Progress Toward Trapping IonsJackie Liu, Liz Donoghue, Patrick Becker, and Steven Olmschenk

Denison University, Department of Physics and Astronomy, Granville, Ohio 43023

Abstract

AcknowledgmentsThis research is supported by the Army Research Office, Research Corporation for Science

Advancement, and Denison University. Additionally, L.D. acknowledges support from the Hodgson,

and J.L. acknowledges support from the Anderson Endowment.

References

[1] “A 750-mW, continuous-wave, solid-state laser source at 313 nm for cooling and

manipulating trapped 9Be+ ions,” A.C. Wilson, C. Ospelkaus, A.P. VanDevender, J.A.

Mlynek, K.R. Brown, D. Leibfried, D.J. Wineland, Applied Physics B. 105, 741 (2011)

[2] Adam V. Steele, Barium Ion Cavity QED and triply ionized Thorium ion trapping,

Georgia Institute of Technology, 2008.

Second Harmonic Generation

of 490nm Light Second-Harmonic Generation (SHG) is an optical phenomenon in which a light beam of

frequency ω passes through a non-linear crystal and is converted into a beam with a frequency of

2ω. Molecules within the non-linear crystal may absorb two photons of the same energy and

consequently emit a single photon with twice the energy of each incident photon, effectively

doubling the frequency of the input light.[1]

The maximum power of our laser diode (~300mW) is too low for any noticeable amount of

frequency doubling, and so we constructed a resonating cavity to amplify the effective input IR

power.

• Barium ions can be laser cooled with 490nm light because they absorb light at this

wavelength.

• Continuous wave 490nm (blue) laser diodes are very expensive, unreliable, and almost

nonexistent. 980nm (Infrared) laser diodes are much cheaper and more stable.

• It is cheaper and more practical to frequency double IR light to get 490nm light.

Dimensions:

M1 to M4=172mm;

M2 to M3=129mm;

M3 to crystal=29mm;

crystal to M4= 23mm;

M4 to M1=127mm;

M1

M4 Radius=5cm

M2

M3Radius=5cm490nm

output

980nm

input24°

BiBO

Power

Supply

Piezo

𝑆𝐻𝐺 𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 ∝ 𝐼𝑛𝑡𝑒𝑛𝑠𝑖𝑡𝑦 ∝1

𝐵𝑒𝑎𝑚𝑊𝑎𝑖𝑠𝑡

We achieved 74.43µW of 490nm light with 72mW of 980nm input

This group plans to trap and laser cool Lanthanum and Barium ions for use in Quantum

Information. To this effect, we present work towards creating a stable laser light source at 490nm

using Second Harmonic Generation to laser cool Barium ions, modelling the quadrupole ion trap

for containing the ions, and modelling and designing the imaging system to be used to extract

information from the trapped and cooled ions. Future goals involve utilizing these three

components as well as an ultra-high vacuum chamber to establish an isolated system of quantum

bits for investigations into quantum information and communication.

Cavity off resonance: very little SHG Cavity on resonance: significant SHG

• Out of the four longer rods, two of the rods have AC voltages and the other two

have DC voltages (labeled with different colors).

• In order to stabilize ions in the trap, we need to find the voltages that are stable

for the ions that we wish to trap and unstable for ions that we wish to eject.

• Computer simulations can be used to determine the appropriate voltages that

are stable for certain ions based on mass selection.

• The a and q factors are proportional to DC and AC voltages respectively.

• The relationship among β, a and q is:

• The boundaries for the stabilized region are created when β is equal to 0 and 1.

Within the equation, a geometric factor α determined by orientation of the trap

can be added.

• By fitting the boundaries with the experiment done by previous researchers, the

geometric factor is approximately 0.42. Based on this value, a graph is

generated to show the stabilization regions for both La2+ and La+.

• The shaded area is where the voltages are stable for La2+ and unstable for La+

since La2+ is what we want to trap. Approximately, the maximum DC voltage is

at 50V and the maximum AC voltage is 380V to trap La2+ while ejecting La+.

Ion Trap Simulation

*Ion trap image generated by CPO software

Imaging SystemThe imaging system allows us to ascertain if trapping and cooling have been successful.

Photons from the trapped ion are collected and mapped onto the pixels of an InGaAs camera

through a series of lenses.

• Photons are given off in all directions, so a lens needs to be close to the atom

• Need diffraction limited image

• The system must be able to resolve multiple ions

• Use multiple lenses to correct for aberrations in any individual lens

• Use OSLO to model potential lenses and see if these criteria are met

An Airy Pattern (left) forms from a

circular aperture. When more than

85% of the light is in the central

bright spot, or Airy disk, the image is

said to be diffraction limited. The

surface plot of intensity (right)

illustrates the same concept, with the

central peak corresponding to the

central bright spot.

The ray-trace diagram generated by OSLO, showing how rays of light pass through the various lenses in the system.

Figures retrieved from URL http://en.wikipedia.org/wiki/Airy_disk