►
From YouTube: Quantum Internet Proposed Research Group
Description
The Quantum Internet Proposed Research Group (QIRG).session at IETF 104 will be held at 15:10 to 17:10 UTC on 25 March 2019.
A
All
right
it's
4:10
p.m.
so.
If
you
all
would
take
your
seats,
are
you
ready
Ben?
Let's
do
it
welcome
to
the
quantum
Internet
research
group
meeting
here
in
Prague,
and
today
we
have
two
hours.
As
you
know,
this
session
is
a
tutorial
session.
I'm
rod,
Van
Meter
I,
am
one
of
the
Working
Group
co-chairs.
My
co-chair
Stephanie
Vayner
is
not
here
today,
but
we
have
with
us
Tracy
Northup
from
Innsbruck
who's,
going
to
help
me
with
the
the
tutorial.
A
So
we'll
do
that
for
a
couple
of
hours
today,
we're
gonna
try
to
take
about
a
five
minute
break
just
to
give
everybody.
You
know
time
to
stretch
their
legs
about
half
way.
Throat
and
also
this
session
is
the
tutorial
tomorrow
will
be
the
working
group
meeting
where
we're
going
through
the
existing
set
of
drafts
and
what
not
hump
you
next
page.
So
yes,
as
you
know,
we
are
in
the
Grand
Ballroom
for
those
of
you
who
are
online
or
if
you
need
the
URLs
there's
the
there's.
A
The
connection
next
page
and
tomorrow
will
be
1120,
we'll
be
downstairs
in
Congress
hall
for
the
for
the
working
group
meeting
there
and
we'll
cover
the
active
set
of
internet
drafts,
of
which
there
are
about
three,
although
they're
not
all
correctly
tracked
in
the
system.
Yet
there
are
at
least
three
that
are
relevant
to
what
we're
doing
and
a
couple
of
other
things
and
see
next
page.
So
the
history
and
status
of
this
group
just
very
very
quickly
for
those
of
you
who
were
in
the
room
for
the
first
time
are
hearing
about
this.
A
So
today,
let's
see
we
have
the
blue
sheets
going
at
around.
We
have
a
a
note-taker
and
a
gem
jabber
scribe
already
taken
care
of,
so
we're
in
good
form,
good
shape
there
and
tutorial
wise.
Although
the
agenda
says
first
half
me
and
architectural
concepts
and
second
half
Tracy
and
implementations,
we're
actually
going
to
sort
of
switch
back
and
forth
a
little
bit
as
we
go.
Instead,
it's
going
to
be
a
little
bit
more
mixed
and
we
would
like
to
make
this
as
interactive
as
possible.
A
So,
if
there's
anything
along
the
way
that
you
have
a
question
about,
feel
free
to
step
to
the
mic
and
ask
we'll
recognize
you,
that's
sort
of
a
reasonable
stopping
point
and
consistent
with
forward
progress.
We'll
take
as
many
questions
as
we
can
during
the
course
of
this.
Let's
go
ahead
and
switch
to
the
other,
the
other
laptop
yeah,
any
comments
or
questions
on
what
we're
doing
before
we
get
started.
A
We
have
presentation
good,
all
right,
so
rough
outline
of
what
we're
going
to
talk
about.
I'm
gonna.
Give
you
a
few
minutes
on
the
T
del
dia,
a
tldr
version
of
what
a
quantum
network
is
spend
some
time
talking
about
what
applications
we
might
run
on
and
which
should
be
kind
of
why
you
care
some
basic
concepts
and
terminology,
and
some
math
and
whatnot
and
then
somewhere
down
and
through
here.
A
Roughly,
there
are
two
kinds
of
quantum
networks:
there
are
unentangled
networks
which
are
good
for
primarily
for
quantum
key
distribution,
which
is
essentially
making
shared
secret
bits
across
a
network
where
the
secrecy
of
those
bits
is
guaranteed
via
the
underlying
physics,
rather
than
some
sort
of
mathematical
function
and
the
these
networks
exist.
They
are
limited
in
distance
and
their
single
purpose,
and
they
have
other
constraints
which
some
of
you
all
are
aware
of,
but
they
do
exist
at
the
other.
A
Also
axel
Dahlberg
from
from
Stephanie's
group
presented
some
of
this
in
bangkok,
with
it,
with
a
really
good
overview
of
that
right.
So,
in
order
to
understand
quantum
networks,
the
single
most
important
concept
you
have
to
understand,
and
one
that's
among
the
most
misunderstood
concepts
anywhere
in
the
world
is
entanglement.
A
If
you
measure
the
one
on
the
left
to
figure
out
what
it
looks
like
what
it's
actually
doing,
it
will
be,
you
will
find
that
it's
either
pointed
up
or
pointed
down,
and
in
this
case
it
was
pointed
down.
At
the
same
time,
you
will
learn
what
the
one
at
the
far
end
is,
even
if
these
two
systems
were
far
apart.
This
is
sort
of
the
basic
idea
of
entanglement.
A
A
The
job
of
a
quantum
repeater
network
is
to
make
this
entanglement
end-to-end
between
pair
of
notes,
modulo,
some
arguments
we're
not
going
to
get
into
it,
get
into
about
the
ordering
of
events
and
whatnot
and
importantly,
entanglement,
is
a
consumable
resource,
and
so
we
have
to
make
lots
and
lots
of
it
as
we
go.
That's
the
job
of
the
quantum
network
is
to
regenerate
this
entanglement
sort
of
continuously.
A
Third
to
monitor
and
manage
errors,
as
it
goes,
we'll
look
at
a
couple
of
techniques,
one
of
the
ones
we'll
talk
about
the
most
is
what's
called
purification.
There's
also
quantum
error.
Correction
and
fourth
is
to
participate
in
the
management
of
the
network
itself,
so
routing
protocols
and
security
and
path,
setup
and
teardown
and
multiplexing,
and
all
those
other
sorts
of
things
that
the
people
in
this
room
know
better
than
anybody.
A
These
are
the
kinds
of
areas
where
the
quantum
physicists,
not
only
I'm,
gonna,
save
this,
even
though
in
front
of
a
physicist,
even
though
Tracy's
here
I'm
the
the
physicists,
not
only
don't
know
a
lot
of
these
things
in
a
lot
of
cases,
they
don't
know
what
they
don't
know
right,
there's
an
awful
lot
of
problems
that
have
to
be
solved
from
going
from
having
a
physical
layer
in
a
network
up
through
layers
to
through
9
or,
however
many
layers
you
want
to
have
right.
So
that's
the.
A
So
they,
however,
make
how
many
protocol
layers
you
happen
to
care
to
have
so
the
job
of
the
people
in
this
room
is
to
help
guide
those
experimentalists
who
are
building
those
networks
and
help
us
to
build
complete
systems
the
same
same
as
was
done
with
radio
and
fiber
and
everything
else
to
so.
We
went
over
the
course
the
last
50
years.
B
A
I
think
the
group
of
Leon
John
from
Yale
University
to
find
a
set
of
generations
of
networks
they
defined
what
they
called
1g
2g
3G
networks
and
we're
going
to
talk
a
little
bit
more
about
what
those
different
kinds
of
network
of
networks
actually
are
and
represent.
You'll
notice
that
on
the
left,
they
describe
two
classes
of
errors,
there's
loss,
error,
meaning
Lee
or
the
loss
of
your
individual
photons
as
they're
going
down
a
fiber
and
then
there's
operational
error
noise
in
the
system,
decay
of
your
memory
and
whatnot.
A
So
the
loss
error
obviously
operates
at
the
link
layer
and
the
operational
layer
you
have
or
the
operations
errors
we
have
to
deal
with
at
the
end,
to
end
layer,
there's
a
whole
bunch
of
stuff
that
has
to
be
done.
We
have
to
you
can't
deal
with
this
simply
hop
by
hop
and
we'll
we'll
explain
how
that
is.
Is
we
go?
A
A
They
think
maybe
will
either
be
able
to
violate
the
speed
of
light
and
transmit
information
faster
than
the
speed
of
light
I'm
here
to
disappoint
you
and
tell
you,
that's
not
the
case,
and
it's
also
not
the
case
that
quantum
networks
are
going
to
be
some
some
pathway
to
tear
a
bit
x
a
bit
got
a
bit
2
per
second
kinds
of
networks.
That's
that's!
Not
what
we're
trying
to
do
here.
A
We're
gonna,
bring
in
new
kinds
of
capabilities
into
the
networks,
improvements
in
the
number
of
communication
rounds
for
certain
distributed
protocols,
higher
precision,
scalability
of
distributed
systems
and
whatnot.
Alright,
so
going
a
little
bit
more
into
the
the
applications
themselves.
I
divided
the
set
of
applications
that
we
can
do
with
a
quantum
internet
into
three
large
areas.
A
In
a
sense
could
be
actually
implemented
on
hardware
that
can
be
built
sometime
in
the
relatively
near
future
and
would
actually
be
applicable
to
systems
out
in
the
real
world
notice
that
everything
in
the
distributed
crypto
bubble
is
intended
to
reduce
our
dependency
on
public
key
cryptography.
1By
functions,
computational
complexity,
those
sorts
of
as
it
happens,
one
of
the
things
we've
realized
in
the
in
the
work
that
we've
been
doing.
The
crypto
functions
are
relatively
low
bandwidth
in
terms
of
their
demands
on
the
network.
A
The
sensor
networks
are
a
high
to
very
high
bandwidth,
and
the
distributed
computation
is
also
high
to
very
high
bandwidth.
So,
certainly
in
the
short
run,
the
crypto
functions
are
going
to
be
the
thing
that's
going
to
be
driving
adoption,
the
others
are
going
to
take
a
little
bit
more
time
to
get
there.
But
let
me
go
through
an
example
with
each
one
of
these
categories
and
show
you
the
kinds
of
things
we
want
to
do.
A
A
You
know
we
can
have
all
sorts
of
discussions
about
that,
but
that's
the
idea
right
and
those
keys
are
exchanged
with
the
IPSec
gateways
in
some
particular
in
some
secure
fashion
and
then
they're
actually
used
to
encrypt
data.
That's
transmitted
across
the
IP
network.
So
that's
the
basic
structure.
This
could
also
be
applied
to
TLS,
Sheila
Frankel
I
think
was
the
one
who
proposed
this.
We
actually
did
a
little
bit
of
analysis
on
it.
A
Obviously,
the
client
and
you're
going
to
need
a
single
connection
and
at
the
server
end,
you're
going
to
need
many
connections
and
for
the
the
clients
connection
you
need
to
be
able
to
generate
maybe
a
hundred
bits
per
second
or
something
and
at
the
server
end,
you're
gonna
need
megabits
on
on
up
and
performance
of
this.
So
the
IPSec
use
case
is
pretty
symmetric,
whereas
the
the
TLS
case
has
concentrated
the
same
as
standard
network
architectures
right.
A
So
is
this
useful?
How
long
is
it
useful
for
let's
look
at
some
use
cases
for
with
a
couple
of
different
possibilities
for
the
key
exchange
mechanism
and
a
couple
of
different
possibilities
for
the
bulk
data,
encryption,
diffie-hellman,
plus
AES,
qkd,
plus
AES
qkd,
plus
something
I'll
call
super
80s
and
qkd,
plus
a
one-time
pad?
A
And
let's
look
at
data
that
we're
encrypting
today
at
some
point,
so
you're
encrypting
data
today
and
you're
sending
across
the
network
at
some
point
in
the
future,
it
may
become
possible
to
factor
large
numbers
or
otherwise
do
some
some
particular
mathematical
operations
farther
on
down
the
line.
Someone
may
find
some
vulnerability
in
AES,
something
we
don't
suspect
that
actually
exists
today
and
then,
maybe
in
some
sort
of
hypothetical
strawman,
maybe
it's
possible
to
test
all
of
the
keys
all
of
the
possible
key
combinations.
A
So
if
your
encrypted
ated
data
today,
the
data
is
secure
from
now
until
someone
factors
a
number
if
they
have
recorded
your
your
encrypted
conversation
today,
that's
being
sent
across
the
network
and
then
in
ten
years
this
factoring
becomes
possible.
Then
they
can
decrypt
the
conversation
you're
having
today
ten
years
from
now
with
qkg
plus
AES.
Instead,
it
stays
secure
until
AES
is
actually
broken,
and
if
you
use
some
sort
of
super
80s,
maybe
it
began.
A
Excuse
me
so
the
question
is:
is
the
gap
between
these
two
states
of
future
history
actually
interesting
the
gap
between
when
factoring
becomes
possible
and
when
a
EES
gets
broken?
If
so,
you
should
be
looking
at
employ
deploying
a
qkd
today
if,
by
the
way,
if
you
haven't
seen
the
website,
we
tweak-d
h
org.
If
you
are
a
particular
cryptographer,
I
would
love
to
have
the
opinion
of
people
on
that
particular
approach
today.
A
If
you
want
to
do
this,
qk
D,
plus
a
yes
you're
gonna
need
data
rates
on
the
order
of
bits
per
second,
in
order
to
roll
your
keys
over
in
sort
of
reasonable
time
with
super
80s,
it's
going
to
be
the
same,
whereas
with
one
time
pad.
Obviously,
you're
gonna
need
to
be
able
to
reach
up
toward
billions
of
bits
per
second
in
order
to
do
this
sort
of
reasonably
so,
as
you
can
see,
we've
got
sort
of
nine
orders
of
magnitude.
A
performance
range
there
as
performance
improves.
A
New
capabilities
will
come
online
it'll
become
possible
to
do
new
things
all
right.
So
that's
the
crypto
use
case
the
crypto
scenario,
from
the
big
bubble
that
I
had
in
the
three
bubbles.
Let's
talk
about
distributed
computing,
there's
a
concept
known
as
blind
computation,
which
is
secure
quantum
time
sharing,
give
or
take
I'm
sure.
Many
of
you
recognize
that
deck
system
ten
up
there,
some
of
you
may
have
actually
programmed
it.
The
original
ARPANET
vision
was
taking
a
system
like
that
and
a
network
that
looked
like
this.
A
This
little
map
or
a
a
copy
thereof,
still
hung
on
the
wall
at
ISI.
When
I
arrived
at
isi
in
1986.
Oh,
this
is
the
1973
version
of
it.
So
this
is
your
art
banette,
and
then
you
have
some
small
system
in
front
that
behaves
as
a
front-end
and
we're
going
we're
going
to
connect
our
small
quantum
can
at
our
house
or
laboratory
and
connect
it
to
a
mainframe
across
the
quantum
internet
and
everything's
gonna
be
hunky-dory
right.
Oh,
this
is
gonna,
be
cool.
A
Well,
that's
not
bad
right,
it's
not
bad,
but
why
is
that
different
from
what
we
can
do
today?
We're
literally
my
group
in
Japan
right
now
is
literally
connecting
via
the
existing
Internet
to
IBM's
research
center
in
Yorktown
Heights
and
using
their
quantum
computers
that
are
in
a
laboratory
in
New
York
remotely
from
from
Japan.
So
right
we
can
already
do
that
right.
So
what
do
we
need?
A
quantum
internet,
for
we
can
already
build
distributed
systems
like
that.
A
Well,
what
you
get
by
being
able
to
do
this
in
a
distributed
fashion
and
doing
this
using
a
quantum
Internet
and
this
blind
computation
is.
It
allows
us
to
execute
a
computation
on
the
server
in
which
the
server
learns
nothing
about
the
clients
data,
either
the
input
or
the
output,
nor
even
the
computation,
except
some
sort
of
upper
bound
on
the
size
of
the
computation
itself.
So
in
that
sense,
it's
actually
even
stronger
than
the
classical
version
of
the
classical
homomorphic
encryption.
If
you're
familiar
with
that,
so
I
really
love
this.
A
This
is
I
think,
ultimately,
one
of
the
driving
reasons
to
build
a
quantum
Internet,
and
it's
also
going
to
open
up
a
whole
lot
of
interesting
applications
across
a
variety
of
things,
and
this
has
actually
even
been
demonstrated
in
the
laboratory
at
sort
of
the
one
qubit
level
and
we're
not
talking
about
some
giant
computation
but
doing
it
via
some
analysis.
We've
actually
found
that
it's
going
to
take
very
high
data
beyond
data
rates
in
order
to
execute
this
for
large
computation,
it's
maybe
10
to
the
10
somewhere
around
there.
A
A
Third
scenario
that
I
mentioned
was
sensor
networks,
so
I
sort
of
defined
sensor
networks
sort
of
broadly.
There
are
algorithms
that
have
defined
for
doing
high-precision
clock
synchronization.
There
are
algorithms
for
doing
high-precision
position
finding
and
in
this
particular
case
there
are
also
algorithms
for
taking
distributed
quantum
states
and
using
them
as
essentially
a
phase
reference
in
astronomical
interferometry,
which
allows
you
to
get
higher
resolution
images
than
couldn't
be
done
using
the
existing
interferometry.
That's
done
between
antennas
like
these
a
couple
of
antennas
in
this
picture,
so
this
looks
this
looks
really
great
too
right.
A
In
theory.
We
can
use
this,
for
you
know
sorts
of
cyber-physical
uses
and
improving
different
kinds
of
sensor
networks
as
we
go.
Sadly,
this
one's
also
an
even
higher
bandwidth.
This
is
probably
going
to
take
something
like
10
to
the
11
operations
per
second
or
bits
per
second
entanglements
per
second.
A
In
order
to
do
this
sort
of
usefully-
and
finally
this
is
an
area
I
actually
haven't,
spent
much
time
looking
at
because
I'm
not
I'm,
not
certain,
it's
actually
practical,
but
there
are
a
number
of
research
papers
out
there
that
are
showing
that,
given
the
existence
of
entanglement,
we
can
actually
get
exponential
reduction
in
the
number
of
rounds.
You
need
to
solve
particular
problems.
You
know
exponential
as
the
size
of
your
network
grows,
so
there's
a
set
of
things
that
are
out
there
potentially
worth
taking
a
look
at
at
some
point
technical
demands.
A
Some
of
these
require
only
the
ability
to
actually
measure
Q
of
photons
that
come
at
you,
so
you're
sitting
at
home.
You
don't
necessarily
have
to
have
a
complete
quantum
computer
at
home,
but
you've
got
a
pipe
coming
in.
You've
got
a
five
or
something
coming
in,
and
individual
photons
are
coming
out
of
that
fiber.
You
need
the
ability
to
measure
those
that's
at
one
end
of
the
technical
spectrum.
A
The
other
end
of
the
technical
spectrum
is
runs
all
the
way
from
all
the
way
up
to
having
really
high
precision
quantum
memories
and
a
large-scale
quantum
computer
at
your
node.
In
order
to
actually
execute
interesting
algorithms
over
that
and
that's
sort
of
a
relatively
long
way
away.
This
is
on
the
lower
left.
There
is
a
series
of
stages
that
the
evolution
these
networks
will
go
through
again,
that's
part
from
the
roadmap
that
was
actually
developed
by
a
Stephanie
Vayner
and
her
team.
A
Any
questions
on
applications
now
might
be
a
reasonable
time
to
ask
for
that.
For
the
first
round
of
questions,
I've
been
talking
for
about
20
minutes
now,
20
minutes.
Yes,
questions
I
can't
possibly
have
convinced
everyone
that
all
of
this
is
entirely
practical,
which
means
that
if
there
are
no
questions
that
none
of
you
have
understood
any
of
it
right,
I,
don't
believe
either
of
those
things
to
be
true.
So
I'm
sure
someone
here
has
a
question.
A
An
important
thing
to
note,
which
I
should
have
said
and
emphasized
repeatedly
way
up
here
at
the
front,
so
to
speak.
The
is
that
quantum
repeaters
are
not
the
same
thing
as
classical
repeaters.
Don't
blame
me:
don't
blame
Tracy
blame
whoever
it
was
that
wrote
the
first
paper
on
these
things
about
20
years
ago
and
called
them
repeaters.
They
are
not
like
classical
repeaters.
They
are
not
so
amplifiers.
A
They
are
nodes
that
are
actually
active
devices
during
a
particular
set
of
operations
that
are
used
to
help
us
extend
entanglement
across
multiple
hops
and
we're
going
to
get
into
the
architecture
of
that
stuff
for
the
next
hour.
So
good
question,
though,
thank
you
for
bringing
that
up,
since
that
was
a
good
technical
point.
Yes,.
B
To
the
sense
of
you
know,
if
you
can
create
a
quantum
state
as
a
resource
to
use
for
your
computation,
then
yeah
at
that
point
it
doesn't
matter
to
us
how
far
apart
it
is,
but
it's
in
order
to
create
those
quantum
states
over
long
distances
that
we
then
need
repeaters.
So
it's
in
the
repeaters
are
kind
of
for
the
creation
of
quantum
states,
as
resources
and
I.
Think
we'll
get
more
to
the
details
of
that
coming
up.
Does.
D
A
At
the
moment,
so
my
team
in
Japan
is
using
a
20,
qubit
superconducting
computer
that
sits
in
a
laboratory
in
Yorktown.
I
was
chatting
with
my
team.
You
know,
via
slack
just
right
before
we
started
this
and
they're
actually
doing
some
stuff
right
now,
but
those
existing
machines,
the
20
cubits
systems,
are
good
enough
to
start
testing
stuff
and
start
running
very,
very
tiny
algorithms
on
top
of
them,
but
nothing
not
like
anything
that
you
would
really
recognize
as
sort
of
a
reasonable
computation.
It's
still
pretty
much
at
the
test
stage.
A
My
group
is
working
on
compiler
technology,
so
we're
trying
to
figure
out
how
to
optimize
programs
that
are
written
by
a
by
a
programmer
in
a
python-based
toolkit
called
kids
get.
This
is
the
kids
kid
t-shirt.
If
you
use
kids
kit,
you
can
you
can
kiss
kit
has
functions
built-in
for
for
logging
into
the
remote
system.
A
Excuse
me
and
sending
your
program
from
your
laptop
to
their
controllers
over
there,
and
then
they
execute
it
10,000
times
over
there,
and
then
they
give
you
back
statistical
data,
there's
no
real,
interactive
control.
It's
very
much
batch
stuff
that
you
can
do
and
the
sets
of
things
that
you
can
do
with
it.
There
are.
There
are
a
handful
of
very
small
algorithms
that
you
can
run
on
that
and
then
sort
of
squint
and
say
yeah.
The
data
kind
of
looks
like
what
it
was
supposed
to,
but
they're
getting
better
rapidly.
A
You
know,
iBM
is
releasing
new
machines.
You
know
a
couple
of
times
a
year
a
couple
times
a
year.
It
might
be
a
little
bit
of
an
exaggeration
but
they're
a
bunch
of
people
out
there
who
have
machines
that
are
actually
available
now
on
the
network.
Some
of
them
are
available
for
free
iBM
has
won
five
qubit
computer
and
114
Cupit
computer
that
anybody
can
go
login
login
on
the
create,
an
account
and
run
things
remotely
from
here.
So
do
Righetti
and
google
and
other
people
well.
A
B
E
A
A
You,
your
bulk
encryption,
using
keys
generated
via
standard
diffie-hellman
and
another
layer
using
keys
generated
by
qkd,
and
you
can
either
view
that
as
a
way
to
mollify
people
who
don't
believe
in
qkd
or
view
it
as
they
don't
have
faith
in
their
own
device
to
sort
of
take
your
pick
but
yeah.
So
this
so.
E
A
Sood
is
the
I
saw
you
moving.
That
way.
Does
that
mean
there
was
a
question
by
a
jabber
or
something
no
okay,
time
wise?
We
should
move
on
so
some
basic
terminology
and
questions
or
concepts.
1
2,
3,
4,
5,
6,
7
concepts,
I'm
not
going
to
go
through
all
of
these
in
detail.
These
are
sort
of
vocabulary
for
you
it
for
you
to
a
vocabulary,
homework
for
you
to
take
home
and
look
at
you'll
get
a
few
of
these.
A
As
we
go
a
few
terms
we
will
actually
use
in
the
course
of
this
quantum
amplitude
means
the
amount
of
your
total
quantum
probability
wavefunction
thingamabob,
that
is
in
a
particular
state,
and
it's
represented
by
a
complex
number.
A
pure
state
means
a
quantum
state
where
your
hardware
actually
worked.
The
way
it
was
supposed
to.
It
actually
did
what
it
was
supposed
to
do,
and
we
described
that
as
having
a
fidelity
of
1.0.
A
So
an
entangled
state,
we've
already
talked
about
a
little
bit.
One
that
has
sort
of
these
shared
properties
means
it
can't
be
separated
and
bellperre
is
a
particular
type
of
entangled
state.
It's
the
canonical
form
of
two
qubit
state
which
we're
going
to
get
to
so
superposition,
so
we've
all
seen
waves,
you've
seen
another
wave
like
this
to
it
with
slightly
different
frequencies.
You
add
them
up
and
you
get
something
that
looks
like
that
right.
This
is
normal
waves
at
the
moment.
A
We're
not
doing
anything
at
all
quantum,
but
this
gets
you
what
you
call
interference
so
over
here
at
the
left,
where
your
two
waves
are
in
phase,
they
add
up
and
you
get
what's
called
constructive
interference
and
they're
in
the
middle,
where
the
waves
are
out
of
phase,
they
cancel
out
and
you
get
what's
called
destructive
interference.
This
happens
at
the
quantum
level
with
individual
photons
and
individual
electrons
and
whatnot.
That's
one
of
the
key
concepts
that
that's
actually
required
to
understand.
Quantum
computing
all
right.
A
So
a
couple
of
things
about
the
basic
mathematical
notation
dude
named
Dirac,
who
is
one
of
the
people
who
helped
create
quantum
mechanics
to
find?
What's
called
the
bra,
ket
notation
you'll
see
there
a
couple
of
examples
or
three
examples
of
two-dimensional
vectors
and
what
we
do
is
we
write
this
like
this
using
this
funny
vertical
pipe
and
an
angle
bracket?
That's
our
what
we
call
our
zero
state,
so
that
vector
is
defined
to
be
the
zero
state.
A
A
This
is
direct
Dirac's,
ket
notation.
You
might
have
guessed
from
from
the
from
the
title
of
the
slide
already.
There
is
also
a
thing
called
the
bra
notation.
The
bra
points,
one
way
that
get
the
other
and
you
put
them
together,
you
get
a
proc.
Yet
how
nice,
when
you
have
two
qubits,
when
we
have
one
qubit,
you
have
two
amplitudes,
because
you
have
two
states
0
and
1.
When
you
have
two
qubits,
you
have
four
states.
You
have
four
amplitudes
0
0,
0,
1,
1,
0
and
1
1.
A
When
you
have
3,
you
have
eight
amplitudes
and
you
can
go
on
from
there
exponentially
large
number
of
possible
amplitudes.
In
this.
There
are
2
to
the
N
elements
in
what
we
call
your
state
vector,
which
describes
the
system
and
each
one
of
those
amplitudes
is
a
complex
number.
When
you
have
n
qubits
in
your
system,
ok,
the
probability
of
measuring.
So
when
you
go
and
you
look
at
this
system,
you
collapse
the
state
so
that
you
find
it
in
exactly
one
of
those
states.
B
B
These
are
both
theoretical
perspectives
and
then
a
series
of
beautiful
experiments,
one
of
the
earliest
experimenters,
is
on
ask
Bay
in
Paris,
really
pointing
out
that
that
these
nonlocality
is
is
not
these.
What's
known
as
a
local
hidden
variable
here,
you
cannot
explain
experiments
and
that,
therefore
we
have
to
sort
of
live
with
this
idea
of
nonlocality,
so
go
into
a
little
bit
more
detail
now
about
these.
These
kind
of
three
different
comments
so
einstein-podolsky-rosen.
This
is
this
1930s
paper.
B
What
we
would
describe
so
here's
here's
a
quote
from
this
paper:
if
without
in
any
way
disturbing
a
system,
we
can
predict
with
certainty
the
value
of
a
physical
quantity.
Then
there
exists
an
element
of
physical
reality
corresponding
to
this
physical
quantity.
So
as
physicists,
we
talk
about
local
realism,
and
this
is
what
we
even
buy.
The
realism
part
that
there
is
a
once.
We
measure
something
we're
going
to
get
this
particular
answer.
B
So,
what's
the
argument
behind
this,
this
einstein-podolsky-rosen
paper
that
we
we're
going
to
assume
that
there's
a
locality
that
is,
we
can't
signal
faster
than
the
speed
of
light
between
distant
locations.
So
no
immediate
signalling,
and
also
we're
going
to
assume
that
of
single
measurement
generates
a
single
result
and
the
result
of
you
know
what
they
come
out
of
after
some
arguments
is
to
say
that
quantum
mechanics
is
either
non-local
at
either
violates
the
first
statement
or
it's
incomplete.
B
He
derives
a
very
specific
inequality
and
he
shows
that
if
you
have
a
local
hidden
variable
theory,
it
has
to
satisfy
that
inequality.
And
then
you
can
take
quantum
mechanics
as
we
know
it,
plug
it
in
and
show
that
quantum
mechanical
States
violate
this
inequality.
So
if
quantum
mechanics
is
true,
we
have
to
accept
that
then
this
nonlocality
again,
that
was
this
theoretical
perspective
and
then
quite
soon.
Afterwards,
the
messages
quantum
mechanics
cannot
be
described
with
the
local,
hidden
variable
theory
and
yeah.
So
what
do
you
do?
Experimentally
with
that?
B
You
know
people
can
always
kind
of
think
of
interesting
loopholes
and
will
continue
to
do
so,
and
that's
very
nice,
but
I
think
that
the
ones
that
people
have
been
most
concerned
about
for
these
felony
qualities
have
been
closed.
Experimentally,
and
so
it's
really
a
beautiful
experimental
demonstration
that
that
quantum
mechanics
is
very
weird
and
and
so
yeah
there's
also
I.
Should
you
know
I'm
talking
about
a
Bell
inequality.
B
So
this
comes
to
this
brings
us
to
these
Bell
States,
and
so
in
the
process
of
deriving
this
inequality,
you
can
kind
of
establish
that
there
are
some
maximally
entangled
states.
These
are
there
some
states,
essentially
that
maximally
violate
these
inequalities
and
so
they're
sort
of
that
the
weirdest
States,
the
most
quantum
states
and-
and
we
give
them
these
names
that
we
always
use
for
them,
this
size
and
and
five
+
and
and
it's
states
of
two
quantum
bits.
B
So
with
this
notation
that
rod
has
already
introduced
the
first
zero
or
one
is
labeling,
the
first
quantum
bit.
The
second
one
is
labeling,
the
second
quantum
bit,
and
so,
for
example,
if
we
look
at
the
first
one,
the
first
state
in
the
upper
left-hand
corner
here,
this
five
plus
state
we're
saying
that
either
both
of
your
quantum
bits
are
in
the
state,
0
or
they're
in
the
state
1.
B
We
normalize
it
with
the
square
root
of
2,
but
the
point
is
that
if
person
a
is
in
possession
of
one
quantum
bit
be
in
possession
of
the
other,
wherever
they
are,
the
minute
that
or
you
know
instantaneously,
we
believe
when
a
measures
her
quantum
bit,
that
we
can
immediately
predict
what
the
outcome
of
B's
measurement
will
be,
and
in
this
case,
if
it's
0,
it
will
be
0.
The
end
for
the
four
side
plus
and
minus
0
will
be
1.
B
So
these
are
these
canonical
Bell
States
entangled
States.
We
say
they
can't
mathematically
written
as
separable
States
and
they
can
also
be
used
as
a
basis
set
to
rewrite
any
state
of
two
quantum
bits
and
yeah.
We
like
to
describe
these
states
as
a
resource
both
for
quantum
communication
and
for
quantum
computation.
B
You
can
imagine
kind
of
sharing
a
bell
pair
and
then
either
adding
on
top
of
it,
some
something
like
a
s
which
would
kind
of
or
sharing
many
Bell
pairs
either
adding
on
top
of
it.
Yes
or
the
best
thing
would
be
to
be
able
to
use
those
Bell
pairs
in
order
to
generate
a
one-time
pad.
But
of
course
you
would
need
a
very
high
rate
of
Bell
pairs
that
you're
sharing
between
each
other.
B
If
you
have
just
one
Bell
pair,
ideally,
then
that
lets
you
send
one
quantum
Steve
one
person
to
the
other
in
what
what's
known
for
better
or
worse,
is
this
quantum
teleportation?
And
yes,
so
we
want
to
I've.
You
know
suggest
sir
I've
explained
that
that
once
one
person
performs
a
measurement
on
her
half
of
this
Bell
pair,
then
that
person
can
predict
immediately
what
the
result
of
the
second
person's
measurement
will
be.
Does
that
mean
we
can
send
signals
faster
than
late?
No,
and
one
can
prove
this
formally
and
for
quantum
computing
right.
B
The
important
thing
is
that,
even
though
person
a
knows
she
can
predict
what
her
partner's
measurement
will
be.
That's
not
yet
the
same
as
signalling,
and
they
will
also
need
to
exchange
information
over
a
classical
channel
and
that's
going
to
be
the
bottleneck
in
terms
of
actual
communication
between
the
two
of
them.
So
they're
not
going
to
be
able
to
use
their
quantum
states
in
some
special
way
that
violates
the
that
that
happens
faster
than
the
speed
of
light.
B
F
F
B
Yes,
so
I
think
there's
maybe
I
guess
I
would
I
would
say
that
we
can't
sort
of
take
shortcuts
with
this.
With
this
speed
of
light
story,
so
there's
no
there's
no
tricks
that
we
can
play
there.
I
think
we're
always
limited
to
the
classical
communication,
speed
separately
with
communication.
There
are
really
interesting
ways
that
people
are
exploring
now
in
the
lab
to
use
kind
of
hybrid,
classical
and
quantum
computing
methods,
but
that's
different
than
then
kind
of
harnessing
this
speed
of
light
story.
I
would.
B
A
A
The
idea
is
to
move
a
quantum
state
from
one
place
to
another
to
another.
So
when
we're
talking
about
teleporting,
something
we're
not
talking
about
you're
physically
taking
this
this
camera
or
this
table,
or
something
and
having
it
reappear
in
a
different
place,
we're
just
moving
the
information
that
represents
it
from
one
place
to
another
in
the
quantum
context.
A
So
that's
Charlie-
and
this
is
the
particular
paper
dates
to
a
1993
and
it
was
actually
demonstrated
experimentally,
not
too
long
after
that,
fairly
quickly
by
a
couple
of
groups.
Let's
see
so
what
is
it?
We
got?
Alice
and
Bob.
Alice
has
a
qubit
a
data
qubit,
so
we'll
label
it
D,
and
the
idea
is
that
Alice
wants
to
take
that
quantum
information
and
send
it
from
where
she
is
over
to
where
Bob
is
sounds
nice
right.
So
how
are
we
going
to
go
about
doing
that?
A
We're
not
going
to
go
through
the
math
in
this
particular
part,
but,
as
we
noted
earlier,
you
can
treat
these
as
a
as
a
basis
set
that
will
fill
any
two-dimensional
space
with
complex
numbers,
and
we
take
advantage
of
that
fact
in
the
teleportation
operation.
So
we
start
with
a
single
qubit,
which
is
in
some
state
that
we
don't
know.
Maybe
it's
something
we
prepared,
or
maybe
it's
something
that
somebody
else
prepared
and
gave
to
us.
We
don't
know
what
it
is,
as
we
already
noted.
A
So,
for
example,
with
this
single
qubit
you've
got
alpha,
is
your
quantum
amplitude
for
the
state
0
and
beta?
Is
your
quantum
amplitude
for
the
state
1
the
probability
that
you'll
measure
alpha
or
measure
0
is
the
absolute
value
of
alpha
squared
and
the
probability
that
you'll
measure
1
is
the
absolute
value
of
beta
squared
and
on
the
right
and
at
the
bottom.
You
can
see
what
happens
when
you
perform.
A
Some
simple
operations
is
on
this:
that
we
call
the
X
and
Z
operation
so
now
I'm
going
to
go
into
the
details
of
what
happens
with
those,
but
those
are
two
basic
operations
on
a
single
qubit
yeah.
So
what
happens?
Alice
has
this
qubit?
She
wants
to
get
it
to
Bob.
So
what
she
does
is
she
begins
by
creating
one
of
these
Bell
pairs.
A
She
takes
this
and
well
some
I'm,
sorry,
not
in
this
case,
in
this
diagram,
we're
showing
them
being
created
here
in
the
middle.
So
somebody
else,
a
third
party
is
creating
this,
this
quantum
Bell
pair
to
two
qubits.
We
call
a
and
B
we
take
those
we
distribute
them,
one
to
Alice
and
one
to
Bob.
So
Alice
now
has
two
qubits
the
data
qubit
that
she
wants
to
send
to
Bob
and
this
a
qubit
which
is
a
generic
resource.
A
So
this
is
something
that
you
know
that
the
network
can
make
and
it
is
used
for
doing
this
teleportation
she
takes
her
qubits
and
she
performs
what's
called
a
Bell
State
measurement,
which
is
a
joint
operation.
The
two
cubans-
it's
not
the
same
thing
as
measuring
the
two
of
them
independently,
but
when
she
does
this
she's
gonna
get
two
bits
of
classical
data
out
of
it
in
this
case
is
zero
and
one,
and
she
has
to
send
those
to
Bob.
A
So
it's
moving
the
information
from
this
and
note
that,
even
though,
in
this
diagram
we
drew
a
and
B
and
coming
from
one
place
and
spreading
out,
there's
not
even
a
requirement
at
the
mathematical
level
that
these
be
the
same
kind
of
physical
qubits,
so
D
could
on
the
Left,
could
be
the
state
of
one
of
the
ions
in
Tracy's
laboratory
and
D
on.
The
right
could
be
the
state
of
one
of
the
superconducting
qubits
in
Yorktown.
A
If
we
can
figure
out
how
to
connect
those
at
the
physical
level
in
the
mathematics
supports
that
all
right,
so
implementation,
stuff
I
think
we
should
take
a
couple
minutes
break.
What
do
you
all
think
who
wants
a
break
all
right?
Let's,
let's
see
it's
503
restart
at
five:
oh
eight,
five
minutes
that
should
be
enough
time
for
everybody
to
walk
down
the
hall
and
back
restart
at
five.
Oh
eight
sharp
stand
up
stretch
and
then
we'll
restart.
A
A
Who
has
come
up
with
questions
over
the
last
five
minutes
while
chatting
with
their
neighbor
or
otherwise
circulating
blood?
A
little
bit
more
closely,
somebody's
stuck
a
hand
up
got
a
question.
Come
ask
her,
come
ask
your
questions
and
then
we'll
go
from
there
into
our
implementations.
Oh
we've
got
actually
several
people.
G
E
G
Jones
so
I
mean
think
you
said
in
the
last
bit
there
that
you
take
the
bell
pair.
One
part
goes
to
each
party,
yes,
there's
some
computation
or
mutual
observation
that
happens
on
the
left
side
and
then
some
classic
state
bits.
So
it's
some
classic
bits
are
sent.
I
eat
normal
data
bits.
Is
that
to
the
far
side
they.
A
Are
they
are
two
million
to
two
data
bits
to
classical
data
bits
that
get
sent
left
to
right?
Yes,
as
it
happens,
because
of
the
way
the
operations
that
Alice
performs,
those
two
bits
are
guaranteed
to
be
completely
random.
There's
no
way
you
can
predict
what
they're
going
to
be
Alice,
just
measures
them
and
gets
to
random
bits
sends
those
to
Bob
and
he
uses
them
to
finish
the
reconstruction
of
that
D,
State.
G
I
Actually,
the
way
I
see
it.
This
looks
a
lot
like
information
theory.
What
you
do
is
you
take
an
amount
of
information.
You
do
a
known
operation
on
it.
You
send
that
operation
result
over
the
network
and,
at
the
other
end,
because
you
know
in
common
with
code,
was
used,
you
transform
it
back.
Is
that
a
good
analogy
would.
B
A
A
J
State
your
name,
Robin,
Wilton,
I,
think
I
can
guarantee
I
won't
be
sitting
down
and
saying.
Yeah
I
understand
this
now.
But
my
question
is
that
in
the
presentation
so
far
it
seems
to
me
that
you
have
treated
quantum
computing
and
quantum
entanglement
is
essentially
the
same
thing,
because
you've
only
talked
about
quantum
computing
and
distributed
nodes.
Will
you
be
talking
about
quantum
computing
on
single
nodes
at
any
point,
or
is
that
something
I
should
just
go
away
and
read
about
not
quite
sure,
I
follow
the
question.
So
ok,
it
was
a
dumb
questions.
B
And
by
focusing
for
the
tutorial
on
quantum
networks
in
quantum
of
Peters
we're
sort
of
putting
quantum
computers
to
the
side,
you
know
we
might
want
to
use
them,
but
they're,
not
the
focus,
because
there's
something
that
would
happen
at
a
single
node
and
they
wouldn't
be
distributed
in
general
I
would
I
think
we
can
make
the
same.
That
you
did
entanglement
as
a
resource
would
be
something
we.
We
would
expect
that
you
need
for
a
quantum
computer,
yeah,
yeah,
ok,.
B
I
didn't
mention
earlier:
I
am
I'm
working
at
the
Institute
for
experimental
physics
at
the
University
of
Innsbruck,
and
we
I'm
the
hardware
person
here,
although
I
don't
usually
think
of
it
as
hardware
I,
think
of
it
as
atomic
physics
or
but
but
yeah
in
this
in
this
audience,
I
think
that's
what's
consoles
Hardware.
So,
let's
think
about
how
I
can
make
my
own
Bell
pair
and
what
we
want
to
remind
you.
We
want
to
come
back
to
this
idea
of
a
quantum
system
with
two
levels
and
and
encode
information
in
those
two
levels.
B
So
we
we
kind
of
look
out
in
the
world
and
we
try
to
find
systems
where
we
would
have
these
kind
of
two
levels:
0
and
1,
where
we
can
have
these
amplitudes.
That
rods
sketched
out
mathematically
and
you
know,
and
we
then
we
start
to
get
picky
and
we
say:
well,
we
don't
just
need
a
system
with
two
levels.
What
else
do
I
want?
B
Well,
my
quantum
bits
should
be
something
I
can
entangle
with
one
another
in
some
straightforward
way,
and
we've
also
heard
that
you
want
to
be
able
to
measure
those
quantum
bits
and
actually
in
different
bases.
So
you
want
to
be
able
to
perform
these
different
measurements.
That
is,
you
want
to
be
able
to
change
the
phase
in
which
you
measure
the
quantum
bits
in
in.
In
this
description,
where
we
said
we
can
describe
two
quantum
bits
in
a
basis
of
these
Bell
Pat,
these
four
Bell
States.
B
We
want
to
be
able
to
measure
them
in
all
the
different
Bell
States
to
project
them
in
this
linear
algebra
picture
onto
one
of
the
four
Bell
States
and
both
entanglement
and
measurement.
We
want
those
to
be
fast
and
we
want
those
to
be
accurate
and
we
don't
want
to
be
losing
information
to
our
environment.
So
we've
drawn
this
very
beautiful,
formal
picture
where
we
only
talked
about
the
quantum
states
and
that's
assuming
that
we
can
isolate
those
quantum
states
from
their
environment.
B
But
you
should
kind
of
keep
in
mind
that,
in
that
sense,
entanglement
and
measurement
are
sort
of
at
odds
with
each
other,
because
in
this
beautiful
space
of
entangled,
we
want
to
keep
everything
as
far
away
from
the
rest
of
the
world
and
only
have
those
states.
But
as
soon
as
we
talk
about
measurement,
this
is
an
interaction
with
the
rest
of
the
world.
So
we
need
to
protect
them,
except
when
we
don't
want
to
protect
them,
and
then
we
need
to
be
able
to
measure
very
fast
right.
B
The
this
interaction
with
the
environment
can
can
cause
what
we
would
describe
as
decoherence.
It
would
create.
What
we've
heard
from
from
Radha
is
a
mixed
state.
It
it
reduces
what
we
would
describe
as
the
the
coherence
between
these
different
parts
of
the
quantum
state,
which
again
you
can
think
of
in
sort
of,
as
as
a
phase
relationship
between
waves.
So
it's
nothing
mystical.
It's
just
this
wave
picture
here
and
you
want
to
establish
a
definite
phase
relationship
and
when
you
start
adding
other
and
other
systems
into
the
picture,
you
lose
that
phase
relationship.
B
You
might
also
like
to
be
able
to
move
those
quantum
bits
around,
especially
since
we're
talking
about
networks-
and
you
know
this
might
be
obvious,
but
actually
you
know-
maybe
not
in
this
community,
where
you.
You
also
know
that,
as
you
make
your
hardware
smaller
and
smaller
you
you
run
into
very
physical
defects,
and
so
it's
it's
a
very
sensible
demand
that
one
qubit
should
be
like
another
qubit
that
we
want
to
not
have
to
deal
with
the
idiosyncrasies
of
individual
qubits,
so
yeah,
there's
okay.
B
This
actually
uses
an
abbreviation
that
I
got
rid
of
earlier
here
and
I.
Don't
I
actually
mean
two
level
system
here
so
and
I
and
I
tried
to
get
rid
of
that
for
lack
of
confusion
and
I
failed,
so
two
level
system
referring
to
these
quantum
mechanical
two-level
systems
and
so
yeah.
There
are
many
different
possible
platforms
and
it's
going
to
depend
on
your
application,
so
photons.
This
is
a
great
idea.
Why?
Because
we
have
this
huge
resource
of
of
optics
as
an
industry
that
we
can
buy
a
lasers
off
the
shelf.
B
We
have
lovely
optical
fibers
wave
plates
detectors.
So
it's
it's.
You
know
a
very,
relatively
straightforward
thing
to
set
up
these
kind
of
optics
experiments
in
the
laboratory,
but
when
we
want
the
stores,
quantum
states
photons,
we
kind
of
start
talking
about
photons
as
individual
objects,
and
it
becomes
a
little
bit
tricky
or
more
than
a
little
tricky
to
work
with
one
and
only
one
photon,
and
so
that
you
know
that
is
a
challenging
story
that
one
could
talk
about
for
a
long
time.
B
Also
yeah,
they
they're
always
moving
right,
and
so
there
might
be
times
where
we're
drawing
these
sketches
of
quantum
states,
for
you
and
you
want
to
say,
put
a
put
a
quantum
state
in
a
box
and
have
it
stay
there
and
for
photons.
The
only
thing
you
could
do
is
have
it
run
around
in
an
optical
fiber
and
eventually
the
losses
in
that
fiber
are
going
to
start
to
catch
up
with
you
atoms.
Okay.
B
So
if
you
want
things
to
stay
in
one
place,
atoms
are
nice
for
that,
and
we
also
have
a
lot
of
tools
with
which
we
can
manipulate
atoms.
We
can
have
very
precisely
controlled
interactions
between
the
electronic
states
of
our
atoms,
using
lasers
or
using
microwaves
depending
on
the
particular
atomic
transition.
So
here
the
two
levels
would
be
about
choosing
different
electronic
states.
We
can
use
these
atoms
for
storage
and
processing,
so
we
can.
That
is.
We
can
not
only
map
States
onto
the
atoms,
but
can
very,
very
precisely
store
and
manipulate
information
within
them.
B
B
But
this
brings
us
back
to
questions
of.
Are
these
systems
really
identical
with
one
another?
Now
that
we're
fabricating
things?
You
know
if
I
have
a
cesium
atom?
I
can
believe
that
it's
gonna
be
identical
to
this
other
cesium
atom
that
I
can
find.
But
you
know
this
gets
a
little
bit
more
challenging
here
with
these
artificial
atoms.
Also,
the
multi-level
structure
that
one
can
fabricate
becomes
a
little
bit
more
complicated
again.
B
Photons
really
seem
like
a
very
clear
choice
here,
and
so
this
also
maybe
comes
back
to
the
first
question
that
was
asked
in
the
first
half
of
the
tutorial
about
about
the
role
of
distance,
because
we
can
think
about.
If
we
want
to
make
bell
pairs,
you
know
what
does
it
mean
to
make
a
bell
pair
and
if
we're
making
them
in
for
making
a
bell
pair
at
a
single
location
in
space
and
then
distributing
that
bell
pair
over
space,
then
we
have
to
think
about
how
we
can
distribute
it
with
the
minimum
loss.
B
Okay,
I
want
to
give
you
a
kind
of
one
slide
on
each
of
these
pictures
on
photons
and
atoms.
So,
just
to
briefly
give
you
the
sense
of
how
we
could
encode
0
and
1
in
a
photon.
Well,
we
can
use
polarization,
so
we
could
take
advantage
of
put
of
photons
having
this
property
of
having
two
orthogonal
polarizations.
We
can
use
time
binnen
coatings
did
a
photon
come
early.
Did
it
come
late
and
sort
of
identify
to
discrete
time
bins?
B
We
can
also
encode
it
in
the
number
of
photons
and
0,
and
1
would
typically
be
the
numbers
that
people
use
so
either
I
have
no
photon
or
I
have
one
and
the
final
one
that
people
often
use
is
a
path.
Having
two
different
paths
and
saying:
did
the
photon
go
left
or
did
it
go
right?
This
is
a
picture
from
Jeremy
O'brien's
science
review
article
back
in
2007,
just
kind
of
some
sketches
where
he
depicts
certain
certain
aspects
of
this
encoding.
B
So
it's
a
here
you
see
in
the
upper
left-hand
corner
a
sketch
of
the
two
orthogonal
polarizations
that
you
could
use
for
a
polarization
based
encoding
and
then
the
question
of
how
you
would
do
gate
operations
that
rod
described
on
your
quantum
bits
here.
So
in
this
case
one
could
use
wave
plates.
This
is
what's
depicted
below.
If
you
can,
you
can
use
half
wave
plates
and
quarter
wave
plates
to
rotate
these
photons
and
those
are
single
qubit
gates.
Those
are
changing
the
state
of
a
single
qubit
and
then
in
the
fourth
picture.
B
It's
a
it's.
Actually.
A
picture
of
this
kind
of
path
story
are
actually
converting
between
a
polarization
encoding
and
a
path
encoding.
So
there
are
lots
of
interesting
techniques
for
manipulating
these
photons
as
quantum
bits
and
then
just
a
kind
of
a
glimpse
at
this
idea
about
atoms.
So
you
want
to
you
know:
you
have
a
whole
periodic
table
to
choose
from,
and
you
want
to
think
about
two
electronic
States
that
be
well
suited
for
for
for
a
qubit,
so
you
want
to
think
about.
You
know
what
the
lifetimes
are
of
these
states.
B
You,
you
certainly
would
want
to
have
the
both
of
the
states
be
be
relatively
stable,
they
don't
they
don't
need
to
be
infinitely
stable,
and
can
you
manipulate
these
states
easily,
for
example,
with
lasers
that
are
available
off
the
shelf
or
with
microwaves
that
you
can
kind
of
dial
in
into
in
in
the
lab?
Maybe
these
states
are
particularly
robust
with
respect
to
environmental
fluctuations,
and
that
would
be
certainly
a
plus.
B
So
under
ultra-high
vacuum
we
apply
radiofrequency
to
these
electrodes
of
this
trap
and
we
this
provides
a
potential
well
in
which
we
can
trap
strings
of
charged
particles.
And
if
we
can
use
lasers
to
cool
these
particles,
then
they
actually
stay
in
these
traps
for
days
or
you
know
even
enough
to
you
know
several
days
or
weeks
depending
on
the
conditions
and
the
species.
This
is
a
really
beautiful
camera
image
from
Ryanair
blots
group
in
innsbruck,
where
they've
really
pioneered
quantum
computing
research
with
trapped,
ions,
and
so
this
is
about.
I
forgot.
B
I
counted
one
side,
something
like
50
ions
and
there
we're
looking
at
fluorescence
from
those
individual
ions
they're
repelling
each
other,
because
they're
all
positively
charged
they're,
all
calcium
ions,
with
a
single
charge
so
on
one
hand,
they're
kind
of
pushing
each
other
away,
but,
on
the
other
hand,
they're
all
sort
of
being
trapped
at
the
same
time
by
the
radiofrequency
voltages
applied
to
this
trap.
So
we
get
this
kind
of
string,
this
register
of
ions
that
one
can
use
potentially
for
computing
or
also
for
networking
capabilities.
B
Okay.
So,
let's
get
back
to
this
plan
of
making
bail
pairs
and
how
would
we
generate
remote
entanglement,
and
so
this
is
I'm
going
to
kind
of
sketch
out
a
couple
of
ways
you
can
do
this.
This
is
an
idea
of
how
to
do
this.
Probabilistically
and-
and
one
idea
would
be
that
you
have
two
atoms
here,
which
again
could
be
these
artificial
atoms
and
you
could
have
each
atom
emit
of
photon.
So
that's
what
you
see
in
this
upper
left-hand
corner
picture
the
atom
at
node,
one
in
the
atom
at
node.
B
Two
are
both
emitting
photons
and
so
there's
a
couple
of
variations
here.
One
variation
is
either
the
atom
emits
a
photon
or
it
doesn't.
That
would
be
what
we
call
a
number
state
encoding
of
the
photon,
and
we
could
say
that
maybe
we
could
engineer
it
so
that
the
atom
state
depends
on
whether
or
not
an
emitted,
a
photon.
B
It's
a
single
photon,
that's
detected
in
the
sketch
below
it's
it's
two
photons
that
are
detected,
but
the
most
important
thing
is
that
the
detectors
can't
tell
which
atom
generated,
which
photon
or
if
it
was
a
one
photon
which
atom
generated
that
one
Photon,
and
that
lack
of
distinguishability
indistinguishability
means
that
the
detection
event
actually
projects
the
atoms
into
an
entanglement
entangled
state.
So
we
would
say
that
this
act
of
measurement
prepares
an
entangled
state
between
these
two
atoms.
So
that
sounds
actually
kind
of
easy.
B
You
can,
you
know,
kind
of
get
each
of
two
atoms
to
make
a
photon
and
you
need
to
measure
the
photons
and
then
they
sort
of
turn
up
entangled
and
yeah.
This
is
again,
as
I
said,
the
key
principle,
this
indistinguishability
from
the
perspective
of
the
detectors,
and
so
the
the
first
experiments
on
this.
B
This
really
pioneering
experiments
were
done
at
the
University
of
Maryland
or
actually
originally
at
University
of
Michigan
and
Kris
Munroe
I
was
the
principal
investigator
is
now
at
the
University
of
Maryland
or
the
joint
quantum
Institute,
and
he
you
know
in
a
series
of
experiments
for
kind
of
more
than
a
decade.
He's
done
exactly
this.
So
here's
a
picture
of
a
of
the
kind
of
ion
trap
that
they
use
in
their
system,
where
it's
a
it's
sort
of
a
more
complex
version
of
the
radiofrequency
trap.
B
That
I
showed
you
earlier,
where
they
can
apply
again
radiofrequency
voltages
to
this
trap
in
order
to
confine
ions
in
this
very
small
space
in
between,
and
actually
they
have
two
different
traps
here
in
this.
This
is
a
picture
taken
from
their
2015
paper,
where
they
have
traps
separated
by
a
couple
of
meters
and
in
each
of
these
boxes,
they're
achieving
ultra-high
vacuum
conditions.
You
know
that,
are
you
know,
twelve
orders
of
magnitude,
thirteen
orders
of
magnitude
lower
than
atmosphere
in
one
of
their
vacuum
chambers.
B
They
have
two
of
these
atoms
and
there
you
terbium
ions
in
both
cases
in
the
other,
they
have
just
one
atom,
and
so
they
pick
one
from
the
first
chamber,
one
atom
from
the
second
chamber
each
atom.
They
managed
to
entangle,
with
an
eye
with
a
photon.
Those
photons
go
on
to
a
beam
splitter
here
to
erase
information
about
the
direction
that
the
photons
came
from,
and
then
they
measure
the
photons
at
the
end-
and
this
is
just
sort
of
a
just,
a
picture
that
described
that
shows
the
electronic
states
for
these
atoms.
B
And
so
the
important
thing
for
us
is
that,
basically,
that
they
are
able
to
choose
two
different
electronic
states,
the
left
one
here
and
the
right
one
there
and
those
they
can
identify
with
their
quantum
bit.
And
then
they
have
a
scheme
where
they
use
a
laser
to
excite
the
atom
and
it
either
decays
in
one
direction,
to
one
state
or
in
the
other
direction
to
the
other
state
generating
different
polarizations.
B
And
basically,
they
can
do
some
measurements
I'm
not
going
to
and
happy
kind
of
later
on
to
go
into
the
details
of
what
it
means,
but
they
can.
They
can
characterize
their
system
in
such
a
way
that
that
proves
that
they
can
have.
They
have
entanglement
first,
they
can
show
entanglement
between
the
atoms
and
the
photons,
and
then
this
is
actually
the
basis
for
their
entangling.
B
B
Their
2007
paper,
you
know
so
on
one
hand
we
have
just
you
know
incredible
improvement
over
the
course
of
a
decade,
but
in
terms
of
rates
that
you
can
then
use
to
generate
one-time
pads,
we're
still
a
long
way
off
yeah.
So
that's
a
story
about
ions,
which
are
the
things
that
I
know
best
experimentally
in
this
context,
but
over
the
past
decade
decade
and
a
half
there
have
been
examples
of
remote
entanglement,
very
similar
experiments.
B
Sort
of
demonstrated
in
in
you
know
a
handful
of
different
settings,
and
also
in
a
few
of
these,
has
not
only
remote
entanglement
but
also
teleportation
has
been
demonstrated.
So
in
this
picture,
I
showed
you
here
we
had
the
two
quantum
bits
above
and
the
one
below
which
looks
very
similar
to
the
picture
that
you
saw
from
rod
where
you
can
then
use
the
entanglement
between
the
pair
of
the
one
above
and
the
one
below
in
order
to
teleport
a
state
between
the
two
chambers.
B
That's
been
done
with
the
ions
with
neutral
atoms,
it's
been
done
with
superconducting,
qubits
and
enemies,
actually
I
think
not
the
assault
on
Tom
walls,
but
pretty
much.
At
least
three
of
the
systems
here,
yeah,
what
I
also
want
to
emphasize
here
is
that
the
state
of
the
art
yet
now
consists
of
two
node
experiments
and
and
really
kind
of
you
know-
maybe
two
systems
over
here
on
one
side
and
once
a
store
here,
where
I'm,
limiting
myself
to
a
discussion
of
things
that
are
really
physically
separated.
B
So
yeah
there's
been
a
lot
of
progress
but
and
and
we're
looking
forward.
You
know
we
know
that
we
as
a
community
really
need
the
kind
of
help
of
people
thinking
about
networks,
but
we
don't
yet
have
those
networks
in
place
and
we're
optimistic
that
these
are
coming
quite
soon.
But
but
the
kind
of
two
node
connections
are
what
people
are
doing
right
now
and
I
think
that
gives
us
brings
us
to
repeaters.
K
B
Doesn't
it
yeah
so
yeah
I
mean
so
something
gets
it's
it's
interesting
right.
Something
gets
destroyed,
so
at
the
start
you
had
you
had
an
atom
and
a
photon
say
over
here
and
you
had
an
atom
and
a
photon
over
here
and
you
measured
the
two
photons
and
the
measurement
was
destructive,
so
the
photon
state
is
the
photons
are
gone.
B
They
were
absorbed
by
your
detector
and
and
and
there
they're
lost,
and
also
the
entanglement
that
you
had
between
the
atoms
and
the
photons.
If
that
that's
lost,
there
are
also
schemes
that
don't
rely
on
entanglement,
but
if
it
was
a
scheme
based
on
entangle,
you've
lost
that
entanglement
and
so
yeah
you
did
get
rid
of
something
in
your
measurement,
but
you
also
were
able
to
harness
this
indistinguishability
in
order
to
create
entanglement.
L
Yes,
Dave
wheeler
one
more
question,
so
you
talked
about
the
rate
at
which
entanglement
was
was
happening
and
I
think
you
said
you
know
five
times
a
second
or
something
like
that
and
that's
an
improvement.
What
is
the
sort
of
speed
or
velocity
that
we're
at
in
in
actually
improving
that
and
getting
to
the
point
where
we
can
get?
You
know
thousands
of
qubits
or
tens
of
thousands
of
qubits
and
tangled,
and
is
that
something
that
is
on
the
horizon
or
is
that
something
that
we
still
see
as
several
decades
away
so.
B
My
group
were
going
in
a
different
direction
and
we
also
think
we
should
be
able
to
talk
about
kind
of
kilohertz
rates
but
yeah,
and
then
you
can
get
more
speculative
about
how
you
keep
scaling
that,
but
but
it
seems
like
first,
you
want
to
kind
of
get
that
improvement
additionally,
having
long,
you
know
thousands
of
qubits
separately.
That
also
seems
very
promising,
but
then
combining
these
different
improvements
can
also
be
a
challenge
or,
for
example,
there
are
ways
that
you
know
extending
the
this
so-called
coherence
time
that
is
reducing
the
interaction
of
the
environment.
B
D
A
All
right,
let's
see
so
a
couple,
quick
things
and
I
forgot
to
mention
right
at
the
beginning,
occurred
to
me.
While
the
trader
Tracy
was
talking
number
one.
The
slides
for
this
are
up
in
the
data
tracker
website,
I
uploaded
them
in
both
PDF
and
PowerPoint
format,
and
both
of
the
files
are
kind
of
large.
So
tens
of
megabytes,
unfortunately,
because
of
all
the
pictures
and
whatnot
there's
a
huge
appendix
in
this
we're
only
using
about
half
of
the
slides
of
this
and
there's
a
huge
appendix
with
a
bunch
of
the
math
in
it.
A
So
if
you
want
that,
you
can
get
it
and
take
a
look
through
that
as
we
go
and
second,
while
Tracy
was
talking,
I
looked
up,
yes,
the
the
title
of
mark.
Well,
while
these
book
is
just
quantum
information
theory
keep
in
mind
that
that's
an
information
theory,
primer
or
textbook,
not
not
an
introduction
to
quantum
computing
and
certainly
not
an
introduction
to
quantum
networking.
So
if
you
like
classical
information,
theory
you'll
like
that
book
alright,
so
we
saw
this
earlier
on.
A
What's
the
job
of
a
quantum
repeater,
it's
to
make
this
base
level
entanglement
over
a
link,
which
is
what
Tracy
just
talked
about
the
ability
to
couple
entangled
links
along
an
end
in
a
and
path
to
meet.
The
applications
needs
to
build
that
to
monitor
and
manage
the
errors
and
to
participate
in
the
management
of
the
network
as
a
whole.
So
what
do
we
have?
Well
conceptual
hardware.
You've
got
you
know
a
series
of
nodes
and
each
one
has
inside
of
it.
A
Some
set
of
stationery
members
stationery
memories,
a
qubit
which
you
know
I've
drawn
using
the
atom
symbol
here,
and
these
stations
are
separated,
perhaps
by
tens
of
kilometers
they're,
not
separated
by
thousands
of
kilometers.
Generally
speaking,
they're
they're
pretty
short
distances
as
we
go.
So
how
do
we
build
entanglement
from
one
to
the
end
of
this
chain
to
the
other?
That's
what
we're
trying
to
accomplish
here.
A
There
are
also
all
optical
approaches
to
doing
this,
with
no
stationary
memories
at
all,
we're
not
going
to
talk
about
those
they
have
their
own
set
of
challenges,
their
pluses
and
minuses
we're
just
not
going
to
talk
about
them
today.
All
right,
so,
ideally,
what
you
might
like
to
have
and
what
everybody
in
this
room
probably
has
in
their
head,
is
a
store
and
for
our
Couture
and
forward
architecture
right
where
you're
taking
a
qubit
and
going
hop-by-hop
across
a
series
of
hops.
A
Unfortunately,
that's
not
gonna
work.
Why
you
take
those
individual
photons
and
you
put
them
in
a
fiber
and
you
lose
them
and
you
do
it
again
and
you
lose
it
and
then
eventually,
maybe
you
succeed
in
getting
one
through
the
through
the
the
fiber
here
and
end,
but
the
loss
in
the
channel
is
always
going
to
be
high.
It's
always
gonna
be
too
high
to
actually
encode
information
and
put
this
on
it.
Well,
always
for
a
very
long
time
now,
we'll
talk
just
a
little
bit
about
that
later.
A
So
we
have
to
find
some
way
of
dealing
with
this
with
this
tremendous
amount
of
loss
in
this,
that
means
we're
gonna
wind
up
using
some
sort
of
acknowledge
to
link
layer,
axial
Dahlberg
who's
around
here
to
axial
sticky
hand
up
so
axles
over
there
he's
from
Stephanie's
group.
He
gave
a
presentation
in
Bangkok
on
some
of
their
hardware
roadmap
stuff,
and
he
also
has
an
internet
draft
on
a
protocol
for
link,
architecture
stuff
and
we're
gonna
talk
about
that
tomorrow
during
the
during
the
meeting.
A
But
you
need
to
essentially
build
entangle
to
build
and
acknowledge
to
link
layer
in
order
to
make
this
whole
thing
work.
We
can
draw
this
sort
of
timewise
and
sort
of
a
with
time
going
down
the
vertical
axis.
You
know
top
to
bottom
and
your
distance
going
left
to
right
there.
We
can
draw
this
as
sort
of
a
gray
trapezoid,
something
that
looks
like
that.
A
If
you
put
a
bunch
of
them
together,
you
might
imagine
stringing
them
into
a
series
of
things
like
this,
and
maybe
we
can
acknowledge
them
as
we
go
and
do
sort
of
hop
by
hop
teleportation,
even
though
we
couldn't
really
just
put
it
on
an
individual
photon
and
send
it
from
one
place
to
the
other.
As
we
go
hop
by
hop,
maybe
we
can
do
teleportation
hop
by
hop
the
problem.
Is
this
takes
long
memory
lifetimes
and
the
fidelity
of
the
operations
the
probability
of
success?
A
In
doing
this
is
insufficient
for
this
to
work
over
more
than
a
couple
of
hops.
Okay,
so
the
group
in
delft
is
building
a
network
with
a
couple
of
hops
and
their
first
implementations
may
in
fact
do
this
or
something
similar
without
applying
some
of
the
error
correction
techniques
we'll
talk
about,
but
if
you're
going
to
extend
beyond
that,
you're
gonna
need
these
kinds
of
things
and
you're
going
to
get
into
these
generations
of
repeaters
here.
So
loss.
M
A
Several
different
repeater
schemes
have
been
defined.
I
listed
five
of
them
here
that
paper
that
just
showed
you
from
Murali
Duran
and
from
long
johns
group
that
they
defined
essentially
three
generations
of
networks,
I
call
them
1g,
2g
and
3G
1g
uses
what
we
call
purification
and
uses
what
we
call
entanglement
swapping
over
acknowledged
links.
This
is
truly
a
distributed
computation.
This
is
not
store-and-forward.
This
is
not
a
simple
data.
Plane
stuff,
like
you,
haven't
any
classical
internet
router.
This
is
end-to-end
a
distributed.
Computation.
Okay,
2g
is
all
right.
A
Let's
do
something
more
sophisticated:
let's
apply
error
correction
to
this
over
acknowledged
links
and
then
it
does
become
a
little
bit
more
akin
to
it
to
store-and-forward,
but
really
you
get
into
that
when
you,
when
your
success
probability
for
doing
this,
gets
to
the
point
where
you
can
live
without
the
acknowledgments
on
the
link
layer
and
then
you
can
do
what's
called
a
a
3G
network
for
doing
this.
So
this
first
generation,
this
quantum
repeater
operation,
I've,
got
three
stations
here:
zero
one
and
two
one
has
one
qubit
station
one
in
the
middle.
A
There
has
two
qubits.
So
what
we
do
is
we
use
the
link
to
make
entanglement
between
station
zero
and
one,
and
we,
as
the
other
link
to
create
an
entanglement
between
station,
1
and
2,
and
then
we
execute
again
one
of
these
things
labelled
with
state
measurement.
This
operation
is
very
much
like
teleportation.
You
could
in
fact
consider
it
to
be
a
form
of
teleportation.
A
This
destroys
the
to
queue
it's
in
the
middle,
but
it
doesn't
destroy
the
two
qubits
on
the
end
and
if
this
works
properly,
what
you're
left
with
is
entanglement
between
the
two
end
points.
This
process
is
what
we
call
entanglement
swapping
now.
Unfortunately,
this
does
introduce
errors.
It
reduces
the
fidelity
of
our
system
and
so
you're
going
to
have
to
apply
some
error
or
management
techniques
on
top
of
those.
But
this
is
the
key
technique
to
get
beyond
a
single
hop.
A
That
has
to
be
done
for
that,
but
this
introduces
errors.
So
how
are
we
going
to
deal
with
this?
The
standard
technique
which
people
have
actually
become
to
demonstrate
experimentally
is
what's
called
purification.
I
think
Traci
is
going
to
talk
about
that
here
in
just
a
couple
minutes.
This
purification
is
a
form
of
error
detection.
This
is
not
error.
Correction.
A
A
On
top
of
this
note
that
these
two
here
at
the
bottom,
they
were
operate
over
distance,
one,
the
others
repeat
at
different
distances,
so
you're
doing
entanglement
swapping
over
or
two
hops
and
then
four
hops
and
then
eight
hops
and
16.
You
also
have
to
repeat
the
purification,
because
at
each
level,
where
you're
doing
this
you're
introducing
new
errors
and
then
ultimately,
finally,
hopefully
one
purification
and
to
end
and
then
the
application
level,
all
the
way
at
the
end
note
that
the
only
quantum
part
of
all
of
this
is
right
there
at
the
bottom.
A
Everything
else
above
that
is
classical
networking
stuff
and
that's
why
everybody
in
this
room
is
needed
to
actually
commit
to
actually
build
this,
because
when
you
put
this
together,
as
I
said,
these
things
are
a
true
distributed.
Computation
right,
you
take
this
even
over
four
hops
you're
going
to
have
a
complicated
set
of
interactions
between
the
four
hops
from
managing
these
some
of
the
operations
over
one
hop,
some
of
them
over
two
hops,
some
of
them
over
four
ups.
A
As
you
go,
some
of
them,
you,
the
end-to-end
as
you
go,
alright,
so
2g
and
3G
s,
that
was
one
gene
networks,
2g
and
3G
are
still
very
far
away.
Even
1g
is
very
hard.
You've,
probably
gotten
an
idea
from
what
Tracy
talked
about
the
entanglement
success
probability
is
low.
There
are
many
round
trips
and
involved
in
the
protocol.
Design
you've
only
got
a
few
qubits
per
node.
A
The
memory
lifetimes
are
still
problematic
and
when
you
want
to
do
entanglement,
swapping
getting
a
successful
entanglement
between
Alice
and
Bob,
at
the
same
time
that
you
have
between
Bob
and
Charlie
in
order
to
make
that
entanglement
swapping.
That's
one
of
the
current
challenges,
experimentally,
for
what
people
are
actually
doing.
A
2G
is
going
to
blow
up
the
resource
requirements
by
an
order
of
magnitude,
give
or
take,
and
the
biggest
problem
that
we
have
besides,
that
is
in
the
existing
quantum
computers
and
in
the
laboratories.
The
operations
themselves
are
not
yet
good
enough
to
make
full-on
error.
Correction
work,
we're
actually
getting
close
to
that,
but
we're
not
there
yet
for
3G.
A
Not
only
are
you
gonna
have
to
have
error
correction
that
works
and
a
lot
of
memory
in
each
one
of
these
nodes,
but
you're
also
going
to
have
to
have
the
probability
of
80
to
93
percent,
depending
on
your
choice
of
code
in
getting
every
single
photon,
you
Pat
you
put
into
the
fiber
out
the
other
end
and
detected
properly,
and
you
know
what
are
the
current?
What
are
the
current
success
rates
in
your
laboratory
for
actually
detecting
a
photon
that
comes
out
of
an
atom.
B
A
B
A
Got
to
get
from
there
from
this
five
to
10%
she
can
achieve
in
the
lab
today
to
80
to
90%
success
rate
and
detecting
every
single
photon,
so
those
three
gene
networks,
which
would
be
real
store
and
forward
networks.
The
same
way
the
data
plane
on
the
internet
runs
today.
Those
are
a
long
ways
away
all
right.
Let's
say
you
want
to
do
this
bit.
B
Perspective
on
experimentally,
where
we
are
on
these
repeaters
and
yeah
we're
not
very
far,
and
so
I'm,
just
gonna
kind
of
capture
that
for
you
and
we're
gonna
kind
of
have
a
little
recap
of
what
these
repeaters
we're
looking
like.
So
so,
hopefully
it's
a
quick
reminder,
so
we
think
about
let's
you
know
when
we
hear
from
you
as
experimentalist
when
we
hear
kind
of
from
theorists
about
this
second
generation
third
generation.
You
know
it's
very
interesting,
intellectually,
but
you're
also
kind
of
like
really
are
you
kidding,
so
you
know
1g.
B
It
looks
from
our
perspective
hard
enough,
and
and
so
what
would
that
look
like
for
these
ions?
Well,
what
you
would
do
is
entangle
one
pair
of
ions
in
the
same
way
that
I've
already
showed
you.
So
you
would
have
a
single
ion
here,
for
example,
that
gets
entangled
the
photon,
a
single
and
that
gets
entangled
in
another
photon
on
the
right-hand
side.
And
then
this
beam
splitter
is
supposed
to
show
you
that
we're
racing,
the
information
about
which
path
each
photon
came
from
and
then
there's
some
detectors
that
I
left
out
of
the
picture.
B
So
you
would
entangle
those
two
ions
on
the
left
and
you
would
entangle
the
other
two
ions
on
the
right
and
then
you
would
do
this
bail
measurement
that
rah
talked
about
on
the
two
central
ions
and
that
bail
measurement
would
then
entangle
the
outermost
two
ions,
so
I
haven't.
Given
you
any
sense
of
how
that
we
do
this
bail
measurement
and
practice
on
the
ions.
Maybe
I
can
try
to
kind
of
give
you
the
the
30-second
version.
B
The
the
key
is
that
we
think,
because
these
ions
are,
on
the
one
hand,
repelling
each
other
and,
on
the
other
hand,
trapped
in
the
same
trap.
You
think
about
them.
You
know
like
a.
We
would
describe
them
as
a
coupled
harmonic,
oscillator,
they're
kind
of
pendulum
and
they're
coupled
to
each
other
and
they're
swinging
together.
So
their
motion
is
linked
to
one
another.
They
have
shared
motion
and
we
can
use
this.
B
What
we
would
talk
about
his
emotional
bus,
so
we
can
on
one
hand
we
have
access
to
the
electronic
states
of
the
ions
and,
on
the
other
hand,
to
their
motion,
and
we
take
advantage
of
that
in
order
to
manipulate
the
joint
states
of
the
ions.
So
we
can
do
measurements.
We
can
project
the
state
of
these
ions
into
one
of
the
four
bail
bases
and
what
we
do
in
the
end
is
we
illuminate
the
ions
with
certain
laser
light.
We
look
at
fluorescence
and
based
on
those
fluorescence
measurements
and
our
manipulations
with
lasers.
B
We
can
say
worth
ayyyye
in
which
one
of
these
four
bail
states
are
the
ions
in
okay.
So
this
bail
measurement
on
the
ions
in
the
middle
then
entangles
the
ions
outside.
So
this
is
if
you're
yeah
still
a
week
after
a
couple
of
hours.
In
a
long
day,
you
learned
already
that
this
is
what's
called
entanglement
swapping
and
it's
really
nice,
and
so
our
tendency
is
to
start
to
chain
together
a
bunch
of
these
things.
But
this
is
approach.
That's
not
scalable,
because
these
errors
are
going
to
accumulate.
B
All
of
these
steps
will
have
intrinsic
errors
and
when
we
start
to
concatenate
things,
it's
going
to
go
downhill,
so
the
approach
would
be
entanglement
purification.
So
you
know
what
we
should
remember
is
that
this
idea
of
a
quantum
repeater,
at
least
in
the
first
generation
you
think
of
it
as
entanglement
swapping
plus
purification
and
the
key
concept
of
purification,
is
that
you
have
multiple
copies
of
entangled
pairs
which
allow
you
to.
B
Then
you
can
start
sacrificing
some
of
your
copies
in
order
to
get
a
higher
fidelity
and
you
need
to
be
able
to
do
gate
operations
between
between
pairs
of
local
qubits.
So
here's
again
this
again
I'm
trying
to
think
of
a
minimal
instance
where
you
could
have
not
only
entanglement
swapping
but
also
purification,
so
that
now
we,
let's
think
about
an
instance
where
we
have
not.
We
double
everything.
B
So
we
have
two
ions
over
here
for
ions
in
the
middle
two
ions
there,
and
then
we
would
entangle
these
two
pairs
of
ions,
so
pairwise
entanglement
on
the
Left
pairwise
entanglement
on
the
right.
We
would
do
a
two
bowel
measurements
here
and
then
we
would
have
two
entangled
pairs
between
the
left
and
the
right
hand
side
and
then
would
come
this
final
step
of
the
purification.
What
we
would
do
is
we
would
do
what's
called
a
parity
measurement
of
the
ions.
B
We
would
ask,
on
the
left
hand,
side
are
the
ions
both
in
the
same
state.
Are
they
in
an
in
in
opposite
States,
and
we
would
also
ask
that,
on
the
right
hand
side,
then
we
would
have
classical
communication
to
share
that
information
and
based
on
the
joint
outcomes.
We
would
either
throw
away
the
pair
or
we
would
if
we
got
the
outcome
that
we
liked.
B
Then
we
would
know
that
the
purity
had
sort
of
had
increased,
or
at
least
the
chances
that
the
period
that
we
have
a
highly
entangled
State
has
increased
at
the
cost
of
sacrificing
one
of
those
pairs.
So
we
do
a
measurement
that
sacrifices
one
of
our
two
ions
on
either
side
and
in
the
end
we
end
up
with
a
pair,
that's
more
highly
entangled,
and
so
you
can
show
that
this
would
then
be
a
scalable
thing
with
the
purification.
If
you
can
break
meet
certain
bounds,
you
could
then
start
to
concatenate
these
systems.
B
So,
in
a
nutshell,
repeater
is
entangle
stopping
plus
purification.
We
have
to
wait
for
classified
information
to
travel
and
the
simplest
version
would
be
what
I've
sketched
here.
Eight
qubits
three
nodes
and
you
need
these
gate
operations
and
the
so
nobody's
done
it.
That's
what
you
should
take
away.
People
are
working
really
hard,
I,
think
it's
quite
likely
than
in
the
next
two
or
three
years.
B
We'll
have
a
of
a
first
proof
of
principle:
experiment,
the
closest
experiment
so
far,
I
wish
I
could
tell
you
it
was
with
ions,
but
it's
actually
with
nitrogen
vacancy
centres
and
Ronald
Hanson's
group
at
Delft.
So
these
diamonds,
where
you
replace
one
of
the
carbons
with
a
nitrogen
and
they've,
done
purification
of
entanglement
with
for
qubits
yeah.
So
in
beautiful
experiments
there
may
be
I'll
pause
there.
So
that's
the
end
of
the
experimental
story
on
where
we
are
with
quantum
repeaters
and
yeah.
F
B
F
B
F
B
Could
be
done
in
parallel
and
that's
a
very
yeah,
so
here
what
you
end
up
at
the
end
with
is
a
single
Bell
pair
of
to
remote
qubits,
which
you
could
use
to
teleport
a
single
qubit
and
then
here
I
sketched
something
in
parallel
and
that's
really
platform
dependent.
So
I
would
argue
that
ions
are
a
nice
system
for
doing
this
kind
of
thing
in
parallel
and
it
will
depend
on
the
system
how
well
you
can
parallelize
it.
H
Juan
Carlos
Juanita
I
was
a
little
worried
when
I
saw
the
diagrams
of
the
protocol
stack
and
the
GS
and
kind
of
remind
me
my
nightmares
about
3gpp
and
si
too,
and
things
that
I
don't
want
to
feel
and
live
here.
But
I
was
even
more
worried
when
I
started
thinking.
You
know.
Disruptive
waste
like
in
this
repeater
is
there
a
way
that
you
can
start
foreseeing
that
there
will
be
attacks
of
a
man-in-the-middle.
A
That's
part
of
that's
dependent
on
the
fact
that
that
we
actually
are
doing
more
of
the
checks
and
to
end,
and
so
those
end-to-end
checks
will
determine
that
the
kinds
of
states
that
are
left
after
these
operations
are
exactly
two
qubit
entangled
States.
If
somebody,
for
example,
you
know
the
man
in
the
middle
tries
to
sneak
in
and
entangle
a
third
qubit
with
it
that
shows
up
in
the
statistics
for
the
tests
that
are
actually
done
in
to
end.
We
can
prove
that
this
isn't
a
two
qubit
entangled
State.
A
We
might
not
know
for
certain
whether
it's
three,
whether
it's
three
cubits
or
whether
it's
just
been
busted-
and
we
don't
know
what
the
problem
is.
But
we
know
it's
not
a
good
two
qubit
state
and
conversely,
we
know
when
we
do
know
that
we
have
them.
We
know
that
the
path
is
working
end
to
end
and
it
doesn't
matter
what's
happening
in
the
middle
and.
M
Floor
you
for
that
security
guarantee,
yet
to
make
sure
that
the
classical
bits
that
you
are
she's
sending
back
and
forth,
but
you
don't
show
I,
actually
been
authenticated,
but
actually
wasn't
my
question.
My
question
was
really
about
how
many
purification
steps
you
need
to
do
for
each
round
is
that
it's
obviously
gonna
be
somewhat
fixed,
based
on
how
strong
how
good
your
physical
layers
are,
how
air
free
they
are,
but
typically
how
much,
how
many
times
you
have
to
expect
before
you
get
good
enough
to
be
able
to
go
up
to
the
next
level.
M
A
Actually,
a
really
good
question
the
I
would
say:
go
read
my
transactions
on
networking
paper
from
2009
and
that
will
actually
give
you
I
think
a
good
framework
for
how
to
think
about
that.
But
that
particular
paper
was
built
on
top
of
a
simulation
of
a
of
a
particular
type
of
system
that
nobody's
really
trying
to
build
anymore.
So
so
the
specific
numbers
that
are
in
that
paper,
I
would
say,
are
outdated.
Do
you
have
you
have
something
more
about
the
current
stuff.
B
The
art,
fidelity's
4-iron
photon,
entanglement
and
shown
that
that
those
are
kind
of
reasonable
for
first
scaling,
so
I
know
that
they
maybe
have
numbers
there.
That
I
don't
have
in
mind
about
how
many
purification
steps,
but
absolutely
so
the
the
better.
Your
states
are
to
start
with
the
fewer
steps
you'll
need,
and
if
you
have,
if
you
have
really
you
know,
states
that
are
quite
close
to
class
well,
you
would
need
sort
of
a
prohibitive
number
of
steps.
I'm.
G
G
A
A
If
you
want
to
do
real
distributed
computation,
you
need
high
90s
of
fidelity,
and
so
that
means
all
not
only
you're
having
your.
Your
hardware
has
to
be
really
good
for
the
purification
that
you're
doing,
but
it
also
means
that
you,
wind
up
spending
a
lot
of
resources
to
do
what's
called
tomography
to
test
the
system,
to
see
how
good
it
is,
the
better
the
system
is,
the
more
you
have
to
test
it,
to
figure
out
what
the
error
rate
is.
B
A
B
Benchmark
my
system
and
then
I
want
to
do
this
and
I
have
to
hope
that
it
didn't
change
from
what
I
benchmarked
it
or
do
I
have
to
how
much
do
I
have
to
interrupt
it
to
benchmark
it
while
I'm
running
it,
and
how
much
does
that
cost
me
in
terms
of
resources
yeah?
So,
okay,
with
that
outlook
on
on
you
know,
what
we
hope
is,
will
be
demonstrations
in
the
next
few
years
of
building
blocks
for
quantum
computers.
B
A
Just
to
give
you
an
idea
of
what
sort
of
things
are
where
the,
where
things
are,
we
have
done
some
work
on
network
architecture
based
on
Joe
touches,
recursive
network
architecture.
For
those
of
you
who
know
Joe
the
protocol
stuff
that
we
already
talked
about
a
little
bit.
We've
done
some
work
on
routing,
we've
done
some
work
on
multiplexing
and
control
in
larger
networks,
and
we've
done
some
work
on
internet
working.
This
was
part
of
shota's
PhD
thesis.
If
we
had
two
different
kinds
of
networks,
how
would
we
connect
them
together?
A
As
as
we
go
from
individual
networks
toward
toward
an
Internet,
and
we've
done
some
work
on
the
security
of
systems?
What
happens
when
somebody
actually
takes
control
of
one
of
these
repeaters?
Do
they
have
more
capabilities
than
they
would
have
in
a
classical
system?
We've
done
some
work
on
resource
analysis
for
applications,
and
we've
done
some
work
on
the
quantum
equivalent
of
network
coding.
A
So
that's
sort
of
you
know
the
range
of
things
that
that
people
have
been
working
for
the
last
few
years
from
Stephanie's
group
Axl
gave
me
that
gave
me
this
list
of
things.
They've
been
working
on
link
layer,
protocols
and
parameter
regimes
for
dealing
with
this
and
how
you
actually
go
about
using
this
for
particular
applications
and
and
a
bunch
of
different
stuff.
They
built
some
simulators
for
doing
this.
That
gives
you
kind
of
an
idea
of
you
know
the
work
that's
actually
going
on,
and
somebody
has
a
question
here:
real
quick.
A
B
B
Free
space,
experiment,
yeah
and
I
guess
I
would
picture
those
as
having
separate
applications
that
the
the
free
space
or
satellite
based
experiments
or
satellite
based
encoding
can
get
you
over
these
really
long
distances.
Right
can
get
you
global
connections,
but
I
guess
we
can
think
about
applications
where
the
connections
will
be
so
local
and
certainly
the
resources
of
satellites.
You
know
you're
not
gonna
have
so
many
yeah,
especially
for
things
like
maybe
a
more
local
distributed
quantum
computing.
A
They
used
to
two
telescopes
on
to
two
mountains:
140
kilometers
apart
or
something,
and
that
in
some
ways
is
actually
harder
than
going
to
a
satellite,
because
140
kilometers
of
air
really
distorts
thing
things
terrifically,
whereas
if
you're
going
vertically,
you
only
got
to
go
through
about
10,
but
then
you
have
to
hit
a
satellite
that's
moving
in
orbit
and
at
the
conference
the
Tracey
and
I
helped
run.
Two
years
ago
we
had
the
speaker
from
who
was
the
chief
engineer
from
from
the
satellite
group
that
did
that,
and
they
have
to
point
the
telescope.
A
B
A
Let's
see
alright
so
just
some
stuff,
some
good
repeater
references
you've
already
seen.
We've
already
talked
about
some
of
these,
though
there's
the
list
for
what
you
want.
If
you
want
to
learn
more
about
the
basics
of
quantum
computing,
I
have
an
online
course.
I
have
a
MOOC
called
called
understanding.
Quantum
computers
and
the
next
run
of
that
actually
starts
April
1st
next
Monday
the
course
is
free.
A
Unless
you
want
the
certificate-
and
you
probably
don't
want
the
certificate,
we
have
subtitles
all
of
its
and
originally
English,
but
but
we
have
subtitles
in
Japanese
and
in
Thai,
and
if
anybody
wants
to
translate
it
in
other
languages,
we
would
be
happy
to
have
that
done
as
well
and
Stephanie
veiners
group
from
TU
delft
has
a
MOOC
on
quantum
internet
stuff
which
I
have
not
gone
through.
Have
you
yeah,
so
I
I
can't
tell
you
anything
at
all
about
the
quality
of
it,
because
I
haven't
looked
at
it
axel?
A
Have
you
have
you
used
to
the
course
the
any
comments
on
it,
but
he's
thumbs
up
right,
of
course,
she's
his
PhD
adviser?
So
right,
it's
got
to
be
got
to
be
thumbs
up
great
I'm,
certain
it's
excellent
I,
just
haven't
had
a
chance
to
look
at
it
and
if
you
want
more
on
quantum
computing,
our
MOOC
is
intended
doesn't
have
a
lot
of
math
in
it.
It's
intended
to
take
you
about
20
hours.
A
Excuse
me,
I
Krong
and
Peter
Shore,
who
are
two
of
the.
The
founders
of
this
field,
have
an
EDX
course
on
this,
and
theirs
is
about
60
hours
and
it
has
more
math
in
it.
I've
taken
a
look
at
some
of
that,
so
the
good
sequence
would
be
to
go
through
mine
and
then
to
go
through.
Theirs
would
be
a
reasonable
way
to
do
things.
You
are
everybody
who's
here
in
the
room
already
knows
about
the
existence
of
this
research
group.
A
A
Does
that
mean
no
final
questions?
Have
you
all
asked
all
of
your
questions?
Thank
you
all
for
being
here.
The
group
meeting
is
tomorrow,
12:20
I
think
maybe
it's
11:20
I'll
have
to
double-check.
It's
on
the
schedule
that
will
be
downstairs
in
Congress.
See
you
there.
Thank
you
all
for
sitting
through
two
hours
of
this.