麻豆淫院

When placed under a powerful laser field (i.e., under strong-field ionization), electrons can temporarily cross the so-called quantum tunneling barrier, an energy barrier that they would typically be unable to overcome. This quantum mechanics phenomenon, known as quantum tunneling, has been the focus of numerous research studies.

Precisely measuring the exact time that an electron spends inside a quantum tunneling barrier during strong-field ionization has so far proved challenging. In recent years, physicists have developed advanced experimental tools called attoclocks, which can measure the timing of ultrafast electron dynamics and could thus help to answer this long-standing research question.

Despite their potential for measuring the tunneling time of electrons, most attoclocks developed to date have had significant limitations and have been unable to yield reliable and conclusive measurements. In a recent paper in 麻豆淫院ical Review Letters, researchers at Wayne State University and Sorbonne University introduced a new attoclock technique that leverages the carrier-envelope phase (CEP), the offset between the peak of a laser's pulse's envelope and its oscillating field, to collect more precise tunneling time measurements.

"The question of tunneling time has been a long-standing issue in quantum mechanics," Wen Li, senior author of the paper, told 麻豆淫院. "Attoclock is a recently developed technique that offers an unprecedented time resolution (down to a few attoseconds, i.e. 10^-18 s). This technique is supposed to be perfectly suited for measuring the tunneling time. However, even after two decades of intensive work using attoclock, the question is still not answered."

The main objective of the recent study by Li and his colleagues was to develop a new and more effective attoclock that could measure the tunneling time of electrons with even greater precision. The technique they developed differs from most existing attoclocks, which are designed to infer time delays leveraging elliptically polarized light (i.e., light in which an electric field rotates in an elliptical pattern).

Despite their potential, these conventional attoclocks require extensive modeling and thus typically yield unreliable results. In contrast, the attoclock method introduced by Li and his colleagues relates elliptical measurements to those collected from circularly polarized light (i.e., in which electric fields rotate following a circular pattern), leveraging the so-called carrier-envelope phase.

"Compared to conventional attoclock measurements, the phase-resolved attoclock truly tracks the peak of the electric field, which is the exact moment when electrons tunnel out," explained Li. "This suppresses any non-time-dependent factors that distort the results."

The researchers have already tested their newly proposed phase-resolved attoclock in a series of experiments which have gathered new valuable insights. Their results suggest that the tunneling time of electrons is very small and that deflection angles are primarily determined by ionization potentials, while the effects of tunneling delay are significantly less pronounced.

The new type of attoclock developed by Li and his colleagues could soon open new possibilities for the study of ultrafast quantum phenomena, which could enrich their understanding.

"With the new technique and joint theory work, we show that tunneling time is vanishingly small, and the measured deflection angles are uniquely associated with the ionization potentials of species," added Li.

"We are now looking into the vanishing but non-zero delays measured in the study. Because the delay is so small, a new 'zeptoclock' might be needed. Furthermore, because the technique is robust, we are currently working to develop it into a spectroscopic method so we can use it to study chemistry in real-time."

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