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Quantum Computers Explained – Limits of Human Technology

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    For most of our history, human
    technology consisted of
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    our brains, fire, and sharp sticks.
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    While fire and sharp sticks became
    power plants and nuclear weapons,
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    the biggest upgrade has
    happened to our brains.
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    Since the 1960s, the power of our brain
    machines has kept growing exponentially,
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    allowing computers to get smaller
    and more powerful at the same time.
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    But this process is about
    to meet its physical limits.
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    Computer parts are approaching
    the size of an atom.
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    To understand why this is a problem,
    we have to clear up some basics.
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    A computer is made up of very simple
    components doing very simple things,
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    representing data, the means of processing
    it, and control mechanisms.
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    Computer chips contain modules,
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    which contain logic gates,
    which contain transistors.
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    A transistor is the simplest form
    of a data processor in computers,
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    basically, a switch that
    can either block or open
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    the way for information coming through.
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    This information is made up of bits,
    which can be set to either zero or one.
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    Combinations of several bits are used to
    represent more complex information.
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    Transistors are combined to create logic
    gates, which still do very simple stuff.
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    For example, an AND gate sends an output
    of one if all of its inputs are one
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    and an output of zero otherwise.
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    Combinations of logic gates finally
    form meaningful modules,
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    say, for adding two numbers.
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    Once you can add, you can also multiply,
    and once you can multiply,
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    you can basically do anything.
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    Since all basic operations are literally
    simpler than first-grade math,
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    you can imagine a computer as
    a group of seven-year-olds
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    answering really basic math questions.
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    A large enough bunch of them can compute
    anything, from astrophysics to Zelda.
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    However, with parts
    getting tinier and tinier,
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    quantum physics are making things tricky.
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    In a nutshell, a transistor
    is just an electric switch.
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    Electricity is electrons moving
    from one place to another,
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    so a switch is a passage that can block
    electrons from moving in one direction.
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    Today, a typical scale
    for transistors is 14 nm,
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    which is about 8 times less
    than the HIV virus’s diameter
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    and 500 times smaller
    than a red blood cell’s.
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    As transistors are shrinking
    to the size of only a few atoms,
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    electrons may just transfer themselves to
    the other side of a blocked passage
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    via a process called quantum tunneling.
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    In the quantum realm, physics
    works quite differently from
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    the predictable ways we’re used to,
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    and traditional computers
    just stop making sense.
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    We are approaching a real physical
    barrier for our technological progress.
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    To solve this problem,
    scientists are trying to
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    use these unusual quantum
    properties to their advantage
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    by building quantum computers.
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    In normal computers, bits
    are the smallest units of information.
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    Quantum computers use qubits, which
    can also be set to one of two values.
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    A qubit can be any
    two-level quantum system,
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    such as a spin in a magnetic field
    or a single photon.
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    Zero and one are this
    system’s possible states,
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    like the photon’s horizontal
    or vertical polarization.
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    In the quantum world, the qubit
    doesn’t have to be in just one of those;
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    it can be in any proportions
    of both states at once.
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    This is called superposition.
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    But as soon as you test its value, say,
    by sending the photon through a filter,
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    it has to decide to be either
    vertically or horizontally polarized.
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    So, as long as it’s unobserved, the qubit
    is in a superposition of probabilities
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    for zero and one, and you can’t
    predict which it will be.
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    But the instant you measure it, it
    collapses into one of the definite states.
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    Superposition is a game-changer.
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    Four classical bits can be
    in one of 2 to the power of 4
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    different configurations at a time.
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    That’s 16 possible combinations,
    out of which you can use just one.
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    Four qubits in superposition, however,
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    can be in all of those
    16 combinations at once!
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    This number grows exponentially
    with each extra qubit.
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    20 of them can already store
    a million values in parallel.
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    A really weird an unintuitive
    property qubits can have
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    is entanglement, a close connection that
    makes each of the qubits
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    react to a change in the other’s
    state instantaneously,
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    no matter how far they are apart.
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    This means that when measuring
    just one entangled qubit,
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    you can directly deduce properties of
    its partners without having to look.
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    Qubit manipulation
    is a mind-bender as well.
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    A normal logic gate gets
    a simple set of inputs
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    and produces one definite output.
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    A quantum gate manipulates
    an input of superpositions,
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    rotates probabilities, and produces
    another superposition as its output.
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    So a quantum computer sets up some qubits,
    applies quantum gates to entangle them
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    and manipulate probabilities,
    then finally measures the outcome,
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    collapsing superpositions to an
    actual sequence of zeros and ones.
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    What this means is that you
    get the entire lot of calculations
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    that are possible with your setup
    all done at the same time.
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    Ultimately, you can only
    measure one of the results,
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    and it will only probably
    be the one you want,
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    so you may have to
    double-check and try again.
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    But by cleverly exploiting
    superposition and entanglement,
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    this can be exponentially more efficient
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    than would ever be possible
    on a normal computer.
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    So, while quantum computers will probably
    not replace our home computers,
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    in some areas they are vastly superior.
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    One of them is database searching.
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    To find something in a database,
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    a normal computer may have
    to test every single one of its entries.
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    Quantum algorithms need only
    the square root of that time,
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    which for large databases
    is a huge difference.
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    The most famous use of quantum
    computers is ruining IT security.
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    Right now, your browsing,
    email, and banking data
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    is being kept secure by an encryption
    system in which you give everyone
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    a public key to encode
    messages only you can decode.
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    The problem is that this
    public key can actually be used
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    to calculate your secret private key.
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    Luckily, doing the necessary math
    on any normal computer
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    would literally take
    years of trial and error.
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    But a quantum computer
    with exponential speedup
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    could do it in a breeze.
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    Another really exciting
    new use is simulations.
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    Simulations of the quantum world
    are very intense on resources,
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    and even for bigger structures,
    such as molecules,
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    they often lack accuracy.
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    So why not simulate quantum physics
    with actual quantum physics?
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    Quantum simulations could provide
    new insights on proteins
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    that might revolutionize medicine.
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    Right now we don’t know
    if quantum computers will be
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    just a very specialized tool
    or a big revolution for humanity.
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    We have no idea where
    the limits of technology are,
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    and there’s only one way to find out!
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    This video is supported by
    the Australian Academy of Science,
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    which promotes and
    supports excellence in science.
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    Learn more about this topic
    and others like it
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    at .
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    It was a blast to work with them,
    so go check out their site!
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    Our videos are also made possible
    by your support on Patreon.com.
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Title:
Quantum Computers Explained – Limits of Human Technology
Description:

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Video Language:
English
Duration:
07:17

English subtitles

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