Scientists time the ‘birth’ of quantum entanglement for the first time

There is a lot Scientists try to understand the “birth” of quantum entanglementthat is, the moment when the quantum states of particles are linked together in a way that cannot be described separately. Entanglement, called “spooky action at a distance” by Einstein himself, has until now been viewed as an “instantaneous” change.

The big question in this concept, which initially defied the laws of classical physics, is knowing exactly when entanglement arises. In this sense, an international team of scientists from the Vienna University of Technology (UT Wien) in Austria and three Chinese universities (Shenzhen, Beijing and Shanxi) has made a spectacular and unprecedented leap.

Using an ultra-fast measurement technique called attosecond chronoscopy, they were able to measure the time of this unique moment for the first time. Like a camera, the tool allows you to observe the orbits of extremely fast electrons and how they interact with each other. In this type of observation, movements are recorded in real time.

Measuring quantum entanglement on the attosecond scale

The time scale at which quantum entanglement occurs is equivalent to an attosecond, an incredibly small unit of time (10^-18 seconds), or a billionth of a billionth of a second. This concept is so minimal that it is difficult for our minds to grasp. Using an implication we can say the ratio of one attosecond to one second, where one second is equal to 31.7 billion years, or 2.3 times the age of the Universe.

When working with entangled particles, scientists want this entanglement to last as long as possible. “We, on the other hand, are interested in something else: discovering how this entanglement developed in the first place and what physical effects are at play on extremely short time scales,” explains co-author Iva Brezinová, professor at UT Wien.

To test their theory, the team used powerful computer simulations to create virtual interactions between atoms and intense laser pulses, according to a press release. In the atoms hit by this fast, intense beam of light, one electron flies away, and the remaining electron jumps to a higher energy level. This is the “recipe” for quantum entanglement.

In quantum entanglement, the electron does not know when it was born

At this point, the biggest advantage of quantum entanglement is that even if one electron is kicked out and the other remains in the atom with unknown energy, “you can only analyze them together – and make measurements on one of the electrons and find out,” says co-author Joachim Burgdörfer from UT Wiesn, “and at the same time, there is something about the other electron.” “There are things,” he says.

In other words, the “birth time” of the electron that flies away is related to the state of the electron left behind. “This means that the time of birth of the flying electron is in principle unknown. You could say that the electron itself does not know when it leaves the atom,” says Burgdörfer.

The concept of quantum superposition is so strange that this electron “leaves the atom at an earlier and later point,” the physicist says. This way it is not possible to answer when it really goes. So there is no answer to this question in quantum physics.

But the answer physically depends on the equally undefined state of the remaining electron. If the particle was in a higher energy state, the escaped electron was expelled at an earlier point in time. However, the simulation concludes that if the energy is lower, the “birth time” of the free electron is on average 232 attoseconds later, and this now needs to be tested in a real-world laboratory setting.

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