# On-Chip Quantum Sensing of Kondo Spins in a High-Mobility Quasi-One-Dimensional Nanoconstriction

## TL;DR

Researchers developed a quantum method to detect magnetic impurities in nanostructures using electronic resonators and quantum point contacts.

## Contribution

A noninvasive quantum sensing technique is introduced to distinguish Kondo spins from other correlated states in nanoconstrictions.

## Key findings

- Local Kondo screening and nonlocal spin singlet states can be controlled by the occupancy parity of an electronic resonator.
- The 0.7 anomaly in quantum point contacts has a different origin and opposes Kondo spin singlet formation.

## Abstract

The precise nature
of Kondo spins has remained enigmatic
when extended
to multiple spin impurities or, more intriguingly, when the localized
spin itself may already be the consequence of many-body interactions
in a presumably delocalized open nanoconstriction, such as a quantum
point contact (QPC). It is experimentally challenging to distinguish
the Kondo state from other coexisting many-body spin states in such
a strongly correlated system. Here we lithographically define an all-on-chip
electronic resonator (ER) and a QPC in a high-mobility GaAs/AlGaAs
heterostructure transistor. Local Kondo screening of the QPC spin
and nonlocal spin singlet across the ER-QPC integration is controllable
in response to ER occupancy parity. We also show that the 0.7 anomaly,
another strongly correlated state in QPCs, not only has a different
physical origin but furthermore counteracts the Kondo spin singlet.
These results demonstrate a noninvasive quantum method for sensing
spontaneous magnetic impurities within an open nanoconstriction.