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China Semiconductor Technology International Conference (CSTIC)

Design and Simulation of a Superconducting Switch Based on Weakly Damped Superconducting Quantum Interference Devices

Xinyu Wu, Rutian Huang, Jianshe Liu, Wei Chen

Published Jun 26, 2023• 0 citations
Publisher

Abstract

Superconducting switches are important components in multiplexers based on superconducting quantum interference devices (SQUIDs). In time-division multiplexing (TDM) circuits, the superconducting switches are mainly used to activate and control input SQUIDs. The superconducting switch has the advantages of low power consumption and easy control. Here, a superconducting switch based on weakly damped SQUIDs is proposed. The dynamic resistance of the superconducting switch can be increased by appropriately adjusting the Stewart-McCumber parameter $\beta _{c}$ of the Josephson junction. This design is expected to reduce the number of SQUIDs in arrays and simplify the fabrication processes of switches.

DOI
10.1109/cstic58779.2023.10219234

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IEEE Transactions on Applied Superconductivity•May 12, 2016•4 citations
Superconducting switches are important components in multiplexers based on superconducting quantum interference devices (SQUIDs). In time-division multiplexing (TDM) circuits, the superconducting switches are mainly used to activate and control input SQUIDs. The superconducting switch has the advantages of low power consumption and easy control. Here, a superconducting switch based on weakly damped SQUIDs is proposed. The dynamic resistance of the superconducting switch can be increased by appropriately adjusting the Stewart-McCumber parameter βc\beta _{c}βc​ of the Josephson junction. This design is expected to reduce the number of SQUIDs in arrays and simplify the fabrication processes of switches.
We present a novel multiplexer scheme for time-division multiplexing in superconducting quantum interference device (SQUID) readout configurations. The channels of our SQUID multiplexer (SQMUX) are dc SQUID sensors which are connected in series to form a column. A superconducting-to-normalconducting switch (SN-switch) in parallel with each channel is actuated in order to activate or deactivate an individual channel of the column. With a switch in the normalconducting state, its corresponding SQUID channel is active and sensitive to an input signal. When a switch is in the superconducting state its corresponding SQUID channel is short-circuited. It is then insensitive to input signals and does not generate noise. The addressing sequence is chosen such that only one SQUID channel is active at a time. We suggest employing SN-switches which are based on dc SQUIDs themselves. Doing so enables the addressing signals of the SN-switches to be applied inductively, i.e., galvanically isolated. The SQMUX operation is demonstrated in a configuration where both the SN-switches and the sensing SQUIDs are based on SQUID series arrays.
Recent experiments on superconducting flux qubits, consisting of a superconducting loop interrupted by Josephson junctions, have demonstrated quantum coherence between two different quantum states. The state of the qubit is measured with a superconducting quantum interference device (SQUID). Such measurements require the SQUID to have high resolution while exerting minimal backaction on the qubit. By designing shunts across the SQUID junctions appropriately, one can improve the measurement resolution without increasing the backaction significantly. Using a path-integral approach to analyze the Caldeira-Leggett model, we calculate the narrowing of the distribution of the switching events from the zero-voltage state of the SQUID for arbitrary shunt admittances, focusing on shunts consisting of a capacitance Cs{C}_{s}Cs​ and resistance Rs{R}_{s}Rs​ in series. To test this model, we fabricated a dc SQUID in which each junction is shunted with a thin-film interdigitated capacitor in series with a resistor, and measured the switching distribution as a function of temperature and applied magnetic flux. After accounting for the damping due to the SQUID leads, we found good agreement between the measured escape rates and the predictions of our model. We analyze the backaction of a shunted symmetric SQUID on a flux qubit. For the given parameters of our SQUID and realistic parameters for a flux qubit, at the degeneracy point we find a relaxation time of $113\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{s}$, which limits the decoherence time to $226\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{s}$. Based on our analysis of the escape process, we determine that a SQUID with purely capacitive shunts should have narrow switching distributions and no dissipation.
We have investigated the transient response of superconducting quantum interference devices (SQUIDs) used in time-division multiplexing schemes for the readout from arrays of superconducting transition-edge sensors (TES). In time-division multiplexing the per channel settling time is an important parameter since it limits the multiplexing frequency as well as the signal-to-noise ratio. Although SQUIDs in general are fast cryoelectronic devices operating at a nanosecond scale, experimental evidence shows that the settling time in bias-switched SQUID multiplexers can, in the case of a low impedance input circuit, reach several microseconds. We have confirmed this behavior through numerical transient analysis using a Josephson circuit simulator. Within the simulation we have found that the transient response can be reduced using an extra inductor in series with the input coil of the dc SQUID. This result in turn has been confirmed experimentally. We furthermore discuss the conflicting constraints that a desired high signal bandwidth places on the parameters of the multiplexer, the readout SQUIDs, and the TES.
Direct current-superconducting quantum interference devices (SQUIDs) characterized by asymmetric Josephson junctions have never been used for applications. In order to demonstrate their potential advantages, a throughout numerical analysis of different asymmetric configurations has been carried out. A damping resistance has been included in the SQUID circuit and the thermal noise associated with junction and damping resistances has been considered in the numerical model. Magnetic modulations and flux noise spectral densities have been computed as a function of many parameters (bias current, asymmetry, SQUID inductance, and damping resistance) and the performance of symmetric and asymmetric devices have been compared. The results show that, by properly optimizing the SQUID design, asymmetric SQUIDs are characterized by higher magnetic flux to voltage transfer coefficient and lower flux noise. As a result, asymmetric configurations can be very useful in all the applications where high sensitivity is required.
Dependence of SQUID Intrinsic Flux Noise on Stewart–McCumber Parameter βc\beta_{c}βc​ of Josephson Junction
It is known that three superconducting quantum interference device (SQUID) parameters, namely, the intrinsic flux noise δΦs, the flux-to-voltage transfer coefficient ∂V/∂Φ, and the dynamic resistance Rd, increase with increasing the Stewart- McCumber parameter βcof Josephson junction. It is very difficult to obtain the low values of δΦsfor a strongly damped SQUID due to its small ∂V/∂Φ. In this paper, we employ a two-stage scheme (TSS) to measure δΦsdirectly. Here, we use single chip readout electronics and a weakly damped SQUID with a βcof flux noise of the readout-SQUID system is about 4.8 μΦ0/√Hz 1.2, both acting as a readout-SQUID system (a preamplifier). The with a corner frequency of about 10 Hz. The front-end SQUID is coupled to the readout SQUID via the input coil with a mutual inductance of Mi. In our experiment, the flux gain for a readout SQUID, i.e., GΦ= Mi× (∂I/∂Φ)front-endis adjusted to be 20. Using the TSS, we measured δΦswith different βcchanging from 0.3 to 13.5 and found δΦsincreasing from 1.0 to 5.0 μΦ0/√Hz. We also discussed the relations between Ls, βc, and δΦsquantitatively. Finally, we proposed designing a suitable βcto match the preamplifier in a direct readout scheme to simplify a SQUID measurement system.