Quantum mechanics is full of weird phenomena, but perhaps none as weird as the role measurement plays in the theory. Since a measurement tends to destroy the “quantumness” of a system, it seems to be the mysterious link between the quantum and classical world.

Furthermore, when dealing with a vast system of quantum data units called “qubits,” the impact of measurements can lead to profoundly different outcomes, even driving the emergence of entirely new phases of quantum information.

This happens when two competing effects come to a head: interactions and measurement. In a quantum system, when the qubits interact with one another, their information becomes shared nonlocally in an “entangled state.”

But if you measure the system, the entanglement is destroyed. The battle between measurement and interactions leads to two distinct phases: one where interactions dominate and entanglement is widespread, and one where measurements dominate, and entanglement is suppressed.

In a study recently published in Nature, researchers at Google Quantum AI and Stanford University have observed the crossover between these two regimes — known as a “measurement-induced phase transition” — in a system of up to 70 qubits.

This is by far the largest system in which measurement-induced effects have been explored. The researchers also saw signatures of a novel form of “quantum teleportation” — in which an unknown quantum state is transferred from one set of qubits to another — that emerges as a result of these measurements. These studies could help inspire new techniques useful for quantum computing.

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