QuAMP Towards large scale quantum informa4on processing: Sta4c magne4c field gradient quantum gates and microfabricated ion traps

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1 QuAMP 2013 Towards large scale quantum informa4on processing: Sta4c magne4c field gradient quantum gates and microfabricated ion traps Kim Lake University of Sussex

2 Talk Outline Ion Trapping and Ytterbium 171 Use magnetic gradient induced coupling to produce..... motional coupling: The key requirement for quantum... gates. Reduce decoherence by 2 orders of magnitude using.... microwave dressed-states. The first 2-Dimensional ion trap array integrated on a.... microchip. Progress towards an operational homogeneous ring trap.

3 RF Paul Trap DC electrodes alone: Saddlepoint potential Ion lost DC and RF electrodes: Pondermotive potential ~10 µm Ion trapped

4 171 Yb + : Cooling 2 P 1/2 F=1 F=0 F=0 2 GHz F=1 935nm 3 D[3/2] 1/2 369nm F=2 1 GHz F=1 2 D 3/2 2 S 1/2 F= GHz F=0

5 171Yb+ Qubit F=0 2 GHz F=1 3 D[3/2] 1/2 2 P 1/2 F=1 F=0 935nm 369nm F=2 1 GHz F=1 2 D 3/2 2 S 1/2 F= GHz F=0 1> 0> Qubit subspace

6 Gate operations Ion-ion coupling achieved using state dependant force 1> 0> 0> 0> State dependant force on ions Coupling mediated via coulomb force State dependant force usually produced using laser beams

7 Gate operations The problems with lasers - Noise - Intensity - spatial - frequency - phase - Off resonant coupling - Individual addressing - Scalability Solution use microwaves with a static field gradient instead Mintert, F. & Wunderlich, C. Phys. Rev. Lett. 87, (2001)

8 Qubit subspace magnetic field sensitive states 0 > +1> 13 MHz F=1-1> 2 S 1/ GHz 0> F=0 Mintert, F. & Wunderlich, C. Phys. Rev. Lett. 87, (2001)

9 Motional coupling with a magnetic field gradient Magnetic field gradient shift in resultant trapping potential state dependent force Mintert, F. & Wunderlich, C. Phys. Rev. Lett. 87, (2001)

10 Creating a magnetic field gradient Four Samarium Cobalt permanent magnets

11 Creating a magnetic field gradient Gradient: 24 T/m

12 Individual addressing Ion 1 Magnetic field Ion 2-1> 0 > +1> -1> 0 > +1> Δf 0> 0> 5.9µm Ion 1 Ion 2 Δf

13 Resolving motional sidebands Motional quanta Blue sideband adds one motional quanta > Red sideband takes one motional quanta GHz Red sideband Blue sideband >

14 Resolving motional sidebands Red and blue motional sidebands = key requirement for entanglement gates M lmer and S rensen gate Apply red and blue sidebands together Coherent two qubit transition which puts the ions in an entangled state GHz Red sideband Blue sideband S rensen, A., M lmer, K., Phys. Rev. Lett. 82, 1971

15 Decoherece Probability in 1> Fluctuations in the magnetic field cause uncontrolled phase rotations Gives rise to fast decoherence Time (us) Coherence time of magnetic field sensitive transition ~ 200us

16 Microwave dressed states Solution = Use microwave dressed-states Microwave dressed-states: Superposition states between bare states and photons - 1> 0 > +1> 0 > d> D> 0> Eigenstates form new dressed state basis u> 2 *N. Timoney, I. Baumgart, M. Johanning, A. F. Varon, M. B. Plenio, A. Retzker, and C. Wunderlich, Nature 476, 185 (2011)

17 Microwave dressed states - 1> 0 > +1> d> 0 > D> 0> u> 2 Bare states mapped to dressed states using STIRAP pulses *N. Timoney, I. Baumgart, M. Johanning, A. F. Varon, M. B. Plenio, A. Retzker, and C. Wunderlich, Nature 476, 185 (2011)

18 Coherent manipulation within microwave dressed states Second order Zeeman shift 0 > +1> d> - 1> RF 0 > D> RF u> 0> 2 Add a single additional RF field to perform Rabi flopping between qubit states * S. C. Webster, S. Weidt, K. Lake, J. J. McLoughlin and W. K. Hensinger, arxiv: , accepted for publication into PRL (2013)

19 Coherent manipulation within microwave dressed states Coherence measurement within dressed- state Graph to show improved decoherence..? Time, t (ms) Coherence time ~500 ms * S. C. Webster, S. Weidt, K. Lake, J. J. McLoughlin and W. K. Hensinger, arxiv: , accepted for publication into PRL (2013)

20 Coherent manipulation within microwave dressed states Ramsey fringes Demonstrates ability to fully manipulate Bloch sphere within dressed state * S. C. Webster, S. Weidt, K. Lake, J. J. McLoughlin and W. K. Hensinger, arxiv: , accepted for publication into PRL (2013)

21 2-Dimensional ion trap lattice Uses - E/B-field sensing - Force sensing - Quantum simulations - Cluster state quantum computing - Protein sorting

22 2-Dimensional ion trap lattice 270.5um *R. C. Sterling, H. Rattanasonti, S. Weidt, K. Lake, P. Srinivasan, M. Kraft and W. K. Hensinger, arxiv: v4 (2013)

23 2-Dimensional ion trap lattice RF voltage: 455 V Trap depth:0.42 ev *R. C. Sterling, H. Rattanasonti, S. Weidt, K. Lake, P. Srinivasan, M. Kraft and W. K. Hensinger, arxiv: v4 (2013)

24 2-Dimensional ion trap lattice Deterministic introduction of defects *R. C. Sterling, H. Rattanasonti, S. Weidt, K. Lake, P. Srinivasan, M. Kraft and W. K. Hensinger, arxiv: v4 (2013)

25 2-Dimensional ion trap lattice Site to site shuttling *R. C. Sterling, H. Rattanasonti, S. Weidt, K. Lake, P. Srinivasan, M. Kraft and W. K. Hensinger, arxiv: v4 (2013)

2-Dimensional ion trap lattice Ultra-high breakdown

26 2-Dimensional ion trap lattice Ultra-high breakdown voltages Voltage breakdown occurs over insulator surface. her Use two SiO2 insulator layers together. instead of one layer. Increased etch rate along interface.... when exposing handle layer. Vdc = 1298(5) V Vrf = 1061(32) V Order of magnitude greater than previously achieved SiO2

27 2-Dimensional ion trap lattice Ultra-high breakdown voltages Voltage breakdown occurs over insulator surface. Use two SiO2 insulator layers together. instead of one layer. Increased etch rate along interface.... when exposing handle layer. Vdc = 1298(5) V Vrf = 1061(32) V Order of magnitude greater than previously achieved Applications - MEMS devices - Larger trap depths - Lower heating rates - Thrusters arrays - Protein sorting

28 Ring Trap Uses - Quantum simulations eg - Homogeneous Kibble-Zurek mechanism. - Space time crystals - Hawking s radiation - Inner segmented static..... electrodes - Buried static and rf wires - Periodic boundary conditions - No RF field mismatch Marcus Hughes (Sussex), Jessica Maclean (Nottingham), Seb Weidt (Sussex), Chris Mellor (Nottingham), Winfried Hensinger (Sussex)

29 Summary Realised magnetic gradient induced coupling. Reduced our decoherence by 2 orders of magnitude..... using microwave dressed-states. New method of dressed state coherent manipulation..... which allows for full manipulation of the Bloch sphere. Demonstrated first 2-Dimensional ion trap array on a.... microchip. Progress towards an operational homogeneous ring trap.

30 Head of Group: Dr. Winfried Hensinger The IQT Group Postdocs: Two ions Dr. Simon Webster Dr. Gouri Giri Research Assistants: Dr. Robin Sterling Dr. James Siverns Seb Weidt Dr. Marcus Hughes PhD Students: Kim Lake Darren De Motte Bjoern Lekitsch David Murgia Joe Randall Eamon Standing We gratefully acknowledge funding from

Experimental Quantum Computing: A technology overview

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