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Nonlinear superconducting resonator circuit for investigating dissipative phase transitions.
Nonlinear superconducting resonator circuit for investigating dissipative phase transitions.
In a significant advancement for quantum science, researchers have successfully observed both first and second-order dissipative phase transitions in a superconducting quantum system—a feat that could reshape future quantum computing technologies.
The study, published March 10 in Nature Communications, documents how a team led by Professor Pasquale Scarlino at EPFL (École Polytechnique Fédérale de Lausanne) created a specialized superconducting resonator that allowed them to witness these elusive quantum phenomena with unprecedented clarity.
“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,” said Guillaume Beaulieu, the study’s lead author.
For most of us, phase transitions are familiar concepts—like water freezing into ice or boiling into steam. But in the quantum realm, phase transitions behave differently and are much harder to observe, especially when coupled with dissipation—the process where quantum systems lose energy to their environment.
The researchers focused on two types of dissipative phase transitions (DPTs). First-order DPTs involve abrupt jumps between states, while second-order DPTs involve more subtle, continuous changes that alter a system’s underlying symmetry.
The team engineered a device called a Kerr resonator—essentially a quantum circuit with controllable properties—and designed it to experience a “two-photon drive,” which injects pairs of photons to carefully manipulate the system’s quantum state.
Watching Quantum States Transform
By meticulously adjusting parameters such as detuning (the difference between the driving frequency and the resonator’s natural frequency) and drive amplitude, the scientists tracked the system as it moved through different quantum phases.
The experiments required temperatures near absolute zero to minimize background noise. The specialized Kerr resonator proved crucial because it amplifies subtle quantum effects and responds to two-photon signals with remarkable sensitivity—capabilities that conventional setups lack.
Using advanced mathematical tools, including Liouvillian spectral theory, the team precisely analyzed the phase transitions occurring in their system. For the second-order DPT, they observed “squeezing,” where quantum fluctuations dropped below the natural background noise of empty space—a clear signal that the system had reached a critical transformation point.
During the first-order DPT, the researchers documented distinct hysteresis cycles, where the system’s current state depended on its previous history. They also identified metastable states, where the system temporarily lingered in one configuration before suddenly switching to another.
Perhaps most significantly, the team measured “critical slowing down” in both types of transitions, confirming theoretical predictions. Near critical points, the system’s response time stretched dramatically—a characteristic that could potentially be harnessed for more precise quantum measurements.
From Theory to Reality
The study’s findings weren’t just theoretical victories; they demonstrated practical ways to control and understand quantum systems under real-world conditions.
“The lack of established extremal principles to describe the steady states associated with DPTs calls for an effort to understand and characterize these critical phenomena,” the researchers wrote in their paper.
This work provides experimental confirmation of theoretical models that had previously been difficult to verify. By systematically scaling their system toward what physicists call the “thermodynamic limit,” the team showed how these transitions emerge and behave—information that could inform the design of future quantum technologies.
Applications Beyond the Lab
The implications extend far beyond academic interest. Understanding DPTs could lead to more robust quantum computing systems and more sensitive quantum sensors.
Second-order DPTs, in particular, are predicted to “enhance efficient encoding of quantum information” and bring “advantageous metrological properties,” according to the researchers. This suggests potential applications in quantum error correction—a critical challenge in building reliable quantum computers.
The team’s achievement in observing both types of DPTs in a single device underscores the versatility of superconducting circuits for quantum engineering. 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 non-equilibrium conditions, this research takes us one step closer to harnessing quantum effects for practical technologies that could eventually transform everything from computing to medicine.
As quantum research continues to advance, studies like this one serve as crucial bridges between abstract theory and real-world applications, offering glimpses of how the strange rules of quantum mechanics might someday become tools in our technological arsenal.
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