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Networking Problems in Using Quantum Repeaters Rodney Van Meter MAUI, 2009/4/16 rdv@sfc.wide.ad.jp

Networking Problems in Using Quantum Repeaters Rodney Van Meter MAUI, 2009/4/16 rdv@sfc.wide.ad.jp http://www.sfc.keio.ac.jp/~rdv/. Assume a Quantum Computer Like This. I want to Build a Distributed Quantum System Like This.

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Networking Problems in Using Quantum Repeaters Rodney Van Meter MAUI, 2009/4/16 rdv@sfc.wide.ad.jp

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  1. Networking Problems in Using Quantum Repeaters Rodney Van Meter MAUI, 2009/4/16 rdv@sfc.wide.ad.jp http://www.sfc.keio.ac.jp/~rdv/

  2. Assume a Quantum Computer Like This...

  3. I want to Build a Distributed Quantum System Like This Laboratory-sized quantum multicomputer or transcontinental network, either one!

  4. Repeater Protocol Stack } Application End-to-End Purification Control (PC)‏ } Repeated at Different Distances Entang. Swapping Ctl (ESC)‏ Purification Control (PC)‏ Entanglement Control (EC)‏ } Distance=1 Physical Entanglement (PE)‏ Only quantum! Van Meter et al., IEEE/ACM Trans. on Networking,Aug. 2009 (to appear), quant-ph:0705.4128

  5. Outline Two types of quantum networks IPsec with QKD IPsec with QKD US & European efforts Open problems & plans Repeaters Basic concepts Our recent results Open problems & plans

  6. Two Types of Quantum Networks UnentangledNetworks EntangledNetworks C G B A E H

  7. Quantum Key Distribution (QKD) Creates a shared, random secretbetween two nodes Uses physical effects to guarantee that key has not been observed Requires authenticated classical channel Limited to <150km per hop

  8. IPsec with QKD (ORF2008)‏

  9. The DARPA Quantum Network slide from Elliott, BBN

  10. SECOQC Prototype - principle layout 81 m FOR LMU Slide from M. Peev, 2008

  11. A Trusted repeater QKD-Network: Abstract Architecture (SECOQC, Europe) VPN-yellow Site 1 VPN-yellow Site 2 Data Plane VPN-green Site 1 QKD Access Node QKD Core Node Secrets Plane QKD Access Node QKD Core Node Quantum Plane Slide from M. Peev, 2008

  12. QKD with IPsec Plans Test over raw fiber, Yagami<->K2 Use key for one-time pad Work w/ NEC, BBN & ITU to standardize Write experimental I-D on IKE changes Take to IETF in Hiroshima?

  13. Outline Two types of quantum networks IPsec with QKD IPsec with QKD US & European efforts Open problems & plans Repeaters Basic concepts Our recent results Open problems & plans C G B A E H

  14. Network Link Technology (Qubus)‏ millimeters to kilometers waveguide coherentoptical source(laser)‏ transceiver qubit innode 2 transceiver qubit innode 1 homodynedetector Munro, Nemoto, Spiller, New J. Phys. 7, 137 (2005)‏ Ladd et al., NJP 8, 184 (2006)‏

  15. Quantum Repeater Operation:Entanglement Swapping Station 0 Station 1 Station 2 Bell State Measurement Results must be communicated Fidelity decreases; you must purify afterwards

  16. Nested Entanglement Swapping

  17. Purification Station 0 Station 2 Results must be communicated (two-way?)

  18. Repeater Protocol Stack Application } End-to-End Purification Control (PC)‏ Repeated at Different Distances Entang. Swapping Ctl (ESC)‏ } Purification Control (PC)‏ Entanglement Control (EC)‏ } Distance=1 Physical Entanglement (PE)‏ Only quantum! Van Meter et al., IEEE/ACM Trans. on Networking,Aug. 2009 (to appear), quant-ph:0705.4128

  19. Four-Hop Protocol Interactions App App PC PC ESC ESC ESC PC PC PC ESC ESC ESC ESC ESC PC PC PC PC PC EC EC EC EC EC PE PE PE PE PE Van Meter et al., IEEE/ACM Trans. on Networking,Aug. 2009 (to appear)

  20. The Repeater’s Jobs Entanglement swapping & purification, which require: A little bit of quantum communication Quantum memory Local quantum operations (gates & measurements) Lots of decision making(both local and distributed) Lots of classical communication

  21. Entanglement Pumping 0.638 0.72 0.638 0.75 0.638 0.77 0.638 0.79 0.638 Ineffective w/ large fidelity difference

  22. Symmetric Purification 0.638 Problems: Exact matching can require long waits. Not realistic when memory effects (decoherence)‏ considered. Can deadlock if resources are limited. 0.72 0.638 0.797 0.638 0.72 X 0.638

  23. Greedy Purification 0.638 Doesn’t wait for anything, uses whatever’s available. Works well w/ large number of qubits per repeater. 0.72 0.638 0.757 0.638 X 0.638

  24. Banded Purification Large gains in throughput. Moderate # qubits (5-50). Avoids deadlock. Realistic memory model. Simple to implement in real time (even in HW). Probably not optimal, but probably close. 0.638 0.72 0.638 0.797 0.638 0.72 X 0.638 Divide fidelity space into multiple bands e.g., above & below 0.70

  25. Banded Purification Performance Van Meter et al., IEEE/ACM Trans. on Networking,Aug. 2009 (to appear), quant-ph:0705.4128

  26. Banded Purification Latency Van Meter et al., IEEE/ACM Trans. on Networking,Aug. 2009 (to appear), quant-ph:0705.4128

  27. Protocol Design

  28. Routing C G B A E D H F Simple: use Dijkstra’s Shortest Path First. ...but we don’t yet know the cost metric.

  29. A Different Meaning of “Which Path?” G C B A E D H F 3 hops: ACGB 4 hops: ACGHB ACEHB ADEHB ADFHB 5 hops: ACEHGB ADEHGB ADECGB ADFHGB 6 hops: ACECGHB 7 hops: ADFHECGB ACEDCHGB

  30. But What is Distance? G C B A E D H F What if hops are not homogeneous? Are 2n-1 hops, 2n hops, and 2n+1 hops significantly different?

  31. How Do We Order These? How does number of links matter? Does number of weak links matter? Does position of weak link matter? Is cost additive? At this logical level,is this technology-independent?

  32. Other Problems Defining swap points Static or dynamic? Avoiding leapfrog Avoiding deadlock Minimizing waits forclassical messages

  33. Other Problems Partial messaging sequence Can this be made more efficient? Due to memory degradation, gains will be better than linear

  34. Leapfrog Station 0 Station 1 Station 2 Station 3

  35. Resource Management (QoS?)‏ C B A D A<->B & C<->D want to talk. Remember, it’s a distributed computation. Worse, fragile quantum memory means thereis a hard real time component. ==>requires circuit switching??? (bottleneck likely is memory per node)‏

  36. Open Repeater Problems Well, repeater HW doesn’t work yet... Sims of “weak links” mostly functional Establishing swapping points More dynamic behavior Non-power-of-two hops Finish & publish protocol state machine

  37. Open Complex Network Problems Coding partially done Using graphviz file format Routing not done Workload generator needs work QoS / resource allocation not implemented Visualization of networks Investigate graph states & quantum network coding More detailed workload definition

  38. Milestones for JSPS Define a cost metric(figure out if it’s additive!) Define a path selection algorithm Define test cases Simulate that set of test cases Extend to topologically complex networks Create static visualizations

  39. Food for Thought When will first Science or Nature paper appear using a quantum computer, but not about the quantum computer? That is, when will a quantum computer do science, rather than be science? Answers from quantum researchers range from “less than five years” to “more than forty years”

  40. Thanks Thanks to Thaddeus Ladd, Bill Munro and Kae Nemoto (coauthors on much of this work), as well as Austin Fowler, Jim Harrington, Kohei Itoh, Agung Trisetyarso, Byung-Soo Choi, Shota Nagayama, and Takahiko Satoh And funding from NICT, MEXT, NSF, the Mori Fund at Keio, and now JSPS for funding.

  41. AQUA: Advancing Quantum Architecture 情報は物理である： Information is physical http://www.sfc.wide.ad.jp/aqua/

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