The Quantum Internet
ザ・量子インターネット
http://aqua.sfc.wide.ad.jp

Rodney Van Meter
Keio University@IIJ
2017/5/23

funding provided by:

3

The	
  Quantum	  Informa0on	
  Technology	
  Industry(Over the last couple of years, it has become possible
to talk about this.)45http://www.sciencemag.org/news/2016/12/scientists-are-close-building-quantum-computer-can-beat-conventional-one

6

7

http://www.nature.com/news/commercialize-early-quantum-technologies-1.21583

• “We	  contend	
  that	  short-­‐term	
  returns	
  are	  possible	
  with	  the	
  small	
  devices	
  that	  will	
  emerge	
  within	
  the	
  next	  ﬁve	
  years”	
  • “three	  commercially	
  viable	
  uses	  for	
  early	
  quantum-­‐compu0ng	
  devices:	
  quantum	
  simula3on,	
  quantum-­‐assisted	
  op3miza3on	
  and	
  quantum	
  sampling.	
  Faster	  compu0ng	
  speeds	
  in	
  these	  areas	
  would	
  be	
  commercially	
  advantageous	
  in	
  sectors	
  from	  ar0ﬁcial	
  intelligence	
  to	
  ﬁnance	
  and	
  health	
  care.”8

Big	
  LabsQuantum	
  Computing	
  Startups

Quantum	  Circuits,	
  Inc.

Quantum	
  Networking	
  (QKD)	
  Startups(2001	  ~	
  )(1999	  ~	
  )(2009	  ~	
  )(2008	
  ~	
  )

13

Outline• Quantum Information Technology Industry:• Why should I be excited?
• Background:• interference, entanglement & teleportation• Applications of quantum networks• Lines of repeaters• Networks & internetworks of repeaters
14

Quantum computing in 2 slides (1)Current computers use bits, 0 and 1, as thefundamental unit of information to store andprocess.
Physically, a transistor either conducts current(“1”) or it doesn't (“0”). The laws of physics thatgovern transistors determine the logical flow of
information in a computer.
Quantum computers use qubits as the basic
information unit.

15

Quantum computing in 2 slides (2)A qubit can be in a statethat is both 0 and 1 at thesame time:

SUPERPOSITION

Two or more qubits can becorrelated more strongly
than bits can:

ENTANGLEMENT

The focus of our research into quantum computing is to
exploit the logic of entanglement and superposition tocreate quantum technologies.

16One Particle (One Photon, One Electron)Two possible states:

17

One Particle (One Photon, One Electron)Two possible states:

17

One Particle (One Photon, One Electron)Two possible states:

|"i
|0i
17

One Particle (One Photon, One Electron)Two possible states:

|"i
|0i
17

One Particle (One Photon, One Electron)Two possible states:|"i |#i|0i |1i
17Superposition & Measurement

18Superposition & Measurement
We can create astate that’s
partially up,
partially down18Superposition & Measurement
We can create astate that’s
partially up,
partially down
“Measure” itand find its
value…

18

Superposition & Measurement
We can create astate that’s
partially up,
partially down
“Measure” itand find its
value…

18

Superposition & Measurement
We can create astate that’s
partially up,
partially down
“Measure” itand find its
value…
50/50 chance ofeach outcome
18Superposition & Measurement
We can create astate that’s
partially up,
partially down
“Measure” itand find its
value…
50/50 chance ofeach outcome
18…destroys thesuperposition!

Making Entanglement (one of many ways)

19

Making Entanglement (one of many ways)

Start with one
qubit, put it insuperposition
19

Making Entanglement (one of many ways)

Start with one
bring in aqubit, put it in second qubit
superposition
19

Making Entanglement (one of many ways)

Start with one
bring in aqubit, put it in second qubit
superposition
19

Entangle them!
(very dependent
on qubit type)Measuring Entanglement20Measuring Entanglement20Measuring Entanglement“Measure” thisone and findits value…
(50/50 chanceof up & down)
20

and you’ll also
know what thisone isMeasuring Entanglement

Even if they
are far apart!
“Measure” thisone and findits value…
(50/50 chanceof up & down)
20

and you’ll also
know what thisone isTwo Qubits, Four States
Just like twoclassical bits,
we can havefour possiblecombinations

21

Two Qubits, Four States
Just like twoclassical bits,
we can havefour possiblecombinations

21

|""i

Two Qubits, Four States
Just like twoclassical bits,
we can havefour possiblecombinations

21

|""i

|"#i

Two Qubits, Four States
Just like twoclassical bits,
we can havefour possiblecombinations

21

|""i

|"#i
|#"i

Two Qubits, Four States
Just like twoclassical bits,
we can havefour possiblecombinations

21

|""i

|"#i
|#"i
|##i

Entanglement

22Entanglement
If this:22

Entanglement
If this:or this:22

Entanglement
If this:but never theother twocombinations…

or this:22

Entanglement
If this:or this:22

Entanglement
If this:or this:22

Entanglement
If this:ENTANGLEMENT!
They are random but
not independent.

or this:22But No Faster-Than-Light Communication

Nope!
You can each get shared,
secret random numbers
upon measuring shared,
entangled states, but that
doesn’t give you the ability
to send messages.

23Teleportation

Teleportation

Quantum teleportation:
Information, not Objects

25Quantum teleportation:
Information, not Objects

25Quantum teleportation:
Information, not Objects
Alice

26

Bob

Quantum teleportation:
Information, not Objects
Alice

26

Bob

Quantum teleportation:
Information, not Objects
Alice

Bob

Use
Entanglement

26

Quantum teleportation:
Information, not Objects
Alice

Bob

Local Quantum
Operations

26

Quantum teleportation:
Information, not Objects
Alice

Bob

Local Quantum
Operations

26

Quantum teleportation:
Information, not Objects
Alice

26

Bob

Quantum teleportation:
Information, not Objects
Alice

Bob
Classical
Communication

26

Quantum teleportation:
Information, not Objects
Alice

Bob

and Local Q Ops
to Recreate
Original

26

Nonlocality - the arguments

29

Nonlocality - the arguments
Hang on, quantum mechanics
as written down requires
things far apart to behave likethey have faster than light
communication?!?

29

Nonlocality - the arguments
Hang on, quantum mechanics
as written down requires
things far apart to behave likethey have faster than light
communication?!?

Einstein29

Nonlocality - the arguments
Hang on, quantum mechanics
as written down requires
things far apart to behave likethey have faster than light
communication?!?

Einstein

There’s a way tostatistically test this.

29Nonlocality - the arguments
Hang on, quantum mechanics
as written down requires
things far apart to behave likethey have faster than light
communication?!?
J.S.Bell

Einstein

There’s a way tostatistically test this.

29Nonlocality - the arguments
Hang on, quantum mechanics
as written down requires
things far apart to behave likethey have faster than light
communication?!?

Einstein

There’s a way tostatistically test this.

J.S.BellI tested it!
29Nonlocality - the arguments
Hang on, quantum mechanics
as written down requires
things far apart to behave likethey have faster than light
communication?!?

Einstein

There’s a way tostatistically test this.

J.S.Bell

AspectI tested it!
29Nonlocality - the arguments

30Nonlocality - the arguments
Einstein

Either quantum mechanics
is nonlocal, or it isincomplete (secret plans)30

Nonlocality - the arguments
Einstein

Either quantum mechanics
is nonlocal, or it isincomplete (secret plans)
J.S.BellEven if it is incomplete, it
is still nonlocal!

30

Nonlocality - the arguments
Einstein

Either quantum mechanics
is nonlocal, or it isincomplete (secret plans)
J.S.BellEven if it is incomplete, it
is still nonlocal!
AspectNo local hidden variable theory
can explain my experiment.

30

The Aspect experiments

31

The Aspect experiments

31

The Aspect experiments

31

Recent Bell Inequality
Violation Experiments• Four major research groups have announced results in testing Bell’s theorem in 2015.
••

Pop science reports:•

Delft group: http://phys.org/news/2015-08-loopholes-entanglement-bellinequality.html•

Vienna group: http://phys.org/news/2015-11-big-quantum.html•

Singapore group: http://www.eurekalert.org/pub_releases/2015-11/cfqtere110915.php•

UNSW group: http://www.gizmag.com/advance-programmable-silicon-quantumcomputers/40420/

btw, the Wikipedia article is a reasonable list of Bell inequality violations going back three
decades:
https://en.wikipedia.org/wiki/Bell_test_experiments

Recent Bell Inequality
Violation Experiments•

Technical papers:•

Hanson group, Delft:
http://www.nature.com/nature/journal/v526/n7575/full/nature15759.html
http://arxiv.org/abs/1508.05949•

Zeilinger group, Vienna: Giustina et al.
http://arxiv.org/abs/1511.03190•(related: http://www.pnas.org/content/early/2015/10/27/1517574112, http://
www.pnas.org/content/early/2015/10/28/1517007112 )•Kurtsiefer group, Singapore:https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.115.180408 or
http://arxiv.org/abs/1506.01865•

Morello group, University of New South Wales (Kohei M. Itoh, Keio, collaborating):
http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2015.262.html

Singapore Experiment

Poh et al., Phys. Rev. Letters 115, 180408, 2015

Super-precise statistical test of Bell inequality

Singapore Experiment

Poh et al., Phys. Rev. Letters 115, 180408, 2015

Vienna Experiment

Closing timing loopholes (strengthening the proof)
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.115.250401

arXiv:1511.03190

Vienna ExperimentarXiv:1511.03190
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.115.250401

Vienna Experiment #2

Gaining distance and linking two
entangled states together!

http://www.pnas.org/content/112/46/14202

UNSW ExperimentFirst Bellinequality
between two
solid-state qubits
in a device

http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2015.262.html

Delft ExperimentOver 1.3 km using
solid-state memories(small pieces of
diamond engineered
to hold a single extra
electron, known as NV
centers)

Hensen et al., Nature, 29 Oct. 2015

Link Architectures

Tx

Rx

Link Architectures

Tx

Rx

Tx

Tx
BSA	
  NodeLink Architectures

Tx

Rx

Tx

Tx
BSA	
  NodeRx

EPPS	  NodeRx

https://qz.com/760804/chinas-new-quantum-satellite-will-try-to-teleport-data-outside-the-bounds-of-space-and-time-and-create-an-unbreakable-code/So the job of a quantum
repeater network is…
•…to make that entanglement.

•(And, it’s a consumable resource, so we have to
make lots of it.)•

But what can we do with it if we have it?
—> Well, obviously, test quantum theory!
But what else?

Outline• Background: entanglement & teleportation• Applications of quantum networks• Lines of repeaters• Networks & internetworks of repeaters

44

Distributed
crypto functions

Distributed
computation

Sensors45

Byzantine
agreement
Leader election

Distributed
crypto functions

Quantum
Quantum key
secret sharing
distribution (QKD)
Blind quantum
computation
InterferometryBasicclient-server
QC
Distributed System-area
computation networks

ClocksOther reference
frame uses

Sensors

45

Reduce dependency on
public key, one-way
functions, computational
complexity

Byzantine
agreement

Leader election

Distributed
crypto functions

Quantum
Quantum key
secret sharing
distribution (QKD)
Blind quantum
computation
InterferometryBasicclient-server
QC
Distributed System-area
computation networks

ClocksOther reference
frame uses

Sensors45

Byzantine
agreement
Leader election

Distributed
crypto functions

Quantum
Quantum key
secret sharing
distribution (QKD)
Blind quantum
computation
InterferometryBasicclient-server
QC
Distributed System-area
computation networks

ClocksOther reference
frame uses

Sensors46

Byzantine
agreement
Leader election

Low
bandwidth

Distributed
crypto functions

Quantum
Quantum key
secret sharing
distribution (QKD)
Blind quantum
computation
InterferometryBasicclient-server
QC
Distributed System-area
computation networks

ClocksOther reference
frame uses

Sensors46

Byzantine
agreement
Leader election

Low
bandwidth

Distributed
crypto functions

Quantum
Quantum key
secret sharing
distribution (QKD)
Blind quantum
computation
InterferometryHigh
to veryBasicclient-server
QC
Distributed System-area
computation networks

high bandwidth
ClocksOther reference
frame uses

Sensors46

Byzantine
agreement
Leader election

Low
bandwidth

Distributed
crypto functions

Quantum
Quantum key
secret sharing
distribution (QKD)
Blind quantum
computation
Interferometry
High
High
to very
Basic to veryclient-serverhigh bandwidth high bandwidth
Clocks
QC
Distributed System-area
Other referencecomputation networks
Sensors
frame uses

46

IPsec with QKD: Quantum-protected
campus-to-campus connection
Dark Fiber
IPsec Gateway
Quantum Path for
Key ExchangeInternet

IPsec Tunnel

IPsec Gateway

Classical internet pathusing Quantum-made key

draft-nagayama-ipsecme-ike-with-qkd-01.txt, 2014/10
1247

IPsec with QKD

IPNetwork

IPsec
Gateway
Secure, Local
Connection

Secure, Local
Connection

Quantum
Network

QKD
Device13

IPsec
Gateway

QKD
Device48

IPsec with QKD

IPNetwork

IPsec
Gateway
Secure, Local
Connection

Secure, Local
Connection

Quantum
Network
Make keys

QKD
Device13

IPsec
Gateway

QKD
Device48

IPsec with QKD

IPNetwork

IPsec
Gatewaykey

Secure, Local
Connection

Secure, Local key
Connection

Quantum
Network
Make keys

QKD
Device13

IPsec
Gateway

QKD
Device48

IPsec with QKD

IPNetwork
Encrypted Connection

IPsec
Gatewaykey

Secure, Local
Connection

Secure, Local key
Connection

Quantum
Network
Make keys

QKD
Device13

IPsec
Gateway

QKD
Device48

IPsec with QKD

IPNetwork
Encrypted Connection

IPsec
Gateway
keyn.b.: QKD requires
an authenticated(but not secret)classical channel toavoid MitM

Secure, Local
Connection

Secure, Local key
Connection

Quantum
Network
Make keys

QKD
Device13

IPsec
Gateway

QKD
Device48

D-H: Diffie-Hellman key exchange
QKD: Quantum Key Distribution
AES: Advanced Encryption Standard
OTP: One Time PadD-H: Diffie-Hellman key exchange
QKD: Quantum Key Distribution
AES: Advanced Encryption Standard
OTP: One Time Pad

D-H +
AES

D-H: Diffie-Hellman key exchange
QKD: Quantum Key Distribution
AES: Advanced Encryption Standard
OTP: One Time Pad

D-H +
AES
QKD +
AES

D-H: Diffie-Hellman key exchange
QKD: Quantum Key Distribution
AES: Advanced Encryption Standard
OTP: One Time Pad

D-H +
AES
QKD +
AES
QKD +
super-AES

D-H: Diffie-Hellman key exchange
QKD: Quantum Key Distribution
AES: Advanced Encryption Standard
OTP: One Time Pad

D-H +
AES
QKD +
AES
QKD +
super-AES
QKD +
OTP

D-H: Diffie-Hellman key exchange
QKD: Quantum Key Distribution
AES: Advanced Encryption Standard
OTP: One Time Pad

Data
encrypted
today
D-H +
AES
QKD +
AES
QKD +
super-AES
QKD +
OTP

D-H: Diffie-Hellman key exchange
QKD: Quantum Key Distribution
AES: Advanced Encryption Standard
OTP: One Time Pad
FactoringData
encrypted
today
D-H +
AES
QKD +
AES
QKD +
super-AES
QKD +
OTP

becomespossibleD-H: Diffie-Hellman key exchange
QKD: Quantum Key Distribution
AES: Advanced Encryption Standard
OTP: One Time Pad
FactoringData
encrypted
today
D-H +
AES
QKD +
AES
QKD +
super-AES
QKD +
OTP

becomespossible

AES broken

D-H: Diffie-Hellman key exchange
QKD: Quantum Key Distribution
AES: Advanced Encryption Standard
OTP: One Time Pad
FactoringData
encrypted
today
D-H +
AES
QKD +
AES
QKD +
super-AES
QKD +
OTP

becomespossible

AES broken

testing all keys
becomes possible

D-H: Diffie-Hellman key exchange
QKD: Quantum Key Distribution
AES: Advanced Encryption Standard
OTP: One Time Pad
FactoringData
encrypted
today
D-H +
AES
QKD +
AES
QKD +
super-AES
QKD +
OTP

becomespossible

AES broken

testing all keys
becomes possible

D-H: Diffie-Hellman key exchange
QKD: Quantum Key Distribution
AES: Advanced Encryption Standard
OTP: One Time Pad
FactoringData
encrypted
today
D-H +
AES
QKD +
AES
QKD +
super-AES
QKD +
OTP

becomespossible

AES broken

testing all keys
becomes possible

D-H: Diffie-Hellman key exchange
QKD: Quantum Key Distribution
AES: Advanced Encryption Standard
OTP: One Time Pad
FactoringData
encrypted
today
D-H +
AES
QKD +
AES
QKD +
super-AES
QKD +
OTP

becomespossible

AES broken

testing all keys
becomes possible

D-H: Diffie-Hellman key exchange
QKD: Quantum Key Distribution
AES: Advanced Encryption Standard
OTP: One Time Pad
FactoringData
encrypted
today
D-H +
AES
QKD +
AES
QKD +
super-AES
QKD +
OTP

becomespossible

AES broken

testing all keys
becomes possible

D-H: Diffie-Hellman key exchange
QKD: Quantum Key Distribution
AES: Advanced Encryption Standard
OTP: One Time Pad
FactoringData
encrypted
today

becomespossible

AES broken

testing all keys
becomes possible

D-H +
AES
QKD +
AES
QKD +
super-AES
QKD +
OTP

?

D-H: Diffie-Hellman key exchange
QKD: Quantum Key Distribution
AES: Advanced Encryption Standard
OTP: One Time Pad
FactoringData
encrypted
today
D-H +
AES

becomespossible

AES broken

testing all keys
becomes possible

Feasible today
for metro nets

QKD +
AES
QKD +
super-AES
QKD +
OTP

?

D-H: Diffie-Hellman key exchange
QKD: Quantum Key Distribution
AES: Advanced Encryption Standard
OTP: One Time Pad
FactoringData
encrypted
today
D-H +
AES

becomespossible

AES broken

testing all keys
becomes possible

Feasible today
for metro nets

QKD +
AES
QKD +
super-AES
QKD +
OTP

?
Is this gap
interesting?

D-H: Diffie-Hellman key exchange
QKD: Quantum Key Distribution
AES: Advanced Encryption Standard
OTP: One Time Pad
FactoringData
encrypted
today
D-H +
AES

becomespossible

AES broken

testing all keys
becomes possible

Feasible today
for metro nets

QKD +
AES
QKD +
super-AES
QKD +
OTP

?
Is this gap
interesting?

See WeakDH.org!
(Am interested in your opinion of this!)D-H: Diffie-Hellman key exchange
QKD: Quantum Key Distribution
AES: Advanced Encryption Standard
OTP: One Time Pad
FactoringData
encrypted
today
D-H +
AES

becomespossible

AES broken⇠ 1bit/sec

testing all keys
becomes possible

Feasible today
for metro nets

QKD +
AES
QKD +
super-AES
QKD +
OTP

?
Is this gap
interesting?

See WeakDH.org!
(Am interested in your opinion of this!)D-H: Diffie-Hellman key exchange
QKD: Quantum Key Distribution
AES: Advanced Encryption Standard
OTP: One Time Pad
FactoringData
encrypted
today
D-H +
AES

becomespossible

AES broken⇠ 1bit/sec

QKD +
AES

testing all keys
becomes possible

Feasible today
for metro nets

⇠ 1bit/sec

QKD +super-AES
QKD +
OTP

?
Is this gap
interesting?

See WeakDH.org!
(Am interested in your opinion of this!)D-H: Diffie-Hellman key exchange
QKD: Quantum Key Distribution
AES: Advanced Encryption Standard
OTP: One Time Pad
FactoringData
encrypted
today
D-H +
AES

becomespossible

AES broken⇠ 1bit/sec

QKD +
AES

testing all keys
becomes possible

Feasible today
for metro nets

⇠ 1bit/sec

QKD +super-AES
QKD +
OTP

?
Is this gap
interesting?

⇠ 109 bit/sec

See WeakDH.org!
(Am interested in your opinion of this!)

Distributed QC: blind computing

A platform forsecuredistributed
quantum
computation, notan “application”
per se.
Assumes MBQC
as programming
model.
Barz et al.,Science 335 (2012)50

Distributed QC: blind computing
Maybe
10

⇠ 10

Bell pairs/sec
for FT Shor?

A platform forsecuredistributed
quantum
computation, notan “application”
per se.
Assumes MBQC
as programming
model.
Barz et al.,Science 335 (2012)50

Blind	  Computation:	
  Secure	
  Quantum	  Time-­‐Sharing

Quantum	
  terminal	
  (low	
  capacity)

Quantum	  repeater	  network

Quantum	  mainframe	  (high	
  capacity,	
  time	
  share)Server	  learns	
  nothing	
  about	
  either	  client’s	
  data	  or	
  computation,	
  except	
  upper	  bound	  on	
  computation	
  size.	
  	
  
(cf.	
  classical	
  homomorphic	
  encryption)	
  	
  Sensors: Interferometry(干渉計)

DOI: http://dx.doi.org/10.1103/PhysRevLett.109.070503

52

Sensors: Interferometry(干渉計)⇠ 1011 Bell pairs/sec
DOI: http://dx.doi.org/10.1103/PhysRevLett.109.070503

52

Distributed
crypto functions

Distributed
computation

Sensors53

Byzantine
agreement
Leader election

Distributed
crypto functions

Quantum
Quantum key
secret sharing
distribution (QKD)
Blind quantum
computation
InterferometryBasicclient-server
QC
Distributed System-area
computation networks

ClocksOther reference
frame uses

Sensors53

3⇠ 10 Bell pairs ⇥ trans/sec

Byzantine
agreement
Leader election

Distributed
crypto functions

Quantum
Quantum key
secret sharing
distribution (QKD)
Blind quantum
computation
InterferometryBasicclient-server
QC
Distributed System-area
computation networks

ClocksOther reference
frame uses

Sensors53

3⇠ 10 Bell pairs ⇥ trans/sec

Byzantine
agreement
Leader election

Distributed
crypto functions⇠ 1bit/sec

Quantum
Quantum key
secret sharing
distribution (QKD)
Blind quantum
computation
InterferometryBasicclient-server
QC
Distributed System-area
computation networks

ClocksOther reference
frame uses

Sensors53

3⇠ 10 Bell pairs ⇥ trans/sec

Byzantine
agreement
Leader election

Distributed
crypto functions⇠ 1bit/sec

Quantum
Quantum key
6⇠ 10 bits/sec
secret sharing
distribution (QKD)
Blind quantum
computation
InterferometryBasicclient-server
QC
Distributed System-area
computation networks

ClocksOther reference
frame uses

Sensors53

3⇠ 10 Bell pairs ⇥ trans/sec

Byzantine
agreement
Leader election

Distributed
crypto functions⇠ 1bit/sec

Quantum
Quantum key
6⇠ 10 bits/sec
secret sharing
distribution (QKD)
9Blind quantum⇠ 10 bit/sec
computation
InterferometryBasicclient-server
QC
Distributed System-area
computation networks

ClocksOther reference
frame uses

Sensors53

3⇠ 10 Bell pairs ⇥ trans/sec

Byzantine
agreement
Leader election

Distributed
crypto functions⇠ 1bit/sec

Quantum
Quantum key
6⇠ 10 bits/sec
secret sharing
distribution (QKD)
9Blind quantum⇠ 10 bit/sec
computation
Interferometry
Maybe
Basic
client-server⇠ 1010 Bellpairs/sec
ClocksQC
for FT Shor?
Distributed System-area
Other referencecomputation networks
Sensors
frame uses53

3

⇠ 10 Bell pairs ⇥ trans/sec

Byzantine
agreement
Leader election

Distributed
crypto functions⇠ 1bit/sec

Quantum
Quantum key
6⇠ 10 bits/sec
secret sharing
distribution (QKD)
9Blind quantum⇠ 10 bit/sec
computation
Interferometry
Maybe
Basic
11
⇠ 10 Bell pairs/sec
10 client-server⇠ 10 Bell pairs/sec
ClocksQC
for FT Shor?
Distributed System-area
Other referencecomputation networks
Sensors
frame uses
53

Entanglement is Independent of Distance54

Entanglement is Independent of Distance...provided we have high-fidelity transmission, memory,and operations

54

Entanglement is Independent of Distance...provided we have high-fidelity transmission, memory,and operations...so that’s what quantum repeater networks are allabout.

54

Losing Photons Affects When We Can Use Info
Losing photons
here
Double lines areclassical
information

B
Photo
n

B

ACK

Select	  	
  successLosing Photons Affects When We Can Use Info
Losing photons
here
Double lines areclassical
information

B
Photo
n

B

ACK

B ( Bell) class:
Bell inequality violations,quantum key distribution(QKD)
no quantum buffering
all classical post-selection

Select	  	
  successLosing Photons Affects When We Can Use Info
Losing photons
here
Double lines areclassical
information

B
Photo
n

B

ACK

B ( Bell) class:
Bell inequality violations,quantum key distribution(QKD)
no quantum buffering
all classical post-selection

Select	  	
  successLosing Photons Affects When We Can Use Info
Losing photons
here
Double lines areclassical
information

B
Photo
n

B

ACK

B ( Bell) class:
Bell inequality violations,quantum key distribution(QKD)
no quantum buffering
all classical post-selection

Select	  	
  successLosing Photons Affects When We Can Use Info
Losing photons
here
Double lines areclassical
information

B
Photo
n

B

ACK

B ( Bell) class:
Bell inequality violations,quantum key distribution(QKD)
no quantum buffering
all classical post-selection

Select	  	
  successLosing Photons Affects When We Can Use Info
Losing photons
here
Double lines areclassical
information

B
Photo
n

B

ACK

B ( Bell) class:
Bell inequality violations,quantum key distribution(QKD)
no quantum buffering
all classical post-selection

Select	  	
  success

ACKing what we
gotLosing Photons Affects When We Can Use Info
Losing photons
here
Double lines areclassical
information

B
Photo
n

B

ACK

B ( Bell) class:
Bell inequality violations,quantum key distribution(QKD)
no quantum buffering
all classical post-selection

Select	  	
  success

ACKing what wegotStore-and-Forward?

56

Store-and-Forward?

56

Store-and-Forward?

56

Store-and-Forward?

Problems:

1) photon loss
2) local operation errors3) memory errors
56

So We Build Repeaters: Conceptual Hardware

57

Tasks of a Quantum Repeater

58Tasks of a Quantum Repeater
1. To make basic entanglement over a distance(e.g., over fiber or free space)58

Tasks of a Quantum Repeater
1. To make basic entanglement over a distance(e.g., over fiber or free space)
2. To manage errors• Loss of photons• Gate errors• Memory errors

58

Tasks of a Quantum Repeater
1. To make basic entanglement over a distance(e.g., over fiber or free space)
2. To manage errors• Loss of photons• Gate errors• Memory errors
3. To extend entanglement across multiple hops

58

Tasks of a Quantum Repeater
1. To make basic entanglement over a distance(e.g., over fiber or free space)
2. To manage errors• Loss of photons• Gate errors• Memory errors
3. To extend entanglement across multiple hops
4. To be part of a network:• Route through a network• Manage resources (time, memory, photons, …)• To be secure; etc.

58

http://www.nature.com/articles/srep20463

59

Repeater Schemes• 1G: Purify and swap
(Dur & Briegel, Lukin, others; since 1998)• 2G & 3G: CSS quantum error correction(Jiang (Lukin) et al., 2009)• 2G & 3G: Surface code quantum error correction(Fowler et al., 2010)• 2.5G: Quasi-asynchronous(Munro et al., 2010)• Memoryless(Munro et al., 2012)• All Optical(physical layer w/ implications for architecture)60

Lengthening Entanglement
Station 0

61

Station 1

Station 2

Lengthening Entanglement
Station 0

61

Station 1

Station 2

Lengthening Entanglement
Station 0

Station 1

Bell State
Measurement

61

Station 2

Lengthening Entanglement
Station 0

Station 2

Bell State
Measurement
Called entanglement swapping.
Fidelity declines; you must purify afterwards
61

Nested Entanglement Swapping

Dur & Briegel, many others

62

Nested Entanglement Swapping

Dur & Briegel, many others

62

Nested Entanglement Swapping

Dur & Briegel, many others622-EPP: Purification
Station 0

62

Station 2

2-EPP: Purification
Station 0

62

Station 2

2-EPP: Purification
Station 0

62

Station 2

1-EPP: Surface code quantum communication

Fowler et al., PRL 104, 201064

http://www.nature.com/articles/srep20463

65

Learning	
  More(Many good references in both 英語 and 日本語; here
are a few of our own recent ones.)

66

MOOC (massive open
online course) on
Quantum Computing
tentatively scheduled for
Fall 2017

67

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68

70

Summary71

Summary
1. Quantum computing and networking are happening:
there are applications, hardware, an ecosystem.

71Summary
1. Quantum computing and networking are happening:
there are applications, hardware, an ecosystem.
2. Network applications: crypto functions, sensor
networks, distributed quantum computing (encrypting
time sharing).

71

Summary
1. Quantum computing and networking are happening:
there are applications, hardware, an ecosystem.
2. Network applications: crypto functions, sensor
networks, distributed quantum computing (encrypting
time sharing).
3. Photon loss, memory are implementation challenges.

71Summary
1. Quantum computing and networking are happening:
there are applications, hardware, an ecosystem.
2. Network applications: crypto functions, sensor
networks, distributed quantum computing (encrypting
time sharing).
3. Photon loss, memory are implementation challenges.
4. Much networking work to be done.

71Summary
1. Quantum computing and networking are happening:
there are applications, hardware, an ecosystem.
2. Network applications: crypto functions, sensor
networks, distributed quantum computing (encrypting
time sharing).
3. Photon loss, memory are implementation challenges.
4. Much networking work to be done.
5. It’s all a great deal of fun, come join us!

71Aqua & Friends

74

75