# B Taking Quantum Computers into Space

#### happyhacker

Can the low temperatures in Space be employed to cool a Quantum computer installed on an operational Space vessel doing away with the need of a super fridge or whatever they use here on Earth? Thank you.

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Staff Emeritus
No. Space is not a good refrigerant, especially in Earth orbit.

#### CWatters

Homework Helper
Gold Member
Perhaps look up how a Thermos/vacuum flask works to keep coffee hot.

#### Drakkith

Staff Emeritus
2018 Award
Can the low temperatures in Space be employed to cool a Quantum computer installed on an operational Space vessel doing away with the need of a super fridge or whatever they use here on Earth? Thank you.
Not unless you want to send the computer waaaaaaay out into the outer solar system. Otherwise sunlight will heat it up.

#### happyhacker

Not unless you want to send the computer waaaaaaay out into the outer solar system. Otherwise sunlight will heat it up.
Well, surely if it kept on the side away from any heat it will be cold?
Would Space temperatures be cold enough?

#### jbriggs444

Homework Helper
Would Space temperatures be cold enough?
Space does not have a temperature. Space is just geometry. Geometry does not have a temperature. It is the contents of space that have a temperature. If we are talking about the near-perfect vacuum of low earth orbit then that near-perfect vacuum might be said to have a temperature.

The temperature is determined by the average kinetic energy of the particles in the vacuum as measured in a frame of reference where the bulk of those particles are at rest. The particles in low Earth orbit are moving fast. Their kinetic energy is high. The vacuum there is "hot", not "cold".

However, that vacuum is also thin. It cannot effectively conduct or convect heat. It will neither warm nor chill objects floating in "space".

What will warm or chill such objects is thermal radiation. The objects will radiate energy away due to their own heat. They will absorb energy due to the radiation from other objects such as the sun, the stars and the cosmic microwave background.

At cold temperatures, radiative cooling is difficult. The rate of thermal radiation goes as the fourth power of absolute temperature. Cut absolute temperature in half and you've cut thermal radiation by a factor of sixteen.

#### Drakkith

Staff Emeritus
2018 Award
Well, surely if it kept on the side away from any heat it will be cold?
Not for long, as heat would soak from the sunlit side to the shaded side without active cooling. Don't get me wrong, you could do it, but the difficulties associated with launching a quantum computer into space and sustaining it there are simply not worth any gain you'd get. It is much easier to just leave it on the ground and cool it.

#### russ_watters

Mentor
Heat management/cooling is a key component of spacecraft and satellite design. Sunlight can be blocked with a simple heat shield and insulation. But as said, radiative cooling is very temperature dependent, so while you can achieve very low temperatures, you can't dissipate much heat at low temperature. It's very important to understand the difference/relationship between heat and temperature.

There is a ton of easily googlable literature on this. Permutations of "satellite [telescope] radiative cooling".

#### happyhacker

Sort of getting it. So if I have a panel on a spacecraft and it is facing away from any external heat source causing its temperature to rise am I right in assuming it will loose heat at a certain rate by radiation of particles from it's surface or by transfer of energy to particles existing in the Space at it's surface? If there are none then it will not reach equilibrium.

#### jbriggs444

Homework Helper
it is facing away from any external heat source causing its temperature to rise am I right in assuming it will loose heat at a certain rate by radiation of particles from it's surface
It is more like it will "glow" with heat. If you've pulled a red hot poker from the fire, the glow is light being emitted from the poker. That light carries away heat energy.

Colder objects "glow" too, but they glow in lower frequency ranges like infrared. They give off heat more slowly. So it's not that particles are emitted. It's that visible, infrared light or even microwave radiation is emitted.

#### happyhacker

OK, thanks. So heat would be given off by electromagnetic radiation. I guess this dissipates over distance. Would it 'heat up' a nearby object?

#### jbriggs444

Homework Helper
OK, thanks. So heat would be given off by electromagnetic radiation. I guess this dissipates over distance. Would it 'heat up' a nearby object?
Yes. But I thought the object was to dissipate heat. You want to "shine" your glow at the dark sky.

#### happyhacker

Thanks. Main object achieved.

#### f95toli

Note that space is not actually very cold; the cosmic background radiation is 3K which is hot by the quantum computing standards (way too hot for them to work).

In order to operate a solid state quantum computer (which is the type that uses a refrigerator) you need to get down to temperatures below about 50 mK; getting from 3K to 50 mK reuquires a lot more equipment and energy than getting from 300K to 3K (which can be done using a relatively cheap cryocooler) . Also, the equipment generates a lot of heat which would be tricky to get rid of in space.

Note that 50mK is easy to get to with modern dilution refrigerators so it is not really a problem for the current generation of processors.

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