1 1 La lumière in vivo Igor Dotsenko Chaire de physique quantique, Collège de France Journée de l'Institut de Biologie du Collège de France Paris, 24 novembre 2009 TexPoint fonts used in EMF. Read the TexPoint manual before you delete this box.: AAAA

Journée de l'Institut de Biologie, 24/11/092 Light for exploring the nature Science: From studies of biological cells to distant galaxies the light is the fist tool to start with. Everyday life: Most information on our environment we obtain through light (about 80%).

Journée de l'Institut de Biologie, 24/11/093 Object of investigation For many centuries, light itself was an object of interest and investigation for scientists. I. Newton, light dispersion T. Young, light interference H. Fizeau and L. Foucault, speed of light Classical properties: electromagnetic wave with speed c, frequency, wavelength, etc.

Journée de l'Institut de Biologie, 24/11/094 The story of light is not over: Light is still very intriguing and fascinating object to explore !!! The story of light is not over: Light is still very intriguing and fascinating object to explore !!! Photon - intrinsically "quantum" state of light Non-classical, quantized photon-number states like: |exactly n photons  The smallest bit of light with unit energy and momentum: Quantum superposition allows more "exotic" states like ( |exactly n photons  + |exactly k photons  ) No way to illustrate and understand such superposition states with classical intuition ! or like: ( |all photons fly left  + |all photons fly right  )

Journée de l'Institut de Biologie, 24/11/095 Catching a photon Several ways to tackle the question "How things work?" 1. observe and wonder 3. catch and have a closer look ! 2. disturb and follow

Journée de l'Institut de Biologie, 24/11/096 Catching a photon Fabry-Perot resonator mirror Requirements: perfect reflection off the mirrors !!! (no absorption, no transmission, no scattering)

Journée de l'Institut de Biologie, 24/11/097 Microwave superconducting cavity: Storage box for photons 5 cm - a light travel distance of km (one full turn around the Earth) -1.4 billion bounces off the mirrors 2.8 cm T light = 130 ms

Journée de l'Institut de Biologie, 24/11/098 Study light in vivo ? But, (usually) to see or explore light means to absorb it, e.g. by an eye retina or a CCD chip! Can we use a transparent (like glass) probe? Yes, use giant (Rydberg) atoms flying one-by-one across the field. 1/4  m

Journée de l'Institut de Biologie, 24/11/099 Rydberg atoms Rydberg states: uniform electron distribution (i.e. no phase information) (n+1) /2 = 2  r n /2 = 2  r number of oscillations (principle quantum number) Superposition of two orbits: induced dipole rotates at atomic frequency  atom Information on  atom is encoded in the dipole phase  Information on  atom is encoded in the dipole phase 

Journée de l'Institut de Biologie, 24/11/0910 Off-resonant interaction light atom è Energy conservation  the field is preserved  Atom-field interaction modifies  atom proportional to n è Phase shift of the atomic dipole (relative to free atom) Phase shift per photon (depends on interaction strength)

Journée de l'Institut de Biologie, 24/11/0911 Phase measurement: Atomic clock 1. Trigger of the atom clock: resonant pulse no photons 1 photon Atomic state (e/g) is correlated with number of photons (1/0)  2. Dephasing of the clock: interaction with the cavity field 3. Measurement of the clock: second pulse & state detection Phase shift per photon adjusted to   

Journée de l'Institut de Biologie, 24/11/0912 Birth, life and death of a photon time [s] atoms photon number

Journée de l'Institut de Biologie, 24/11/0913 Birth, life and death of a photon "Warm" cavity excites a thermal photon (black body radiation): time [s] atoms photon number (i.e. 5% of time there is one photon; from Planck's law)

Journée de l'Institut de Biologie, 24/11/0914 Larger number of photons Dephasing per photon  0 <  for instance,  0 =  Distinguish up to 7 photons n = 0 n = 1 n = 2 n = 3 n = 4 n = 5 n = 6 n = 7 with probability depending on  (n) Measure dipole orientation with many (~50) atoms

Journée de l'Institut de Biologie, 24/11/0915 Seeing quantum jumps of light Repeatability of QND measurement Random projection onto one of n values Quantum jumps between discrete values of n: damping of the field caught in the act Photon number, n Quantum non-demolition measurement: Light in vivo Initial state is classical electro-magnetic field injected from a usual microwave source (number of photons is not defined !)

Journée de l'Institut de Biologie, 24/11/0916 Perspectives: Non-local light Cavity 1 Cavity 2 Study non-local states, e.g.: |all photons in Cavity 1, not in 2  + |all photons in Cavity 2, not in 1  What are their properties? Why not observed in our classical "macroscopic" world? Where is the transition from quantum to classical?

Journée de l'Institut de Biologie, 24/11/0917 The cavity QED team Julien Bernu (→ Canberra) Christine Guerlin (→ Zurich) Samuel Deléglise (→ Munchen) Clément Sayrin Xingxing Zhou Bruno Peaudecerf Michel Brune Jean-Michel Raimond Serge Haroche Igor Dotsenko Sébastien Gleyzes