Temperature Dependence of 1/f Charge Noise Coupled to a Quantum Dot Confined in a 2DHG

Abstract

Reliable operation of semiconductor quantum dot-based qubits relies on a stable electrostatic environment. However, charge noise stemming from the randomized motion of trapped charge carriers poses a significant challenge to qubit coherence. This thesis presents experimental results acquired from a quantum dot confined within a 2DHG formed at the interface of a cs-GoS heterostructure, with the motivation of characterizing the 1/f charge noise coupled to the dot. Charge stability diagrams reveal irregularities in transition between adjacent stable charge states, motivating the investigation into the behavior of charge noise in cs-GoS lateral quantum dot devices. Charge noise likely originates within the amorphous dielectric layer or at the dielectric-semiconductor interface where bonding mismatch serves as charge trapping sites, each with their own characteristic activation energy. To characterize the spectral and temperature-dependent behavior of the charge noise, current fluctuations across the quantum dot sensor were measured and analyzed to compare with the Dutta-Horn model for 1/f noise. During the process, a novel technique was developed to mitigate the effects of charge noise induced device drift and account for the quantum dot’s changing transfer function. To precisely characterize the behavior of the charge noise, the quantum dot sensor needs to maintain a constant sensitivity to surrounding electrostatic fluctuations. However, while studying charge noise, the operating point of the quantum dot sensor is inherently prone to changes. Thus, the technique involved implementing an AC modulation on a nearby gate to determine a time-averaged transfer function. Using the AC modulation technique, an ensemble of current spectra revealed an average frequency exponent value of 1.06±0.19, consistent with Dutta-Horn’s model for 1/f noise arising from a uniform distribution of two-level systems. Additionally, analysis incorporating the time-averaged transfer function showed that the charge noise increased nearly linearly with temperature. Across the ensemble of experiments, the average temperature exponent value was 1.01±0.19, also consistent with the model’s prediction for thermally activated two-level systems with a uniform distribution of activation energies. Furthermore, at 1 Hz and 100 mK, the average noise magnitude was determined to be √(S_E )=0.94 μeV/√Hz, with a significant spread likely stemming from thermal cycling and abrupt gate voltage changes, leading to a redistribution of trapped charges within the quantum dot’s environment. These results highlight the sensitivity of charge noise to device history and operating conditions, suggesting it is not entirely intrinsic. While the exact source of charge noise has not been identified, future work focused on dielectric engineering and improved gate control may open pathways towards reduced chare noise and eventually improved qubit coherence.