Applications of an
Entangled Quantum Internet
Conference on Future Internet Technologies
Seoul, Korea
June 20, 2008

Rodney Van Meter (Keio) (rdv@sfc.wide.ad.jp)
Byung-Soo Choi (Ewha Woman’sUniversity)
Copyright © 2006 KeioUniversity

Outline• Quantum Key Distribution (QKD)• Extending QKD: switching and trusting• Quantum Repeaters• What would a distributed quantum system begood for?
• What problems do we have to solve to getthere?

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What's a Qubit?
= |0>
= |1>

A qubit has two states that canbe 0 and 1, such as horizontal
and vertical polarization of aphoton, or up and down spinof an electron.

What is this?

= |0> + |1>
A qubit can be in asuperposition of both states atonce!

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Quantum Key Distribution• “Tamper-evident” generationof shared random numbers• Ideal use: generate bit
stream for one-time pad– Mostly, too slow for that
• Use as Diffie-Hellman replacement• Still requires classical authentication

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Quantum Key Distribution• Basic use is <150km, dedicated point-to-pointfiber, no amplifiers• Can be optically switched &multiplexed w/ other data
• Longer distance requires:– trusting intermediate nodes, or– entanglement-based quantum repeaters• Everything but repeaters in actual use now(thanks, Chip Elliott!)5Putting It All Together
IKE
IKEandandIPsec
IPsec
Authentication

Authentication

Privacy Amplification

Privacy Amplification

IKE

IKE

Error Correction
Sifting

QKD
QKDProtocols
Protocols

VPN / OPC Interface

Error Correction
Sifting
VPN / OPC Interface

Alice

Bob
SPD

Ethernet
DeviceDriver

SAD

IP

SPDIP

Ethernet
DeviceDriverEthernet
DeviceDriverEthernet
DeviceDriverEthernet
DeviceDriverSAD

Ethernet
DeviceDriver

VPN
VPNTunnel
TunnelVPN / OPC Interface

VPN / OPC Interface

OpticalProcess Control

OpticalProcess Control

Traffic
Traffic
ininthetheClear
Clear

slide from Elliott, BBN

Source SuiteQKD
QKDPhotons
Photons

Create Key
Use Key

Detector Suite

The DARPA Quantum Network
BBN

PrivateEnclave

HarvardEavesdropping

PrivateEnclaveQKD Switch
QKD Endpoi nt

QKD Switch

QKD Endpoi nt

Dark Metro
Fiber

BU

Lab Fiber

PrivateEnclaveQKD Switch

Conventional
Ethernet
QKD En dpoint

slide from Elliott, BBN

Going the Distance• Longer distance requires:– trusting intermediate nodes, or– entanglement-based quantum repeaters• Quantum repeaters are not amplifiers• Repeaters use teleportation• Teleportation requires entangled states
known as Bell pairs

8Network Link Technology (Qubus)
millimeters to kilometers

coherent
optical source(laser)9

waveguidetransceiver
qubit innode 1transceiver
qubit innode 2

Munro, Nemoto, Spiller, New J. Phys. 7, 137 (2005)

homodyne
detector

Teleportation
1) Start with an EPR pair,and the qubit to be sent

4) Transmit classical results todestination

2) Entangle locally at the source5) Local operations recreate
original qubit3) Measure both qubits at source

1,1

1,1?
Source10Bennett et al., Phys. Rev. Letters 70, 1993

Destination

Quantum Repeater Operation
Station 0Station 1Station 2

Bell State
Measurement
Called entanglement swapping.
Fidelity declines; you must purify afterwards
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Purification
Station 012Station 2

Nested Entanglement Swapping

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Destination

Repeater Protocol Stack
Application
Purification Control (PC)
Entang. Swapping Ctl (ESC)
Purification Control (PC)
Entanglement Control (EC)
Physical Entanglement (PE)14

Van Meter et al., IEEE/ACM Trans. on Networking,Aug. 2009 (to appear)}}}

End-to-End
Repeated at
Different
Distances
Distance=1
Only quantum!

Four-Hop Protocol Interactions
AppPC
ESC
PC
ESC
PC
EC
PE
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ESC
PC
EC
PE

ESC
PC
ESC
PC
EC
PE

Van Meter et al., IEEE/ACM Trans. on Networking,Aug. 2009 (to appear)

ESC
PC
EC
PE

App
PC
ESC
PC
ESC
PC
EC
PE

What about Distributed QC?
• Two types: those that use entanglement, andthose that don’t• Quantum key distribution can be done
either way• Entanglement can be either a digital
resource, or a gyroscopic reference16Long-Distance Entanglement:
Digital Uses
• Quantum Key Distribution• Distributed leader election• Same as classical distrib. systems: connect– People– Machines– Data/databases...that are in distant locations

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Gyroscopic (Physical) Uses
• Entanglement can also be used to improve
precision of measurements– Phase/timing– Directional information• Better atomic clocks• Quantum imaging

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Gravity Waves?

From Goda et al., Nature Physics, 2008.

GW detector using “squeezed” states.
Squeezed states are non-classical, but notentangled; can they be created using
entanglement?
Doeslong-distanceentanglement
help?
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Problems to Solve• Well, repeaters don’t work yet...
(QKD does)• Lots of networking problems:– Routing of “messages”– Resource management in networks– Protocol design– Network Coding (Net. Info. Flow)– Effective use of wide-area, large-scaleentanglement
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Routing

A

Simple.
...but we don’t yet know the cost metric.
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BResource Management (QoS?)
A<->B & C<->D
want to talk.

CA

Remember, it’s a
distributed computation.

DWorse, fragile quantum memory means there
is a hard real time component.

==>requires circuit switching???
(bottleneck likely is memory per node)
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BProtocol Design

23Conclusions• Entangled Quantum Internet will be buildable(eventually)• Digital applications include quantum key
distribution, leader election, simple
connection of distributed resources• Gyroscopic uses include possible “BigScience” projects like gravity wave
observatories• ...and there are lots of fun networking
24 problems before we get there

AQUA: Advancing Quantum
Architecture
What will you build your
http://www.sfc.wide.ad.jp/aqua/
computer out of?
with thanks toChip Elliott,
Kohei M. Itoh, Thaddeus Ladd,Kae Nemoto, Bill Munro,
Gerard Milburn, C. Walker, Min Yun
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