<s>
Within	O
quantum	O
technology	O
,	O
a	O
quantum	B-Algorithm
sensor	I-Algorithm
utilizes	O
properties	O
of	O
quantum	O
mechanics	O
,	O
such	O
as	O
quantum	O
entanglement	O
,	O
quantum	O
interference	O
,	O
and	O
quantum	O
state	O
squeezing	O
,	O
which	O
have	O
optimized	O
precision	O
and	O
beat	O
current	O
limits	O
in	O
sensor	O
technology	O
.	O
</s>
<s>
The	O
field	O
of	O
quantum	B-Algorithm
sensing	I-Algorithm
deals	O
with	O
the	O
design	O
and	O
engineering	O
of	O
quantum	O
sources	O
(	O
e.g.	O
,	O
entangled	O
)	O
and	O
quantum	O
measurements	O
that	O
are	O
able	O
to	O
beat	O
the	O
performance	O
of	O
any	O
classical	O
strategy	O
in	O
a	O
number	O
of	O
technological	O
applications	O
.	O
</s>
<s>
In	O
photonics	O
and	O
quantum	O
optics	O
,	O
photonic	O
quantum	B-Algorithm
sensing	I-Algorithm
leverages	O
entanglement	O
,	O
single	O
photons	B-Application
and	O
squeezed	O
states	O
to	O
perform	O
extremely	O
precise	O
measurements	O
.	O
</s>
<s>
Quantum	B-Algorithm
sensors	I-Algorithm
are	O
often	O
built	O
on	O
continuously	O
variable	O
systems	O
,	O
i.e.	O
,	O
quantum	O
systems	O
characterized	O
by	O
continuous	O
degrees	O
of	O
freedom	O
such	O
as	O
position	O
and	O
momentum	O
quadratures	O
.	O
</s>
<s>
Quantum	B-Algorithm
sensing	I-Algorithm
can	O
also	O
be	O
utilized	O
in	O
non-photonic	O
areas	O
such	O
as	O
spin	O
qubits	O
,	O
trapped	O
ions	O
,	O
flux	O
qubits	O
,	O
and	O
nanoparticles	O
.	O
</s>
<s>
In	O
solid-state	O
physics	O
,	O
a	O
quantum	B-Algorithm
sensor	I-Algorithm
is	O
a	O
quantum	O
device	O
that	O
responds	O
to	O
a	O
stimulus	O
.	O
</s>
<s>
There	O
are	O
4	O
criteria	O
for	O
solid-state	O
quantum	B-Algorithm
sensors	I-Algorithm
:	O
</s>
<s>
Quantum	B-Algorithm
Sensors	I-Algorithm
have	O
applications	O
in	O
a	O
wide	O
variety	O
of	O
fields	O
including	O
microscopy	O
,	O
positioning	O
systems	O
,	O
communication	O
technology	O
,	O
electric	O
and	O
magnetic	O
field	O
sensors	O
,	O
as	O
well	O
as	O
geophysical	O
areas	O
of	O
research	O
such	O
as	O
mineral	O
prospecting	O
and	O
seismology	O
.	O
</s>
<s>
Many	O
measurement	O
devices	O
utilize	O
quantum	O
properties	O
in	O
order	O
to	O
probe	O
measurements	O
such	O
as	O
atomic	O
clocks	O
,	O
superconducting	B-Protocol
quantum	I-Protocol
interference	I-Protocol
devices	I-Protocol
,	O
and	O
nuclear	O
magnetic	O
resonance	O
spectroscopy	O
.	O
</s>
<s>
A	O
good	O
example	O
of	O
an	O
early	O
quantum	B-Algorithm
sensor	I-Algorithm
is	O
an	O
avalanche	O
photodiode	O
(	O
APD	O
)	O
.	O
</s>
<s>
APDs	O
have	O
been	O
used	O
to	O
detect	O
entangled	O
photons	B-Application
.	I-Application
</s>
<s>
With	O
additional	O
cooling	O
and	O
sensor	O
improvements	O
can	O
be	O
used	O
where	O
photomultiplier	B-Algorithm
tubes	I-Algorithm
(	O
PMT	O
)	O
in	O
fields	O
such	O
as	O
medical	O
imaging	O
.	O
</s>
<s>
The	O
Defense	O
Advanced	O
Research	O
Projects	O
Agency	O
(	O
DARPA	O
)	O
launched	O
a	O
research	O
program	O
in	O
optical	O
quantum	B-Algorithm
sensors	I-Algorithm
that	O
seeks	O
to	O
exploit	O
ideas	O
from	O
quantum	O
metrology	O
and	O
quantum	O
imaging	O
,	O
such	O
as	O
quantum	B-Algorithm
lithography	I-Algorithm
and	O
the	O
NOON	O
state	O
,	O
in	O
order	O
to	O
achieve	O
these	O
goals	O
with	O
optical	O
sensor	O
systems	O
such	O
as	O
lidar	O
.	O
</s>
<s>
The	O
United	O
States	O
judges	O
quantum	B-Algorithm
sensing	I-Algorithm
to	O
be	O
the	O
most	O
mature	O
of	O
quantum	O
technologies	O
for	O
military	O
use	O
,	O
theoretically	O
replacing	O
GPS	O
in	O
areas	O
without	O
coverage	O
or	O
possibly	O
acting	O
with	O
ISR	O
capabilities	O
or	O
detecting	O
submarine	O
or	O
subterranean	O
structures	O
or	O
vehicles	O
,	O
as	O
well	O
as	O
nuclear	O
material	O
.	O
</s>
<s>
A	O
practical	O
application	O
of	O
quantum	B-Algorithm
sensing	I-Algorithm
is	O
realized	O
in	O
gravitational	O
wave	O
sensing	O
.	O
</s>
<s>
Quantum	B-Algorithm
sensing	I-Algorithm
also	O
has	O
the	O
capability	O
to	O
overcome	O
resolution	O
limits	O
,	O
where	O
current	O
issues	O
of	O
vanishing	O
distinguishability	O
between	O
two	O
close	O
frequencies	O
can	O
be	O
overcome	O
by	O
making	O
the	O
projection	O
noise	O
vanish	O
.	O
</s>
<s>
In	O
neuroimaging	B-Algorithm
,	O
the	O
first	O
quantum	O
brain	O
scanner	O
uses	O
magnetic	O
imaging	O
and	O
could	O
become	O
a	O
novel	O
whole-brain	O
scanning	O
approach	O
.	O
</s>
