<s>
Cross-entropy	B-Device
benchmarking	I-Device
(	O
also	O
referred	O
to	O
as	O
XEB	O
)	O
is	O
quantum	B-Architecture
benchmarking	O
protocol	O
which	O
can	O
be	O
used	O
to	O
demonstrate	O
quantum	B-Device
supremacy	I-Device
.	O
</s>
<s>
In	O
XEB	O
,	O
a	O
random	O
quantum	B-Application
circuit	I-Application
is	O
executed	O
on	O
a	O
quantum	B-Architecture
computer	I-Architecture
multiple	O
times	O
in	O
order	O
to	O
collect	O
a	O
set	O
of	O
samples	O
in	O
the	O
form	O
of	O
bitstrings	B-Data_Structure
.	O
</s>
<s>
where	O
is	O
the	O
number	O
of	O
qubits	O
in	O
the	O
circuit	O
and	O
is	O
the	O
probability	O
of	O
a	O
bitstring	B-Data_Structure
for	O
an	O
ideal	O
quantum	B-Application
circuit	I-Application
.	O
</s>
<s>
If	O
,	O
the	O
samples	O
were	O
collected	O
from	O
a	O
noiseless	O
quantum	B-Architecture
computer	I-Architecture
.	O
</s>
<s>
This	O
means	O
that	O
if	O
a	O
quantum	B-Architecture
computer	I-Architecture
did	O
generate	O
those	O
samples	O
,	O
then	O
the	O
quantum	B-Architecture
computer	I-Architecture
is	O
too	O
noisy	O
and	O
thus	O
has	O
no	O
chance	O
of	O
performing	O
beyond-classical	O
computations	O
.	O
</s>
<s>
Since	O
it	O
takes	O
an	O
exponential	O
amount	O
of	O
resources	O
to	O
classically	O
simulate	O
a	O
quantum	B-Application
circuit	I-Application
,	O
there	O
comes	O
a	O
point	O
when	O
the	O
biggest	O
supercomputer	O
that	O
runs	O
the	O
best	O
classical	O
algorithm	O
for	O
simulating	O
quantum	B-Application
circuits	I-Application
ca	O
n't	O
compute	O
the	O
XEB	O
.	O
</s>
<s>
Crossing	O
this	O
point	O
is	O
known	O
as	O
achieving	O
quantum	B-Device
supremacy	I-Device
;	O
and	O
after	O
entering	O
the	O
quantum	B-Device
supremacy	I-Device
regime	O
,	O
XEB	O
can	O
only	O
be	O
estimated	O
.	O
</s>
<s>
The	O
Sycamore	B-Device
processor	I-Device
was	O
the	O
first	O
to	O
demonstrate	O
quantum	B-Device
supremacy	I-Device
via	O
XEB	O
.	O
</s>
<s>
Generating	O
samples	O
took	O
200	O
seconds	O
on	O
the	O
quantum	B-Architecture
processor	I-Architecture
when	O
it	O
would	O
have	O
taken	O
10,000	O
years	O
on	O
Summit	B-Device
at	O
the	O
time	O
of	O
the	O
experiment	O
.	O
</s>
<s>
Improvements	O
in	O
classical	O
algorithms	O
have	O
shortened	O
the	O
runtime	O
to	O
about	O
a	O
week	O
on	O
Sunway	B-Device
TaihuLight	I-Device
thus	O
collapsing	O
Sycamore	B-Device
's	O
claim	O
to	O
quantum	B-Device
supremacy	I-Device
.	O
</s>
<s>
As	O
of	O
2021	O
,	O
the	O
latest	O
demonstration	O
of	O
quantum	B-Device
supremacy	I-Device
by	O
Zuchongzhi	O
2.1	O
with	O
,	O
24	O
cycles	O
and	O
an	O
XEB	O
of	O
holds	O
.	O
</s>
