Tra
vis
S.
Hu
mb
le,
Ry
an
S.
Be
nn
ink
, a
nd
Wa
rre
n P
. G
ric
e
Oa
k R
idg
e N
ati
on
al
La
bo
rato
ry
Oa
k R
idg
e,
Te
nn
es
se
e,
US
A
We
des
crib
e t
he
use
of q
ua
ntu
m-m
ech
an
ica
lly
en
tan
gle
d p
ho
ton
s f
or
sen
sin
g i
ntr
usi
on
s a
cross
a p
hysi
cal
per
imet
er.
Ou
r a
pp
roa
ch t
o i
ntr
usi
on
det
ecti
on
use
s t
he
no-c
lon
ing
pri
nci
ple
of
q
uan
tum
in
form
ati
on
sc
ien
ce as
p
rote
ctio
n ag
ain
st a
n i
ntr
ud
er’s
ab
ilit
y t
o s
po
of
a s
enso
r r
ecei
ver
usi
ng
a ‘
cla
ssic
al’
in
terc
ept-
rese
nd
att
ack
. W
e e
xp
lore
th
e b
ou
nd
s on
det
ecti
on
usi
ng
qu
an
tum
det
ecti
on
an
d e
stim
ati
on
th
eory
, an
d w
e e
xp
erim
enta
lly
dem
on
stra
te t
he u
nd
erly
ing
pri
nci
ple
of
enta
ngle
men
t-b
ase
d d
etec
tion
usi
ng
th
e v
isib
ilit
y d
eriv
ed
fro
m p
ola
riza
tion
-corr
ela
tio
n m
easu
rem
ents
.
Isra
el
J.
Ow
en
s
Lo
s A
lam
os
Na
tio
na
l L
ab
ora
tory
L
os
Ala
mo
s,
Ne
w M
ex
ico
, U
SA
AB
ST
RA
CT
Intr
usi
on
s c
an
be
det
ecte
d b
y m
on
ito
rin
g t
ran
smis
sio
n o
f a
pro
be
bea
m,
e.g
., a
la
ser
‘tr
ip w
ire’
, w
her
e a
bse
nce
of
the
pro
be
at
a r
ecei
ver
sig
nifi
es a
n i
ntr
usi
on
. !
Bu
t
an
in
tru
der
ca
n
spo
of
th
is
sen
sor
b
y
sen
din
g
a d
op
pel
ga
nger
bea
m t
hat
per
fect
ly r
epli
cate
s th
e p
rob
e.
PR
OB
LE
M A
DD
RE
SS
ED
Th
e n
o-c
lon
ing
pri
nci
ple
of
qu
an
tum
in
form
ati
on
sci
ence
p
roh
ibit
s a
n i
ntr
ud
er f
rom
rel
iab
ly c
op
yin
g a
n a
rbit
rary
q
ub
it
of
in
form
ati
on
.
Th
is
‘qu
an
tum
fe
nce
’
ag
ain
st
intr
usi
on
ca
n b
e i
mp
lem
ente
d b
y t
ran
smit
tin
g a
pa
tro
l p
ho
ton
acr
oss
th
e p
erim
eter
wh
ile
ret
ain
ing
an
en
tan
gle
d g
uard
in
a s
ecu
re l
oca
tion
. T
he
ab
sen
ce o
f e
nta
ngle
men
t b
etw
een
rec
eiv
ed p
art
icle
s in
dic
ate
s an
in
tru
der
’s p
rese
nce
. T
his
ad
dit
ion
al
lay
er o
f se
curi
ty c
ou
ld c
om
ple
men
t ex
isti
ng
met
hod
s
fo
r
mo
nit
ori
ng
th
e
sta
te
of
se
nso
r
or
com
mu
nic
ati
on
ch
an
nel
."
SO
LU
TIO
N P
RO
PO
SE
D
Intr
uder
Gu
ard
ph
oto
n
Patr
ol p
ho
ton
En
tan
gle
men
t
so
urc
e A
naly
zer
(!P)
An
aly
zer
(!G)
A s
ou
rce o
f en
tan
gle
d p
ho
ton
s t
ran
sm
its a
patr
ol
ph
oto
n a
cro
ss
a p
eri
mete
r to
a d
ista
nt
receiv
er
(an
aly
zer)
an
d s
en
ds t
he g
uard
p
ho
ton
to
a s
eco
nd
, secu
re r
eceiv
er.
An
ala
rm s
yste
m m
on
ito
rs
the
en
tan
gle
men
t,
an
d
the
ala
rm
so
un
ds
if
the
measu
red
en
tan
gle
men
t d
rop
s b
elo
w a
th
resh
old
valu
e.
Laser
Tripw
ire
Dete
cto
r
Inte
rcept-
resend
Laser
Ala
rm
does n
ot
sound
Va
lid
ati
ng
th
e a
uth
enti
city
of
a p
rob
e s
ign
al
is f
un
dam
enta
l
to m
an
y s
ensi
ng
ap
pli
cati
on
s, i
ncl
ud
ing
fen
ces,
lo
cks,
sea
ls,
surv
eill
an
ce a
nd
eaves
dro
pp
er d
etec
tio
n m
eth
od
s."
CO
NC
EP
T D
IAG
RA
M
Intr
us
ion
De
tec
tio
n w
ith
Qu
an
tum
Me
ch
an
ics
:
A P
ho
ton
ic Q
ua
ntu
m F
en
ce
(Left
) M
easu
red
vis
ibilit
ies
for
no
rmal
an
d
intr
usio
n
scen
ari
os.
Sam
ple
s co
llecte
d in
a 1-s
w
ind
ow
at
a m
ax ra
te o
f 35 p
air
s/s
.
(Rig
ht)
P
rob
ab
ilit
y
for
dete
cti
on
at
co
nsta
nt
fals
e
ala
rm
rate
mo
dele
d w
ith
resp
ect
to t
ran
sm
issio
n d
ista
nce.
Co
nd
itio
ns h
ere
:
0.2
dB
/km
best
weath
er,
2 d
B/k
m lig
ht
rain
, 20 d
B/k
m h
eavy m
ist.
Intr
us
ion
De
tec
tio
n w
ith
Qu
an
tum
Me
ch
an
ics
:
A P
ho
ton
ic Q
ua
ntu
m F
en
ce
AC
KN
OW
LE
DG
EM
EN
TS
Th
is p
ost
er h
as b
een
au
tho
red
by
a c
on
trac
tor
of
the
U.S
. G
ov
ern
men
t u
nd
er
Co
ntr
act
No
. D
E-A
C0
5-0
0O
R2
27
25
. A
cco
rdin
gly
, th
e U
.S.
Go
ver
nm
ent
reta
ins
a no
n-e
xcl
usi
ve,
ro
yal
ty-f
ree
lice
nse
to
pub
lish
o
r re
pro
du
ce t
he
pu
bli
shed
form
of
this
co
ntr
ibuti
on
, o
r al
low
oth
ers
to d
o s
o,
for
U.S
. G
ov
ernm
ent
pu
rpose
s. T
his
mat
eria
l is
bas
ed o
n w
ork
su
pp
ort
ed b
y t
he
Def
ense
Ad
van
ced
Res
earc
h P
roje
ct A
gen
cy,
Gen
era
tio
n o
f p
ola
rizati
on
-en
tan
gle
d p
ho
ton
pair
s u
sin
g a
cro
ss-
rin
ged
, ty
pe-I
I S
PD
C
co
nfi
gu
rati
on
w
ith
a
1-m
m
BB
O
cry
sta
l p
um
ped
by a
cw
Ar+
laser
op
era
tin
g a
t 351.1
nm
.
En
tan
gle
d p
ho
ton
pair
s w
ere
gen
era
ted
usi
ng
sp
on
tan
eou
s p
ara
met
ric
dow
n c
on
ver
sion
(S
PD
C).
Non
-loca
l co
rrel
ati
on
s in
po
lari
zati
on
wer
e q
ua
nti
fied
usi
ng
th
e v
isib
ilit
y V
, i.
e.,
the
con
tra
st i
n t
he
inte
rfer
ence
fri
nges
. "
PR
OO
F O
F P
RIN
CIP
LE
Patr
ol P
ath
Guard
Path
Sch
em
ati
c
illu
str
ati
ng
th
e
role
o
f S
PD
C
in
the
pro
du
cti
on
o
f p
atr
ol
an
d g
uard
ph
oto
n p
air
s.
Th
e p
ho
ton
po
lari
zati
on
sta
tes i
s m
on
ito
red
by a
co
incid
en
ce c
ou
nte
r.
SE
NS
OR
PE
RF
OR
MA
NC
E
A R
OC
cu
rve w
as
der
ived
fro
m v
isib
ilit
ies
for n
orm
al
an
d in
tru
sio
n
case
s.
Per
form
an
ce
ov
er
lon
ger
tr
an
smis
sio
n d
ista
nce
s w
as
mod
eled
ass
um
ing
atm
osp
her
ic a
tten
ua
tio
n."
Tra
vis
S.
Hu
mb
le,
Ry
an
S.
Be
nn
ink
, a
nd
Wa
rre
n P
. G
ric
e
Oa
k R
idg
e N
ati
on
al
La
bo
rato
ry
Oa
k R
idg
e,
Te
nn
es
se
e,
US
A
Isra
el
J.
Ow
en
s
Lo
s A
lam
os
Na
tio
na
l L
ab
ora
tory
L
os
Ala
mo
s,
Ne
w M
ex
ico
, U
SA
Pum
p
Laser
SU
MM
AR
Y
Intr
usi
on
det
ecti
on
usi
ng
en
tan
gle
d p
ho
ton
s w
as p
rop
ose
d a
nd
d
emo
nst
rate
d. W
her
eas
a
n in
tru
der
co
uld
sp
oo
f a
cla
ssic
al
‘tri
p w
ire’
sen
sor,
a p
ho
ton
ic q
ua
ntu
m f
ence
ca
n d
isce
rn b
etw
een
bet
wee
n n
orm
al
an
d i
ntr
usi
on
sce
na
rio
s. T
his
con
cep
t sh
ou
ld p
rov
e u
sefu
l a
ny
wh
ere t
he i
nte
gri
ty o
f a
tran
smit
ted
or p
rob
e s
ign
al
is p
ara
mo
un
t, e
.g.,
in
per
imet
er
pro
tect
ion
, ea
ves
dro
pp
er d
etec
tio
n,
an
d c
on
tain
men
t a
nd
surv
eill
an
ce t
ech
no
log
ies."
Gu
ard
De
tec
tor
Pa
tro
l
De
tec
tor
En
tan
gle
me
nt
So
urc
e
V!