Light used to detect information stored in 100,000 nuclear qubits

Quantum sensing with single magnon precision.

Researchers have found a way to use light and a single electron to communicate with a cloud of quantum bits and sense their behavior, making it possible to detect a single quantum bit in a dense cloud.

The researchers, from the University of Cambridge, were able to inject a ‘needle‘ of highly fragile quantum information in a ‘haystack’ of 100,000 nuclei. Using lasers to control an electron, they could then use that electron to control the behavior of the haystack, making it easier to find the needle. They were able to detect the ‘needle’ with a precision of 1.9 parts per million: high enough to detect a single qubit in this large ensemble.

Using the light from a laser, the researchers are able to communicate with an electron, which then communicates with the spins, or inherent angular momentum, of the nuclei.

By talking to the electron, the chaotic ensemble of spins starts to cool down and rally around the shepherding electron; out of this more ordered state, the electron can create spin waves in the nuclei.

In other words, injecting a spin wave made of a single nuclear spin flip into the ensemble makes it easier to detect a single nuclear spin flip among 100,000 nuclear spins.

Using this technique, the researchers are able to send information to the quantum bit and ‘listen in‘ on what the spins are saying with minimal disturbance, down to the fundamental limit set by quantum mechanics. (

The results are reported in the journal Nature Physics.

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