Long term operation of semiconductor spin qubits requires active stabilization of quantum dot potentials against low-frequency charge noise. To address this, we demonstrate a gradient-descent feedback approach in a silicon double quantum dot device using high-bandwidth radio-frequency (rf) reflectometry readout and a field-programmable gate array (FPGA) for digital signal processing. This architecture enables continuous multi-parameter gradient calculation and quick gate voltage updates, significantly increasing the effective feedback bandwidth compared to previous methods relying on slow direct-current transport measurements. By operating with 8 steps per feedback cycle and an integration time of 25.6
μs, this high-speed stabilization scheme maintains better than -6 dB of noise suppression up to 5 kHz, achieving an attenuation of
−7.4±0.2 dB at the maximum measured frequency. This effectively suppresses low-frequency 1/f noise, maintaining device stability over longer time periods, and potentially enables real-time control in large-scale quantum dot arrays.
Systems of mesoscopic Josephson junctions are at present among the leading candidates for development of practical qubits for quantum information devices. Although different qubit structures have been realized with Josephson junctions, their common feature is the design that is optimized to overcome the problem of decoherence by the low-frequency noise that exists in all solid-state structures. In the presented dissertation research, we propose and study an alternative approach of direct suppression of noise by a feedback loop based on the low-frequency quantum measurements. The minimal noise induced in the qubit by such a feedback loop is calculated under the conditions of continuous quantum-limited measurements. Another obstacle facing the quantum Josephson junction circuits is the information transfer between the circuit elements. Here we study the quantum dynamics of dual-rail arrays of nSQUIDs characterized by a negative inductance between its arms, which hold promise for quantum information transfer. The scaling and decoherence properties of these arrays are analyzed. Information transfer along nSQUID arrays can also be used to implement adiabatic quantum computation (AQC), an alternative to the gate-model approach to quantum computation that is expected to be more stable against the decoherence. Here we suggest fidelity of the ground state as the quantitative measure of the ultimate effect of decoherence on AQC. We show that decoherence-induced deformation of the ground state of an AQC algorithm is characterized by the same noise correlators as those that determine the decoherence time in the gate-model approach. Results for fidelity of a 16-qubit array at finite temperatures are obtained numerically. | 117 pages
Resonance-frequency fluctuations can limit the sensitivity and stability of superconducting microwave cavities used for qubit readout, optomechanical displacement sensing, and magnetic flux detection. Here, we demonstrate the suppression of resonance-frequency fluctuations by locking a noisy nonlinear superconducting microwave cavity to a strong pump tone. The Kerr nonlinearity of this system, whereby the resonance frequency depends on the intracavity field amplitude, gives rise to an intrinsic feedback mechanism that enables passive stabilization without active external feedback. Using two-tone spectroscopy, we experimentally characterize the intrinsic nonlinear feedback mechanism and investigate its temporal stability through Allan deviation analysis. The frequency fluctuations of the locked cavity mode are reduced by nearly two orders of magnitude, reaching the
1/f noise floor, without continuous frequency tracking or active control. Kerr locking provides a general approach for self-stabilizing nonlinear microwave resonators by suppressing low-frequency cavity noise while preserving sensitivity to signals outside the locking bandwidth. This approach may benefit a broad range of systems, including SQUID-based resonators, optomechanical devices, and parametric amplifiers.
The measurement accuracy of laser precision measurement is mainly limited by optical field noise and various technical noises. After the de-coupling technical noises, quantum noise becomes the main factor limiting the measurement accuracy. Based on the intensity noise characteristics of solid-state single-frequency lasers, the main sources of intensity noise and their influence on the power noise spectrum were described, and three kinds of intensity noise suppression techniques, including traditional DC feedback control, optical AC coupled feedback control and quantum squeezer, were reviewed in this paper. By reviewing the development history of relevant technologies, the current development level and future development trend of intensity noise suppression technology were summarized-the noise suppression scheme combining three technologies is an important approach to solve high sensitivity detection.