From: mk_thisisit
Introduction to Ultrafast Processes and Attosecond Pulses
The study of ultrafast processes in physics involves examining phenomena occurring on incredibly short timescales, specifically those lasting less than a billionth of a billionth of a second [01:17:19], or “Millionth of one Millionth of one Millionth of a second” [01:49:52]. Research in this field, particularly on attosecond pulses, has been significant enough to warrant a Nobel Prize [01:11:00]. These extremely short light pulses allow scientists to “look inside the atom” [01:22:00] and explore the intricate dynamics within atoms and molecules that constitute our reality [01:31:00].
The Significance of Ultrafast Timescales
While typical timescales for electrons in an atom are longer, around a femtosecond [02:42:00], and molecular vibrations are even slower (femtosecond spectroscopy earned Ahmed Zewail a Nobel Prize for this) [03:08:00], true chemical reactions involving the movement of atomic nuclei occur on much faster, attosecond scales [03:31:00]. This is critical because the Born-Oppenheimer approximation, which describes chemistry based only on electron movements with fixed nuclei, breaks down when a strong laser is shone into a molecule, causing everything to move “like spaghetti that’s boiling” [04:00:00]. To understand the dynamics of complex molecules, especially biomolecules, a time resolution in the attosecond range is necessary [04:11:00].
The “Pump-Probe” Experiment
The “pump-probe” experiment is a key method in ultrafast physics [04:43:00]. It involves exciting a molecule with a femtosecond pulse and then, a few femtoseconds later, shining another pulse to observe its response [04:32:00]. The response depends on the time interval between the pulses, allowing for the characterization of molecular dynamics [04:49:00]. This technique can be extended to attosecond pulses, offering a thousand times smaller timescale resolution [04:55:00].
Theoretical Foundations: The Lewenstein Model
Professor Maciej Lewenstein, a prominent Polish physicist, co-authored a fundamental article in physics, considered foundational to attosecond science, alongside this year’s Nobel Prize winner [05:05:00]. This work described the process of generating attosecond pulses in experiments, which are compact, often table-sized setups [05:21:00].
High Harmonic Generation
The process involves “high harmonic generation” [05:35:00], where a strong, short, non-linear laser pulse is shone onto a target (atoms, molecules, or solid bodies) [05:40:00]. This excites the target, causing it to produce photons at frequencies that are multiples (harmonics) of the incident laser’s frequency, similar to harmonics in music [06:03:00]. In atomic physics, due to certain symmetries, these harmonics often appear as odd numbers [06:20:00].
The Three-Step Model (Simple Man’s Model)
The process of high harmonic generation was initially explained by Ken Kulander and Kenneth Schafer in 1993 through a “three-stage model” or “simple man’s model” [08:02:00]. This model is largely classical in its description of electron dynamics:
- Tunneling Ionization: A strong laser field causes an electron, normally bound by the atom’s Coulomb potential, to “tunnel” through the potential barrier and become almost free [07:13:00].
- Acceleration: The now free electron is accelerated by the oscillating laser field [07:37:00].
- Recombination: The laser field changes direction, causing the electron to return to its “father ion” or nucleus and recombine, producing high harmonics [07:46:00]. This model can calculate the maximum energy an electron can gain and thus the highest possible harmonics [08:28:00].
The Fully Quantum Description
Professor Lewenstein recognized that the classical model could be formulated using a fully quantum description that accounts for more quantum effects [08:53:00]. This approach, known today as the “strong field approximation,” was developed by Lewenstein and his colleagues [09:06:00]. Their “famous paper” [09:20:00] provides a fully quantum description of the tunneling and recombination process [09:47:00]. This article is highly cited because it provides simple formulas that experimenters can directly use to compare with their data [10:13:00]. The work is widely referred to as the “Lewenstein model” [10:50:00].
“this paper contains such a fully quantum description of this whole process” [09:47:00]
Applications and Future Prospects
While the developments are still within the framework of normal quantum mechanics, they open up many unknown possibilities, especially concerning the dynamics and control of complex systems [12:05:00].
Medical Diagnostics
One significant application of attosecond technology is in medicine, particularly for cancer diagnostics and the characterization of complex molecules [15:06:00]. High-frequency photons from attosecond pulses can penetrate deep into molecules, allowing scientists to understand how they respond to disturbances [15:26:00]. This could potentially reveal differences in how cancerous cells react compared to non-cancerous cells [17:03:00]. Research in this area is being conducted in laboratories like the Extreme Light Infrastructure (ELI) in Hungary, Prague, and Romania [14:43:00].
Quantum Computing and Machine Learning
The field of quantum computing is still developing, with no fault-tolerant quantum computers currently existing [17:35:00]. However, there are significant advancements in areas like:
- Quantum simulators: Systems like cold atoms, cold ions, or Josephson junctions that simulate other physical systems, demonstrating “quantum advantage” in understanding the dynamics of large quantum systems [18:20:00].
- Quantum communication: Especially in cryptography, this area is developing “fantastically” [19:11:00].
- Precision Measurement: Quantum mechanics helps improve the precision of measurements, such as atomic clocks and magnetic field detection [19:21:00]. This improved accuracy in time and frequency measurement will enhance technologies like GPS [19:50:00].
While quantum computers are not expected to “take over the world” [19:38:00], their technical applications are crucial for technology and society [19:42:00].
Regarding quantum physics in machine learning, while it’s a classical field, research explores whether quantum computers can offer an advantage over traditional classical neural networks and machine learning. As of now, a clear, significant advantage has not been demonstrated, but it remains an open and active area of research [20:21:00].
Emergent Phenomena and Chaos Theory and Its Relation to Quantum Physics
When considering the philosophical question of “What is life” [21:55:00] and the difference between animate and inanimate nature, the concept of “emergence” arises [23:13:00]. This idea suggests that when a system contains many simple elements with complex dynamics and non-linear interactions, new qualities can emerge at a certain point [23:24:00]. For example, individual spins interacting weakly can collectively settle magnetically in one direction at low temperatures, a collective phenomenon [23:43:00]. This perspective allows one to imagine that life itself could be an emergent phenomenon [23:58:00].
Quantum Physics and Art
Quantum physics even finds its way into art, specifically music. For example, quantum random number generators have been used to create music [25:38:00]. This interdisciplinary approach between art and science is seen as a valuable educational program [26:02:00].