Wolfson College, University of Oxford

Edward Laird - Atomic clock in your pocket

• Portable time keeping then and now
  • The Scilly Naval disaster 1704, needed access to an accurate chronometer
• GPS
  • 10ns <-> 30m location, doesn’t need an accurate clock
  • time keeping needed to make it resistant
  • One satellite goes down
  • Signal is jammed:
    • civilian code vs military code
    • civilian code is over a narrow band width
• GPS denied env,
• caesium, rubidium, quartz crystal: 10^-16, 10^-12, 10^-9
• Principles of an atomic clock
  • laws of nature vs manufacture limitations
  • Oscillator, reference medium, detector feedback mechanism
  • making a reference medium is a little tricky
  • N in C60 —> nature’s atom trap
  • The N atom doesn’t bond, it just floats in the middle of the cage. It is a bit squashed but behaves like a free atom
    • offers protection of spin states due to cage.
    • 50us coherence time at room temperature
    • But if your magnetic field changes your spin state frequency changes. So you need the magnetic field to be as accurate as the clock
    • You also have to think about the nuclear spin:
      • If you sit at the minimum of the transition field you no longer depend on magnetic field - The clock field
• Kyriakos: Synthesis N in C60 like clay pigeon shooting, yield of 0.6%
• Need to improve the line width of the absorption of the C60 at the clock transition by a factor of 1000.
• LocatorX - company willing to put money
• What is limiting the line width of the clock transition? - we don’t know
  • It seems to be limited by the magnetic modulation to get a signal strong enough to measure.
  • The next step is to measure line width at the clock transition
• Gerrard: how about optically trapping the molecules, maybe even at vacuum

Ian Walmsley - How is big different than small? Shedding light on complexity.

• Starting small, two photons coming into the beam splitter.
  • You’d expect them to come out the same port 50% of the time as classical particles
  • But you get quantum interference
• What happens with more photons?
  • independent single photons , elastic scattering, no interaction
  • Feasible quantum advantage
• S Aaronson’s blog: Shtetl Optimised
• He has been eight years upon a project for extracting sunbeams out of cucumbers.

Gerrard Milburn - The thermodynamics of time and learning

• what do clocks do?
• They measure coincidences between local events here and now. Must specify the temperature of the local environment
• Physical time is relational - time is always local.
• The larger the limit cycle the more regular the clock signal. But the larger the limit cycle the more energy is dissipated.
• Good clocks are necessarily dissipative Erker PRX 2017
• Entropy increases into the future and into the past from the perspective of a local agent. Physical time is manifest time.
• learning machines - they are driven to learn because that is the most efficient way to exploit their thermodynamic environment.
• Heat and entropy must be dissipated during training
• too much noise, random number generator basically
• quantum perceptron is a dissipative switch subject to quantum noise
• Thermodynamic efficiency of learning a rule in neural networks. Nothing done in the quantum case yet.
• Anil Seth - the brain isn’t a video recorder. It takes in what it observes, forms an emulation and continuously updates its own emulation based on more information input.
• What if communication between agents is more efficient than learning individually
• Spiking is always a bit better

Natalia Ares - Electrons and Mechanics

• semiconductor platforms are some of the best devices to investigate questions on quantum and mechanics
• semiconductors given you many options to couple quantum to mechanical effects
• Szilard engine - electron driving a piston
• The thermodynamic cost of timekeeping
  • resource to drive them
  • heat to dissipate - waste
• silicon nitride membrane 50 atoms thick
• Drive the membrane with white noise - it acts as an effective temperature
• what is the thermodynamic cost of processing quantum information

Tim Cook - Is Consciousness Physical?

Three questions

• Wigner’s friend
• Entanglement
• Teleportation

Does consciousness collapse quantum states?

• Ooh a qubit in a superposition state. If I observe it, i’ll project its state.
• Against measurement - John Bell. Would you get a better measurement if the person had a phd
• are frogs conscious - can frogs be entangled
• can consciousness be teleported
• you can’t have consciousness without learning but you can’t have learning without irreversibility.