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Petahertz electronics: For years, the performance and efficiency of conventional electronics have stagnated, limited by fundamental constraints of physical laws. To break through these barriers, revolutionary approaches to electron control are being explored. Lightwave electronics introduces a transformative concept; it utilizes the oscillating electric field of light to manipulate charge carriers on timescales shorter than a single optical cycle. This holds the potential to enable ultrafast, energy-efficient electronics operating at optical clock rates, far surpassing the limits of traditional electronic technologies. However, questions remain: What is the ultimate speed limit of electrons in an electric circuit? Which materials and systems are suited? How can we control and, most importantly, measure such ultrafast processes? Can we use these concepts to generate quantum devices operating at room temperature?
Light an electromagnetic wave or photon? Today, electromagnetic fields oscillating with gigahertz frequencies control currents in nanostructures and, ultimately, control processes in modern computers and phones. But what is the ultimate speed limit of this control? Can we use optical fields to control electronics at petahertz frequencies, which is about one million times faster than our current technology?
When optical fields, i.e., light interacts with matter, the interaction is often described perturbatively. In this framework, photon absorption excites an electron in a solid-state medium, which may generate a photocurrent. Although this process can occur rapidly, the electrons—and consequently currents—do not respond directly to the oscillating optical field of light, which oscillates at petahertz frequencies.
Approximately 30 years ago, the first observation of high harmonic generation (HHG) in atoms was reported, marking a milestone in developing attosecond science and, most importantly, attosecond-fast control. These early experiments revealed how strong optical fields could tunnel-ionize atoms within fractions of an optical cycle. Once ionized, the electrons are accelerated by the laser field and then driven back to their parent ions. Upon recollision, these electrons release their excess energy through ultrashort bursts of high-frequency radiation. This phenomenon, known as HHG, provided the foundation for generating coherent extreme ultraviolet (XUV) and soft X-ray radiation, ultimately enabling the creation of attosecond light pulses. This breakthrough opened new frontiers in ultrafast science, allowing us to explore processes occurring on attosecond timescales—the natural time scale of electron dynamics.
More recently, we have utilized intense few-cycle laser pulses, advanced nanostructures, and quantum materials to explore condensed matter systems that are intrinsically sensitive to the electric field waveform of light. Recent breakthroughs have brought petahertz-scale electronic components and signal processing closer to realization. Logic gates, light-field current switching, random-access memory, spintronics, valleytronics, Bloch electron wave control, and data encoding have been demonstrated or predicted at terahertz-to-petahertz frequencies. Beyond technological applications, coherent lightwave control of charge carriers in solids has emerged as a powerful tool for material spectroscopy. It provides direct access to novel solid-state properties, including quantum-mechanical phases, topological properties, strong electron correlations, and ultrafast magnetism, heralding a new paradigm for lightwave spectroscopy and electronics.
Our group is at the forefront of this emerging field. We have successfully harnessed the carrier wave of intense laser pulses to steer charge carriers coherently using light waves, enabling record-breaking current injection and electron control faster than any scattering in a solid.
Electric field sampling; Figure adapted from Nature Photonics 15, 456 (2021)
Electric Field Sampling: An exciting breakthrough in understanding light-matter interaction in solids and nanostructures on extreme timescales is the development of sub-femtosecond gates. These ultrafast gates enable us to capture snapshots of the electromagnetic field on timescales shorter than a single oscillation of light, allowing the direct recording of its waveform—analogous to a sampling oscilloscope for optical fields. Why is this important? The motion of an electron leaves an imprint on the electromagnetic field. By analyzing the waveform, we can reconstruct the electron’s trajectory, offering a unique window into ultrafast processes beyond the reach of conventional pump-probe spectroscopy.
In our group, we strive to advance and expand field-resolved spectroscopies into the THz and PHz frequency domains, unlocking unprecedented sensitivity to vibrational and electronic transitions in various quantum materials. By harnessing the unique capability of field-resolved spectroscopy to capture the sub-cycle response of solids to lightfields, we aim to probe and control band engineering, many-body excitations, and ultrafast scattering dynamics inside of solids, at nanostructures and their interfaces. These insights may pave the way for optimizing energy conversion processes in optoelectronic devices. Ultimately, the sub-cycle control of electronic and photonic devices forms the foundation for lightwave electronics, promising to drive computing speeds to fundamental physical limits.
To learn more about petahertz electronics, check out the following articles.
Heide, C., Keathley, P., & Kling, M. (2024). Petahertz electronics. Nature Reviews Physics, 6, 648–662. https://doi.org/10.1038/s42254-024-00764-7
Borsch, M., Meierhofer, M., Huber, R., & Kira, M. (2023). Lightwave electronics in condensed matter. Nature Reviews Materials, 8, 668–687. https://doi.org/10.1038/s41578-023-00592-8
Boolakee, T., Heide, C., Garzón-Ramírez, A., Weber, H. B., Franco, I., & Hommelhoff, P. (2022). Light-field control of real and virtual charge carriers. Nature, 605(7909), 251–255. https://doi.org/10.1038/s41586-022-04565-9
Herbst, A., Scheffter, K., Bidhendi, M. M., Kieker, M., Srivastava, A., & Fattahi, H. (2022). Recent advances in petahertz electric field sampling. Journal of Physics B: Atomic, Molecular and Optical Physics, 55(17), 172001. https://doi.org/10.1088/1361-6455/ac8032
Bionta, M. R., Ritzkowsky, F., Turchetti, M., Yang, Y., Cattozzo Mor, D., Putnam, W. P., Kärtner, F. X., Berggren, K. K., & Keathley, P. D. (2021). On-chip sampling of optical fields with attosecond resolution. Nature Photonics, 15(6), 456–460. https://doi.org/10.1038/s41566-021-00792-0
Higuchi, T., Heide, C., Ullmann, K., Weber, H. B., & Hommelhoff, P. (2017). Light-field-driven currents in graphene. Nature, 550(7675), 224–228. https://doi.org/10.1038/nature23900
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