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

Fast flux locked loop

Ganther, Jr., Kenneth R. (Olathe, KS); Snapp, Lowell D [Independence, MO]

Published Jan 23, 2023• 0 citations
OpenAlex

Abstract

A flux locked loop for providing an electrical feedback signal, the flux locked loop employing radio-frequency components and technology to extend the flux modulation frequency and tracking loop bandwidth. The flux locked loop of the present invention has particularly useful application in read-out electronics for DC SQUID magnetic measurement systems, in which case the electrical signal output by the flux locked loop represents an unknown magnetic flux applied to the DC SQUID.

Related papers

Dc-SQUID Readout with High Dynamic Range and Intrinsic MHz Frequency-Division Multiplexing Capability

Daniel Richter, A. Fleischmann, C. Enss +1 more

We present a novel dc-SQUID readout scheme that provides linearization of the relation between the input and output signal without using a conventional flux-locked loop circuit. It relies on applying a periodic, sawtooth-shaped magnetic flux signal to the modulation coil of the SQUID to continuously measure the flux-to-voltage SQUID characteristic within each period of the flux ramp. In case that the amplitude and repetition rate of the ramp are chosen such that multiple flux quanta are induced in the SQUID and that the input signal is quasistatic within one period of the flux ramp, the input signal adds a constant magnetic flux offset to the SQUID that leads to a phase shift of the SQUID characteristic being proportional to the input signal. We show that this scheme allows for significantly increasing the dynamic range and that it intrinsically allows for MHz frequency-division SQUID multiplexing.

IEEE International Superconductive Electronics Conference (ISEC)•Jul 1, 2019•1 citation

Double dc SQUID for flux-locked-loop operation

Vittorio Foglietti

A novel double dc superconducting quantum interference device (SQUID) is proposed. It consists of two SQUIDs with different geometries in cascade configuration. The structure makes the device particularly suitable for flux-locked-loop operation without need of a room-temperature heterodyne modulation circuitry and a matching network between the SQUID and the preamplifier, thus simplifying the readout electronic system. The noise performance is calculated as a function of the electrical parameters of the device. The noise contribution of the room-temperature preamplifier can be made negligible using <m1;&2p>appropriate SQUID parameters while the slew rate of the system can approach 106Φ0/s.

Applied Physics Letters•Jul 22, 1991•29 citations

Progress towards a double flux-locked-loop scheme for SQuID readout of TES detector arrays

G. Torrioli, Simona Lombardo, C. Macculi +2 more

Frequency Division Multiplexing technique for reading TES detectors with SQuID devices, requires high loop-gain up to MHz frequency range in the SQuID feedback loop. Such a requirement is difficult to achieve when the feedback loop has a physical length that makes the propagation times of signals not negligible, as in the case in which the readout electronics is placed at room temperature. A novel SQuID readout scheme, called Double Loop-Flux Locked loop (DLFLL), has been proposed earlier. According to this scheme it is possible to make use of a simplified cryogenic electronics, AC coupled, featuring low power dissipation, in order to obtain a cryogenic feedback loop that results in reduced propagation times of signals. The DC and low frequency signals are managed by a standard FLL electronics working at room temperature. Here we present the progress of the integrated Double Loop system.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Jul 24, 2014•0 citations

Improved dc SQUID read-out electronics with low 1/f noise preamplifier

D. Drung

An improved read-out electronics without flux modulation for dc superconducting quantum interference devices (dc SQUIDs) is presented where the preamplifier is directly coupled to the SQUID. Compared to our previous designs, the 1/f voltage and current noise levels of the preamplifier were reduced by about a factor of 4 (rms) by using bipolar matched transistors instead of operational amplifiers at the input. Three types of flux-locked-loop electronics were developed and successfully tested: a low-power (120 mW) version for large multichannel arrays, a high-speed version with a 15 MHz bandwidth and a very fast (300 ns) reset mode, and a low-noise (0.44 nV/Hz) version with a fast and precise bias reversal circuit. The flux-locked-loop electronics are compatible with each other, so that only one type of low-power (180 mW) control unit is required to operate them. All essential specifications of practical SQUID systems (noise, dynamic behavior, and temperature stability) were determined by using liquid-helium and liquid-nitrogen cooled SQUIDs, respectively.

Review of Scientific Instruments•Nov 1, 1997•43 citations

OF JOSEPHSON MICROBRIDGES COUPLED BY SUPERCONDUCTING LOOPS

C. Varmazis

We have studied the phase locking of two and eight microbridge arrays shunted by superconducting loops in a dc SQUID configuration. The difference in phase between adjacent bridges is controlled by the applied flux, and thus the radiated power is a periodic function of this flux. With adjustment of the external flux, the individual bridge voltages can be made to add in phase. The effect of additional normal shunts on the phase locking is also investigated. MICROBRIDGES COUPLED BY SUPERCONDUCTING LOOPS Experiment sly on two Josephson microbridges have shown that it is possible to obtain nearly complete in phase coherent radiation with narrowed linewidth by coupling the microbridges with external shunts. To obtain greater ouput power and narrower linewidth it is desirable to phase lock larger arrays of bridges. The narrow range of bias currents over which locking occurs, however, imposes strict tolerances on the uniformity of bridge characteristics if a single current bias is used. In this paper we discuss experiments which eliminate this difficulty by using a superconducting loop to couple the junctions, i.e., a dc SQUID configuration, so that the average frequency of each junction is always equal even for non-identical junctions. Also the phase difference between the junctions in the absence Of noise is set by the amount of externally applied flux due to the fluxoid quantization condition. With identical bridges and zero applied flux, the junctions oscillate in phase. In the geometry used in

•Jan 1, 1979•0 citations

Flux ramp modulation based MHz frequency-division dc-SQUID multiplexer

Daniel Richter, Ludwig Hoibl, T. Wolber +6 more

We present a MHz frequency-division direct-current superconducting quantum interference device (dc-SQUID) multiplexer that is based on flux ramp modulation and a series array of N identical current-sensing dc-SQUIDs with tightly coupled input coil. By running a periodic, sawtooth-shaped current signal through additional modulation coils being tightly but non-uniformly coupled to the individual SQUIDs, the voltage drop across the array changes according to the sum of the flux-to-voltage characteristics of the individual SQUIDs within each cycle of the modulation signal. In this mode of operation, an input signal injected in the input coil of one of the SQUIDs and being quasi-static within a time frame adds a constant flux offset and leads to a phase shift of the associated SQUID characteristics. The latter is proportional to the input signal and can be inferred by channelizing and down-converting the sampled array output voltage. Using a prototype multiplexer as well as custom readout electronics, we demonstrate the simultaneous readout of four signal sources with MHz bandwidth per channel.

•Jan 1, 2021•5 citations
A flux locked loop for providing an electrical feedback signal, the flux locked loop employing radio-frequency components and technology to extend the flux modulation frequency and tracking loop bandwidth. The flux locked loop of the present invention has particularly useful application in read-out electronics for DC SQUID magnetic measurement systems, in which case the electrical signal output by the flux locked loop represents an unknown magnetic flux applied to the DC SQUID.
We present a novel dc-SQUID readout scheme that provides linearization of the relation between the input and output signal without using a conventional flux-locked loop circuit. It relies on applying a periodic, sawtooth-shaped magnetic flux signal to the modulation coil of the SQUID to continuously measure the flux-to-voltage SQUID characteristic within each period of the flux ramp. In case that the amplitude and repetition rate of the ramp are chosen such that multiple flux quanta are induced in the SQUID and that the input signal is quasistatic within one period of the flux ramp, the input signal adds a constant magnetic flux offset to the SQUID that leads to a phase shift of the SQUID characteristic being proportional to the input signal. We show that this scheme allows for significantly increasing the dynamic range and that it intrinsically allows for MHz frequency-division SQUID multiplexing.
A novel double dc superconducting quantum interference device (SQUID) is proposed. It consists of two SQUIDs with different geometries in cascade configuration. The structure makes the device particularly suitable for flux-locked-loop operation without need of a room-temperature heterodyne modulation circuitry and a matching network between the SQUID and the preamplifier, thus simplifying the readout electronic system. The noise performance is calculated as a function of the electrical parameters of the device. The noise contribution of the room-temperature preamplifier can be made negligible using <m1;&2p>appropriate SQUID parameters while the slew rate of the system can approach 106Φ0/s.
Frequency Division Multiplexing technique for reading TES detectors with SQuID devices, requires high loop-gain up to MHz frequency range in the SQuID feedback loop. Such a requirement is difficult to achieve when the feedback loop has a physical length that makes the propagation times of signals not negligible, as in the case in which the readout electronics is placed at room temperature. A novel SQuID readout scheme, called Double Loop-Flux Locked loop (DLFLL), has been proposed earlier. According to this scheme it is possible to make use of a simplified cryogenic electronics, AC coupled, featuring low power dissipation, in order to obtain a cryogenic feedback loop that results in reduced propagation times of signals. The DC and low frequency signals are managed by a standard FLL electronics working at room temperature. Here we present the progress of the integrated Double Loop system.
An improved read-out electronics without flux modulation for dc superconducting quantum interference devices (dc SQUIDs) is presented where the preamplifier is directly coupled to the SQUID. Compared to our previous designs, the 1/f voltage and current noise levels of the preamplifier were reduced by about a factor of 4 (rms) by using bipolar matched transistors instead of operational amplifiers at the input. Three types of flux-locked-loop electronics were developed and successfully tested: a low-power (120 mW) version for large multichannel arrays, a high-speed version with a 15 MHz bandwidth and a very fast (300 ns) reset mode, and a low-noise (0.44 nV/Hz) version with a fast and precise bias reversal circuit. The flux-locked-loop electronics are compatible with each other, so that only one type of low-power (180 mW) control unit is required to operate them. All essential specifications of practical SQUID systems (noise, dynamic behavior, and temperature stability) were determined by using liquid-helium and liquid-nitrogen cooled SQUIDs, respectively.
We have studied the phase locking of two and eight microbridge arrays shunted by superconducting loops in a dc SQUID configuration. The difference in phase between adjacent bridges is controlled by the applied flux, and thus the radiated power is a periodic function of this flux. With adjustment of the external flux, the individual bridge voltages can be made to add in phase. The effect of additional normal shunts on the phase locking is also investigated. MICROBRIDGES COUPLED BY SUPERCONDUCTING LOOPS Experiment sly on two Josephson microbridges have shown that it is possible to obtain nearly complete in phase coherent radiation with narrowed linewidth by coupling the microbridges with external shunts. To obtain greater ouput power and narrower linewidth it is desirable to phase lock larger arrays of bridges. The narrow range of bias currents over which locking occurs, however, imposes strict tolerances on the uniformity of bridge characteristics if a single current bias is used. In this paper we discuss experiments which eliminate this difficulty by using a superconducting loop to couple the junctions, i.e., a dc SQUID configuration, so that the average frequency of each junction is always equal even for non-identical junctions. Also the phase difference between the junctions in the absence Of noise is set by the amount of externally applied flux due to the fluxoid quantization condition. With identical bridges and zero applied flux, the junctions oscillate in phase. In the geometry used in
We present a MHz frequency-division direct-current superconducting quantum interference device (dc-SQUID) multiplexer that is based on flux ramp modulation and a series array of N identical current-sensing dc-SQUIDs with tightly coupled input coil. By running a periodic, sawtooth-shaped current signal through additional modulation coils being tightly but non-uniformly coupled to the individual SQUIDs, the voltage drop across the array changes according to the sum of the flux-to-voltage characteristics of the individual SQUIDs within each cycle of the modulation signal. In this mode of operation, an input signal injected in the input coil of one of the SQUIDs and being quasi-static within a time frame adds a constant flux offset and leads to a phase shift of the associated SQUID characteristics. The latter is proportional to the input signal and can be inferred by channelizing and down-converting the sampled array output voltage. Using a prototype multiplexer as well as custom readout electronics, we demonstrate the simultaneous readout of four signal sources with MHz bandwidth per channel.