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

Noise reduction in low-frequency SQUID measurements with laser-driven switching

Charles E. Cunningham, George S. Park, Blas Cabrera, M. E. Huber

Published Aug 23, 1993• 6 citations
Publisher

Abstract

We have developed a technique to modulate the input to a superconducting quantum interference device (SQUID) using a very low noise double-pole, double-throw switching network. This network is composed of four niobium microbridges that are driven normal in pairs by pulses of laser light. An input signal is modulated at a frequency above the 1/f noise regime, amplified by the SQUID, and subsequently demodulated to obtain an output in which the excess low-frequency SQUID noise has been removed. With this technique, we have reduced the low-frequency noise by an order of magnitude in energy over measurements made without this technique.

DOI
10.1063/1.109808

Related papers

Studies of a low noise, laser actuated superconducting switch

Charles E. Cunningham, Blas Cabrera

A SQUID is the most sensitive magnetometer available. The sensitivity is limited by the intrinsic noise which is white at high frequencies and increases inversely with frequency below a frequency called the 1/f knee. The sensitivity above the 1/f knee is typically better than 10−10GHz−1/2, but below the 1/f knee it can be orders of magnitude worse. This is a serious problem for those measurements which are intrinsically low frequency or dc; for them it is important to circumvent the 1/f noise. A well-known technique for reducing amplifier noise is applied schematically to a SQUID in Fig. 1.1 The low frequency signal is modulated at a frequency above the 1/f knee. The SQUID sees a high frequency signal and in amplification adds white noise rather than 1/f noise. The signal from the SQUID is then demodulated, recovering the original signal. This scheme requires a high speed, low noise superconducting switch. We have developed and tested such a switch.

Conference on Lasers and Electro-Optics•Apr 24, 1989•0 citations

Investigation and reduction of excess low-frequency noise in rf superconducting quantum interference devices

Michael Mück, Christoph Heiden, John L. Clarke

A detailed study has been made of the low-frequency excess noise of rf superconducting quantum interference devices (SQUIDs), fabricated from thin niobium films and operated at 4.2 K, with rf bias frequencies of 0.15, 1.7, and 3 GHz. When the SQUIDs were operated in an open-loop configuration in the absence of low-frequency flux modulation, the demodulated rf voltage exhibited a substantial level 1/f noise, which was essentially independent of the rf bias frequency. As the rf bias frequency was increased, the crossover frequency at which the 1/f noise power was equal to the white noise power moved to higher frequencies, because of the reduction in white noise. On the other hand, when the SQUID was flux modulated at 50 kHz and operated in a flux locked loop, no 1/f noise was observed at frequencies above 0.5 Hz. A detailed description of how the combination of rf bias and flux modulation removes 1/f noise due to critical current fluctuations is given. Thus, the results demonstrate that the 1/f noise observed in these SQUIDs is generated by critical current fluctuations, rather than by the hopping of flux vortices in the niobium films.

Journal of Applied Physics•May 1, 1994•26 citations

1/f noise in radio frequency SQUIDs made of niobium thin films

Michael Mueck, John L. Clarke, Christoph Heiden

Applications of Superconducting Quantum Interference Devices (SQUIDs) usually require high sensitivity at relatively low frequencies, often down to 1 Hz or lower. Excess noise, typically with a spectral density scaling inversely as the frequency, can substantially reduce the sensitivity of SQUIDs at low frequencies. We have studied 1/f noise in niobium rf-SQUIDs in some detail. To reduce any noise contribution of the readout electronics, a cryogenic preamplifier was used. When one measures the signal voltage of the SQUID directly, a pronounced 1/f noise was observed in all samples, and was nearly independent of the bias frequency used. The crossover between 1/f and white noise moved towards higher frequencies as the bias frequency was increased, because of a lower white noise contribution. The 1/f noise scaled approximately as the inductance of the SQUID. When operated in a flux locked loop, however, no 1/f noise could be observed above 0.5 Hz. Operating a rf SQUID in a flux locked loop can thus substantially reduce 1/f noise in rf SQUIDs.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Jul 2, 1994•0 citations

A low-noise, two-stage DC SQUID amplifier with high bandwidth and dynamic range

R. Cantor, L. P. Lee, Andrei N. Matlashov +1 more

We describe a low-noise, two-stage dc Superconducting QUantum Interference Device (SQUID) amplifier that is designed for applications requiring high bandwidth and dynamic range. The output signal of a low-noise SQUID in the input stage coherently modulates a series array of identical SQUIDs in the output stage via a common modulation line. The input stage is designed so its output signal does not produce multiple modulation periods in the output stage. The output stage is designed to have sufficient gain so the output noise is dominated by the amplified noise of the input SQUID and exceeds the noise of a preamplifier in the room temperature readout electronics. The SQUID amplifier may therefore be operated without flux modulation or any impedance matching network, resulting in a large dynamic range and high bandwidth.

IEEE Transactions on Applied Superconductivity•Jun 1, 1997•11 citations

Thermal-noise-limited performance in single-chip superconducting quantum interference devices

Norio Fujimaki, K. Gotoh, T. Imamura +1 more

The single-chip superconducting quantum interference device (SQUID) we made using niobium Josephson junctions integrates a two-junction SQUID and a superconducting feedback circuit. The switching probability, its derivative to input flux, and the flux spectral density measured by varying the sinusoidal bias frequency and amplitude agree well with thermal noise theory. The best sensitivity and cutoff frequency were 6.2×10−6 Φ0■√Hz and 1.1 kHz for a bias frequency at 10 MHz. The dynamic range was 2.5×105. These data show the SQUID to be suited to practical biomagnetic application.

Journal of Applied Physics•Jun 15, 1992•9 citations

Study of Low-Frequency Noise Performance of Nanobridge-Based SQUIDs in External Magnetic Fields

S. Rozhko, T. Hino, A. Blois +4 more

We report on the low-frequency noise performance of niobium dc superconducting quantum interference devices (SQUIDs), which contain nanobridges fabricated by focused ion beam lithography as the active Josephson elements. The devices have feature sizes down to 70 nm. We have measured devices of different loop sizes in two readout configurations: nano-scale loop sizes in small signal mode using a series SQUID array as a low-temperature pre-amplifier, and larger micron-scale loop sizes in a conventional flux-locked loop. We investigate the different contributions to the low frequency noise and report on electrical measurements made in applied magnetic fields of up to 0.5 T (in-plane) and 0.1 T (perpendicular to the plane) at operating temperatures around 7 K. We compare the measurements with the existing theories of noise in a dc SQUID.

IEEE Transactions on Applied Superconductivity•Dec 11, 2012•6 citations
We have developed a technique to modulate the input to a superconducting quantum interference device (SQUID) using a very low noise double-pole, double-throw switching network. This network is composed of four niobium microbridges that are driven normal in pairs by pulses of laser light. An input signal is modulated at a frequency above the 1/f noise regime, amplified by the SQUID, and subsequently demodulated to obtain an output in which the excess low-frequency SQUID noise has been removed. With this technique, we have reduced the low-frequency noise by an order of magnitude in energy over measurements made without this technique.
A SQUID is the most sensitive magnetometer available. The sensitivity is limited by the intrinsic noise which is white at high frequencies and increases inversely with frequency below a frequency called the 1/f knee. The sensitivity above the 1/f knee is typically better than 10−10GHz−1/2, but below the 1/f knee it can be orders of magnitude worse. This is a serious problem for those measurements which are intrinsically low frequency or dc; for them it is important to circumvent the 1/f noise. A well-known technique for reducing amplifier noise is applied schematically to a SQUID in Fig. 1.1 The low frequency signal is modulated at a frequency above the 1/f knee. The SQUID sees a high frequency signal and in amplification adds white noise rather than 1/f noise. The signal from the SQUID is then demodulated, recovering the original signal. This scheme requires a high speed, low noise superconducting switch. We have developed and tested such a switch.
A detailed study has been made of the low-frequency excess noise of rf superconducting quantum interference devices (SQUIDs), fabricated from thin niobium films and operated at 4.2 K, with rf bias frequencies of 0.15, 1.7, and 3 GHz. When the SQUIDs were operated in an open-loop configuration in the absence of low-frequency flux modulation, the demodulated rf voltage exhibited a substantial level 1/f noise, which was essentially independent of the rf bias frequency. As the rf bias frequency was increased, the crossover frequency at which the 1/f noise power was equal to the white noise power moved to higher frequencies, because of the reduction in white noise. On the other hand, when the SQUID was flux modulated at 50 kHz and operated in a flux locked loop, no 1/f noise was observed at frequencies above 0.5 Hz. A detailed description of how the combination of rf bias and flux modulation removes 1/f noise due to critical current fluctuations is given. Thus, the results demonstrate that the 1/f noise observed in these SQUIDs is generated by critical current fluctuations, rather than by the hopping of flux vortices in the niobium films.
Applications of Superconducting Quantum Interference Devices (SQUIDs) usually require high sensitivity at relatively low frequencies, often down to 1 Hz or lower. Excess noise, typically with a spectral density scaling inversely as the frequency, can substantially reduce the sensitivity of SQUIDs at low frequencies. We have studied 1/f noise in niobium rf-SQUIDs in some detail. To reduce any noise contribution of the readout electronics, a cryogenic preamplifier was used. When one measures the signal voltage of the SQUID directly, a pronounced 1/f noise was observed in all samples, and was nearly independent of the bias frequency used. The crossover between 1/f and white noise moved towards higher frequencies as the bias frequency was increased, because of a lower white noise contribution. The 1/f noise scaled approximately as the inductance of the SQUID. When operated in a flux locked loop, however, no 1/f noise could be observed above 0.5 Hz. Operating a rf SQUID in a flux locked loop can thus substantially reduce 1/f noise in rf SQUIDs.
We describe a low-noise, two-stage dc Superconducting QUantum Interference Device (SQUID) amplifier that is designed for applications requiring high bandwidth and dynamic range. The output signal of a low-noise SQUID in the input stage coherently modulates a series array of identical SQUIDs in the output stage via a common modulation line. The input stage is designed so its output signal does not produce multiple modulation periods in the output stage. The output stage is designed to have sufficient gain so the output noise is dominated by the amplified noise of the input SQUID and exceeds the noise of a preamplifier in the room temperature readout electronics. The SQUID amplifier may therefore be operated without flux modulation or any impedance matching network, resulting in a large dynamic range and high bandwidth.
The single-chip superconducting quantum interference device (SQUID) we made using niobium Josephson junctions integrates a two-junction SQUID and a superconducting feedback circuit. The switching probability, its derivative to input flux, and the flux spectral density measured by varying the sinusoidal bias frequency and amplitude agree well with thermal noise theory. The best sensitivity and cutoff frequency were 6.2×10−6 Φ0■√Hz and 1.1 kHz for a bias frequency at 10 MHz. The dynamic range was 2.5×105. These data show the SQUID to be suited to practical biomagnetic application.
We report on the low-frequency noise performance of niobium dc superconducting quantum interference devices (SQUIDs), which contain nanobridges fabricated by focused ion beam lithography as the active Josephson elements. The devices have feature sizes down to 70 nm. We have measured devices of different loop sizes in two readout configurations: nano-scale loop sizes in small signal mode using a series SQUID array as a low-temperature pre-amplifier, and larger micron-scale loop sizes in a conventional flux-locked loop. We investigate the different contributions to the low frequency noise and report on electrical measurements made in applied magnetic fields of up to 0.5 T (in-plane) and 0.1 T (perpendicular to the plane) at operating temperatures around 7 K. We compare the measurements with the existing theories of noise in a dc SQUID.