speed-quantum-entanglement-attosecond-scale

Scientists Explore the Speed of Quantum Entanglement at the Attosecond Scale

Understanding Quantum Theory

Quantum theory explains phenomena that occur over extraordinarily brief time scales, Historically, such occurrences were seen as 'instantaneous': An electron circles an atomic nucleus—only to be abruptly ejected by a flash of light. Two particles interact—then suddenly become 'quantum entangled.'

New Frontiers in Quantum Research

Today, it is possible to explore the temporal progression of these seemingly 'instantaneous' effects. In collaboration with Chinese research teams, TU Wien (Vienna) has developed simulations that allow for the study of ultrafast processes. These simulations enable researchers to observe how quantum entanglement forms on an attosecond time scale.

The outcomes of the study have been published in the journal Physical Review Letters.

Two Particles Forming One Quantum System

In the case quantum entanglement between two particles, separate descriptions are ineffective. Even with perfect understanding of the two-particle system, one cannot clearly define the state of a single particle.

"You might contend that the particles do not possess individual traits; instead, they have collective properties. Mathematically, they are tightly bound, even if they occupy completely different spaces," explains Prof. Joachim Burgdörfer from TU Wien's Institute of Theoretical Physics.

In experiments involving entangled quantum particles, researchers typically aim to preserve quantum entanglement for extended durations, particularly for applications in quantum cryptography or quantum computing.

"In a different vein, we are interested in understanding how this entanglement originates and which physical effects are relevant at extremely short times scales," notes Prof. Iva Březinová, one of the authors of the current publication.

The Ejection of Electrons

One electron speeds away, leaving one bound to the atom

The researchers examined atoms exposed to an extremely intense, high-frequency laser pulse. This pulse ejects an electron from the atom, causing it to escape. If the radiation intensity is sufficient, a second electron may also be impacted, transitioning into a higher energy state and subsequently orbiting the atomic nucleus along a different trajectory.

As a result, after the laser pulse, one electron is ejected while the other remains with the atom, possessing an unspecified energy.

"We can establish that these two electrons are now quantum entangled," remarks Burgdörfer. "They must be analyzed as a pair, and conducting a measurement on one will simultaneously yield information about the other."

The Concept of 'Birth Time'

The electron is unaware of the specific moment of its 'birth'

The research team has successfully demonstrated, through a specialized measurements protocol utilizing two distinct laser beams, that it is feasible to establish a connection between the 'birth time' of the escaping electron—specifically, the moment it departed from the atom—and the state of the electron that remains. These two characteristics are quantum entangled.

According to Burgdörfer, "This implies that the birth time of the departing electron is fundamentally unknown. One could argue that the electron itself is unaware of when it separated from the atom. It exists in a quantum superposition of various states, having left the atom at both an earlier and a later moment in time."

Which point in time it 'really' was cannot be definitively addressed—the 'actual' answer simply does not exist in the context of quantum physics. Nonetheless, the answer is quantum—mechanically connected to the uncertain state of the electron remaining with the atom. If the remaining electron occupies a higher energy state, it suggests that the departing electron was more likely to have been ejected earlier; conversely, if the remaining electron is in a lower energy state, the 'birth time' of the escaping electron would be likely later—averaging about 232 attoseconds.

The Significance of Attoseconds

This duration is nearly beyond comprehension: an attosecond equals one billionth of a billionth of a second.

"However, these distinctions can not only be computed but also experimentally measured," explains Burgdörfer. "We are currently in discussions with research teams eager to validate such ultrafast entanglements."

Rethinking 'Instantaneous' Phenomena

The time structure underlying 'instantaneous' phenomena

This research demonstrates that considering quantum effects merely as 'instantaneous' is insufficient. Significant correlations emerge only when one can discern the ultra-short time scales associated with these effects.

"The electron doesn't merely jump out to the atom; it propagates as a wave that gradually emanates from the atom, a process that requires time," says Březinová. "Entanglement occurs during this phase, allowing for precise measurements later through the observation of both electrons.

Source

Dive Deeper into Quantum Mechanics! Explore more about the fascinating world of quantum entanglement and its implications for the future of computing and cryptography. Read our related articles!