Anomalous conditional counting statistics in an electron-spin-resonance quantum dot measured by a quantum point contact

A detailed understanding of the full measurement statistics in experiments is the basis for thorough device characterization and advanced applications such as quantum metrology. In this spirit, we investigate the conditional counting statistics of an electron-spin-resonance pumped quantum dot (QD), which is tunnel-coupled to a side electrode and continuously monitored by a quantum point contact (QPC). For such a noninvasive detector, we find that the spin current through the QD and its related cumulants exhibit intriguing features and system parameter dependences when conditioned on the QPC current, which are in strong contrast to the unconditional cumulants. By turning the perspective around and considering the counting statistics of the QPC current conditioned on the QD current, we reveal an anomalous conditional QPC current noise, which is surprisingly suppressed for increasing coupling to the environment. Our results show that information backaction can substantially render statistical transport fluctuations. This unique advantage of the conditional counting statistics in probing the underlying correlations between system and detector, even for noninvasive measurements, can thus be employed for improving measurement protocols in quantum metrology.