Quantum jumps of light: birth and death of a photon in a cavity

Transcription

1 QCCC Workshop Aschau, 27 Oct 27 Quantum jumps of light: birth and death of a photon in a cavity Stefan Kuhr Johannes-Gutenberg Universität Mainz S. Gleyzes, C. Guerlin, J. Bernu, S. Deléglise, U. Hoff, M. Brune, J. M. Raimond, S. Haroche Laboratoire Kastler Brossel École Normale Supérieure, Paris Durch wiederholte Messungen an einem QS ist es uns Lebensgeschichte eines Photons in einer Cavity zu beobachten. Die Experimente habe ich durchgeführt in der Gruppe von Serge Haroche an der ENS in Paris, 1

2 Quantum Jumps Fluorescence of a Ba + -Ion: Ion jumps into and out of a metastable state Quantum jumps! Dehmelt, Toschek (1986) electromagnetic field observe? massive particles Can one observe quantum jumps of non-massive particles? 2 Quantensprünge stellen einenen fundamentalen quantenmechanischen Effekt dar. Dieser Effekt, dass ein mikroskopisches System zufällig von einem Quantenzustand in den anderen springen kann, wurde zuerst An einzelnen gespeicherten Ionen beobachtet. Das Ion konnen von einem erlaubten Übergang, wo es Fluoreszenzlicht aussendet, in einen metastabilen Zustand springen und dort wieder in den ursprünglichen Zustand. Diese Quqntensprünge manifestierten sich als ein abruptes Aufhören und Wiederaufleben des Fluoreszenzsignals. also: molecules, electrons 2

3 Quantum jumps of light? Difficulties: - Storage of one photon? - Seeing a photon without destroying it? superconducting microwave cavity Rydberg atom Atom g QND e g if 1 photon if photons (= CNOT gate) T c > 1 ms Several hundreds of atoms can interact with the same photon 3 Massive particles very difficult experiments - isolation and trapping of a single particle Ü: Wie könne wir das tun? 3

4 Outline Experimental setup QND measurement of a field in a cavity: Life and death of a photon Photon cascade Perspectives 4 4

5 Experimental setup Rydberg atoms Microwave cavity 5 5

6 Circular Rydberg atoms 85 Rb n = GHz n = 5 g e n big, l = m = n -1 lifetime: 3 ms huge dipole two-level system small dissipation large atom-field coupling But: very complicated preparation needs electric field E open cavity 6 6

7 Microwave cavity Fabry-Pérot cavity 28 mm TEM 51,1 GHz 5 mm Niobium mirrors (superconducting) Very small surface resistance Small dissipation Small mode volume (some λ 3 ) Increases coupling 7 7

8 The cavity atoms piezos 5 cm 8 8

9 Temps de vie Damping time: T c =.13 K!!! (previously: T c =.1 s) quality factor: Q = ω T c = finesse: F = One photon bounces 1.1 billion times (3 km) 415 ms 3 times around the earth Enough time to send > 1 atoms across the cavity 9 9

10 circularization box ² Ramsey zones 5 cm Detectors atoms Shielding box (thermal field, B field) Cavities 1 1

11 11 11

12 ² atoms Too far from resonance 12 12

13 2. QND measurement of a cavity field: Observing birth, life and death of a photon 13 13

14 Dispersive Interaction e g δ ω cav e g π 2 2 Ω Δ Ee= ( n+ 1) 4δ π 2 2 Ω ΔEg = n 4δ Dephasing between e and g : ( e g ) + iδφ( ) ( e e n g ) n + n ( e Δ g) ΔΦ ( n) = ΔE - E dt = velocity Ω 2 t ( n +1 /2 ) 2δ light shift Lamb shift 14 14

15 Detecting a single photon by Ramsey interferometry g π 2 e: 1 photon π 2 g: photon 1. P g π Operation point Empty.8 cavity 2 Cavity with 1 photon Transfer phase Ω t ΔΦ ( n) = ( n+1/2) 2δ = π 15 15

16 Repeated measurement of a thermal field Thermal field at.8 K R1 R2 position R2 π/2 π/2 1 probe atom pulses π/2 π/2 π/2 π/2 π/2 cavity R1 π/2 π/2 π/2 π/2 π/2 π/2 π/2 π/2 7 µs time 16 16

17 Birth and death of a photon e g 1,,5 1, 1,5 2, 2,5 time (s) S. Gleyzes, S. Kuhr et al., Nature 446, 297 (27) 17 17

18 Birth and death of a photon e,9,95 1, 1,5 1,1 1,15 1,2 g e g 1,,5 1, 1,5 2, 2,5 time (s) S. Gleyzes, S. Kuhr et al., Nature 446, 297 (27) 18 18

19 Birth and death of a photon e g 1,,5 1, 1,5 2, 2,5 time (s) S. Gleyzes, S. Kuhr et al., Nature 446, 297 (27) 19 19

20 Birth and death of a photon 1..8 Transfer.6.4 contrast.2. e g 1 Majority vote of 8 atoms,,5 1, 1,5 2, 2,5 time (s) S. Gleyzes, S. Kuhr et al., Nature 446, 297 (27) 2 2

21 Birth and death of other photons S. Gleyzes, S. Kuhr et al., Nature 446, 297 (27) 21 21

22 Measurement of a photon initially prepared in the cavity 22 22

23 Deposition of a photon in the cavity e g ω cav e, Ω g,1 P g 1..8 g,1.6 e,.4.2 Ω t = π produces a photon interaction time t (µs) 23 23

24 Observing a photon absorb the field sweeper atoms deposit a photon emitter atom field measurement 35 probe atom pulses position R2 π/2 π/2 π/2 π/2 π/2 π/2 π/2 cavity π R1 π/2 π/2 π/2 π/2 π/2 π/2 π/2 π/2 g g e g g g g g 7 µs time 24 24

25 Quantum jumps: : a single photon T =.8 K n th =.5 deposition of a photon photon number Nombre de photon Time (ms) time (ms) 25 25

26 Lifetime of n=1> 1 sequence : Time (s) 26 26

27 Lifetime of n=1> 5 sequences: Time (s) 27 27

28 Lifetime of n=1> 15 sequences: 1 damping time: 19(5) ms t cav = 13 ms!?

29 Lifetime of n=1> 94 sequences: 1 damping time: 19(5) ms t cav = 13 ms!? Time (s) 29 29

30 Lifetime of n=1> 94 sequences: n = 2 1 damping time: 19(5) ms t cav = 13 ms!? 2 n / t th cav n = 1 ( nth + 1)/tt 1/ cav cav Time (s) n th =.5 thermal photons T = T.8 = K n = We measure parity: impossible to distinguish between n= and n=2 n = 1 Lifetime of : t /(3n + 1) 13 ms cav th 3 3

31 Observing n = 2? 31 31

32 Measuring, 1 or 2 photons dephasing: π/2 per photon Pg photon 1 photon 2 photons [extrapolated] Phase (x π) 32 32

33 Measuring, 1 or 2 photons dephasing: π/2 per photon e photon number g time (ms) majority vote of 24 atoms 33 33

34 Seeing more photons? 34 34

35 Principle of QND counting A clock whose ticking rate is determined by the number of photons in a box Clock hand s position directly measures the photon number 35 35

36 Detecting n > 1 n e> g> π 2 π/2 pulse interaction with cavity field z n = y x 2 1 Φ = π

37 A step-by by-step acquisition of information Idea: 4 n = 4 n = 5 n = 6 n = 7 Change direction of spin detection to decimate different photon numbers 3 n = 3 2 n = 2 1 n = 1 n = Example: Detection along axis 4: optimal decimation between n= and n=

38 Information acquisition by detecting 1 atom 1. e P(n/e),2,1.2 P(n) photon number n.5. g P(n/g),,2, photon number n Repeating the measurement with other values of ϕ decimates other photon numbers, photon number n Probabilities P(n) that are incompatible with the measurement result are cancelled

39 Convergence of coherent state towards Fock state: wave function collapse in real time! Spin reading Direction Pn ( ) δ ( n n) Wave function collapse due to progressive acquisition of information Flat initial distribution Pn ( ) P( n) δ ( n n ) C. Guerlin et al., Nature (to be published) 39 This is real data, not a simulation! 39

40 Evolution of mean photon number n = n np( n) Repeated measurements confirm n=5 Projection of coherent state on n=5 Quantum jumps towards vacuum due to field decay in cavity 4 Here counting 5 photons 4

41 Reconstructing the photon number statistics n /2 e 2 Coherent field: n = 3.4 ±.8 α α α >= n > n n! 2 n α α pn ( ) = e n! 41 41

42 And even n = 8! Finally jumps to 7: it was not but 8! n = 8 n = Interferometer counts n modulo 8: does not distinguish and 8? c + c

43 Perspectives 43 43

44 Non-local Schrödinger cat + α, +, α A mesoscopic state delocalized in two boxes! Complete characterization and monitoring of decoherence T c = 13 ms violation of Bell s inequalities Teleportation of atomic quantum states from one cavity to the other 44 44

45 Conclusion Fabry-Pérot rot cavities: t c = 13 ms Quantum jumps of light Direct measurement of photon number number of photons time (ms) Two-cavity experiments within reach 45 45

46 The Team Sébastien Gleyzes Christine Guerlin Julien Bernu Samuel Deléglise Clément Sayrin Ulrich Hoff Stefan Kuhr Jean-Michel Raimond Michel Brune Serge Haroche Laboratoire Kastler Brossel École Normale Supérieure, Paris 46 46

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48 Ramsey zones - principle Constraints Spatially well-defined mode (addressing individual atoms) cavity with high Q Solution S «High Q» cavity (Q = 2) filter TEM mode Gold coated glass plate Avoid enhancement of spontaneous emission cavity with low Q Low Q cavity (Q = 2) Microwave absorber 48 48

49 Ramsey zones - principle Contraintes mode spatialement bien défini (adresser des atomes) cavité à grand Q éviter d augmenter l émission spontanée atoms cavité à faible Q Solution S «High Q» cavity (Q = 2) filter TEM mode Gold coated glass plate Low Q cavity (Q = 2) Microwave absorber 49 49