# Quantum computers may hold the secret to achieving absolute zero, finds study

Light, sound, and heat are all types of energy around us. Thermodynamics is a branch of science that helps us understand how energy moves between objects. According to the third law of thermodynamics, it is impossible to cool any object to -273.15 degrees C (or absolute zero), which is the lowest temperature possible.

Now a research team from the Vienna University of Technology in Austria has found a way to cool an object to absolute zero. The study published in *PRX Quantum* demonstrates this alternate route using quantum computing.

The findings could help us better understand how thermodynamics works at the quantum scales.

## Information theory and Landauer's principle

The third law of thermodynamics has been formulated for classical systems and objects, which means it does not account for quantum systems. Even to date, the interaction of quantum mechanics and thermodynamics is poorly understood, and this understanding is what led the researchers to their findings.

According to Lansauer's principle in information theory, a minimum and finite amount of energy is needed to delete one bit of information. On the other hand, the laws of thermodynamics state that you need an infinite amount of energy to cool a system or object to absolute zero. Here's the problem, they both mean the same thing.

You don't necessarily need infinite energy to achieve absolute zero, you could also take an infinite amount of time with finite energy to achieve absolute zero. This is where the team found a hidden parameter, complexity.

They found that if you had complete infinite control over an infinitely complex system, like quantum systems, then an object can be cooled to absolute zero with finite energy in finite time. In reality, this is not possible, as we are dealing with infinities.

## Quantum computers and information

The findings of this study highlight an underlying problem with practical quantum computers. In theory, if we had an infinitely complex quantum computer, we could erase the data stored in qubits.

In reality, this is not possible. No machines are perfect. While it is possible to build quantum computers which work well, they cannot be infinitely complex. This leads us to another problem with quantum computers, instability at higher temperatures.

Quantum computers generally break down at higher temperatures due to noise breaking down the quantum states, making them unstable for use. Both these problems emphasize the need for more research in the area of quantum thermodynamics. The underlying principles are necessary to understand and implement better quantum technologies in the future.

**Study abstract:**

Thermodynamics connects our knowledge of the world to our capability to manipulate and thus to control it. This crucial role of control is exemplified by the third law of thermodynamics, Nernst’s unattainability principle, which states that infinite resources are required to cool a system to absolute zero temperature. But what are these resources and how should they be utilized? And how does this relate to Landauer’s principle that famously connects information and thermodynamics? We answer these questions by providing a framework for identifying the resources that enable the creation of pure quantum states. We show that perfect cooling is possible with Landauer energy cost given infinite time or control complexity. However, such optimal protocols require complex unitaries generated by an external work source. Restricting to unitaries that can be run solely via a heat engine, we derive a novel Carnot-Landauer limit, along with protocols for its saturation. This generalizes Landauer’s principle to a fully thermodynamic setting, leading to a unification with the third law and emphasizes the importance of control in quantum thermodynamics.