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<div class="moz-cite-prefix">Dne 09. 01. 26 v 9:15 Peter Gutmann via
cryptography napsal(a):<br>
</div>
<blockquote type="cite"
cite="mid:SYCPR01MB3661119D587B46C9236BF9C5EE82A@SYCPR01MB3661.ausprd01.prod.outlook.com">
<pre wrap="" class="moz-quote-pre">Jon Callas <a class="moz-txt-link-rfc2396E" href="mailto:jon@callas.org"><jon@callas.org></a> writes:
</pre>
<blockquote type="cite">
<pre wrap="" class="moz-quote-pre">Some quantum computers might need more power than supercomputers
</pre>
</blockquote>
<pre wrap="" class="moz-quote-pre">
The German government (via the BSI) wrote a report on this and estimated that
it would take 100 days and €4M in electricity to recover a single 2048-bit key
on a quantum computer that doesn’t exist. That's one single key. There are 7
trillion keys negotiated each year just for TLS web connections.
Oh, and that's for integer factorisation, not (EC)DLP, so not actually useful
for attacking the shopping list of common crypto protocols I mentioned
earlier.
Peter.
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</pre>
</blockquote>
<p>
</p>
<div class="moz-text-flowed"
style="font-family: -moz-fixed; font-size: 12px;" lang="x-unicode">Some
information, which may could be useful.</div>
<div class="moz-text-flowed"
style="font-family: -moz-fixed; font-size: 12px;" lang="x-unicode"><br>
</div>
<div class="moz-text-flowed"
style="font-family: -moz-fixed; font-size: 12px;" lang="x-unicode">If
I consider a quantum computer as a refrigerator and it behaves as
an absolute black body, I am talking about the necessary cooling
power to maintain this radiation from environment, which could be
460W/m<sup class="moz-txt-sup"><span
style="display:inline-block;width:0;height:0;overflow:hidden">^</span>2</sup>
(environment with temperature 20˚C). But this is an ideal
condition, there will be also heat transfers through supports,
cable lines and other parts of the overall structure. More, any
energy provided to system needs to be appropriately cooled also.</div>
<div class="moz-text-flowed"
style="font-family: -moz-fixed; font-size: 12px;" lang="x-unicode"><br>
</div>
<div class="moz-text-flowed"
style="font-family: -moz-fixed; font-size: 12px;" lang="x-unicode">The
question is what will be the construction of a quantum computer.
All the power that is sent to the chips (light or microwave pulses
and others) needs to be cooled again. Due to the efficiency of
cooling under normal conditions, at least half as much cooling
power is needed for each input power. At temperatures close to
absolute zero, the cooling efficiency is reduced to hundredths per
thousand. At absolute zero, the efficiency is zero - it would take
infinite work to remove the finite heat. Therefore, I would
simplify it to reach a temperature in certain orders. <br>
</div>
<div class="moz-text-flowed"
style="font-family: -moz-fixed; font-size: 12px;" lang="x-unicode"><br>
</div>
<div class="moz-text-flowed"
style="font-family: -moz-fixed; font-size: 12px;" lang="x-unicode">If
I take the cooling of an absolutely black body with an area of
1m<sup class="moz-txt-sup"><span
style="display:inline-block;width:0;height:0;overflow:hidden">^</span>2</sup>
from 20˚C to mK and μK, then I have some heat flow
characteristics. But if I take the Carnot machine calculation,
then the worst possible scenario produce list of needs. For
cooling an absolutely black body with a surface area of 1m<sup
class="moz-txt-sup"><span
style="display:inline-block;width:0;height:0;overflow:hidden">^</span>2</sup>
that means:<br>
- To a temperature of 1K requires an input of 122KW</div>
<div class="moz-text-flowed"
style="font-family: -moz-fixed; font-size: 12px;" lang="x-unicode">-
To a temperature of 0.1K requires an input of 1.22MW
<br>
- To a temperature of 0.01K requires an input of 12.2MW
<br>
- To a temperature in mK requires an input of 122MW
<br>
- To a temperature in μK requires an input of 122GW <br>
</div>
<div class="moz-text-flowed"
style="font-family: -moz-fixed; font-size: 12px;" lang="x-unicode"><br>
</div>
<div class="moz-text-flowed"
style="font-family: -moz-fixed; font-size: 12px;" lang="x-unicode">To
cool the delivered 1W (Carnot cooling, the best possible option
and optimistic attitude) for perfectly insulated body, we need the
following cooling device power:
<br>
- To a temperature of 1K requires an input of 293W
<br>
- To a temperature of 0.1K requires an input of 2.93kW
<br>
- To a temperature of 0.01 K requires an input of 29.3 kW
<br>
- To a temperature of 1mK requires an input of 293W
<br>
- To a temperature of 1μK requires an input of 293MW <br>
</div>
<div class="moz-text-flowed"
style="font-family: -moz-fixed; font-size: 12px;" lang="x-unicode"><br>
</div>
<div class="moz-text-flowed"
style="font-family: -moz-fixed; font-size: 12px;" lang="x-unicode">For
my surprise, the possible heat conductivity by construction is
very low, about 2,0-2,2W. I estimated rod with a circular
cross-section of diameter 18,3mm. I choose it because QC in ball
of surface are 1m<sup class="moz-txt-sup"><span
style="display:inline-block;width:0;height:0;overflow:hidden">^</span>2</sup> probably
cannot be heavier than iron ball. But radiation could make things
worse than thermal conductivity. This is a reason why I did not
count that. </div>
<div class="moz-text-flowed"
style="font-family: -moz-fixed; font-size: 12px;" lang="x-unicode"><br>
</div>
<div class="moz-text-flowed"
style="font-family: -moz-fixed; font-size: 12px;" lang="x-unicode">So
two parameters are needed:
<br>
- the outer surface of the quantum computer where, according to
the cooling system, it is possible to think with pessimistic
estimates
<br>
- the energy input of a quantum computer (problems with the
efficiency of real devices, it is advisable to multiply at least
1.5 times the value of Carnot cooling. I do not have enough
knowledge) <br>
</div>
<div class="moz-text-flowed"
style="font-family: -moz-fixed; font-size: 12px;" lang="x-unicode"><br>
</div>
<div class="moz-text-flowed"
style="font-family: -moz-fixed; font-size: 12px;" lang="x-unicode">Based
on that result, we need QC which will be able to work in
temperature of degrees or tenth of degrees of K. Anything else is
... expensive refrigerator and physical experiment, not
sustainable quantum computer.</div>
<div class="moz-text-flowed"
style="font-family: -moz-fixed; font-size: 12px;" lang="x-unicode"><br>
</div>
<div class="moz-text-flowed"
style="font-family: -moz-fixed; font-size: 12px;" lang="x-unicode">Technology;Operating
temperature;Computer power;Cooling power;System
power;Volume;Number of qbits
<br>
Superconducting qubits (IBM, Google);10-20 mK;~mW;15-25 kW;15-25
kW;~1-2 m<sup class="moz-txt-sup"><span
style="display:inline-block;width:0;height:0;overflow:hidden">^</span>3</sup>
(cryostat + electronics);50-127 qubits
<br>
Trapped ions (IonQ, Honeywell); μK; few mW; ~20 kW (lasers +
vacuum); ~25 kW; ~1 m<sup class="moz-txt-sup"><span
style="display:inline-block;width:0;height:0;overflow:hidden">^</span>3</sup>;
10-32 qubits
<br>
Neutral atoms / optical traps; μK; few mW; 5–10 kW (lasers,
vacuum); 5–10 kW; <1 m<sup class="moz-txt-sup"><span
style="display:inline-block;width:0;height:0;overflow:hidden">^</span>3</sup>;
50–200 qbits
<br>
Photonic qubits; room temperature; few mW; 0.5-1 kW (detectors,
optics); 4-5 kW; <1 m<sup class="moz-txt-sup"><span
style="display:inline-block;width:0;height:0;overflow:hidden">^</span>3</sup>;
50-200 qubits
<br>
Spin qubits in semiconductors (Si, SiGe); 10–100 mK; few mW; 10–20
kW; <1 m<sup class="moz-txt-sup"><span
style="display:inline-block;width:0;height:0;overflow:hidden">^</span>3</sup>;
10–50 </div>
<br>
<div class="moz-text-flowed"
style="font-family: -moz-fixed; font-size: 12px;" lang="x-unicode">Jan</div>
<div class="moz-text-flowed"
style="font-family: -moz-fixed; font-size: 12px;" lang="x-unicode"><br>
<div class="moz-txt-sig"><span class="moz-txt-tag">-- <br>
</span>--
<br>
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Jan Dušátko
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class="moz-txt-link-abbreviated moz-txt-link-freetext"
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<p><br>
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<p><br>
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<p><br>
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<pre class="moz-signature" cols="72">--
--
-- --- ----- -
Jan Dušátko
Tracker number: +420 602 427 840
e-mail: <a class="moz-txt-link-abbreviated" href="mailto:jan@dusatko.org">jan@dusatko.org</a>
GPG: <a class="moz-txt-link-freetext" href="https://keys.dusatko.org/2E7D58B90FC2867C.asc">https://keys.dusatko.org/2E7D58B90FC2867C.asc</a></pre>
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