We detect correlations in qubit-energy fluctuations of non-neighboring qubits
defined in isotopically purified Si/SiGe quantum dots. At low frequencies
(where the noise is strongest), the correlation coefficient reaches 10% for a
next-nearest-neighbor qubit-pair separated by 200 nm. Assigning the observed
noise to be of electrical origin, a simple theoretical model quantitatively
reproduces the measurements and predicts a polynomial decay of correlations
with interqubit distance. Our results quantify long-range correlations of noise
dephasing quantum-dot spin qubits arranged in arrays, essential for scalability
and fault-tolerance of such systems.