Exploring the realm of quintillionths of a second where electrons dance and quantum phenomena unfold
Imagine a timescale so brief that one second seems eternal. This is the realm of attosecond science, the cutting-edge field of physics that studies phenomena occurring within quintillionths of a second (10⁻¹⁸ s). To grasp this incredible speed, consider this: an attosecond is to one second what one second is to the age of the universe—a ratio of 1:31.5 billion4 . At this timescale, scientists are no longer watching atoms move but are instead capturing the dizzying dance of electrons within them.
This isn't merely abstract science. Understanding and controlling electron dynamics unlocks revolutionary advances in quantum computing, the development of novel materials, and medical imaging at the atomic level2 5 .
Over the past two decades, attosecond science has grown from a theoretical possibility to an experimental reality, recognized by the 2023 Nobel Prize in Physics. Today, researchers are pushing boundaries to create ever-shorter light pulses to illuminate nature's most fleeting processes, opening windows into the quantum world that were previously the domain of theory alone.
1 attosecond = 10⁻¹⁸ seconds
Ratio to one second is equivalent to one second to the age of the universe
2023 Nobel Prize in Physics awarded for attosecond science breakthroughs
Field has evolved from theory to experimental reality in two decades
Electrons don't operate on our everyday clock. In atoms, molecules, and solids, electrons move, interact, and transition between energy states on attosecond timescales4 . When an electron is excited to a higher energy level, the resulting quantum superposition state oscillates with a period determined by the energy difference between levels. For typical atomic and molecular energy gaps, these oscillation periods fall squarely in the attosecond domain4 .
This fundamental timescale makes attosecond pulses essential tools for real-time observation of electron dynamics. Without them, studying these processes would be like trying to photograph a hummingbird's wings with a long exposure—you might know something happened, but you'd miss all the details.
Creating attosecond pulses requires both broad spectral bandwidth and very short wavelengths4 . Through Fourier analysis, we know that shorter time pulses require broader bandwidths. Additionally, to achieve pulses shorter than a single oscillation of an optical cycle, scientists must push into the extreme ultraviolet (XUV) and soft X-ray regions of the electromagnetic spectrum4 .
The two primary methods for generating these pulses are:
The current record for the shortest human-made light pulse stands at 43 attoseconds4 , but as we'll see, recent breakthroughs are pushing this frontier even further.
In a groundbreaking 2025 study, researchers demonstrated they could not only generate but also manipulate the quantum properties of light with attosecond precision1 . They created the shortest ultrafast synthesized quantum light pulses to date, spanning an incredible frequency range from 0.33 to 0.73 PHz (petahertz).
These weren't ordinary light pulses—they were "squeezed" light pulses that exhibit unique quantum properties. In the quantum world, there's always a trade-off between certain properties. For these pulses, researchers achieved amplitude squeezing, meaning the intensity fluctuations were smaller than those of conventional laser light, but at the expense of increased phase uncertainty1 .
This ability to manipulate quantum uncertainty in real time opens possibilities for ultra-secure quantum communication, where data can be encoded on these squeezed ultrafast light waveforms1 . The amplitude squeezing inherent in these pulses also enhances the signal-to-noise ratio beyond what's possible with classical light, promising major advances in studying delicate biological systems and quantum materials.
In June 2025, a team from the University of Wisconsin-Madison and SLAC National Accelerator Laboratory announced they had created the first attosecond atomic X-ray laser2 . This breakthrough came with several remarkable advantages over previous X-ray sources.
| Feature | Traditional XFELs | New Attosecond Atomic X-ray Laser |
|---|---|---|
| Pulse Duration | Multiple irregular spikes | Clean, controlled pulses under 100 attoseconds |
| Pulse Characteristics | Irregular, spiky | Smooth, laser-like |
| Key Phenomenon | Self-amplified spontaneous emission | Demonstrates Rabi cycling |
| Potential Applications | Limited by pulse irregularity | Enables traditional laser techniques with X-rays |
To create this laser, researchers focused incredibly powerful X-ray pulses from existing XFELs onto copper and manganese targets2 . The input pulse was so powerful—equivalent to concentrating all sunlight hitting Earth onto a square millimeter target—that it excited the atoms' innermost electrons2 .
The experiment utilized two of the world's most powerful X-ray sources—the Linac Coherent Light Source (LCLS) at SLAC in the United States and the SACLA XFEL in Japan2 .
Researchers focused short, powerful X-ray pulses onto specific metal targets—either copper or manganese. The photon energy was precisely tuned to excite the innermost electrons of these atoms2 .
The initial pulse excited the atoms' inner-shell electrons, which then emitted X-ray photons as they returned to ground state. These photons subsequently stimulated already-excited atoms to emit more photons in the same direction, creating a coherent avalanche of X-ray emission2 .
The resulting X-ray laser light emitted in the same direction as the initial pulse was then isolated and characterized2 .
The experimental results confirmed several extraordinary properties that distinguish this new light source from conventional XFELs:
The observation of Rabi cycling is particularly significant. This quantum phenomenon occurs when the driving pulse is so strong that atoms repeatedly absorb and re-emit light. Demonstrating this effect with X-rays suggests that many laser techniques currently used with optical lasers could potentially be adapted for X-ray applications, opening unprecedented possibilities for controlling matter at the electronic level2 .
There are so many technologies and phenomena that the laser community uses now, but very few of those have dared to have been tried with hard X-rays. This work is a step towards pushing the exciting field of real laser science into this powerful hard X-ray regime.
The dramatic advances in attosecond science are enabled by sophisticated tools and technologies. Here are the key components driving this field forward:
| Tool/Technology | Function | Application Example |
|---|---|---|
| Ti:sapphire Lasers | Generate fundamental femtosecond pulses | Primary driver for high harmonic generation4 |
| Chirped Pulse Amplification | Amplifies ultrashort pulses to high intensities | 2018 Nobel Prize-winning technique; enables strong-field ionization4 |
| Chirped Mirrors | Compensate for dispersion in ultrashort pulses | Controls pulse duration down to few-cycle pulses4 |
| Carrier-Envelope Phase Stabilization | Stabilizes the relationship between pulse envelope and carrier wave | Essential for reproducible attosecond pulse generation4 |
| Free-Electron Lasers (XFELs) | Produce bright, coherent X-ray pulses | Enables attosecond experiments in hard X-ray regime |
| Light Field Synthesizers | Combine multiple color pulses into one | Creates few-cycle pulses for studying electron dynamics1 |
| Attosecond Streaking | Measures the duration of attosecond pulses | Characterizes pulse duration by mapping time to photoelectron momentum3 |
Advanced lasers and XFELs provide the ultrashort pulses needed for attosecond experiments.
Precision optics and stabilization techniques ensure consistent attosecond pulse generation.
Advanced measurement techniques like attosecond streaking capture electron dynamics.
The ability to control light and electron dynamics at attosecond timescales is paving the way for petahertz-scale electronics—devices that could potentially operate at frequencies a million times faster than current gigahertz technology1 . The 2025 demonstration of amplitude-squeezed light pulses already introduced an attosecond quantum encryption protocol that leverages squeezed synthesized light for secure digital communication at unprecedented speeds1 .
Attosecond soft-X-ray spectroscopy has emerged as a powerful tool for studying and controlling many-body dynamics in quantum materials6 . In 2023, ICFO researchers used this technique to observe a light-induced increase and control of conductivity in graphite by manipulating the material's quantum state6 . Unlike conventional approaches that physically manipulate samples, this method uses powerful light pulses to excite electrons into high-energy states, then watches how they relax back while observing the interactions between charge carriers and the lattice itself6 .
Attosecond techniques reveal:
| Field | Application | Impact |
|---|---|---|
| Fundamental Physics | Study of electron correlation effects, photoemission delays | Testing quantum mechanics in previously inaccessible regimes4 |
| Materials Science | Investigation of exciton dynamics in 2D materials, carrier motion | Designing materials with tailored quantum properties4 6 |
| Chemistry | Tracking charge transfer in molecules, light-induced fragmentation | Understanding and controlling chemical reactions at electronic level4 |
| Biology | Imaging metalloenzymes in photosynthesis and respiration | Revealing the quantum mechanics of biological processes5 |
| Quantum Computing | Developing laser techniques for quantum control | Potential for faster quantum operations and communications2 |
Attosecond science has progressed from demonstrating its first tools to becoming a transformative force across multiple disciplines. From illuminating the mysterious process of quantum tunneling to generating squeezed light for secure communication and creating the first atomic X-ray lasers, this field continues to push the boundaries of what we can observe and control.
As Jens Biegert from ICFO notes, these advances "open a new realm of physics, offering novel ways to investigate and manipulate correlated phases of matter in real-time, which are crucial for modern technologies"6 .
The coming years will likely see attosecond techniques become more accessible, moving from large facilities like XFELs to table-top setups, and finding applications we can scarcely imagine today.
The ability to capture electron motion in real-time represents more than just a technical achievement—it offers us a front-row seat to the fundamental processes that underlie our physical world, reminding us that even in the briefest moments, the universe contains wonders worth studying.