Facts about quantum computation & speculation about the human brain Tim Hugo Taminiau Kavli Institute of Nanoscience, Delft University Quantum superposition Entanglement A quantum brain?
Lets play the CHSH game (Bell inequalities) John ClauserJohn Bell Albert Einstein Nathan Rosen TEAM 1 TEAM 2 The rules: AA -> same (both yes or both no) AB -> same BA -> same BB -> different Score: TEAM 2: 75% TEAM 1: ~85% What the #!? They must be cheating. What the #!? They must be cheating. Lets play a game 75% nice! Quantum information really changes what is possible!
Outline The power of quantum computers Building a quantum computer out of diamond Does this have anything to do with the human brain?
Quantum bits can be in superpositions Classical bitQubit or p(0) = 0.5p(1) = 0.5 Coin toss The essence is interference: XX Measurement:
Entanglement: spooky action on a distance The particles have no state of their own, but a well defined state together! TEAM 1: ~85 % TEAM 2 Spooky!
The exponential power of quantum systems 1x 2x 3x Classical computers Quantum systems 1x 2x 3x Scales with nScales with 2 n Feynman: we need quantum systems to simulate quantum systems!
Media: A massively parallel (classical) computer that computes al possibilities at the same time, after which you just have to pick the right answer. A quantum computer is not: Measurement More subtle: Must make use of interference and ask the right question!
Quantum algorithms: factoring numbers Factoring is hard? 15= 3 x 5 91= 7 x = 19 x = 587 x digits1 day (impossible today) days days days days ~ 3 years years years Shor’s algorithm: for a quantum computer factoring is easy!
Outline The power of quantum computers Building a quantum computer (out of diamond) Does this have anything to do with the human brain?
Qubits come in many flavours PhotonsTrapped ions/atoms Superconducting circuits Electrons in Quantum dots Majorana fermions Spins in diamond
The NV in diamond: An ion trapped in a solid V N
MW pulse length (ns) Fluorescence image Solid immersion lens Microwave line Electron microscope 10 um The NV in diamond: An ion trapped in a solid
Entangling two spins in two different diamonds Click !
The lab
Does it always work? Success probability Attempts: Events: Total time: ≠ 0! ~ hours (1 per 10 minutes)
But… 3 meters is not enough 1.3 km
Outline The power of quantum computers Building a quantum computer (out of diamond) Does this have anything to do with the human brain?
Argument of two mysteries “The brain is mysterious, quantum mechanics is mysterious, therefore there might be a relation.” Nevertheless many scientists, such as Penrose, Eddington, Turing and Popper have wondered/speculated about it. Is the brain a quantum computer? Does quantum mechanics limit how well we can understand and predict the brain?
Quantum nonsense? New age quantum mysticism
Is the brain a quantum computer? Probably not… 1)Evolutionary advantage of factoring integers and breaking RSA encoding is not obvious. No real evidence that humans solve these problems efficiently. (No offense!) 2) Physically implausible: Coherence time s << timescales of neurons s (See e.g. Tegmark 1999) from Scott Aaronson: Quantum information and the Brain = 587 x 773
Quantum limits on the predictability of the brain? Possibly… Quantum measurement Can be tested: just measure the entire brain. from Scott Aaronson: Quantum information and the Brain
Conclusion The experiments are coming: Quantum computers are impossible -> new laws of physics OR Quantum technology will be realized -> quantum simulations, computations Thank you!