The practical barriers to observing the Schwinger effect have long anchored it firmly in the realm of theory. Estimates suggest that electric fields on the order of 10^18 volts per meter or higher are necessary to induce such vacuum pair production—a scale that challenges the limits of current high-energy physics facilities. This absence of empirical verification sparked a new line of inquiry among theorists at the University of British Columbia (UBC), who sought to circumvent the towering technological hurdles by devising an analogous system more amenable to direct observation. Their innovative approach replaces the vacuum with a thin film of superfluid helium and substitutes the homogenous electric field with a background flow within the superfluid, creating a parallel effect that retains the fundamental physics but renders it experimentally accessible.

Superfluid Helium-4, a phase of helium cooled near absolute zero, displays remarkable quantum properties. When confined into films only a few atomic layers thick and cooled sufficiently, it essentially forms a frictionless quantum vacuum. Dr. Philip Stamp, a leading theorist at UBC, explains the significance of this state: “Superfluid Helium-4 is a wonder. At a few atomic layers thick, it can be cooled very easily to a temperature where it’s basically in a frictionless vacuum state.” This unique environment mimics key characteristics of the vacuum in quantum field theory, allowing the researchers to translate the Schwinger effect into the realm of condensed matter physics. Instead of electron-positron pairs emerging from nothingness, this superfluid system predicts the spontaneous formation of vortex/anti-vortex pairs—quantized whirlpools of superfluid circulation spinning in opposite directions.

The mathematics underlying these vortex phenomena is deeply intertwined with the physics of quantum tunneling. Dr. Stamp and his collaborator, Michael Desrochers, have formulated a robust theoretical framework describing how these vortex pairs form spontaneously as a result of the superfluid’s flow. Their model bridges abstract quantum field theory with tangible experimentation, allowing researchers to probe vacuum-like behavior without constructing unfeasible setups. Crucially, their paper, recently published in Proceedings of the National Academy of Sciences, outlines a detailed pathway for laboratory experiments that could conclusively detect and characterize these vortex tunneling events.

Quantum vacuum tunneling holds a central place in modern physics, offering insights into processes from particle physics to cosmology. Contrary to intuition, vacuum states in quantum theory are not empty voids but dynamic fields bubbling with transient virtual particles that flicker into and out of existence. Dr. Stamp articulates the profound analogy embodied in their work, stating, “We believe the Helium-4 film provides a nice analog to several cosmic phenomena.” This includes the quantum vacuum permeating deep space, the enigmatic quantum aspects of black holes, and even the nascent moments following the Big Bang—phenomena otherwise inaccessible due to insurmountable scale or energy requirements.

While analogies always carry caveats—no replica can capture every nuance of the original—this research emphasizes the dual utility of the experiment. Beyond serving as a proxy for inaccessible cosmic phenomena, it reshapes our fundamental understanding of superfluid dynamics and phase transitions in two-dimensional quantum systems. “These are real physical systems in their own right, not analogs. And we can do experiments on these,” Dr. Stamp stresses, highlighting the broad implications for condensed matter physics and quantum turbulence research.

One of the pivotal breakthroughs in Stamp and Desrochers’ theory stems from a revised understanding of vortex mass. Traditional approaches often treat the mass of vortices within superfluids as a fixed constant, simplifying their behavior. However, the UBC team reveals that this mass is in fact highly variable, fluctuating dramatically as vortices move through the superfluid film. This discovery challenges long-standing assumptions and compels a re-examination of how vortices interact with their environment, both in condensed matter physics and potentially in the context of the early universe’s quantum fields.

Michael Desrochers highlights the excitement surrounding this finding: “It’s exciting to understand how and why the mass varies, and how this affects our understanding of quantum tunneling processes, which are ubiquitous in physics, chemistry and biology.” This insight not only deepens our grasp of superfluid vortex dynamics but also suggests possible modifications to canonical models of quantum tunneling across disciplines. The mass variability could influence reaction rates, coherence phenomena, and transport properties in various quantum materials.

Intriguingly, Stamp posits that the variable vortex mass discovered in their superfluid analog may have direct implications for the original Schwinger effect involving electron-positron pairs. “The same mass variability will occur with electron-positron pairs in the Schwinger effect,” he argues, implying that Schwinger’s original theoretical framework might require refinement. This concept, whimsically dubbed the ‘revenge of the analog,’ underscores how insights gained from condensed matter systems can reverberate back into fundamental particle physics, fostering a virtuous cycle of discovery across disciplines.

The broader impact of this work extends beyond the immediate experimental ambitions. By providing a workable platform to study vacuum tunneling phenomena experimentally, the research opens new vistas for exploring non-equilibrium quantum phase transitions, topological excitations, and emergent quantum coherence. Moreover, it offers a promising bridge between quantum gravity concepts and laboratory physics, bringing abstract theoretical conjectures closer to empirical testing.

Support for this pioneering research came from the National Science and Engineering Research Council, underscoring the importance of foundational science in advancing both knowledge and technological capability. The collaboration and cross-pollination of ideas between condensed matter physics and high-energy theory exemplify the interdisciplinary spirit driving modern physics. As further experiments validate and extend these predictions, we may soon witness a radical expansion in our ability to manipulate and understand quantum vacuum phenomena in controlled settings.

In sum, the University of British Columbia team’s innovative reinterpretation of the Schwinger effect through the lens of superfluid helium films represents a milestone in quantum physics research. It transcends traditional boundaries by pairing elegant theoretical insights with practical experimental designs, unlocking new pathways to probe the elusive frontier where quantum mechanics, particle physics, and cosmology converge. These findings not only enrich our fundamental comprehension of the vacuum and quantum tunneling but also underscore the transformative potential of analog research systems in illuminating the mysteries of the universe.

Subject of Research: Not applicable

Article Title: Vacuum Tunneling of Vortices in 2-Dimensional 4He Superfluid Films

News Publication Date: 1-Sep-2025

Web References:
10.1073/pnas.2421273122

Keywords

Quantum tunneling, Quantum mechanics, Physics

At the heart of this innovation lies graphene, a two-dimensional lattice of carbon atoms known for its exceptional electrical, thermal, and mechanical properties. The researchers explored the electrical conductivity of custom-engineered graphene samples, with a focus on how electrons respond when excited by laser pulses lasting less than a trillionth of a second—specifically, pulses as fleeting as 638 attoseconds (an attosecond is a quintillionth of a second). These ultrashort laser bursts generate energy waves capable of moving electrons so rapidly that they seem to bypass traditional physical constraints.

Central to their experimental achievement is the exploitation of the quantum phenomenon known as tunneling. Unlike classical transport, where electrons must surmount energy barriers, tunneling allows them to effectively "pass through" barriers instantaneously, a behavior that defies conventional expectations. In this study, graphene’s symmetrical atomic arrangement initially produced balanced, opposing currents that canceled each other out under laser excitation. However, by introducing a specialized silicon layer and carefully modifying the graphene transistor, the team induced asymmetric electron flow, permitting them to observe and capture the elusive tunneling current in real time.

Harnessing a commercially available graphene phototransistor, the researchers transformed it into what they describe as the world’s fastest petahertz quantum transistor. This device functions as an ultrafast electronic switch powered by light rather than traditional electronic signals. Its operation hinges on the light-induced quantum tunneling currents, which allowed electrons to jump across potential barriers at speeds that reach the petahertz spectrum—equating to quadrillions of cycles per second. Such an astounding rate heralds a new era for ultrafast electronics, potentially revolutionizing how information is processed, transmitted, and controlled.

Mohammed Hassan, associate professor of physics and optical sciences and lead researcher in this project, highlights the paradigm shift this technology could herald. He underscores the disparity between explosive advances in artificial intelligence software and the comparatively languid pace of hardware development. By integrating quantum principles derived from cutting-edge quantum computing research, this petahertz transistor exemplifies the kind of hardware innovation that can bridge this gap, facilitating breakthroughs across scientific domains including space exploration, chemical analysis, and biomedical diagnostics.

The experiment’s success represents not only a scientific marvel but also a viable technological platform since the device operates under ambient conditions. Unlike many quantum phenomena that demand ultra-sophisticated, low-temperature environments, this transistor’s functionality in room temperature and standard atmospheric pressure conditions markedly eases the path toward real-world applications and mass production. Such practicality could accelerate commercialization efforts and spur new markets centered on petahertz-speed electronics.

Behind this advancement is a collaboration among faculty and students at the University of Arizona, notably researchers like Nikolay Golubev, Jalil Shah, Mohamed Sennary, and Mingrui Yuan, alongside scientists from the Jet Propulsion Laboratory at Caltech and Ludwig Maximilian University of Munich. Their multidisciplinary synergy brought expertise in optics, physics, and materials science to tackle the technical challenges inherent in capturing and controlling electron dynamics at attosecond timescales.

Technically, the team’s methodology focused on adapting the graphene phototransistor by embedding a silicon layer to create structural asymmetry. When irradiated with the highly controlled laser pulses, this configuration enabled the generation of non-canceling electron currents via quantum tunneling. Imaging analysis and temporally precise measurements revealed that electrons effectively leap across the potential barrier within the graphene framework, a phenomenon that, up until now, was theorized but never recorded at these speed scales with such clarity.

The implications extend far beyond incremental tech improvements. The integration of light-driven, quantum tunneling transistors into electronic circuits could unlock fundamentally new architectures in computing, with transistor switching times millions of times faster than current silicon-based devices. This catapult could energize quantum information science by providing new hardware platforms capable of managing the tremendous data flows required for quantum processors and complex simulations.

One of the most exciting prospects is the enhancement of computational power aiding advances in artificial intelligence. Ultrafast transistors leveraging petahertz speeds will be capable of feeding AI algorithms with data at unprecedented rates, shortening training times and refining decision-making processes. This breakthrough could also spur innovations in fundamental science, accelerating research that depends on real-time data analysis, such as experiments in particle physics, molecular interactions, and astrophysical observations.

Moreover, the successful demonstration of a light-induced petahertz transistor acquaints us with a future where electronic and photonic devices converge. Optical computing has long been hailed as the next frontier, aiming to overcome electrical resistance and thermal bottlenecks inherent to electron transport. By controlling electron flow with rapid light pulses, this research bridges the gap between photonics and electronics, paving the way for hybrid devices that capitalize on the speed and efficiency of photons while retaining the versatility of electronic components.

Currently, the team is working to integrate their discovery with commercially accessible equipment, striving to develop petahertz-speed transistors that can be manufactured at scale. With support from entities such as Tech Launch Arizona, these efforts involve refining device architecture to be compatible with existing microchip fabrication techniques and collaborating with industry stakeholders to transition this technology from laboratory curiosity to everyday reality.

This groundbreaking study, published in Nature Communications, marks a milestone in the ongoing quest to revolutionize the speed capacities of transistors. By harnessing the peculiarities of quantum mechanics with a practical, scalable device, researchers have charted a course toward the ultrafast computers of tomorrow that will redefine computational boundaries and enable scientific and technological frontiers once thought unreachable.

Subject of Research: Not applicable

Article Title: Light-induced quantum tunnelling current in graphene

News Publication Date: 9-May-2025

Web References:
10.1038/s41467-025-59675-5

Image Credits: Mohammed Hassan

Keywords:
Electronics, Photonics, All optical transistors, Optical computing, Semiconductors, Single electron transistors, Laser physics, Computational science, Computer science, Quantum information, Quantum processors, Optoelectronics