Dr. Mohammed Th. Hassan, University of Arizona
From Attosecond Electron Microscopy Imaging To Petahertz Quantum Photonics
Abstract – We present groundbreaking advancements in ultrafast electron microscopy, quantum current tunneling in graphene, and ultrafast squeezed light, establishing transformative capabilities in attosecond science and technology1,2. First, we achieved attosecond temporal resolution in a transmission electron microscope by generating a single isolated attosecond electron pulse, far surpassing the highest reported imaging resolutions3-5. This novel tool, termed the “attomicroscope,” represents the world’s fastest electron microscope, enabling the imaging and control of electron motion dynamics in graphene. The attosecond electron imaging method offers real-time and spatial insights into the electron motion of neutral matter, unlocking long-anticipated applications in quantum physics, chemistry, and biology5.
Next, we report the generation of light-induced quantum tunneling currents in graphene phototransistors in ambient conditions. This phenomenon allows precise measurement and control of field-driven currents, demonstrating current switching at an unprecedented 630 attoseconds (~1.6 petahertz)6. By modulating the density of photoexcited charge carriers with variable pump laser powers, we enhanced the graphene phototransistor conductivity and realized various logic gate operations. These findings pave the way for optical switches, lightwave electronics, and optical quantum computing7-9.
Lastly, we extend the use of squeezed light to ultrafast quantum science, demonstrating the generation of broadband quantum light pulses spanning 0.33 to 0.73 petahertz using a light field synthesizer and four- wave mixing10. These pulses exhibit amplitude squeezing consistent with theoretical predictions, enabling real-time studies of quantum light-matter interactions. Furthermore, we demonstrate binary digital data encoding onto these synthesized attosecond-resolved quantum light waveforms, showcasing potential applications in secure quantum communication. This work sets the stage for ultrafast quantum optoelectronics, next- generation quantum computing, and encrypted communication networks capable of petahertz-scale data transmission speeds.
References
- Corkum, & Krausz, F. Nat. Phys. 3, 381-387, (2007).
- Hassan, T. et al. Nature 530, 66-70, (2016).
- Hassan, T. et al. Nat. Photon. 11, 425-430, (2017).
- Hui, , Alqattan, H., Sennary, M., Golubev, N. V. & Hassan, M. T. Science Advances 10, eadp5805, (2024).
- Hassan, T. Physics Today 77 38–43 (2024).
- Sennary, et al. Nature Communications 16, 4335, (2025).
- Hui, et al. Nat. Photon. 16, 33-37, (2022).
- Hassan, T. ACS Photonics 11, 334-338, (2024).
- Hui, et al. Science Advances 9, eadf1015, (2023).
- Sennary, et al. arXiv preprint arXiv:2412.08881, (2024).
Bio – Dr. Mohammed Hassan is an Associate Professor of Physics and Optical Sciences at The University of Arizona (UA). He earned his Ph.D. from the Max Planck Institute for Quantum Optics in Munich, Germany, in 2013, working in the research group of Prof. Ferenc Krausz (Nobel Laureate, 2023). He then joined the California Institute of Technology (Caltech) as a postdoctoral scholar in the group of Prof. Ahmed H. Zewail (Nobel Laureate, 1999), where he conducted research until 2017.
Some of Dr. Hassan scientific achievements can be summarized as follows:
Dr. Hassan is widely recognized for pioneering the field of attosecond electron microscopy, introducing the “Attomicroscope“—the world’s fastest electron microscope capable of imaging electron motion in real time. This revolutionary tool has opened a new frontier in ultrafast imaging, enabling direct visualization of electron behavior in solid-state materials and advancing quantum science.
Dr. Hassan group developed the first petahertz quantum phototransistor , capable of switching on and off in just 630 attoseconds—a speed equivalent to 1.6 petahertz, or over a million billion times per second. This unprecedented speed was demonstrated using a novel graphene-silicon-graphene (Gr-Si- Gr) transistor structure, marking a significant leap toward the future of ultrafast light-driven electronics.
Most recently, Dr. Hassan has demonstrated all-optical switching and quantum current switching on the attosecond timescale, setting a new world record for switching speed. Leveraging his expertise in light field synthesis, he has also developed methods to digital encode data onto ultrafast laser pulses. Additionally, he has introduced novel methodologies for sampling ultrafast laser light fields and measuring electronic response delays in neutral matter.
His research group has also achieved a major milestone in ultrafast quantum optics by demonstrating amplitude-squeezed quantum light, which he has applied to developing highly secure, high-speed quantum communication technologies.
Early in his career, Dr. Hassan developed the light field synthesizer, which enabled the generation of the first optical attosecond pulse—the shortest light pulse ever recorded, earning recognition in the Guinness World Records. Using this breakthrough technology, he measured the time it takes for an electron to respond and move, providing unprecedented insight into ultrafast electron dynamics. He also utilized synthesized waveforms to generate extreme ultraviolet radiation from solids, offering a new temporal perspective on high harmonic generation and electron behavior in condensed matter.
During his postdoctoral tenure at Caltech, Dr. Hassan optimized ultrafast optical gating techniques to generate electron pulses, achieving the shortest electron pulse in an electron microscope. He also contributed to the first imaging of nanoparticle motion in a liquid state using ultrafast electron microscopy. His early breakthroughs were published in leading scientific journals.
Dr. Hassan’s contributions have earned him numerous prestigious honors, including the International Max Planck Fellowship (2009), the Air Force Young Investigator Award (YIP, 2019), and major research grants from the Gordon and Betty Moore Foundation (2018) and the W. M. Keck Foundation (2019). In 2022, he received both the Inaugural AFOSR Director’s Research Initiative (DRI) Award and the Historically Black Colleges and Universities and Minority-Serving Institutions (HBCUs/MSIs) Award for his institution.