1. Cryogenic, near-field quantum logic
with passive field nulling on Ca43
Jochen Wolf
Ion Trap Group
University of Oxford
U.S. AROwww.physics.ox.ac.uk/users/iontrap

2. The goal:
error correction
Using surface code, from S.C.Benjamin & Y.Li

3. 43Ca+ intermediate-field
hyperfine qubit
• certain hyperfine transitions are
magnetic-field-independent at
particular fields
• all-diode laser system
• 3D5/2 level in Ca+ allows for high-
fidelity shelving readout
• 99.7(1)% two qubit gate fidelity
• 99.9999(1)% single qubit gate fidelity
• 𝑇2
∗
= 50 10 s
• 0.34(3)% SPAM error
T. P. Harty et al., arXiv:1606.08409v1
T. P. Harty et al., PRL 113, 220501 (2014)

4. My Contribution
• Design, building experiment
• Includes many, many small problems
• Initial study of electroplating
• Argon ion surface cleaning

5. Centre of vacuum system
Copper braid
Flow cryostat
Ceramic feet
Microwave lines
25 D-sub
DC feedthrough
CF100 flange
10 cm
Ion trap
Pillbox

6. Motional Heating
D. A. Hite et al., PRL 109, 103001 (2012)
D. A. Hite et al., MRS 38, 826 (2013)

7. Example problems
• Heat budget calculation
• Researching cryogenic thermal conductivit
• Weighing thermal vs electrical performance
• Microwave connector
• Commercial option not available
• Reverse engineer non-UHV connector
• Dissolve & replace plastics inside
• Is attenuation ok?
• Abandoned designs
• Small additional pump inside pillbox
• Use of alternative cooling system

8. Valves
Electrical connection
Readout optics
Trim coil pair
Main field coils
Ion pump
Flow cryostat
Overview of vacuum system
Ion gauge

9. After David Allcock 2015
Electroplating Setup
• Why electroplating?
• Lift-off procedure difficult at this thickness
• Good heating rates achievable
• Why custom?
• In-cleanroom needed
• Commercial baths big

10. Electroplating Setup

11. Electroplating Setup
Linear Actuator
Removable
Anode
Wafer/Cathode
Temperature
sensor

12. Electroplating Setup

13. 20 µm
Electroplating Setup
20 µm
20 µm

14. Argon Ion Cleaning
http://www.mi-net.co.uk/physical-vapour-deposition-PVD.php, accessed 27/09/16
D. A. Hite et al., PRL 109, 103001 (2012)
D. A. Hite et al., MRS 38, 826 (2013)

15. Argon Ion Cleaning
43 cm
Argon ion source
Argon ion gun
Leak valve
Current meter
feedthrough Ion trap

16. • Experimental design
• Electroplating WIP
• Argon ion cleaning ready
Summary

17. Laser Experiments
Microwave Experiments
Group Members
Prof. David Lucas
(Group Leader)
Prof. Andrew Steane
(Group Leader)
Prof. Derek Stacey
(Emeritus Professor)
Tom Harty
(Post Doc)
Martin Sepiol
(DPhil student)
Vera Schäfer
(DPhil student)
Jamie Tarlton
(PhD student)
Chris Ballance
(Post Doc)
Diana Aude Craik
(DPhil student)
Jochen Wolf
(DPhil student)
Laurent Stephenson
(DPhil student)
Keshav Thirumalai
(DPhil student)

19. Overview of vacuum system

20. Qubit operations
Need:
• Addressing
• Coupling to motion
Microwaves:
• Negligible motional coupling
• Hard to localise
(see poster 63: Diana Aude Craik)
• Otherwise perfect
Lasers:
• Photon scattering errors
• Noise, stability, phase control
• Scalability, integration with trap
• Strong motional coupling

21. Ion counter lid

22. Overview

23. Overview

24. Overview