Browsing by Author "Zhang, Jinli"

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Broadband tunable phase shifter for microwaves
(2020-06-01) Zhang, Jinli; Li, Tianyi; Kokkoniemi, Roope; Yan, Chengyu; Liu, Wei; Partanen, Matti; Tan, Kuan Yen; He, Ming; Ji, Lu; Grönberg, Leif; Möttönen, Mikko
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
We implement a broadly tunable phase shifter for microwaves based on superconducting quantum interference devices (SQUIDs) and study it both experimentally and theoretically. At different frequencies, a unit transmission coefficient, |S21| = 1, can be theoretically achieved along a curve where the phase shift is controllable by the magnetic flux. The fabricated device consists of three equidistant SQUIDs interrupting a transmission line. We model each SQUID embedded at different positions along the transmission line with two parameters, capacitance and inductance, the values of which we extract from the experiments. In our experiments, the tunability of the phase shift varies from 0.07 × π to 0.14 × π radians along the full-transmission curve with the input frequency ranging from 6.00 GHz to 6.28 GHz. The reported measurements are in good agreement with simulations, which is promising for future design work of phase shifters for different applications.
A low-noise on-chip coherent microwave source
(2021-12) Yan, Chengyu; Hassel, Juha; Vesterinen, Visa; Zhang, Jinli; Ikonen, Joni; Grönberg, Leif; Goetz, Jan; Möttönen, Mikko
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The scaling up of quantum computers operating in the microwave domain requires advanced control electronics, and the use of integrated components that operate at the temperature of the quantum devices is potentially beneficial. However, such an approach requires ultralow power dissipation and high signal quality to ensure quantum-coherent operations. Here we report an on-chip device that is based on a Josephson junction coupled to a spiral resonator and is capable of coherent continuous-wave microwave emission. We show that the characteristics of the device accurately follow a theory based on the perturbative treatment of a capacitively shunted Josephson junction as the gain element. The infidelity of typical quantum gate operations due to phase noise of this cryogenic 25 pW microwave source is less than 0.1% up to 10 ms evolution time, which is below the infidelity caused by dephasing in state-of-the-art superconducting qubits. Together with future cryogenic amplitude and phase modulation techniques, our approach may lead to scalable cryogenic control systems for quantum processors.