Avoiding Postselection in Quantum Measurements

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A protocol to explore entanglement dynamics via spacetime duality

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+  Researchers at Stanford University have recently carried out a study exploring the role of quantum measurements in many-body dynamics. In their paper, published in Physical Review Letters, they specifically presented a protocol that can be used to realize dynamics that include quantum measurements in quantum computers and quantum simulators, while avoiding a procedural step known as postselection.

“From an experimental standpoint, the randomness of quantum measurements poses a big problem: In order to reliably make the same state (necessary to measure its properties, or to use it in applications), one must replicate the same random sequence of measurement outcomes over and over,” Ippoliti and Khemani explained. “This is an exponentially rare occurrence, like tossing a coin many times and getting a straight sequence of heads, and it is not a technical limitation but rather a consequence of basic rules of quantum mechanics. This is the problem of ‘postselection.'”


+  “Measurements have a special place in quantum physics: They cause the system to abruptly ‘collapse’ onto one of several possible measurement outcomes, chosen at random,” Matteo Ippoliti and Vedika Khemani, the two researchers who carried out the study, told Phys.org. “For instance, think of Schrodinger’s cat in a ‘superposition’ of alive and dead in a box—as soon as the box is opened, the cat’s state collapses to either alive or dead. In contrast, quantum systems that are ‘left alone’ evolve in a deterministic way, also known as ‘unitary’ dynamics.”

+  The ‘virtual evolution’ of the system examined by the researchers turned out to be non-unitary, which essentially means that it includes some measurement elements. These elements, however, are fully deterministic and can be reliably and repeatedly reproduced. This crucial characteristic allowed them to translate their idea into a protocol to realize and study entanglement dynamics in quantum simulators.

+  “The ideas behind our study may seem pretty abstract, but we translate them into a specific protocol that can be executed on present-day digital quantum simulators,” Ippoliti and Khemani said. ” This creates a direct route to experimentally study these new types of quantum dynamics involving measurements, while also bringing some exciting theoretical ideas closer to fruition.”

Source:  PHYS ORG.  Ingrid Fadelli,  A protocol to explore entanglement dynamics via spacetime duality…

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