As some of my fellow bloggers focus on how to program applications on the D-Wave One™, I’m going to delve into one important subsystem that is essential to keep the Rainier processor running, cooling!
Why does it need to be cold? Noise.
There are many reasons that the chip and its supporting infrastructure needs to be cold. However, the first and foremost reason is noise. For our processors to work, they need to be in as quiet of an environment as possible. In order for the problem to be set as accurately as possible, we need to know that the signal each qubit or coupler sees during computation is the one generated from our electronics. Filtering on the signal lines going to the chip reduces the majority of the noise to the chip. However, there is also noise associated with temperature. The lower the temperature, the lower the noise.
… the lowest temperature in nature and in the universe is 2.73K. This background temperature exists everywhere in the universe because of the photon energy which is still being radiated from the ‘big bang’. If we compare low-temperature physics to other branches of physics we realize that it is actually one of the very few branches of science where mankind has surpassed nature, an achievement which has not yet proved possible, for example, in high-pressure physics, high energy physics or vacuum physics.
-Frank Pobell, Matter and Methods at Low Temperatures
Of the “knobs” in nature, temperature is one we can adjust to the very limit of what nature permits. This ability to manipulate temperature enables many different technologies . The Large Hadron Collider is able to smash particles together at near the speed of light generating temperatures 100,000 times the temperature of the sun because of its 27km accelerator ring cooled to 1.9K. Superconducting cell phone receivers are able to better pick you cell signal out of noisy urban areas because they are cooled to below 77K . MRI technology is an incredibly useful diagnostic tool for doctors and would not be nearly as sensitive if their magnets were not cooled to 4K. Similar to these other technologies, at D-Wave we are able to operate processors that use some of the most fundamental behaviors of nature because of our systems ability to cool to a fraction of a degree above absolute zero.
These go to 11mK!!
At D-Wave, dilution refrigerators (DR) are used to cool our hardware. The coldest (base) temperature of these DRs is less than 0.02K! That is multiple kilograms of metal per system cooled to 100x colder than you can find anywhere in nature outside of a lab! Because of our rapid design cycle, there is usually at least one fridge taking the trip between 300K and base every week. At these temperatures, we are able to adjust the settings of each qubit and coupler to the precisely the values corresponding to the problem we want to solve.
In the coming weeks, I will be describing the purpose and workings of each of the main components of the system that cools our processors from room temperature all the way down to below 20mK. These posts should be at a level that a person with minimal exposure to physics should be able to follow.
See you next time!
Bonus: To see just how cold the D-Wave One™ gets in comparison to the temperatures we live in, click the image on the left (works best in Firefox).