Quantum systems don’t just transition between phases, they do so in ways that defy classical intuition.
A new experiment has directly observed these “dissipative phase transitions” (DPTs), revealing how quantum states shift under carefully controlled conditions. This breakthrough could unlock powerful new techniques for stabilizing quantum computers and sensors, making them more resilient and precise than ever before.
Quantum Phase Transitions: A New Frontier
Phase transitions, like water freezing into ice, are a familiar part of everyday life. In quantum systems, however, these transitions can be far more extreme, governed by principles like Heisenberg’s uncertainty. Additionally, external influences can cause quantum systems to lose energy to their surroundings, a process known as dissipation. When this occurs, it can drive the system into a new state, a phenomenon known as a “dissipative phase transitions” (DPT).
There are different types of DPTs, classified by their “order.” First-order DPTs are abrupt, like flipping a switch, causing the system to jump from one state to another. Second-order DPTs are more gradual but still significant, altering a fundamental property of the system, such as its symmetry, in a subtle yet transformative way.
Why DPTs Matter for Quantum Technology
Understanding DPTs is crucial for studying quantum systems that operate outside thermal equilibrium, where classical thermodynamics offers little insight. Beyond their theoretical interest, these transitions have practical applications in quantum technology. Second-order DPTs, for instance, could improve quantum information storage, while first-order DPTs provide insights into system stability and control—both critical for advancing quantum computing and sensing technologies.
For years, physicists have theoretically predicted that DPTs would exhibit distinct characteristics, such as bistability (coexistence of two states) and critical slowing down (a delayed response near transition points), following specific mathematical patterns. However, directly observing these effects, especially in second-order DPTs, has been a major challenge.
Breakthrough: Experimenting with a Kerr Resonator
Now, a breakthrough experiment has achieved just that. A research team led by Professor Pasquale Scarlino at EPFL has successfully observed DPTs using a superconducting Kerr resonator—a highly tunable quantum device. By introducing a two-photon drive, which injects pairs of photons into the system, they precisely controlled and monitored its quantum state, allowing them to track how it transitioned between phases.
By systematically varying parameters like detuning and drive amplitude, they were able to study the system’s transitions from one quantum state to another. The approach allowed them to observe both a first-order and second-order DPT.
Why Extreme Conditions Were Necessary
To ensure accuracy, the experiments were carried out at temperatures near absolute zero, reducing background noise to almost nothing. The Kerr resonator was pivotal because it can amplify quantum effects that are often too subtle to observe. Because it can respond to two-photon signals with extreme sensitivity, the researchers were able to use it to explore phase transitions with unprecedented precision—something traditional setups simply cannot achieve.
The setup allowed the team to monitor the behavior of photons emitted by the resonator with ultra-sensitive detectors. By using advanced mathematical techniques, like the connection with the spectral properties of the Liouvillian superoperator, a tool that models complex quantum processes, the scientists were able to precisely track and analyze the system’s phase transitions.
Key Findings: Squeezing, Metastability, and Slowing Down
For the second-order DPT, the team observed a phenomenon called “squeezing,” where quantum fluctuations drop to levels lower than the natural background noise of empty space, signaling that the system has reached a highly sensitive and transformative state. Meanwhile, the first-order DPT showed distinct hysteresis cycles, where the system could exist in two states depending on how parameters were tuned.
Second, they found clear evidence of metastable states during the first-order DPT, where the system temporarily remained in one stable state before abruptly transitioning to another. This behavior, leading to a dependence of the system’s state on its previous history known as hysteresis, showcases how first-order DPTs involve competing phases.
Lastly, they observed “critical slowing down” in both types of transitions reproducing the expected scaling obtained from theoretical consideration. This ultimately demonstrates the validity of theoretical predictions based on the Liouvillian theory used by the authors. Near the critical points, the system’s response slowed significantly, highlighting a universal feature of phase transitions that could be harnessed for more precise quantum measurements.
How This Could Change Quantum Technologies
Understanding DPTs opens new possibilities for engineering quantum systems that are both stable and responsive. This could revolutionize quantum information technologies, such as error correction in quantum computing or the development of ultra-sensitive quantum sensors.
More broadly, this research showcases the power of interdisciplinary collaboration—blending experimental physics, advanced theoretical models, and cutting-edge engineering to explore the frontiers of science.
“In fact, a very interesting aspect of this work is that it also demonstrates how close collaboration between theory and experiment can lead to results far greater than what either group could have achieved independently,” says Guillaume Beaulieu, the paper’s first author.
Reference: “Observation of first- and second-order dissipative phase transitions in a two-photon driven Kerr resonator” by Guillaume Beaulieu, Fabrizio Minganti, Simone Frasca, Vincenzo Savona, Simone Felicetti, Roberto Di Candia and Pasquale Scarlino, 10 March 2025, Nature Communications.
DOI: 10.1038/s41467-025-56830-w
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1 Comment
The first rule of science should read , collaboration leads the out come of discovery .