The thermodynamics of computing

April 11, 2018

As steam engines became increasingly widespread in the 19th century, the question soon arose as to how to optimise them. Thermodynamics, the physical theory that resulted from the study of these machines, proved to be an extremely fruitful approach; it is still a central concept in the optimisation of energy use in heat engines.

Heat is a critical factor

Even in today's information age, physicists and engineers hope to make use of this theory; it is becoming ever clearer that the clock rate or the number of chips used are not the limiting factors for a computer's performance, but rather its energy turnover. "The performance of a computing centre depends primarily on how much heat can be dissipated," says Renato Renner, Professor for Theoretical Physics and head of the research group for Quantum Information Theory.

Renner's statement can be illustrated by the Bitcoin boom: it is not computing capacity itself, but the exorbitant energy use -- which produces a huge amount of heat -- and the associated costs that have become the deciding factors for the future of the cryptocurrency. Computers' energy consumption has also become a significant cost driver in other areas.

For information processing, the question of completing computing operations as efficiently as possible in thermodynamic terms is becoming increasing urgent -- or to put it another way: how can we conduct the greatest number of computing operations with the least amount of energy? As with steam engines, fridges and gas turbines, a fundamental principle is in question here: can the efficiency be increased indefinitely, or is there a physical limit that fundamentally cannot be exceeded?

Combining two theories

For ETH professor Renner, the answer is clear: there is such a limit. Together with his doctoral student Philippe Faist, who is now a postdoc at Caltech, he showed in a study soon to appear in Physical Review X that the efficiency of information processing cannot be increased indefinitely -- and not only in computing centres used to calculate weather forecasts or process payments, but also in biology, for example when converting images in the brain or reproducing genetic information in cells. The two physicists also identified the deciding factors that determine the limit.

"Our work combines two theories that, at first glance, have nothing to do with one another: thermodynamics, which describes the conversion of heat in mechanical processes, and information theory, which is concerned with the principles of information processing," explains Renner.

The connection between the two theories is hinted at by a formal curiosity: information theory uses a mathematical term that formally resembles the definition of entropy in thermodynamics. This is why the term entropy is also used in information theory. Renner and Faist have now shown that this formal similarity goes deeper than would be assumed at first glance.

No fixed limits

Notably, the efficiency limit for the processing of information is not fixed, but can be influenced: the better you understand a system, the more precisely you can tailor the software to the chip design, and the more efficiently the information will be processed. That is exactly what is done today in high-performance computing. "In future, programmers will also have to take the thermodynamics of computing into account," says Renner. "The decisive factor is not minimising the number of computing operations, but implementing algorithms that use as little energy as possible."

Developers could also use biological systems as a benchmark here: "Various studies have shown that our muscles function very efficiently in thermodynamic terms," explains Renner. "It would now be interesting to know how well our brain performs in processing signals."

As close to the optimum as possible

As a quantum physicist, Renner's focus on this question is no coincidence: with quantum thermodynamics, a new research field has emerged in recent years that has particular relevance for the construction of quantum computers. "It is known that qubits, which will be used by future quantum computers to perform calculations, must work close to the thermodynamic optimum to delay decoherence," says Renner. "This phenomenon is a huge problem when constructing quantum computers, because it prevents quantum mechanical superposition states from being maintained long enough to be used for computing operations."

ETH Zurich

Related Quantum Computers Articles from Brightsurf:

Optical wiring for large quantum computers
Researchers at ETH have demonstrated a new technique for carrying out sensitive quantum operations on atoms.

New algorithm could unleash the power of quantum computers
A new algorithm that fast forwards simulations could bring greater use ability to current and near-term quantum computers, opening the way for applications to run past strict time limits that hamper many quantum calculations.

A new technique prevents errors in quantum computers
A paper recently published in Nature presents a protocol allowing for the error detection and the protection of quantum processors in case of qubit loss.

New method prevents quantum computers from crashing
Quantum information is fragile, which is why quantum computers must be able to correct errors.

Natural radiation can interfere with quantum computers
Radiation from natural sources in the environment can limit the performance of superconducting quantum bits, known as qubits.

New model helps to describe defects and errors in quantum computers
A summer internship in Bilbao, Spain, has led to a paper in the journal Physical Review Letters for Jack Mayo, a Master's student at the University of Groningen, the Netherlands.

The first intuitive programming language for quantum computers
Several technical advances have been achieved recently in the pursuit of powerful quantum computers.

Hot qubits break one of the biggest constraints to practical quantum computers
A proof-of-concept published today in Nature promises warmer, cheaper and more robust quantum computing.

Future quantum computers may pose threat to today's most-secure communications
Quantum computers that are exponentially faster than any of our current classical computers and are capable of code-breaking applications could be available in 12 to 15 years, posing major risks to the security of current communications systems, according to a new RAND Corporation report.

Novel error-correction scheme developed for quantum computers
Experimental quantum computers are plagued with errors. Here Dr Arne Grimsmo from the University of Sydney and colleagues from RMIT and the University of Queensland offer a novel method to reduce errors in a scheme applicable across different types of quantum hardware.

Read More: Quantum Computers News and Quantum Computers Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to