Quantum macroscopicity and life

1. Quantum macroscopicity and life VlatkoVedral University of Oxford & National University of Singapore vlatko.vedral@qubit.org

2. Questions • Can we understand laws of chemistry and biology as consequence of • microsopic quantum physics? (Do physical facts fix all facts?); • Or is quantum physics actually not needed to understand life? Perhaps all we need are the laws of thermodynamics; • Quantum phenomena might simply be used because they are there at some level • Are we able to create states that are useful for information processing but don’t exist naturally?

3. Quantum macroscopicity Which states are macroscopic and maximally quantum? |GHZ>=|0000>+|1111> (aka “cat” states) versus |W>=|00..1>+|0..10>+|01...0>+|10…0> (aka “fluffy bunny” states) T. Farrow and V.V., arXiv:1406.0659, to appear in Optic. Comm.

4. Noise • GHZ states sensitive to noise, but best at phase estimation (such as in magneto-reception); • W states not sensitive to noise, appear in energy transport. V.V. Nature Physics (2014)

5. GHZ vs W • W is more entangled in the sense that there are more terms in the superposition and it is more difficult to mimic with classical correlations. • However, GHZ requires measurements of all qubits to reveal its entanglement (because the phase cannot be inferred from the reduced states), while W can already be seen at the level of two qubits.

6. QUANTUM BIOLOGY • Where to look for quantum coherence? • Phenomena driven by small number of particles • Limited degrees of freedom • Many open questions • Are effects genuinely quantum? • Can we measure them experimentally? • Do they play a role in biological function? • Discuss two types of phenomena – transport and metrology

7. Dynamics: Timescales • Four different timescales in biology: • Optical excitations (and some phonons): fs • Coherent energy transfer: ps • Chemistry: nano and microseconds • Biology: ms - seconds Given the size of biomolecules (10000 atoms +), nanometer distances, and room temperatures, expect quantum coherence only in 1 and 2. (In other words, 3 and 4 might be fine with classical.)

8. Transport: e. g. Electron transfer in biology -RCI Left:. L. A. Sazanov, Biochemistry, 46, 2275 (2007). Right: J. Hirst, Biochem. J., 425, 327 (2010).

9. Holstein Hamiltonian Low temperature: Dorner et al, PRE 2012; Farrow and V.V., to appear in scientific reports

10. Marcus theory – High Temperature

11. Experiments • Vibronic coupling strength from DFT simulations of inner sphere reorganisation energy2: g = 10 – 30 THz • Vibronic frequencies from NRVS, resonance Raman spectroscopy and DFT2: ω = 5 - 10 THz • Tunnelling rates fitted from DFT simulations of in situ electron tunnelling within RC-I1: t = 1 - 10 GHz 1. T. Hayashi and A. A. Stuchebrukhov, PNAS 45, 19157 (2010). 2. D. Mitra et al, Biochem.US. 50, 5220 (2011)

12. Inject single exciton into a single PDA chain (Pump condition: low power (<20uW CW) => Proba photoexcitation <1) Overlap lightfrom 2 spatiallydistinctregionof a singlepolymerchainincrystal

13. t=90ps T=10K Low disorder=> no inhomogenousbroad Frequency invariant=> Regularconfinenementpot'l=>1D q.wire Ultrafast spatial extention of state over length of chain - conventional (diffusive or ballistic) transport don't account for it Single stationaryq. statewithdelocalisedCoM Dephasingis alsostationary(dependsonopticalpath lengthonly)

14. Gethighcontrastfringes Limitedonlyby chainlength(20um)

15. Metrology: e.g. Bird migration (Taken from www.pandemic360.com) R. & W. Wiltschko:Magnetic compass of European robins, Science, 176 (4030): 62-64, 1972

16. Bird metrology • Not exploiting the quantum advantage of GHZ states • All to do with the phase oscillation between |01> and |10> • states of two electrons, which is effectively a single qubit • effect. • The phase depends on the inclination of the Earth’s • Magnetic field which is what the bird detects, but • entanglement is not crucial. Gauger el al, PRL (2012).

17. The Colloid and the Crystal (Joseph Wood Krutch) No wonder that enthusiastic biologists in the nineteenth century, anxious to conclude that there was no qualitative difference between life and chemical processes, tried to believe that the crystal furnished the link, that its growth was actually the same as the growth of a living organism. But excusable though the fancy was, no one, I think, believes anything of the sort today. Protoplasm is a colloid and the colloids are fundamentally different from the crystalline substances. Instead of crystallizing they jell, and life in its simplest known form is a shapeless blob of rebellious jelly rather than a crystal eternally obeying the most ancient law.