<s>
Cryogenic	B-Algorithm
particle	I-Algorithm
detectors	I-Algorithm
operate	O
at	O
very	O
low	O
temperature	O
,	O
typically	O
only	O
a	O
few	O
degrees	O
above	O
absolute	B-Application
zero	I-Application
.	O
</s>
<s>
These	O
sensors	B-Application
interact	O
with	O
an	O
energetic	O
elementary	O
particle	O
(	O
such	O
as	O
a	O
photon	B-Application
)	O
and	O
deliver	O
a	O
signal	O
that	O
can	O
be	O
related	O
to	O
the	O
type	O
of	O
particle	O
and	O
the	O
nature	O
of	O
the	O
interaction	O
.	O
</s>
<s>
While	O
many	O
types	O
of	O
particle	O
detectors	B-Application
might	O
be	O
operated	O
with	O
improved	O
performance	O
at	O
cryogenic	O
temperatures	O
,	O
this	O
term	O
generally	O
refers	O
to	O
types	O
that	O
take	O
advantage	O
of	O
special	O
effects	O
or	O
properties	O
occurring	O
only	O
at	O
low	O
temperature	O
.	O
</s>
<s>
Two	O
such	O
commonly	O
used	O
properties	O
are	O
heat	O
capacity	O
and	O
electrical	O
resistivity	O
,	O
particularly	O
superconductivity	O
;	O
other	O
designs	O
are	O
based	O
on	O
superconducting	O
tunnel	O
junctions	O
,	O
quasiparticle	O
trapping	O
,	O
rotons	O
in	O
superfluids	O
,	O
magnetic	O
bolometers	B-Application
,	O
and	O
other	O
principles	O
.	O
</s>
<s>
Originally	O
,	O
astronomy	O
pushed	O
the	O
development	O
of	O
cryogenic	B-Algorithm
detectors	I-Algorithm
for	O
optical	O
and	O
infrared	O
radiation	O
.	O
</s>
<s>
Later	O
,	O
particle	O
physics	O
and	O
cosmology	O
motivated	O
cryogenic	O
detector	B-Application
development	O
for	O
sensing	O
known	O
and	O
predicted	O
particles	O
such	O
as	O
neutrinos	O
,	O
axions	O
,	O
and	O
weakly	O
interacting	O
massive	O
particles	O
(	O
WIMPs	O
)	O
.	O
</s>
<s>
A	O
calorimeter	B-Algorithm
is	O
a	O
device	O
that	O
measures	O
the	O
amount	O
of	O
heat	O
deposited	O
in	O
a	O
sample	O
of	O
material	O
.	O
</s>
<s>
A	O
calorimeter	B-Algorithm
differs	O
from	O
a	O
bolometer	B-Application
in	O
that	O
a	O
calorimeter	B-Algorithm
measures	O
energy	O
,	O
while	O
a	O
bolometer	B-Application
measures	O
power	O
.	O
</s>
<s>
This	O
makes	O
it	O
practical	O
to	O
make	O
a	O
calorimeter	B-Algorithm
that	O
has	O
a	O
very	O
large	O
temperature	O
excursion	O
for	O
a	O
small	O
amount	O
of	O
heat	O
input	O
,	O
such	O
as	O
that	O
deposited	O
by	O
a	O
passing	O
particle	O
.	O
</s>
<s>
The	O
temperature	O
rise	O
can	O
be	O
measured	O
with	O
a	O
standard	O
type	O
of	O
thermistor	O
,	O
as	O
in	O
a	O
classical	O
calorimeter	B-Algorithm
.	O
</s>
<s>
In	O
general	O
,	O
small	O
sample	O
size	O
and	O
very	O
sensitive	O
thermistors	O
are	O
required	O
to	O
make	O
a	O
sensitive	O
particle	O
detector	B-Application
by	O
this	O
method	O
.	O
</s>
<s>
A	O
very	O
sensitive	O
calorimetric	O
sensor	O
known	O
as	O
a	O
transition-edge	B-Algorithm
sensor	I-Algorithm
(	O
TES	O
)	O
takes	O
advantage	O
of	O
superconductivity	O
.	O
</s>
<s>
A	O
photon	B-Application
absorbed	O
on	O
one	O
side	O
of	O
a	O
STJ	O
breaks	O
Cooper	O
pairs	O
and	O
creates	O
quasiparticles	O
.	O
</s>
<s>
In	O
the	O
presence	O
of	O
an	O
applied	O
voltage	O
across	O
the	O
junction	O
,	O
the	O
quasiparticles	O
tunnel	O
across	O
the	O
junction	O
,	O
and	O
the	O
resulting	O
tunneling	O
current	O
is	O
proportional	O
to	O
the	O
photon	B-Application
energy	O
.	O
</s>
<s>
The	O
STJ	O
can	O
also	O
be	O
used	O
as	O
a	O
heterodyne	B-Algorithm
detector	I-Algorithm
by	O
exploiting	O
the	O
change	O
in	O
the	O
nonlinear	O
current	O
–	O
voltage	O
characteristic	O
that	O
results	O
from	O
photon-assisted	O
tunneling	O
.	O
</s>
<s>
STJs	O
are	O
the	O
most	O
sensitive	O
heterodyne	B-Algorithm
detectors	I-Algorithm
available	O
for	O
the	O
100GHz	O
–	O
1THz	O
frequency	O
range	O
and	O
are	O
employed	O
for	O
astronomical	O
observation	O
at	O
these	O
frequencies	O
.	O
</s>
<s>
The	O
kinetic	B-Algorithm
inductance	I-Algorithm
detector	I-Algorithm
(	O
KID	O
)	O
is	O
based	O
on	O
measuring	O
the	O
change	O
in	O
kinetic	O
inductance	O
caused	O
by	O
the	O
absorption	O
of	O
photons	B-Application
in	O
a	O
thin	O
strip	O
of	O
superconducting	O
material	O
.	O
</s>
<s>
The	O
change	O
in	O
inductance	O
is	O
typically	O
measured	O
as	O
the	O
change	O
in	O
the	O
resonant	O
frequency	O
of	O
a	O
microwave	O
resonator	O
,	O
and	O
hence	O
these	O
detectors	B-Application
are	O
also	O
known	O
as	O
microwave	B-Algorithm
kinetic	I-Algorithm
inductance	I-Algorithm
detectors	I-Algorithm
(	O
MKIDs	B-Algorithm
)	O
.	O
</s>
<s>
Paramagnetic	O
rare-earth	O
ions	O
are	O
being	O
used	O
as	O
particle	O
sensors	B-Application
by	O
sensing	O
the	O
spin	O
flips	O
of	O
the	O
paramagnetic	O
atoms	O
induced	O
by	O
heat	O
absorbed	O
in	O
a	O
low-heat-capacity	O
material	O
.	O
</s>
<s>
Calorimeters	B-Algorithm
assume	O
the	O
sample	O
is	O
in	O
thermal	O
equilibrium	O
or	O
nearly	O
so	O
.	O
</s>
<s>
A	O
good	O
deal	O
more	O
information	O
can	O
be	O
found	O
by	O
measuring	O
the	O
elementary	O
excitations	O
of	O
the	O
crystal	O
lattice	O
,	O
or	O
phonons	B-Language
,	O
caused	O
by	O
the	O
interacting	O
particle	O
.	O
</s>
<s>
This	O
can	O
be	O
done	O
by	O
several	O
methods	O
including	O
superconducting	O
transition	B-Algorithm
edge	I-Algorithm
sensors	I-Algorithm
.	O
</s>
<s>
The	O
superconducting	B-Algorithm
nanowire	I-Algorithm
single-photon	I-Algorithm
detector	I-Algorithm
(	O
SNSPD	B-Algorithm
)	O
is	O
based	O
on	O
a	O
superconducting	O
wire	O
cooled	O
well	O
below	O
the	O
superconducting	O
transition	O
temperature	O
and	O
biased	O
with	O
a	O
dc	O
current	O
that	O
is	O
close	O
to	O
but	O
less	O
than	O
the	O
superconducting	O
critical	O
current	O
.	O
</s>
<s>
The	O
SNSPD	B-Algorithm
is	O
typically	O
made	O
from	O
≈	O
5nm	O
thick	O
niobium	O
nitride	O
films	O
which	O
are	O
patterned	O
as	O
narrow	O
nanowires	O
(	O
with	O
a	O
typical	O
width	O
of	O
100nm	O
)	O
.	O
</s>
<s>
Absorption	O
of	O
a	O
photon	B-Application
breaks	O
Cooper	O
pairs	O
and	O
reduces	O
the	O
critical	O
current	O
below	O
the	O
bias	O
current	O
.	O
</s>
<s>
The	O
main	O
advantages	O
of	O
this	O
type	O
of	O
photon	B-Application
detector	B-Application
are	O
its	O
high	O
speed	O
(	O
a	O
maximal	O
count	O
rate	O
of	O
2GHz	O
makes	O
them	O
the	O
fastest	O
available	O
)	O
and	O
its	O
low	O
dark	O
count	O
rate	O
.	O
</s>
<s>
In	O
superfluid	O
4He	O
the	O
elementary	O
collective	O
excitations	O
are	O
phonons	B-Language
and	O
rotons	O
.	O
</s>
<s>
analogous	O
to	O
a	O
superconducting	O
tunnel	O
detector	B-Application
.	O
</s>
