Ion-trap quantum computation

Summer School of CQIQC 2012

Laser Lab

Prof. Vasant Natarajan

Department of PhysicsIndian Institute of Science

Bangalore

May 25, 2012

Paul trap – dynamic stabilization

Mathieu equation

Mechanical analogue of the stabilization – from Paul’s Nobel lecture

Mathieu stability plot

Spectrum from harmonically-oscillating particle

fm modulation with depth of modulation kx0

Tight confinement – Lamb-Dicke regime x0 << λ

Sideband cooling

Cooling laser tuned to lower motional sideband

, , , ,

| e >

| g>

4S1/2

3D3/2

850 nm

397 nm

866 nm

4P1/2

4P3/2

3D5/2

Ca+ energy levels

Cooling

Shelving

Repumping

Life time measurement

• Shelving technique by Dehmelt observation of quantum jumps to determine the lifetime

• Both lasers run continuously and we observe the fluorescence photons at a rate of a few kHZ.

• For a time in order of 1 s we apply a third laser at 4P3/2 –3D3/2 transition.

• By decay of 4P3/2 level the ion may fall into the metastable 3D5/2 state and the fluorescence vanishes.

• Repeat the process and determine the time intervals where no fluorescence is observed after blocking the shelving laser.

Life time measurement

Histogram of the dark periods for a single ion. The experimental data are fitted by an exponential

Linear Paul trap design

Each section length = 15mmRod diameter = 6 mmr0 = 2.66 mm For axial trapping additional DC field = 150 VRF between diagonal rods for radial trapping V0 = 100 Vω0 = 2 MHZUHV= 10-10 torr Ions get trapped in a linear chain on the axis of the trap

Photos of linear ion trap

Experimental requirements

• Need three lasers working simultaneously – Cooling (397), Repumping (866), and shelving (850)

• Use 397 nm fluorescence from hollow cathode lamp to lock cooling laser

• Mix all the beams in a hollow-core fiber and transport them to the experiment

• Use an ICCD Camera for detection

Experimental Schematic

4S1/2

3D3/2

850 nm

397 nm

866 nm

4P1/2

4P3/2

3D5/2

Ca+ energy levels

Cooling

Shelving

Repumping

Why Calcium

• Has a lambda level scheme with two lying metastable 3D states

• Ca+ has a closed shell plus a single valance electron.

• No outer correlation exist but core effects play an important role

• Electric field of the valence electron causes a core polarization leading to modified nuclear electric field seen by the outermost electron to explore new physics.

Advantages of trapped ions for quantum computation

• Near-perfect two level system formed of a ground level and a metastable excited level

• Decoupled from the environment and well isolated in vacuum for long storage times

• Internal states can be initialized and measured with extremely high accuracy

• Laser pulses can be used to manipulate electronic and motional degrees of the ion string

Acknowledgements

Workshop – Manohar, Sharief

Students – Ayan Banerjee, Dipankar Das, Dipankar Kaundilya, Lal Muanzuala, Durgesh Datar, Zeba Naqvi

Money – DST and CQIQC

Sideband Cooling