so let's do it okay so while it's spinning is it heads or tails head while it's spinning oh it i would know it's sort of it's sort of a combination of heads and tails right would you say

so superposition is this idea that my penny is not just either heads or tails it's in this state which is a combination of heads and tails this quantum property is something that we can have in real real physical objects in the world so that's super position and the second thing that we'll talk about is called entanglement so now i'm going to give you a penny wow when we use the word entangled in everyday language what do we mean that something's intertwined or exactly that there's two things that are connected in some way and usually we

can separate them again yeah your hair is tangled or whatever you can you can untangle it right yeah but in the quantum world when we entangle things they're really now connected it's much much harder to separate them again so using the same analogy we spin our pennies and eventually eventually they both stop right and when they stop it's either heads or tails right so in my case i got tails and you got heads you see how they're totally disconnected from each other right our pennies in the real world now if our pennies were entangled and

we both spun them together right when we stopped them if you measured your penny to be ahead i would measure my penny to be ahead and if you measured your penny to be a tails i would measure my opinion to be a tails if we measured it at exactly the same time we would still find that they were both exactly correlated that's crazy that's so cool right oh my god the way that we are able to actually see these quantum properties is by making our quantum chips really really cold so that's what this is all

about actually this is called a dilution refrigerator and it's a refrigerator it doesn't look like a normal refrigerator right but it's something that we use actually there's usually a case around it to cool our quantum chips down cold enough that we can create superpositions and we can entangle qubits and the information isn't lost to the environment like what could those chips be used to do so one of the things that we're trying to use quantum computers to do is simulating chemical bonding use a quantum system to model a quantum system yeah i mean i'm definitely

going to impress all my friends when i tell them about this they're going to be like quantum what so what do you think that thing is is it some sort of conjecture circuit that is a really good guess there's parts of that that are definitely about conducting this is the inside of a quantum computer oh wow yeah this whole infrastructure is all about creating levels that get progressively colder as you go from top to bottom down to the quantum chip which is how we actually control the state of the cupids oh wow so when you

say cold or you mean like physically colder yeah like physically colder so room temperature is 300 kelvin as you get down all the way to the bottom of the fridge it's at 10 milli kelvin oh wow yeah amanda what do you study so i'm studying computer science currently a sophomore and the track that i'm in is the intelligent systems track machine learning artificial intelligence you ever heard of quantum computing from my understanding with a quantum computer rather than using transistors is using spins you can have superposition of spins so different states more combinations means more

memory so that's pretty good so you mentioned superposition but you can also use other quantum properties like entanglement have you heard of entanglement i have not okay so it's this idea that you have two objects and when you entangle them together they become connected and then they're sort of permanently connected to each other and they behave in ways that are sort of a system now so superposition is one quantum property that we use entanglement is another quantum property and a third is interference how much you know about interference um not much okay so how do

noise-canceling headphones work um they read like wave like ambient wavelengths and then produce like the opposite one to cancel out they create interference so you can have constructive interference and you can have destructive interference we have constructive interference you have amplitudes wave amplitudes that add until the signal gets larger and if you have destructive interference the amplitudes cancel by using a property like interference we can control quantum states and amplify the kinds of signals that are towards the right answer and then cancel the types of signals that are leading to the wrong answer so given

that you know that we're trying to use superposition entanglement and interference for computation how do you think we build these computers i have no idea so step one is you need to be able to have an object or physical device we call it a qubit or quantum bit that can actually handle those things can actually be put into superpositions of states you know two cubit states that you can physically entangle with each other that's not really trivial right and things in our classical world you can't really entangle things in our classical world so easily we

need to use devices where they can they can support a quantum state and we can manipulate that quantum state atoms ions and in our case superconducting qubits we make qubits out of superconducting materials but as like a programmer how would quantum computing affect a different way of writing a program it's a perfect question i mean it's very early for quantum computing but we're building assembly languages we're building layers of abstraction that are going to get you to a point as a programmer where you can interchangeably be programming something the way that you already do and

then make calls to a quantum computer so that you can bring it in when it makes sense we're not envisioning quantum computers completely replacing classical computers anytime soon we think that quantum computing is going to be used to accelerate the kinds of things that are really hard for for classical machines so what exactly are some of those problems simulating nature is something that's really hard because if you take something like you know modeling atomic bonding and electronic orbital overlap instead of now writing out a giant summation over many terms you try and actually mimic the

system you're trying to simulate directly on a quantum computer which we can do for chemistry and uh we're looking at ways of doing that for other types of things there's a lot of exciting research right now on machine learning trying to use quantum systems to accelerate machine learning problems so would it be like in five years or ten years that i would be able to have like one of these sitting in my laptop just in my dorm i don't think you're going to have one in your dorm room anytime soon but you'll have access to

one there's three free quantum computers that are all sitting in this lab here that anyone in the world can access through the cloud okay so quantum computing creates new possibilities and new ways to approach problems that classical computers have difficulty doing couldn't have said it better myself so i'm a first year master's student and i'm studying machine learning so it's in the computer science department but it mixes computer science with math and probability and statistics so have you come upon sort of any limits to machine learning certainly depending on the complexity of your model uh

then computational speed is one thing i have colleagues here that tell me it can take up to weeks to train certain neural networks right sure yeah and actually machine learning is one research direction where we're really hoping that we're going to find um key parts of the machine learning computation that can be sped up using quantum computing yeah it's exciting so in a classical computer you know you have all sorts of logical gates that perform operations and they change an input to some sort of output but i guess it's not immediately obvious how you do

that with quantum computers if you think about even just classical information like bits right at the end of the day when you store a bit in your hard drive there's a magnetic domain and you have a magnetic polarization right sure you can change the magnetization to be pointing up or pointing down right quantum systems we're still manipulating a device and changing the quantum state of that of that device you can imagine if it's a spin that you could have spin up and spin down but you can also if you isolate it enough you can have

a superposition of up and down sure so what we do when we try to solve problems with a quantum computer is we encode parts of the problem we're trying to solve into a complex quantum state and then we manipulate that state to drive it towards what will eventually represent the solution so how do we actually uh encode it to start with yeah that's a really good question this actually is a model of the inside of one of our quantum computers okay so you need a chip with qubits each qubit is a carrier of quantum information

and the way we control the state of that qubit is using microwave pulses you send them all the way down these cables and we've calibrated these microwave pulses so that we know exactly this kind of pulse what this frequency and this duration will put the cupid into superposition or we'll flip the state of the qubit from zero to one or if we apply a microwave pulse between two qubits we can entangle them how do we measure yes exactly also through microwave signals okay the key is to come up with algorithms where the result is deterministic

interesting so what do those algorithms look like there's sort of two main classes of quantum algorithms there's algorithms which were developed for decades right things like shore's algorithm which is for factoring grover's algorithm for unstructured search and these algorithms were designed assuming that you had a perfect fault tolerant quantum computer which is many decades away so we're currently in a phase where we're exploring what can we do with these near-term quantum computers and the answer is going to be well we need different kinds of algorithms to really even explore that question yeah certainly having a

search algorithm is very useful um factoring those are definitely useful things that i would imagine could be done a lot faster on a quantum computer yeah they also unfortunately require fault tolerance right now the algorithms that we know of today to do those things um on a quantum computer require you to have millions of error-corrected qubits today we're at like 50. it's actually amazing that we're at 50. there's things that we know or we have strong reason to believe um are going to be faster to do on a quantum computer and then there's things that

we'll discover just by virtue of having one sure how could someone like me who's a grad student get involved in this or what kinds of challenges are you facing that someone like me could help out with i'm glad you're interested i think the place where lots of people can get involved right now is by going and trying it out and thinking about what they could do with it there's a lot of opportunity to find these near-term applications that are only going to be found by trying things out i'm a theoretical physicist i started out in

condensed matter theory theory that studies superconductors and magnets and i had to learn a new field of quantum optics and apply those ideas one of the nice things about being a theorist is you get to keep learning new things so steve tell me about your research and the work you've been doing in quantum computing my main focus right now is quantum error correction and trying to understand this concept of fault tolerance which everybody thinks they know it when they see it but nobody in the quantum case can precisely define it it's something that we've already

figured out for classical computing like something that amazes me is all the parallels between what we're going through now for quantum computing and what we went through for classical computing i was asking a computer scientist recently where to read about fault tolerance in classical computing he said oh they don't teach that in computer science classes anymore because the hardware has become so reliable in a quantum system when you look at it or make measurements it it can change in a way that's beyond your control we have the following task build a nearly perfect computer out

of a whole bunch of imperfect parts common myth how many qubits do you have that's the only thing that matters like just add more qubits what's the big deal pattern them on your chip the great power of a quantum computer is also its achilles heel that it's very very sensitive to perturbations and noise and environmental effects you're just multiplying your problems if all you're doing is adding uh exactly so i think something that frustrates a lot of people about quantum computing is the concept of decoherence right you can only keep your information quantum for so

long right and that limits how many operations you can do in a row before you lose your information that's the challenge i would say as much progress as we've made it's a frustration to still be facing it let's talk about some of the things we think need to happen between now and fully fault tolerant quantum computers to get us to that reality i mean there's so many things that need to happen in my mind one of the things we need to do is build all these different layers of abstraction that make it easier for programmers

to come in and just enter at the ground level you know yeah exactly so i think there's going to be a kind of co-evolution of the hardware and the software up here and the sort of middleware and the whole stack another common myth in the next five years quantum computing will solve climate change cancer [Laughter] right in the next five years there'll be tremendous progress in the field but people really have to understand that we're either at the vacuum tube or transistor stage we're trying to invent the integrated circuit and scale up it's still very

very very early in the development of the field one last myth i think we should bust steve quantum computers are on the verge of breaking into your bank account and breaking encryption and creative cryptography there does exist an algorithm shores algorithm which has been proven mathematically that if you had a large enough quantum computer you could find the prime factors of large numbers the basis of the rsa encryption it's the most commonly used thing on the internet first we're far away from being able to have a quantum computer big enough to execute schwarz algorithm on

that scale second there are plenty of other encryption schemes that don't use factoring and i don't think anybody has to be concerned at the moment and in the end quantum mechanics goes to the side of privacy enhancement if you have a quantum communication channel you can encode information and send it through there and it's provably secure based on the laws of physics you know now that everybody around the world can access a quantum computer through the cloud people are doing all kinds of cool things they're building games we've seen the emergence of quantum gains right

what do you think people want to do with them i have no idea what people are going to end up using them for i mean if you had gone back 30 years and handed somebody an iphone they would have called you a wizard so things are going to happen that we just can't foresee so i hope you enjoyed that foray into the field of quantum computing i know i've personally enjoyed getting to see quantum computing through other people's eyes coming at it from all these different levels this is such an exciting time in the history

of quantum computing only in the last couple years have real quantum computers become available to everyone around the world this is the beginning of a many decade adventure where we'll discover so many things about quantum computing and what it will do we don't even know all the amazing things it's going to do and to me that's the most exciting part [Music] you