Quantum Weirdness - Carleton University · 2019. 10. 23. · Quantum Weirdness Part 6 Quantum...

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Quantum Weirdness Part 6 Quantum Weirdness in Materials Quantum Cryptography Quantum Teleportation Quantum Snake Oil
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Transcript of Quantum Weirdness - Carleton University · 2019. 10. 23. · Quantum Weirdness Part 6 Quantum...

  • Quantum WeirdnessPart 6

    Quantum Weirdness in Materials

    Quantum Cryptography

    Quantum Teleportation

    Quantum Snake Oil

  • Quantum Weirdness in MaterialsWhy Materials Behave as they do

  • Combining Atoms Into Molecules

    • Molecular Orbital Theory The two 1s levels of two hydrogen atoms combine to form the 1σ orbitals in H2

    Still producing discrete energy levels

    Gerhard Herzberg, Nobel prize 1971

  • Carbon Dioxide CO2

    • Triatomic molecule


    • Shape depends on the shape of the orbitals, which depends on the wave equations

  • • Symmetric stretch does not absorb infra-red radiation

    • The three asymmetric stretches do absorb in the infra-red

    • This is what makes CO2 a Greenhouse Gas

  • Electronic Orbitals in a Solid

    • Now we are combining ~1023

    atoms together.

    • The discrete energy levels are so close together, that they form a BAND

    • Note this a gap in energy, not a distance


  • • The bands in the solid are filled up from the bottom with the electrons

    Part filled

    Like this multilevel fountain in Garda, Italy

  • MetalConduction Band partly filled with


    • If a band is full, then the electrons can’t go anywhere and can’t be used for conducting electricity

    • If a band is partly full, then the electrons can slosh about, if a voltage is applied, and can move

  • Valence Band

    Conduction Band

    InsulatorValence band full

    Conduction band emptyLarge energy gap


  • Valence Band

    Conduction Band


    Valence band fullConduction band empty

    Small energy gap


  • • A semiconductor has a filled band, but the gap to the next level is small.

    • At room temperature, a few electrons have sufficient energy to jump the gap, into the conducting band

    Valence Band

    Conduction Band

    Conduction Band

    Valence Band

    • Now we have a few electrons in the conduction band and a partly empty valance band

    • Both can now conduct


  • Semiconductors and Doping

    • We can control the conductivity by adding impurities like Boron or Phosphorus to the semiconductor


    Valence Band

    Conduction BandEgap

    Donor level

    Valence Band

    Conduction BandEgap

    Acceptor level

    Doping with n-type Doping with p-type

  • Diodes: Very Useful In Circuits

    • Devices which only let current (charge) flow one way

    • They were invented in 1905 by Sir John Fleming (tubes/valves)

  • Semiconductor Diodes

    • A semiconductor device which does the same thing as the vacuum tube device

    • A p-type and an n-type semiconductor placed back-to-back

    p- type Electron deficient

    n- type Electron rich

    Current can flow

  • Valence Band

    Conduction Band

    Donor level

    Valence Band

    Conduction Band

    Acceptor level


    Inside the diode, electrons are moving between quantum states

  • Light Emitting Diodes

    • If the electrons drop between levels, they can give off visible light, if the energy difference is correct

    Running lights on an Audi

  • • Very efficient, as they only produce light in a very narrow set of wavelengths

    • Low power

    • Good replacements for incandescent lightbulbs, as they don’t emit in the infra-red

    • 2 Watts LED equivalent to a 15 W incandescent

  • • Some LEDs emit infra-red light, so invisible to the human eye

    • Most TV remote controllers use an IR-LED to send the signals

  • • Blue LEDs proved very difficult to make!

    Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura:Nobel Prize in Physics 2014


  • Photodiodes

    • The diode can be used to detect photons. Increased current when light shines on the diode

    Valence Band

    Conduction Band

    Valence Band

    Conduction Band

  • • The TV has an infra-red photodiode receiver to pick up signals from the remote control

    • A solar cell, which makes energy from sunlight is an example of a photodiode

  • Diode Lasers

    • In the ordinary LED, the photons are emitted in random directions, because it is a spontaneous decay process

    • Careful design of the semiconductor layers can result in photons being produced by stimulated emission

  • Photodiodes

    • Some diodes are designed to be light sensors.

    • Light falling on them causes an electron to be excited into the conduction band, increasing the conductivity

    • These photodiodes can be made to detect many different frequencies of electromagnetic radiation (IR, visible UV being the most common)

    Circuit Symbol for Photodiode

  • • A solar cell, which makes energy from sunlight is an example of a photodiode

    • This type of operation is known as Photovoltaic Mode

    • The photon energy is used to create an electron-hole pair, which increases conductivity of the device.

  • Transistors

    • The transistor normally uses two p-n junctions back to back. It is a current amplification device


    1955 GE transistor radio

  • Nanotechnology: Quantum Dots

    • These are small particles of semiconductors. Usually clusters of 100-10,000 atoms.

    • They do not show full band structures

    Cluster of 5 atoms


    • By varying the size of the particle, the value of ΔE can be altered.

  • • Cadmium Selenide

  • • Lead Selenide, stabilised with oleic acid

    • Form regular arrays when deposited on a surface

  • • Etch them on silicon or other semiconductors

    • Photo NIST, USA

  • • Quantum dots act as potential wells, to trap electrons

    • The electrons have quantized energy levels

  • • One application is to make the energy gap equivalent to visible wavelengths.

    • If the upper energy levels are occupied, then the quantum dot will fluoresce in the visible range as the electron drops back into the lower state

    Cluster of 5 atoms



  • • Changing the size of the particle, changes the energy gap, and hence changes the colour of the emitted radiation



  • Crystals and Quantum WeirdnessYes, there is Crystal Energy

  • Crystal Lattices and Quantum Weirdness

    Sodium ChlorideSpace Fill

    The regular nature of the atoms in a solid material leads to quantum effects and interactions with the electrons

  • Sodium Chloride

  • Sapphire is an aluminium oxide, Al203 (corundum) with titanium and iron impurities

  • Sapphires

    • Absorbs red and yellow light, white light passing through it emerges as blue


    • An electron bound to an iron impurity jumps to a nearby titanium impurity


  • Ruby

    • Ruby is also corundum

    • Different cause of colour – impurities of chromium.

    • Chromium is larger than aluminium, so it distorts the lattice out of shape, so the orbitals change energy


    Natural ruby from Tanzania


  • Thermal Motion in Solids

    • Atoms oscillate around a fixed position

    • There are lots of possible oscillations!


    Vibrations of one of the structures of ice (crystalline water)


  • Waves and Phonons

    • The vibrations inside the crystal are waves

    • Because of wave particle duality, we can also think of them as quasi-particles of energy called PHONONS

    • They carry energy through the material


    We can watch the ripples of the waves at the surfaces of crystals using laser light

    𝐸 = ℎ𝑓 =ℎ𝑐

    𝜆Phonon energy


  • The idea of the phonon was introduced in 1932 by the Russian physicist Igor Tamm(Nobel Prize 1958)

    • Long wavelength phonons carry sound through materials

    • Short wavelength phonons carry heat energy through materials

  • Electrical ConductivityWhen Electrons Move Through a Conducting Material

  • + + + + +

    + + + + +

    + + + + +

    + + + + +


    • Electrons moving through the metal collide with the positive metal ions and lose energy

    • To push them through the metal lattice against resistance needs energy (from a battery)

  • • The moving electrons bump into lattice ions, and give energy to the lattice

    • The lattice ions have more energy (get hotter).

    • Metal heats up as electric current flows through it

  • SuperconductorsWhen the Phonons Become Important

  • Superconductivity

    • At extremely low temperatures, many metals (and other materials) become superconductors

    • No energy is lost as the electrons pass through the material

    • There are no heat losses

  • • At low temperature there is an interaction between the electrons and the phonons in the lattice

    • This results in the electrons forming pairs (Cooper pairs)

    • These can pass through the metal without interacting!

    • Very subtle quantum weirdness, involving interactions between quantum particles and quantum quasi-particle!

  • Quantum ComputingPromising, but early days

  • Digital Computing: The Bit

    • The basic piece of digital data

    • Either 0 or 1

    • Stored in a logic gate (a collection of a few transistors)

    1 0 1 1 1 0 1 0

    (1 × 28) + (0 × 27) + (1 × 26) + (1 × 25) + (1 × 25) + (0 × 23) + (1 × 22) + (0 × 21)

    = 186

  • Qubit

    • A two level quantum state

    • The information is stored as a quantum superposition

    Spin states

    • It contains more information than a conventional bit

    • Conventional bit must be pointing either up or down

    • Qubit can point in any direction on what is known as the Bloch sphere


  • • Each qubit contains information in a superposition of states

    • If qubits interact with each other, they can process multiple possible answers simultaneously

    • You then measure the final state of the qubits, to get a final answer

    • Do it many times to get a range of possible answers

    • To make a qubit, use a superconducting junction

  • Josephson Junctions

    • Two superconductors, with a very thin layer or insulating material between them

    Cooper Pairs of electrons can tunnel from one superconductor to the other

  • https://en.wikipedia.org/wiki/Superconducting_quantum_computing

    The Cooper pairs exist as different quantum levels whilst tunnelling

    They can act as a Qubit


  • IBM Quantum Experience

    • IBM Q Experience: two 5-qubit processors and a 16-qubit processor.

    Superconductors –cooled to 0.100 mK(very cold)

    3 nm thick layer (0.00000001 cm)

  • Quantum Supremacy

    • A task which can be carried out much more quickly on a quantum computer, than can be feasibly carried out on a regular computer

    • Paper published yesterday!

    • https://www.nature.com/articles/s41586-019-1666-5


  • Quantum CryptographyMaking Unbreakable Codes

  • Codes and Cyphers

    • Transposition of letter for letter or letter to number

    • Can be done mechanically (Enigma machine)

    • Must have some repeating patterns to the encoding

    • Can be solved, if you have fast enough computing power

    Cyphers – same length as the encoded textCodes – different length

  • • Mechanical computer – the Bletchley Park Bombe

    • Based on the Polish bomba kryptologiczna(cryptological bomb)

  • • To crack the German Naval codes (which had an extra wheel on the Enigma, and were more complicated), they built the first computer Colossus

  • One Time Pad Cyphers

    • One time pad

    • Used by both the sender (Alice) to code

    • And the receiver (Bob) to decode

    • If both destroy the pad after use, then it is unbreakable

    • Requires both to share the pad

  • • Alice and Bob create an entangled quantum system as the key (a quantum one time pad)

    If anyone else tries to break into the system and measure the key, they will change the state of the system, so it has security built in

    A B

  • Quantum TeleportationNot What You Think It Is!

  • Moving Matter From Place To Place

    • Using a device like the “Transporter” – Star Trek

    • https://www.youtube.com/watch?v=jDFI87zn9t0&feature=youtu.be

    • What’s the reality?


  • Quantum Teleportation is Different

    • It does not transport for matter

    • It is a communication stream

    • It moves quantum information (a Qubit)

    • To reconstruct the quantum object requires instructions, which must be transmitted conventionally (at the speed of light)

    • The process destroys the original qubit

  • • Alice and Bob share a pair of entangled photons

    • Alice now uses her entangled photon to measure another photon (the one we want to teleport)

  • • The net result is that Alice’s two photons are now in undetermined states, and Bob’s photon is now in the same state as Alice’s was originally

    • However, you have to transmit the information about how many possible states there are to Bob by another (conventional) channel – the process is not instantaneous

  • • We can entangle photons, then send one elsewhere

    • The two photons are still entangled – action performed one, affects the other instantaneously

    143 km

  • • Satellite to Ground communication using the Chinese Quantum Space Satellite Micius / Mozi

    • 1400 km ranges

  • Three State Systems

    • Recent experiments (15th August 2019!) have demonstrated that a three state system can be teleported

    • Qutrit (states 0, 1 & 2) instead of a qubit (0 & 1)



  • Quantum Snake OilFake News

  • Things to be Cautious About

    • Quantum Medicine

    • Quantum University

    • Quantum Healing

    • Quantum Resonance Spectroscopy

    Not to be confused with Magnetic Resonance Spectroscopy and Magnetic Resonance Imaging (MRI), which are genuine!

    • Look for information coming from a well-known, publicly funded University. Avoid information from private research organizations, Think-Tanks, etc

  • Summary of Quantum Weirdness

    Quantum WeirdnessQuantum Weirdness in MaterialsCombining Atoms Into MoleculesCarbon Dioxide CO2Slide 5 Electronic Orbitals in a SolidSlide 7 Slide 8 Slide 9 Slide 10 Slide 11 Semiconductors and DopingDiodes: Very Useful In CircuitsSemiconductor DiodesSlide 15 Light Emitting DiodesSlide 17 Slide 18 Slide 19 PhotodiodesSlide 21 Diode LasersPhotodiodesSlide 24 TransistorsNanotechnology: Quantum DotsSlide 27 Slide 28 Slide 29 Slide 30 Slide 31 Slide 32 Crystals and Quantum WeirdnessCrystal Lattices and Quantum WeirdnessSodium ChlorideSlide 36 SapphiresRubyThermal Motion in SolidsWaves and PhononsSlide 41 Electrical ConductivitySlide 43 Slide 44 SuperconductorsSuperconductivitySlide 47 Quantum ComputingDigital Computing: The BitQubitSlide 51 Josephson JunctionsSlide 53 IBM Quantum ExperienceQuantum SupremacyQuantum CryptographyCodes and CyphersSlide 58 Slide 59 One Time Pad CyphersSlide 61 Quantum TeleportationMoving Matter From Place To PlaceQuantum Teleportation is DifferentSlide 65 Slide 66 Slide 67 Slide 68 Three State SystemsQuantum Snake OilThings to be Cautious AboutSummary of Quantum Weirdness