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Science behind Quantum Computing

Sibi
July 26, 2013

Science behind Quantum Computing

Sibi

July 26, 2013
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  1. Introduction
    Basics
    Breakdown in Classical Physics
    Heisenberg’s Uncertainty Principle
    Schrodinger’s Cat
    Science behind Quantum Computing
    TCS Innovation Labs
    Cyber Physical Systems Lab
    July 26, 2013
    Sibi Quantum Mechanics

    View Slide

  2. Introduction
    Basics
    Breakdown in Classical Physics
    Heisenberg’s Uncertainty Principle
    Schrodinger’s Cat
    Outline
    1 Introduction
    2 Basics
    3 Breakdown in Classical Physics
    Anomalous stability of atom and molecule
    Rayleigh Jeans Catastrophe
    Wave Particle Duality
    4 Heisenberg’s Uncertainty Principle
    5 Schrodinger’s Cat
    Sibi Quantum Mechanics

    View Slide

  3. Introduction
    Basics
    Breakdown in Classical Physics
    Heisenberg’s Uncertainty Principle
    Schrodinger’s Cat
    No one fully understands quantum mechanics. - Steven
    Weinberg
    Sibi Quantum Mechanics

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  4. Introduction
    Basics
    Breakdown in Classical Physics
    Heisenberg’s Uncertainty Principle
    Schrodinger’s Cat
    Definition
    Branch of physics which deals with physical phenomena at
    microscopic scales.
    Best understood by unlearning many classical physics
    concepts ( Similar to learning functional language from an
    imperative background.)
    Sibi Quantum Mechanics

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  5. Introduction
    Basics
    Breakdown in Classical Physics
    Heisenberg’s Uncertainty Principle
    Schrodinger’s Cat
    Quantum Mechanics asserts that a particle’s does not
    have a position and a velocity.
    Aim of Quantum Mechanics is to calculate the range of
    possible particle positions and the relative probability of
    these functions.
    Explanation of particle has a position of 100 (+ or -) 1:
    Classical Mechanics: Particle has a position in the range
    99-101.
    Quantum Mechanics: Particle is simultaneously all over the
    range 99-101. (Thinking about wave which can spread out
    helps here.)
    Sibi Quantum Mechanics

    View Slide

  6. Introduction
    Basics
    Breakdown in Classical Physics
    Heisenberg’s Uncertainty Principle
    Schrodinger’s Cat
    Anomalous stability of atom and molecule
    Rayleigh Jeans Catastrophe
    Wave Particle Duality
    Outline
    1 Introduction
    2 Basics
    3 Breakdown in Classical Physics
    Anomalous stability of atom and molecule
    Rayleigh Jeans Catastrophe
    Wave Particle Duality
    4 Heisenberg’s Uncertainty Principle
    5 Schrodinger’s Cat
    Sibi Quantum Mechanics

    View Slide

  7. Introduction
    Basics
    Breakdown in Classical Physics
    Heisenberg’s Uncertainty Principle
    Schrodinger’s Cat
    Anomalous stability of atom and molecule
    Rayleigh Jeans Catastrophe
    Wave Particle Duality
    According to classical physics, an electron orbiting a
    nucleus should lose energy by emission of radiation.
    Because of energy loss, it should gradually spiral in
    towards the nucleus.
    But this does not happen.
    Sibi Quantum Mechanics

    View Slide

  8. Introduction
    Basics
    Breakdown in Classical Physics
    Heisenberg’s Uncertainty Principle
    Schrodinger’s Cat
    Anomalous stability of atom and molecule
    Rayleigh Jeans Catastrophe
    Wave Particle Duality
    Outline
    1 Introduction
    2 Basics
    3 Breakdown in Classical Physics
    Anomalous stability of atom and molecule
    Rayleigh Jeans Catastrophe
    Wave Particle Duality
    4 Heisenberg’s Uncertainty Principle
    5 Schrodinger’s Cat
    Sibi Quantum Mechanics

    View Slide

  9. Introduction
    Basics
    Breakdown in Classical Physics
    Heisenberg’s Uncertainty Principle
    Schrodinger’s Cat
    Anomalous stability of atom and molecule
    Rayleigh Jeans Catastrophe
    Wave Particle Duality
    Also famously called as the Ultraviolet Catastrophe
    Prediction of late 19’th century classical physics.
    Prediction: An ideal black body at thermal equilibrium will
    emit radiation with infinite power.
    This too doesn’t happen.
    Sibi Quantum Mechanics

    View Slide

  10. Introduction
    Basics
    Breakdown in Classical Physics
    Heisenberg’s Uncertainty Principle
    Schrodinger’s Cat
    Anomalous stability of atom and molecule
    Rayleigh Jeans Catastrophe
    Wave Particle Duality
    Outline
    1 Introduction
    2 Basics
    3 Breakdown in Classical Physics
    Anomalous stability of atom and molecule
    Rayleigh Jeans Catastrophe
    Wave Particle Duality
    4 Heisenberg’s Uncertainty Principle
    5 Schrodinger’s Cat
    Sibi Quantum Mechanics

    View Slide

  11. Introduction
    Basics
    Breakdown in Classical Physics
    Heisenberg’s Uncertainty Principle
    Schrodinger’s Cat
    Anomalous stability of atom and molecule
    Rayleigh Jeans Catastrophe
    Wave Particle Duality
    Sibi Quantum Mechanics

    View Slide

  12. Introduction
    Basics
    Breakdown in Classical Physics
    Heisenberg’s Uncertainty Principle
    Schrodinger’s Cat
    Anomalous stability of atom and molecule
    Rayleigh Jeans Catastrophe
    Wave Particle Duality
    Classical Physics can deal with wave or particles.
    However various experiments show that waves sometimes
    act as if they were stream of particles, and stream of
    particles act as if they were waves.
    Einstein’s Photoelectric Effect showed light behaved as a
    particle.
    Young’s double slit experiment showed light behaves like a
    wave.
    Sibi Quantum Mechanics

    View Slide

  13. Introduction
    Basics
    Breakdown in Classical Physics
    Heisenberg’s Uncertainty Principle
    Schrodinger’s Cat
    Both position and velocity of a particle cannot be
    measured accurately.
    This is because by taking a measurement we inadvertently
    disturb the system as well.
    Sibi Quantum Mechanics

    View Slide

  14. Introduction
    Basics
    Breakdown in Classical Physics
    Heisenberg’s Uncertainty Principle
    Schrodinger’s Cat
    Thought Experiment
    Experiment involves an imaginary setup.
    A cat sealed inside a box with Geiger counter attached to it.
    Inside the Geiger counter is a small amount of radioactive
    substance.
    The box is set up so that when the radioactive substance
    decays, a device smashes a vial of toxic gas, killing the cat
    inside.
    After an hour, until the box is open, there is no way to
    determine whether the cat inside is alive or dead, thus
    allowing the cat to be both alive and dead.
    Sibi Quantum Mechanics

    View Slide

  15. Introduction
    Basics
    Breakdown in Classical Physics
    Heisenberg’s Uncertainty Principle
    Schrodinger’s Cat
    Interpretation
    HUP show’s that it’s impossible to directly observe this
    decay because it involves particles so small that any
    equipment we have to monitor them would interfere with
    what they’re doing.
    What actually happens is the entire world splits into a
    superposition of worlds where cat is alive, and those
    where it is dead.
    Subatomic particles routinely exist in superposition of
    states and correct predictions of the outcomes of certain
    experiments can only be made by taking these effects into
    account.
    In Quantum mechanical world, it is possible for a atom in
    the combined state ’decayed-not decayed’ in which it is
    neither one nor the other but somewhere in between.
    Sibi Quantum Mechanics

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  16. Introduction
    Basics
    Breakdown in Classical Physics
    Heisenberg’s Uncertainty Principle
    Schrodinger’s Cat
    Superpositon
    Atomic particles can exist in two or more states at once.
    Example: Room with five chairs all exactly the same size.
    Classical theory: You sit in one of the chair. End of story.
    Quantum theory: Electron enters the room and sits down
    in all five of them at once!
    Sibi Quantum Mechanics

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  17. Introduction
    Basics
    Breakdown in Classical Physics
    Heisenberg’s Uncertainty Principle
    Schrodinger’s Cat
    Entanglement
    When two particles interact, the can become linked such
    that the alteration of one causes a mirrored response in the
    other, despite a separation by arbitrarily large distances.
    It is a sub case of quantum superposition: Two particles
    continue to form a system even after they have been
    separated and continue to share a quantum state until a
    measurement has been made.
    Measuring the state of one, causes the other to take
    different state.
    Sibi Quantum Mechanics

    View Slide

  18. Introduction
    Basics
    Breakdown in Classical Physics
    Heisenberg’s Uncertainty Principle
    Schrodinger’s Cat
    Recent development
    23 July, 2013 (2 days ago) it was presented in Moscow that
    the rules of quantum mechanics may extend to much
    larger objects than we thought.
    Earlier people have been able to build superposition states
    containing only a few photons, but now it has been
    demonstrated successfully with 160 million photons.
    Raises interesting question:
    Is there a border between micro and macro level where
    quantum rules apply ?
    Or does quantum mechanics applies on all scales ?
    Sibi Quantum Mechanics

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