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.

__Provided by Vienna University of Technology__