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Photonic Quantum Interface for Trapped Ion Quantum Computers

This workshop discusses the advantages of trapped ion systems for quantum computing, including high fidelity operation and the use of photons to entangle ions. It also explores the potential for quantum repeaters and scalable modular quantum computers. Fiber coupling using high NA optics is discussed as an efficient optical interface.

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Photonic Quantum Interface for Trapped Ion Quantum Computers

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  1. Photonic Quantum Interfacefor Trapped Ion Quantum Computers Jungsang Kim1,4, Christopher Monroe2,4, Peter Maunz3 1Department of ECE, Physics and CS, Duke University 2Department of Physics, JQI, University of Maryland and NIST 3Sandia National Laboratories 4ionQ, Inc. Quantum Transduction Workshop Pasadena, CA, September 20th, 2018

  2. Advantages of Trapped Ion Systems • “Best” Qubits and High Fidelity Operation • 1–1,000 sec coherence times routine in hyperfine qubits • State preparation and measurement (SPAM) errors in the 10-3–10-4 range (<10-5 possible) • Single-qubit gate errors in the 10-4–10-6 range • Two-qubit gate errors in the 10-3 range (<10-5 possible) • Introduction of New Technologies P. T. H. Fisk et al., IEEE T. Ultrason. Ferr. 44, 344 (1997) C. Langer et al., PRL 95, 060502 (2005) S. Olmschenk et al., PRA 76, 052314 (2007) A. H. Myerson et al., PRL 100, 200502 (2008) R. Noek et al., Opt. Lett. 38, 4735 (2013) J. Benhelm et al, Nature Phys. 4 463 (2008) K. Brown et al, PRA 84 030303 (2011) T. Harty et al, PRL 113 220501 (2014) C. Ballance et al, arXiv:1512.04600 (2015) J. Gaebler et al, arXiv:1604.00032 (2016) R. Blume-Kohout et al, arXiv:1605.07674 (2016)

  3. Entangling Ions using Photons • Remote Entanglement Generation • Entanglement of internal atomic state and photon (e.g., color) • From a pair of such systems, interfere the photons • Based on measurement, entanglement is generated probabilistically between ions through entanglement swapping • Use the entanglement for logic operation 171Yb+ Ion-Photon (2004) NV-Photon (2010) QD-Photon (2012) Ion-Ion (2007) NV-NV (2013) Duan et al., Quant. Inf. Comput. 4, 165 (2004) Experiments from C. Monroe group Gottesman and Chuang, Nature 402, 390 (1999)

  4. Quantum Repeater Platform • Quantum Repeater for Long-Distance Quantum Communication • Small quantum computer with two optical ports function as a quantum repeater Entangled!! Entangled!! Entangled!! Monroe and Kim, Science 339, 1164 (2013)

  5. Scalable Modular Quantum Computer • Quantum Computation in Small Quantum Registers (e.g., ions) • Linear ion chain with 20-100 ions (Elementary Logic Unit, or ELU) • Arbitrary quantum logic operation among the qubits in the chain • Interconnect of Multiple Such Registers via Photonic Channel • Reconfigurable interconnect using optical crossconnect (OXC) switches • Efficient optical interface for remote entanglement generation Up to N ~ 1,000 ELUs in a QC Up tomNqubits in a QC Monroe, Duan, Kim (2009) Monroe and Kim, Science 339, 1164 (2013) m ~ 10-100 qubits / ELU

  6. General Purpose Quantum Computer (UMD) High NA objective Individual Beams Global Beam 355nm Raman beams Dk 355nm pulsed laser • 5-segment linear Paul trap • High NA objective (0.37) • Tightly focused Raman beams • 32ch AOM and PMT for indiv. addressing/detection Diffractive optic (х10) Harris Corp 32channel AOM • 2μm pixels S. Debnath et al., Nature 536, 63 (2016)

  7. All Possible 5-Qubit CNOT Gates CNOT [1:2] F=96.4(6)% CNOT [1:5] F=97.9(5)% CNOT [1:3] F=97.6(7)% CNOT [1:4] F=95.9(7)% CNOT [2:3] F=95.6(6)% CNOT [2:4] F=98.4(7)% CNOT [2:5] F=96.8(7)% SPAM errors reduce all fidelities by ~2% CNOT [3:5] F=97.6(6)% CNOT [4:5] F=97.2(5)% CNOT [3:4] F=96.6(5)% 1 0.8 0.6 0.4 0.2 0

  8. Suites of Algorithms Execution in the System

  9. Remote Entanglement Generation via Photons Heralded coincident events (psuc=1/4): (H1 & V2) or (V1 & H2) → |↓↑ - |↓↑ (H1 & V1) or (V2 & H2) → |↓↑ + |↓↑ (H1 & H1) or (H2 & H2) → |↓↓ (V1 & V1) or (V2 & V2) → |↑↑ V2 H2 H1 V1 50/50 BS l/4 l/4 optical fiber G : Repetition Rate hD: Detector Efficiency dW: Collection Solid Angle F: Fiber Collection Efficiency 171Yb+ ion 171Yb+ ion Simon & Irvine, PRL 91, 110405 (2003) L.-M. Duan, et. al., QIC 4, 165 (2004) Y. L. Lim, et al., PRL 95, 030505 (2005) D. Moehring et al., Nature 449, 68 (2007)

  10. Current Status on Entanglement Generation 50/50 PBS 50/50 PBS Heralded coincident events (psuc=1/2): (H1 & V2) or (V1 & H2) → |↓↑ - |↓↑ (H1 & V1) or (V2 & H2) → |↓↑ + |↓↑ (H1 & H1) or (H2 & H2) → |↓↓ (V1 & V1) or (V2 & V2) → |↑↑ Heralded coincident events (psuc=1/4): (H1 & V2) or (V1 & H2) → |↓↑ - |↓↑ (H1 & V1) or (V2 & H2) → |↓↑ + |↓↑ (H1 & H1) or (H2 & H2) → |↓↓ (V1 & V1) or (V2 & V2) → |↑↑ V2 V1 H2 H1 50/50 BS l/4 l/4 optical fiber G 171Yb+ ion 171Yb+ ion NA 0.6 Lens Simon & Irvine, PRL 91, 110405 (2003) L.-M. Duan, et. al., QIC 4, 165 (2004) Y. L. Lim, et al., PRL 95, 030505 (2005) D. Moehring et al., Nature 449, 68 (2007) Hucul et al, (UMD) Nature Phys. 11, 37 (2015) Kim, Maunz & Kim, PRA 84, 063423 (2011)

  11. Fiber Coupling using High NA Optics ion #1 ion #2 D. Hucul, et al., Nature Physics 11, 37 (2015) success prob. per ion solid angle trial rate Airy Radius 135mm (Diffraction Limit) Waist in x: 176mm Waist in y: 217mm After gross correction After fine correction J. Wong-Campos et al., Nat. Phot. (2016)

  12. Cavity Integrated Trap at Duke Planar-concave cavity • Small waist, modest length leads to good coupling • while lowering requirements for the mirror coatings • Alignment is critical, mirror needs to be positioned to better than 1mm in all directions • ≥70% collection efficiency expected in a practical system Lcavity = 300 mm g = 60 MHz Zion = 50mm k = 160 MHz Wion= 4mm gYb=10 MHz ~300mm

  13. Ideal Communicator Qubit: 133Ba+ • Pros • Nuclear spin ½ - simple hyperfine structure • Favorable wavelengths: 493nm and 650nm • Cons • Does not exist naturally in nature • Radioactive element • Solutions • ½ - life is ~11 years (very stable) • Commercially produced for medical applications • Progress in UCLA team (Hucul, Campbell & Hudson)

  14. pump / signal combiner #1 Fully Integrated Wavelength Conversion DFG QPM 2.2 um / 650 nm U-bend for 923 nm 1595 nm output DFG QPM 2.2 um / 923 nm pump / signal combiner #2 • Two-step conversion to eliminate spontaneous parametric down-conversion (SPDC) and Stokes-Raman noise • Fully integrated device to convert 650nm photon to 1595nm Double-pass configuration w/ integrated U-bend & WDMs

  15. Fully Integrated Wavelength Conversion • Two-step conversion to eliminate spontaneous parametric down-conversion (SPDC) and Stokes-Raman noise • Fully integrated device to convert 650nm photon to 1595nm DFG-A 650 nm → 923 nm DFG-B 923 nm → 1595 nm 99% 99% Both processes can be driven to near unity conversion Both processes operate at identical pump wavelength and temperature

  16. Conclusions • Trapped ion is a compelling platform for realizing quantum repeaters & networked quantum computers • Good memory-photon interface • “Full blown” quantum computer with deterministic gate operations is available • Performance enhancement efforts are on the way • Demonstration of “useful” quantum repeater remains a challenge, yet within reach!! • Overall system efficiencies need dramatic improvements • Necessary technologies are under development • System integration will require substantial effort

  17. Team and Collaboration • Duke Team • Peter Maunz • Taehyun Kim • So-Young Baek • Kai Hudek • Rachel Noek • Emily Mount • Daniel Gaultney • Stephen Crain • Caleb Knoernschild • Andre van Rynbach • Geert Vrijsen • YuhiAikyo • Clinton Cahall • Chao Fang • Robert “Tripp” Spivey • George Schwartz • Sarah Brandsen • Seo Ho Youn • Jinhyun Cho • Kyle McKay • Hui Son • Ryan Clark • Muhammed Ahsan • John Montoya • University of Maryland • Chris Monroe • Jonathan Mizrahi • Marko Cetina • Jason Amini • Norbert Linke • Ken Wright • Shantanu Debnath • Kale Johnson • David Wong-Campos • David Hucul • VolkanInlek • Aaron Lee • Stanford University • Martin Fejer • Carsten Langrock • VahidEsfandyarpour • Sandia National Labs • Peter Maunz • Christian Arrington • Drew Hollowell • NIST • Sae Woo Nam • Varun Verma • University of Waterloo • Norbert Lütkenhaus • David Luong • Ryo Namiki • Filippo Miato • JPL • Matthew Shaw • Francesco Marsili • Emma Wollman • Yale University • Liang Jiang • SreMuralidharan • Linshu Li

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