How To Build A Quantum Computer

today I want to answer one question how can I build a quantum computer you may think about math superpositions entanglement and all these other buzzwords that you hear on the news but what physically is a quantum computer it's not any of these abstract Concepts it's something real it's something physical that you can hold in a lab some of you might think this is an easy question oh those cold metal chandeliers that we see in those IBM videos those are quantum computers right well kind of those are actually the cooling mechanisms that are used to keep quantum computers at near absolute zero temperatures so the question still kind of stands what are these things and how do we make them unlike classical computers which have been optimized for the past 60 years using transistors quantum computers still have a bunch of possible different implementations we're essentially in the vacuum tube era of quantum computers we can make a few qubits and we can do some cool operations with them but we haven't gotten to the point yet where we can scale up to billions and billions of qubits like we have with transistors so a normal classical bit made out of a transistor can be in two states either zero or one in the zero State the transistor is off and in the one state the transistor is on Quantum bits or qubits for short must also be able to have two states a zero into one state the difference is that quantum computers must also be able to be in a superposition of the zero in one state a superposition is just when you take one state and another state and combine them together by adding them we can combine these states using constants out front that tell us about the probability that we will measure our Quantum system in one of these given States now most of the time these states are energy states the zero corresponds to a certain amount of energy and the one corresponds to a different amount of energy by interacting with our system I.E shining a photon or using some other method of putting energy into our system we can drive transitions between zero and one States or put our qubits into a superposition so now that we know what we're looking for we can start looking in the lab for Quantum systems that have a zero and a one state two different energy states that we can go between and use as our computational basis to do this we solve the Schrodinger equation the Schrodinger equation is a differential equation that allows us to solve for the energies allowed in a specific system because we're in quantum mechanics not all energies are allowed in fact only a certain specific set of energies are allowed in a quantum mechanical system all other energies are forbidden and we will not measure our system ever to be in that energy state for example if we take an equal superposition of the zero and the one state that does not mean that our particle has half the energy between the zero and the one state what it actually means is that you have a 50 chance of measuring your particle in the zero State and a 50 chance of measuring your particle in the one state there's no classical analog to this you can never have a switch that has a 50 probability of one thing or another this inherent uncertainty is actually where the power of quantum Computing comes from if we go a little bit deeper a quantum computer must satisfy several criteria these criteria are known as the divachenzo criteria and describe what a fully functional quantum computer must have well that's enough stalling but let's actually answer this question right what does a quantum computer look like [Music] first I'm going to talk about neutral atom quantum computers neutral atom quantum computers use individual atoms trapped in an optical lattice in order to do Quantum computation we can address each one of these atoms by shining lasers at them and then we pick two states in the atoms to serve as our zero state in our one state these two states are the hyperfine states of the specific atom that we're using hyperfine states are specific energy states that come from the interaction between electron and nuclear spin we use these states as the zero and one States and we can use lasers to go between them so for example if you wanted to perform a not gate where you swap a zero to a one what you would do is shoot a laser at the frequency that corresponds to the energy difference between 0 and 1. you can calculate this using some basic physics formulas but if you know the difference in energy between the zero and the one state then you can calculate the frequency of light needed to make the transition from 0 to 1. [Music] another type of quantum computer is a trapped ion Quantum compute Computing in this case our qubits are no longer atoms but instead are ions which are charged atoms similarly to neutral atom quantum computers the computational states used in these qubits are the hyperfine states of the ions unlike neutral atoms however the trapping mechanism is very different because ions are charged they can be trapped using oscillating electric and magnetic fields when an oscillating electric or magnetic field is applied to a cavity that contains ions the ions can become trapped in the oscillating field then to address the ions individually we shine lasers at them to change them between the zero and the one state [Music] foreign [Music] superconducting quantum computers are one of the types of quantum computers that most closely resemble a classical computer these are chips made in a nano fabrication facility much like the computer chips that you use in your laptop phone desktop or whatever that said there are some important differences between a classical computer chip and a superconducting qubit chip a superconductor is a material that allows electricity to pass through it with no electrical resistance if you look at a normal conductor as you decrease temperature the resistance decreases slowly in many materials this is where it stops as you decrease temperature the resistance decreases slowly but it never reaches zero however in some materials known as superconductors there is a phase transition this phase transition leads to a state where the material will conduct electricity with absolutely zero resistance this allows for some very interesting circuits to be made superconductors arise due to quantum mechanical effects and so they lend themselves to making quantum computers we can make superconducting circuits that work as qubits and use them very similarly to the trapped ion or neutral atom quantum computers we can assign energy states to different ways that current flows depending on the type of superconducting qubit you make and yes there are many types each one of them has a different circuit pattern different components different materials and whatnot but depending on the type of superconducting circuit you make you get different modes of current flow as your zero in one States these zero in one States much like the neutral atoms and the trapped ions however are still good for Quantum Computing and we can use them as our basis states by sending in electrical pulses we can swap between the zero and the one States much like we could with the laser pulses and neutral atoms and trapped ions foreign [Music] qubits are similar to superconducting qubits and that they're made on a chip they're not like individual atoms in the sense that you have a material that you're actually sending electrical signals into however we are still looking at single electron physics you can use these semiconductor structures to confine the electron to a single area in space then you can use magnetic fields to split the energy levels of this electron this is known as Siemens splitting specifically what we're doing is splitting the electron spin States usually there are two spin States for electrons spin up and spin down spin up and spin down are usually degenerate which means that they have the same energy there's no preferred direction for the electron to spin however in the presence of magnetic field the electron spin does have a preference and so the energy levels shift which again is known as semen splitting by then using an electrical pulse we can go between these two states and use them as our computational basis States we call this concept spin because it interacts in the same way that a macroscopic particle with some charge on it would interact with a magnetic field if it were spinning foreign Quantum Computing goes super deep and this video just scratches the surface each one of these different types of quantum computers that I gave a quick five minute introduction into is its own deep research field with its own deep Concepts that being said if you guys want to learn more about each type of quantum computer stay tuned because I'm going to be coming out with a series of videos doing deeper dives into the individual physics for each architecture I'm also going to go over some more interesting different qubit designs that I haven't talked about here things like Envy diamonds for example thank you guys so much for watching I've been Lucas this has been Lucas's lab and I'll see you next time [Music] thank you

Channel: Lukas's Lab

Views: 80,360

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Id: N06hC1GL1ns

Length: 9min 26sec (566 seconds)

Published: Sun Aug 06 2023