Ground state cooling via Sideband cooling. Fabian Flassig TUM June 26th, 2013

Transcription

1 Ground state cooling via Sideband cooling Fabian Flassig TUM June 26th, 2013

2 Motivation Gain ultimate control over all relevant degrees of freedom Necessary for constant atomic transition frequencies Do many fancy experiments!!! Entangled states of trapped atomic ions, R. Blatt, D. Wineland, Nature 453 (2008) State manipulation of single atoms in an optical cavity, M. Uphoff

3 Context Sideband cooling Raman sideband cooling Temperature Lamb-Dicke regime Ion vs. Atom trapping Cooling of single 87Rb atom to ground state Outlook

4 Sideband cooling

5 Free atom in space

6 Captured in a trap

7 Cooling the atom

8 Quantized states of motion

9 For every excitation level

10 Resonant optical excitation

11 Detuned optical excitation Resonance freqency Resolved-sideband cooling of a micromechanical oscillator, A. Schliesser et al., Nature Physics 4, (2008)

12 Red shifted optical excitation

13 Rabi oscillations Oscillation between ground and excited state Without pumping no cooling effect Quantum computing with trapped ions, H. Häffner et al., Physics Reports 469, 4 (2008)

14 Pump to fast-decaying higher level

15 In sum =

16 Raman sideband cooling

17 Raman process Transition between two states via virtual excited state using two laser beams

18 Why use Raman process? Raman allows sub-natural line width resolution of sidebands (due to long-lasting ground states) => Allows addressing sidebands individually Resolved-sideband cooling of a micromechanical oscillator, A. Schliesser et al., Nature Physics 4, (2008)

19 Raman sideband cooling

20 Transfer atom via Raman

21 Pump atom back

22 Temperature

23 Heating effects Cooling rate limited by Lamb-Dicke factor Heating caused by: Trap laser phase instabilities Raman lasers causing excitations Lowest temperature: heating rate = cooling rate

24 How to determine temperature? -1) is given by: ( Ω) =Γ 2( Ω) + Γ Γ is decay rate of state is Lamb-Dicke factor Ω is Rabi frequency Mean occupation state is: = Quantum dynamics of single trapped ions, Leibfried, D., et al., Reviews of Modern Physics 75.1, 281 (2003)

25 How to determine temperature? < Extreme cases: =0 =0 = = = =0 P = Resolved-sideband cooling of a micromechanical oscillator, A. Schliesser et al., Nature Physics 4, (2008)

26 Lamb-Dicke regime

27 Lamb-Dicke regime Lamb-Dicke factor gives probability of photon recoil energy leading to an increase in state of motion = with being recoil frequency Confinement of atom to 15nm to achieve 0.1

28 Low Lamb-Dicke factor

29 High Lamb-Dicke factor

30 Ion vs. Atom trapping

31 Trap For ions: Traps providing a quadratic potential, e.g. Paul trap For atoms: dipole traps and MOTs are used

32 Ion vs. Atom Basically no difference for cooling process To reach Lamb-Dicke regime for atoms high laser power is necessary Plus high stability for trap

33 Cooling of single 87Rb atom to ground state Ground-state cooling of a single atom at the center of an optical cavity Andreas Reiserer, Christian Nölleke, Stephan Ritter, and Gerhard Rempe Phys. Rev. Lett. 110, (2013)

34 Aim of experiment Cool a single 87Rb atom to ground state of motion Using a dipole trap and Raman sideband cooling

35 Preprocedure Capture 87Rb atoms in MOT Transfer them to a dipole trap Precool via laser cooling Via imaging select a single atom and bring it to the center of the trap Bring atom to F=1 state Do the actual cooling process

36 87Rb

37 87Rb

38 Cooling process Apply Raman beams for 5ms for all three sideband frequencies (corresponding to dimensions of trap) Apply repump pulse for 10ns every 200ns to repump atom to F=1 state Needs to be pulsed due to Rabi oscillations Quantum computing with trapped ions, H. Häffner et al., Physics Reports 469, 4 (2008)

39 Experiments with atoms = (89±2)% of atoms in 3D ground state of motion

40 Outlook

41 Schrödinger Cat state

42 Ion lattices and quantum gates Entangled states of trapped atomic ions, R. Blatt, D. Wineland, Nature 453 (2008)

43 Some bigger stuff For single atoms, successful sideband cooling is relatively new Cool whole mechanical parts? Sideband cooling of micromechanical motion to the quantum ground state, J. D. Teufel et al., Nature 475 (2011)

44 Thank you Especially to M. Uphoff! And to you for your attention!