Cryogenic, near-field quantum logic with passive field nulling on
Jochen WolfIon Trap Group
University of Oxford
U.S. AROwww.physics.ox.ac.uk/users/iontrap
The goal:error correction
Using surface code, from S.C.Benjamin & Y.Li
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• s• 0.34(3)% SPAM error
T. P. Harty et al., arXiv:1606.08409v1T. P. Harty et al., PRL 113, 220501 (2014)
My Contribution
• Design, building experiment• Includes many, many small problems
• Initial study of electroplating• Argon ion surface cleaning
Centre of vacuum system
Copper braid
Flow cryostat
Ceramic feet
Microwave lines
25 D-sub DC feedthrough
CF100 flange
10 cm
Ion trap
Pillbox
Motional Heating
D. A. Hite et al., PRL 109, 103001 (2012)D. A. Hite et al., MRS 38, 826 (2013)
Example problems
• Heat budget calculation• Researching cryogenic thermal conductivities• 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
Valves
Electrical connection
Readout optics
Trim coil pair
Main field coils
Ion pump
Flow cryostat
Overview of vacuum system
Ion gauge
91 cm
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
Electroplating Setup
Electroplating Setup
Linear Actuator
Removable Anode
Wafer/Cathode
Temperature sensor
Electroplating Setup
20 µm
Electroplating Setup
20 µm
20 µm
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)
Argon Ion Cleaning
43 cm
Argon ion source
Argon ion gun
Leak valve
Current meterfeedthrough Ion trap
• Experimental design
• Electroplating WIP
• Argon ion cleaning ready
Summary
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)
Overview of vacuum system
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
Ion counter lid
Overview
Overview
Overview
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