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