Ground state coolingvia

Sideband cooling

Fabian FlassigTUM

June 26th, 2013

Motivation

• Gain ultimate control over all relevant degreesof freedom

• Necessary for constant atomic transitionfrequencies

• 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

Context

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

Sideband cooling

Free atom in space

Captured in a trap

Cooling the atom

Quantized states of motion

| ⟩

For every excitation level

| ⟩

| ⟩| ⟩

Resonant optical excitation

| ⟩

| ⟩| ⟩

Detuned optical excitation

Resolved-sideband cooling of a micromechanical oscillator, A. Schliesser et al., Nature Physics 4, 415 - 419 (2008)

| ⟩

| ⟩ Resonance freqency

Red shifted optical excitation

| ⟩

| ⟩| ⟩

Rabi oscillations

Quantum computing with trapped ions, H. Häffner et al., Physics Reports 469, 4 (2008)

• Oscillation between ground and excited state• Without pumping no cooling effect

Pump to fast-decaying higher level

| ⟩

| ⟩| ⟩

In sum

| ⟩| ⟩

| ⟩ =

| ⟩| ⟩

| ⟩

Raman sideband cooling

Raman process

• Transition between two states via virtualexcited state using two laser beams

http://en.wikipedia.org/wiki/Raman_cooling

Why use Raman process?

• Raman allows sub-natural line widthresolution of sidebands (due to long-lastingground states)=> Allows addressing sidebands individually

Resolved-sideband cooling of a micromechanical oscillator, A. Schliesser et al., Nature Physics 4, 415 - 419 (2008)

Raman sideband cooling

| ⟩| ⟩

| ⟩

Transfer atom via Raman

| ⟩| ⟩

| ⟩

Pump atom back

| ⟩| ⟩

| ⟩

Temperature

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

How to determine temperature?

Quantum dynamics of single trapped ions, Leibfried, D., et al., Reviews of Modern Physics 75.1, 281 (2003)

• -1) is given by:= Γ ( Ω)2( Ω) + Γ• Γ is decay rate of state• is Lamb-Dicke factor• Ω is Rabi frequency• Mean occupation state is:= −

How to determine temperature?

Resolved-sideband cooling of a micromechanical oscillator, A. Schliesser et al., Nature Physics 4, 415 - 419 (2008)

= −• <• Extreme cases:

– = 0→ = 0→ = 0

– = → = ∞→ = ∞

P

Lamb-Dicke regime

Lamb-Dicke regime

• Lamb-Dicke factor gives probability ofphoton recoil energy leading to an increase instate of motion

• = with being recoil frequency

• Confinement of atom to ≤ 15nm to achieve≤ 0.1

Low Lamb-Dicke factor

High Lamb-Dicke factor

Ion vs. Atom trapping

Trap

• For ions: Traps providing a quadratic potential,e.g. Paul trap

• For atoms: dipole traps and MOTs are used

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

Cooling of single 87Rb atom toground state

Ground-state cooling of a single atom at the center of an optical cavityAndreas Reiserer, Christian Nölleke, Stephan Ritter, and Gerhard Rempe

Phys. Rev. Lett. 110, 223003 (2013)

Aim of experiment

• Cool a single 87Rb atom to ground state ofmotion– Using a dipole trap and Raman sideband cooling

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

87Rb

87Rb

• Apply Raman beams for 5ms for all threesideband frequencies (corresponding todimensions of trap)

• Apply repump pulse for 10ns every 200ns torepump atom to F=1 state– Needs to be pulsed due to Rabi oscillations

Cooling process

Quantum computing with trapped ions, H. Häffner et al., Physics Reports 469, 4 (2008)

Experiments with atoms

• (89±2)% of atoms in 3D ground state of motion

= −

Outlook

Schrödinger Cat state

Ion lattices and quantum gates

Entangled states of trapped atomic ions, R. Blatt, D. Wineland, Nature 453 (2008)

Some bigger stuff

• For single atoms, successful sideband coolingis relatively new

• Cool whole mechanical parts?

Sideband cooling of micromechanical motion to the quantum ground state, J. D. Teufel et al., Nature 475 (2011)

Thank you

• Especially to M. Uphoff!• And to you for your attention!