Building a quantum computer with superconducting qubits (QuantumCasts)

Summary

This video by TensorFlow explores the fascinating realm of quantum computing, particularly focusing on the construction of quantum computers using superconducting qubits. It begins by discussing the limitations of classical physics and transitions into quantum mechanics. The video is narrated by Daniel, a research scientist from Google's AI quantum computing lab. He explains the intricacies of quantum bits, the differences between classical and quantum states, and the challenges involved in creating circuits that use superconductivity to avoid quantum errors. The discussion highlights how superconducting qubits operate at extremely low temperatures to reduce error rates and the ongoing research efforts to improve the reliability of these qubits for quantum computation.

Highlights

• Daniel from Google AI lab explains the construction of quantum computers with superconducting qubits 🧑‍🔬.
• Quantum bits allow for computing beyond traditional physics, harnessing superposition 🌌.
• Understanding the physical differences of classical vs. quantum bits is key to quantum computing 🗝️.
• Superconducting qubits operate in extreme cold to prevent errors and maintain stability ❄️.
• Google's innovation reduces quantum errors through cutting-edge fabrication techniques and superconductivity 🛠️.

Key Takeaways

• Classical physics limits classical computers, while quantum mechanics opens new possibilities for faster computations 🚀.
• Quantum bits, or qubits, leverage superposition, allowing multiple states at once, unlike classical bits 💡.
• Superconducting qubits are developed to minimize quantum errors through superconductivity 🔧.
• Quantum errors occur due to the delicate nature of qubits being observed even by single photons 👀.
• Google's research involves using superconducting metals like aluminum, cooled to near zero Kelvin, to stabilize qubits ❄️.

Overview

Ever wondered how quantum computers defy the old rules of classical physics? This fascinating dive into the mechanics of quantum computing explains it all! 🧠 Starting with an introduction to classical versus quantum states, the video expands on the revolutionary idea of qubits being in multiple states at once through superposition.

The hero of this narrative is the superconducting qubit, cooled to nearly unimaginable temperatures to ward off quantum errors. By leveraging superconductivity, these qubits can hold onto their delicate quantum states longer, thus performing more reliable computations.

Despite advancements, the field faces challenges - charged particles interacting with qubits pose constant threats of errors. Yet, the relentless pursuit by researchers, like those at Google, promises a future where these obstacles are diminished, making quantum computing more accessible and powerful than ever! 🔍

Chapters

• 00:00 - 00:30: Introduction to Classical and Quantum Physics The chapter introduces the concept that all forms of information, whether written, spoken, or digital, are governed by physical laws. These fundamental principles are rooted in classical physics, which was developed in the 1800s. The text sets up a contrast by mentioning advancements in our understanding of physical laws, hinting at the transition to quantum physics, though the transcript cuts off before elaborating on this newer framework.
• 00:30 - 01:00: Quantum Mechanics and Quantum Bits The chapter titled 'Quantum Mechanics and Quantum Bits' introduces a quantum computing chip designed to utilize the principles of quantum mechanics, allowing it to process information in ways unattainable for classical computers. Daniel, a research scientist at Google AI Quantum Computing Lab, aims to demystify how these quantum bits manifest physically and discusses the applicability of quantum mechanics beyond microscopic objects like atoms.
• 01:00 - 01:30: Classical vs Quantum Information The chapter delves into the fundamental differences between classical and quantum information on a physical level. It aims to help the reader understand the rationale behind the construction of quantum bits. The chapter introduces the concept of 'states' as understood by physicists and computer scientists, using a physical state like position—such as being on the left or right—as an example. It also touches upon how physical laws influence the transition from one state to another, exemplified by a scenario where an external force, such as a push, alters a person's physical state.
• 02:00 - 02:30: Quantum Algorithms and Superposition The chapter explores the concept of how computers change states based on memory bits and computer programs dictate these state changes. It introduces the idea that, similar to physics which has physical states and natural laws, computer science operates with memory states and programs. A comparison is drawn explaining computer memory as a string of bits, specifically for n bits, highlighting the role of these bits in transitioning computer states.
• 05:00 - 05:30: Challenges in Quantum Computation In classical computation, a computer can only be in one state among 2^N possible strings at any given time, transitioning from one state to another with each step of an algorithm. For instance, a logic operation may change a state from 000 to 110, and applying the same operation again could change it from 110 to 010.
• 06:30 - 07:00: Superconducting Qubits The chapter delves into the concept of superconducting qubits within quantum computing. It explains how quantum states differ from classical states, emphasizing their richness and ability to be in superposition, which means having probability weights distributed over all possible classical states concurrently. It further elaborates on how each step in a quantum algorithm manipulates these states into complex superpositions. An example is provided starting from the state 0 0 0, which evolves into a superposition of multiple states such as 1 0 0, 1 0 1, and 1 1 1, each branching into further superpositions.
• 09:00 - 09:30: Physical Errors in Quantum Computing The chapter explores the physical differences between classical and quantum computing, focusing on how quantum mechanics is implemented in a quantum computer chip. It highlights how quantum computers can solve problems faster than classical computers and delves into the complexity and physical characteristics of classical bits to provide a foundational understanding of the transition from classical to quantum at a physical level.
• 10:00 - 10:30: Continuous Improvement in Superconducting Qubits The chapter delves into the basics of classical and quantum computing, focusing on how classical computer bits are stored using the presence or absence of charge on a capacitor in a dynamic RAM (de-RAM) circuit. A logical '1' is indicated by the presence of charge, while a logical '0' by its absence. Interestingly, even though these logical states could conceivably be represented by a single electron, they actually consist of the presence or absence of around 300,000 electrons. This chapter likely explores this distinctive aspect in relation to advances in superconducting qubits.
• 10:30 - 11:00: Conclusion and Further Engagement This chapter discusses the challenges associated with DRAM (Dynamic Random-Access Memory) where physical properties at the microscopic level result in erratic behavior of electrons. Electrons, being very small and light, tend to move around and can escape from storage cells, causing potential data errors. To address this, DRAM uses many electrons to ensure that even if some escape, the data remains accurate. Additionally, DRAM circuits regularly check and refresh the stored electric charge to maintain data integrity.

Building a quantum computer with superconducting qubits (QuantumCasts) Transcription

• 00:00 - 00:30 [Music] information is physical written letters are carbon grains on paper spoken words or vibrations of air molecules computer Bitzer electric charge each of these examples shares a common limitation they work under physics that was understood in the 1800s known as classical physics science has progressed since then we've discovered a new set of laws called
• 00:30 - 01:00 quantum mechanics here's one of our chips designed to leverage the rules of quantum mechanics to process information in ways impossible on a computer based in classical physics you may have heard that quantum mechanics only applies to microscopic objects like atoms so how does this chip bring out quantum behavior I'm Daniel thank a research scientist working in the Google AI quantum computing lab in this video we'll look at how our quantum bits are made physically I want to explain the
• 01:00 - 01:30 fundamental differences between classical and quantum information at the physical level so that you can understand why our quantum bits are made how they are physicists and computer scientists both think in terms of States a physical state could be my position I can be on the left or on the right and physical laws determine how nature goes from one state to another observe if Sergio pushes me my state
• 01:30 - 02:00 changes a computer state is the value of its memory bits in computer programs determine how the computer goes from one state to the next for example when you hit the play button youtube's program started manipulating your computer's memory to show this video where physics has physical states and natural laws computer science has memory states and programs think of the state of computer memory as a string of bits for n bits
• 02:00 - 02:30 there are 2 to the N possible strings but because we're based in classical physics the state of the computer is just one of these states at each point in time on each step of a classical algorithm we go from one state to the next for example the logic operation shown here takes the state 0 0 0 2 1 1 0 if we were to apply the same operation again we go from 1 1 0 2 0 1 0 compared to
• 02:30 - 03:00 classical States quantum states are more rich they can have weight in all possible classical States a situation physicists call superposition each step of a quantum algorithm mixes the states into complex super positions for example starting in 0 0 0 we go to a superposition of 1 0 0 1 0 1 and 1 1 1 then each of those 3 parts of the superpose state branches out to even
• 03:00 - 03:30 more states the extra complexity of quantum computers allows them to solve some problems faster than a classical computer ever could we've discussed the computational difference between classical and quantum but how do classical and quantum differ physically how do we bring out quantum mechanics in our chip which is so much bigger than the tiny atoms in which quantum mechanics was first discovered let's take a detailed look at classical bits at the physical level so that we can understand the physical difference
• 03:30 - 04:00 between classical and quantum classical computer bits are stored in the presence or absence of charge on a capacitor and a circuit called dynamic Ram or de Ram for short if there's charge it's a logical one and if there's no charge it's a logical zero but there's more going on here our logical 0 & 1 are actually made up of the presence or absence of 300,000 electrons why u so many in principle we could just use the presence or absence of one electron as
• 04:00 - 04:30 our logical bed well physical bittern noisy electrons are tiny and light so they jiggle around and leak out of the DRAM if we had only one electron and it were to leak out our bit would change value which is an error by using lots of electrons we're ok if you leak out DRAM circuits periodically check the logical level and replenish missing electrons encoding one
• 04:30 - 05:00 logical bit in the state of so many physical bits gives classical information a level of reliability that we take for granted we don't have to think about all those electrons bumping around when we write our programs okay so why can't we just put our DRAM into a quantum superposition of zero and one well suppose we did have that superposition it wouldn't last long as soon as we do the first check to protect against a DRAM error
• 05:00 - 05:30 we'd force the bit into either 0 or 1 removing the quantum superposition state in fact that collapse happens even without us checking for errors a single photon interacting with just one of our electrons can carry off information when that happens it's as if the photon observed the quantum state and the state collapses you can think of this as nature observing and thus destroying our
• 05:30 - 06:00 quantum states errors like this are unique to quantum information in classical computing you might be upset if somebody peeks at your bits but that peak doesn't completely destroy them note that an error occurs whenever nature observes any one of our physical bits so while we normally stack up more physical bits for redundancy that approach actually makes quantum errors worse that's the main difficulty in
• 06:00 - 06:30 quantum computation the fundamental quantum constituents of matter are small and easily subjected to noise but we can't brute force our way around that noise with redundancy because bigger systems are more subject to quantum errors at Google we use a technique that gets the best of both worlds we use circuits with a huge number of electrons but we prevent quantum errors with superconductivity in regular metals like with a conventional DRAM circuit every
• 06:30 - 07:00 individual electron does its own thing as electrons move around they can bounce off the positively charged ions of the metal radiating vibrational waves that carry off quantum information about the electrons this hectic bustling cauldron of physical interactions generates a lot of quantum errors and the information gets lost before we can use it however when certain metals are cooled down their electrons joined together in a single unit the individual electrons no
• 07:00 - 07:30 longer scatter and the rate of quantum errors drops to almost zero our quantum bits are in fact just electoral oscillators both from aluminium which becomes superconducting when cooled to below 1 degree Kelvin the oscillators store tiny amounts of electrical energy when the oscillator is in the zero state it has zero energy when it's in the 1 state and has a single quantum of energy the two states of the oscillator with zero or one quantum of energy are the
• 07:30 - 08:00 logical states of our quantum bit or qubit for short here's a picture of a superconducting qubit along with a circuit diagram the crosses indicate joseph´s and tunnel junctions which are nonlinear superconducting inductors we picked the resonance frequency of our oscillator x' to be about 6 gigahertz which sets the energy difference between the 0 and 1 States that's a low enough frequency that we can build control electronics from readily available
• 08:00 - 08:30 commercial parts but also high enough that the ambient thermal energy doesn't scramble the oscillation and introduce errors 6 gigahertz corresponds to 300 millikelvin fortunately refrigerators that get 215 millikelvin are relatively standard commercial products for comparison outer space is about 2.5 Kelvin I think it's cool that the cryostats in our lab are colder than deep space now let's take a minute to
• 08:30 - 09:00 make a few comments on how superconducting qubit architecture differs from conventional computers in a conventional computer memory and logic processing are separated into the RAM and CPU when we want to do a computation we first move the data from the RAM to the CPU then the circuits and the CPU do the compute and finally the resulting data is written back to RAM in quantum computing
• 09:00 - 09:30 with superconducting qubits we can't afford the errors that would come from moving the data around instead we build a grid of qubits each one connected to its neighbors the qubits stay put and we do logic operations by sending control signals into individual qubits or pairs of qubits now that you have a basic picture of superconducting qubits let's take a look at one of the challenges that we're still working on superconductivity greatly reduces errors
• 09:30 - 10:00 but there are still some for example the electrons flowing in the oscillator interact with charged particles in the surroundings leading to errors suppose there were a charged ion inside the metal of our qubit the oscillating energy and the qubit can transfer into that ion causing the qubits logic state to flip thus creating an error improving the qubit fabrication process to reduce these atomic imperfections is a big part
• 10:00 - 10:30 of our research over the last several years improvements in micro fabrication techniques have decreased our qubit error rates a lot and we're still improving in this video we focus on the idea that information is physical we discussed the physical incarnation of classical and quantum computer bits we introduced quantum errors and explained why we need superconductivity to eliminate those errors if you'd like to know more you can leave questions in the comment section below
• 10:30 - 11:00 it's important to me that you can understand the physical aspects of quantum computation as clearly as possible I'm also pretty active on physics Stack Exchange you can find great questions and answers there too [Music]