Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Applied Physics Letters

Improved superconducting quantum interference devices by resistance asymmetry

G. Testa, S. Pagano, E. Sarnelli, Claudia Roberta Calidonna, Mario Mango Furnari

Published Oct 29, 2001• 9 citations
Publisher

Abstract

Direct current superconducting quantum interference devices made by Josephson junctions with asymmetric shunt resistances have been numerically investigated in the low temperature regime. When combined with a damping resistance, the asymmetry leads to a flux to voltage transfer coefficient several times larger than the one typical of symmetric devices, together with a lower magnetic flux noise. These results show that this type of asymmetric device may replace the standard ones in a large number of magnetometric applications, improving the sensitivity performance. The large transfer coefficient may also simplify the readout electronics allowing a direct coupling of asymmetric devices to an external preamplifier, without the need of an impedance matching flux transformer.

DOI
10.1063/1.1413733

Related papers

Characteristics of asymmetric superconducting quantum interference devices

G. Testa, E. Sarnelli, S. Pagano +2 more

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.

Journal of Applied Physics•May 1, 2001•15 citations

Direct current superconducting quantum interferometers with asymmetric shunt resistors

M. Rudolph, J. Nagel, J. M. Meckbach +5 more

We have investigated asymmetrically shunted Nb/Al-AlO$_x$/Nb direct current (dc) superconducting quantum interference devices (SQUIDs). While keeping the total resistance $R$ identical to a comparable symmetric SQUID with $R^{-1} = R_1^{-1} + R_2^{-1}$, we shunted only one of the two Josephson junctions with $R = R_{1,2}/2$. Simulations predict that the optimum energy resolution $ε$ and thus also the noise performance of such an asymmetric SQUID can be 3--4 times better than that of its symmetric counterpart. Experiments at a temperature of 4.2\,K yielded $ε\approx 32\,\hbar$ for an asymmetric SQUID with an inductance of $22\,\rm{pH}$. For a comparable symmetric device $ε= 110\,\hbar$ was achieved, confirming our simulation results.

arXiv:1207.0082•Applied Physics Letters•Jul 30, 2012•8 citations

An insight into voltage-biased superconducting quantum interference devices

Chao Liu, Yi Zhang, Michael Mück +5 more

We experimentally studied two important parameters of helium-cooled superconducting quantum interference devices (SQUIDs) in the voltage bias mode: the dynamic resistance Rd and the flux-to-current transfer coefficient ∂i/∂Φ, with different junction shunt resistors RJ. We investigated a voltage-biased SQUID using the direct readout current-to-voltage converter scheme involving an operational amplifier. At higher RJ, the flux-to-voltage conversion coefficient ∂V/∂Φ becomes sufficiently large to effectively suppress the room-temperature amplifier's noise without any need for additional feedback circuits. The McCumber parameter limits the rise of ∂V/∂Φ. We discuss the performance of voltage-biased SQUIDs at different effective McCumber parameters.

Applied Physics Letters•Nov 26, 2012•20 citations

Performance of dc SQUIDs with resistively shunted inductance

Vittorio Foglietti, W. J. Gallagher, M. B. Ketchen +3 more

We have fabricated and characterized the noise performance of well-coupled Nb-Pb alloy edge junction dc superconducting quantum interference devices (SQUIDs) with a resistively shunted inductance. The extra damping resistor removes the resonances in the current-voltage characteristics resulting in a very low value of the extrinsic energy sensitivity in flux-locked-loop operation. Numerical simulations, with the junction capacitance included, indicate that the damping resistance does not degrade noise performance until it is significantly less than the junction-shunting resistance. We also tested different SQUID designs and demonstrated that a large SQUID inductance, proposed earlier to be desirable when resistively shunted, can seriously affect the low-frequency flux noise.

Applied Physics Letters•Oct 2, 1989•45 citations

Characterization and design of a low-noise second-order gradient SQUID with asymmetric shunt resistors

Yuxiao Guo, Jinjin Li, Xiaolong Xu +4 more

A low-noise superconducting quantum interference device (dc-SQUID) with simplified design and readout electronics is highly desirable for various applications. We demonstrate that introducing an asymmetric shunt resistor significantly enhances the noise performance while maintaining the inherent simplicity and tunability of the SQUID design. By optimizing the asymmetry factor, our asymmetric shunted second-order gradient SQUID current sensor reaches a low white flux noise of 0.65 μΦ0/√Hz using a direct readout strategy, representing a threefold improvement over its symmetric counterpart. This noise level surpasses that of the SQUID with the additional positive feedback method and is comparable to the series SQUID arrays, making the asymmetric shunted SQUID suitable for meeting the readout requirements of various scientific instruments.

Applied Physics Letters•Mar 1, 2025•4 citations

The current–voltage characteristics of the resistive direct current superconducting quantum interference device

Ya. S. Greenberg, G.S. Krivoy, H. Koch

Partly resistive superconducting quantum interference devices (RSQUIDs) are used in noise thermometry in the liquid helium temperature range. Here we analyze one type of RSQUID that has not been thoroughly investigated until now: the direct current biased with two Josephson junctions and a resistive part connected in series with the junctions and closed by a superconducting ring. The resistive shunted model of the Josephson junctions is used for the analysis. Two cases of the RSQUID ring inductance were analyzed: (i) negligibly small and (ii) small but finite inductance. The expressions for the low frequency output signal, the current–voltage (I–V) characteristics, and the current flowing through the resistive part are obtained. In the dependence of the output frequency versus the dc current passed through the resistive part often an offset is observed experimentally. This phenomenon can be explained as an influence of an asymmetry in the critical currents of the junctions.

Journal of Applied Physics•Feb 15, 1997•9 citations
Direct current superconducting quantum interference devices made by Josephson junctions with asymmetric shunt resistances have been numerically investigated in the low temperature regime. When combined with a damping resistance, the asymmetry leads to a flux to voltage transfer coefficient several times larger than the one typical of symmetric devices, together with a lower magnetic flux noise. These results show that this type of asymmetric device may replace the standard ones in a large number of magnetometric applications, improving the sensitivity performance. The large transfer coefficient may also simplify the readout electronics allowing a direct coupling of asymmetric devices to an external preamplifier, without the need of an impedance matching flux transformer.
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.
We have investigated asymmetrically shunted Nb/Al-AlOx_xx​/Nb direct current (dc) superconducting quantum interference devices (SQUIDs). While keeping the total resistance RRR identical to a comparable symmetric SQUID with R−1=R1−1+R2−1R^{-1} = R_1^{-1} + R_2^{-1}R−1=R1−1​+R2−1​, we shunted only one of the two Josephson junctions with R=R1,2/2R = R_{1,2}/2R=R1,2​/2. Simulations predict that the optimum energy resolution εεε and thus also the noise performance of such an asymmetric SQUID can be 3--4 times better than that of its symmetric counterpart. Experiments at a temperature of 4.2\,K yielded ε≈32 ℏε\approx 32\,\hbarε≈32ℏ for an asymmetric SQUID with an inductance of 22 pH22\,\rm{pH}22pH. For a comparable symmetric device ε=110 ℏε= 110\,\hbarε=110ℏ was achieved, confirming our simulation results.
We experimentally studied two important parameters of helium-cooled superconducting quantum interference devices (SQUIDs) in the voltage bias mode: the dynamic resistance Rd and the flux-to-current transfer coefficient ∂i/∂Φ, with different junction shunt resistors RJ. We investigated a voltage-biased SQUID using the direct readout current-to-voltage converter scheme involving an operational amplifier. At higher RJ, the flux-to-voltage conversion coefficient ∂V/∂Φ becomes sufficiently large to effectively suppress the room-temperature amplifier's noise without any need for additional feedback circuits. The McCumber parameter limits the rise of ∂V/∂Φ. We discuss the performance of voltage-biased SQUIDs at different effective McCumber parameters.
We have fabricated and characterized the noise performance of well-coupled Nb-Pb alloy edge junction dc superconducting quantum interference devices (SQUIDs) with a resistively shunted inductance. The extra damping resistor removes the resonances in the current-voltage characteristics resulting in a very low value of the extrinsic energy sensitivity in flux-locked-loop operation. Numerical simulations, with the junction capacitance included, indicate that the damping resistance does not degrade noise performance until it is significantly less than the junction-shunting resistance. We also tested different SQUID designs and demonstrated that a large SQUID inductance, proposed earlier to be desirable when resistively shunted, can seriously affect the low-frequency flux noise.
A low-noise superconducting quantum interference device (dc-SQUID) with simplified design and readout electronics is highly desirable for various applications. We demonstrate that introducing an asymmetric shunt resistor significantly enhances the noise performance while maintaining the inherent simplicity and tunability of the SQUID design. By optimizing the asymmetry factor, our asymmetric shunted second-order gradient SQUID current sensor reaches a low white flux noise of 0.65 μΦ0/√Hz using a direct readout strategy, representing a threefold improvement over its symmetric counterpart. This noise level surpasses that of the SQUID with the additional positive feedback method and is comparable to the series SQUID arrays, making the asymmetric shunted SQUID suitable for meeting the readout requirements of various scientific instruments.
Partly resistive superconducting quantum interference devices (RSQUIDs) are used in noise thermometry in the liquid helium temperature range. Here we analyze one type of RSQUID that has not been thoroughly investigated until now: the direct current biased with two Josephson junctions and a resistive part connected in series with the junctions and closed by a superconducting ring. The resistive shunted model of the Josephson junctions is used for the analysis. Two cases of the RSQUID ring inductance were analyzed: (i) negligibly small and (ii) small but finite inductance. The expressions for the low frequency output signal, the current–voltage (I–V) characteristics, and the current flowing through the resistive part are obtained. In the dependence of the output frequency versus the dc current passed through the resistive part often an offset is observed experimentally. This phenomenon can be explained as an influence of an asymmetry in the critical currents of the junctions.