Absolute zero in the quantum computer: Formulation for the third law of thermodynamics

Complex systems can emerge from interactions between lots of quantum entities. And because of this intricacy, it is theoretically possible to achieve absolute zero.

The lowest potential temperature is -273.15°C. Any item can never be cooled precisely to this degree; one can only get close. The third rule of physics is this.

A research team from TU Wien (Vienna) has now looked into how to make this law consistent with the laws of quantum physics in a paper that was released in PRX Quantum. A "quantum version" of the third law of thermodynamics was successfully created by them: Absolute zero is theoretically possible to achieve. But you need three things to make any formula for it work: energy, patience, and complexity. And you can only get to total zero if you have an unlimited supply of one of these components.

Thermodynamics and information: a seemingly incompatible relationship

The exact state of a quantum entity at absolute zero is known: it is always the state with the lowest energy. The knowledge about their previous condition is then lost from the particles. The atom has completely forgotten anything that might have occurred to it in the past. Thus, from the perspective of quantum physics, cooling and information deletion are tightly linked.

At this juncture, thermodynamics and information theory—two significant physical theories—intersect. But the two seem to be at odds with one another. "We are familiar with the so-called Landauer principle from information theory. One bit of information can be erased with a very precise minimum quantity of energy, according to this theory, reveals Prof. Marcus Huber of the TU Wien's Atomic Institute. However, according to thermodynamics, nothing can be cooled all the way down to absolute zero without requiring an endless supply of energy. But how does that work if erasing data and reaching total zero are the same thing?

Effort, duration, and intricacy

The origin of the issue is that traditional objects—such as steam engines, freezers, or glowing coal—were the focus of the 19th-century formulation of thermodynamics. People were unaware of quantum theory at the moment. Marcus Huber and his team conducted an analysis of the interactions between thermodynamics and quantum physics in order to better comprehend the thermodynamics of individual entities.

Marcus Huber explains, "We soon realized that you don't absolutely have to use infinite energy to achieve absolute zero. It is also possible using limited energy, but you would need an endless amount of time to complete the task. The factors are still consistent with classical thermodynamics as we know it from texts up to this point. But later, the group discovered a further, very significant detail:

No one had anticipated that, but Marcus Huber explains that it is possible to describe quantum systems that enable the absolute ground state to be achieved even at finite energy and in finite time. However, another significant characteristic of these unique quantum systems is that they are endlessly complicated. So, in order to cool a quantum object to absolute zero in finite time with finite energy, you would need to exert indefinitely fine control over an infinite number of aspects of the quantum system. Naturally, in reality, this is equally impossible to achieve as indefinitely high energy or infinitely lengthy time.

deleting information from a quantum computer

According to Marcus Huber, "theoretically, you would need an infinitely complex quantum computer that can perfectly control an infinite number of particles if you wanted to perfectly erase quantum information in a quantum computer and in the process transfer a qubit to a perfectly pure ground state." However, since no mechanism is ever flawless, perfection is not required in reality. It suffices for a quantum computer to function reasonably well. Therefore, the new findings do not, in theory, prevent the creation of quantum computers.

Temperature is a crucial factor in today's real uses of quantum technologies because it affects how easily quantum states can break and become useless for technical purposes at higher temperatures. Marcus Huber explains that this is exactly why it is crucial to comprehend how quantum theory and thermodynamics are related. "This field is currently seeing a lot of intriguing development. It is gradually becoming feasible to see how these two crucial physics components interact.