Quantum failure: Scientists capture natural ‘state changes’ in superconducting circuits

In a major advance in quantum science, researchers have successfully observed first-order and second-order dissipative phase transitions in superconducting quantum systems (a feat that could reshape future quantum computing technologies.

The study, published on March 10 in Nature Communications, documented how the team led by Professor Pasquale Scarlino at the EPFL (École Polytechnique Fédérale de Lausanne) created a professional superconducting resonator that enables them to witness these elusive quantum phenomena with unprecedented transparency.

“In fact, a very interesting aspect of this work is that it also demonstrates that close collaboration between theory and experiment can lead to much greater results than independent achievements of any group,” said Guillaume Beaulieu, lead author of the study.

For most of us, phase transitions are familiar concepts—such as water freezing into ice or boiling into steam. However, in the quantum field, the behavior of phase transitions is different, and it is difficult to observe, especially when dissipation occurs, when the quantum system loses energy to the environment.

The researchers focused on two types of dissipative phase transitions (DPTs). First-order DPT involves sudden jumps between states, while second-order DPT involves more subtle continuous changes that change the underlying symmetry of the system.

The team designed a device called a KERR resonator, essentially a quantum circuit with controllable properties, and designed to experience a “two-optical driver” that injects a pair of photons to carefully manipulate the quantum state of the system.

Watch the quantum state transformation

By carefully adjusting parameters such as guidance (the difference between driving frequency and natural frequency of the resonator) and driving amplitude, scientists track the system as it travels through different quantum stages.

Experiments require temperatures close to absolute zero to minimize background noise. A dedicated Kerr resonator proves crucial because it amplifies subtle quantum effects and responds to two-photon signals with significant sensitivity – functionality lacking in conventional settings.

The team used advanced mathematical tools, including Liouvillian spectroscopy theory, to accurately analyze the phase transitions occurring in the system. For second-order DPTs, they observed “squeezing”, where quantum fluctuations fell under natural background noise in blank space, a clear signal that the system has reached a critical conversion point.

During first-order DPT, the researchers recorded different lag cycles, and the current state of the system depends on its previous history. They also identified a metastable state where the system temporarily hovered in one configuration before suddenly switching to another configuration.

Perhaps most importantly, the team measured “critical slowdowns” in both types of transitions, confirming theoretical predictions. Near the critical point, the system’s response time extends sharply, a feature that may be used for more precise quantum measurements.

From theory to reality

The findings of this study are more than just theoretical victory. They demonstrate practical ways to control and understand quantum systems in real-world situations.

“The lack of established extreme principles that describe homeostasis associated with DPT requires efforts to understand and characterize these key phenomena,” the researchers wrote in the paper.

This work provides experimental confirmation of previously difficult-to-verify theoretical models. By systematically extending its system to what physicists call “thermodynamic limitations,” the team demonstrates how these transformations emerge and behave, which could inform future quantum technology designs.

Applications outside the laboratory

The meaning goes far beyond academic interests. Understanding DPT may lead to more robust quantum computing systems and more sensitive quantum sensors.

The researchers believe that second-order DPT, in particular, is expected to “enhance the effective encoding of quantum information” and bring “favorable metrological characteristics.” This suggests a potential application in quantum error correction – a key challenge in building reliable quantum computers.

The team’s achievements in observing two DPTs in a single device emphasize the versatility of quantum-engineered superconducting circuits. It also highlights how interdisciplinary collaboration – combining experimental physics, theoretical modeling and engineering – can push the boundaries of scientific exploration.

By providing a clearer understanding of how quantum systems behave under unequal conditions, this study brings us closer to leveraging the quantum effects of practical technologies that may eventually transform from computers to medicine.

As quantum research continues to evolve, studies like this are the key bridge between abstract theory and real-world applications, thus glimpsing the strange rules of quantum mechanics may one day become a tool for our technology Arsenal.