Rf Superconducting Quantum Interference Device Research Articles

Qualification of Microwave SQUID Multiplexer Chips for Simons Observatory

AbstractThe Simons Observatory is a cosmic microwave background experiment stationed atop Cerro Toco, at an elevation of 5200 ms in Chile’s Atacama Desert. The receivers of the Observatory will contain more than 60,000 transition edge sensor bolometers. In order to read out this large detector count in a scalable manner, we utilize a microwave superconducting quantum interference device (SQUID) multiplexing scheme where each detector is inductively coupled to an rf SQUID, which in turn is inductively coupled to a GHz resonator. More than 2000 SQUIDs and resonators are fabricated on a single 76.2-mm-diameter silicon wafer. To qualify wafers before integration, we cryogenically screen $$\sim$$ ∼ 10% of the devices on each wafer by use of a standard set of measurements. From these data, we report parameter value trends in 47 wafers that were fabricated in the past two years. We show good control in key parameters such as frequency placement, internal quality factor, and response to applied flux. We demonstrate a wafer acceptance yield of 86%.

Variation of the performance of YBa[formula omitted]Cu[formula omitted]O[formula omitted] radio frequency superconducting quantum interference device with bicrystal grain boundary angle

High transition temperature (high-Tc) superconducting quantum interference devices (SQUIDs) based on bicrystal grain boundary junctions have been utilized in a wide range of applications. To explore the effect of the bicrystal grain boundary angle on the property of the high-Tc SQUID, we fabricated and characterized YBa2Cu3O7−δ (YBCO) radio frequency (rf) SQUIDs using [001]-tilt grain boundary junctions on SrTiO3 (STO) bicrystal substrates with three different misorientation angles of θ=18∘, 24°, and 30°. Unlike the device of θ=18∘ showing only the triangular waveform of the voltage–flux (V−Φ) characteristics, for device of θ=24∘ and 30°, the shape of the V−Φ curve can be tuned from approximately triangular into nearly rectangular by adjusting the working point of the device. It suggests that, as θ increases from 18° to 30°, the operation of the device may change from the hysteretic mode into the nonhysteretic mode. This is backed by electrical transport measurements of YBCO bicrystal junctions on separate STO substrates, which help to reveal that lying behind the indicated changeover of the SQUID operation mode is the exponential decrease of the junction critical current density Jc as θ increases. The white noise of the device, which decreases with increasing flux-to-voltage transfer coefficient ∂V/∂Φ, shows a large drop as θ increases to 24°. For both 24° and 30° devices, the white field noise at 77 K is about 90 fT/Hz1/2 at respective optimum working points. For device of 30° with nearly rectangular V−Φ characteristics showing the largest ∂V/∂Φ among the fabricated samples, the white noise region extends below 10 Hz and a field noise of 145 fT/Hz1/2 at 1 Hz is shown, demonstrating the potential of obtaining high-performance bicrystal YBCO rf SQUIDs with this grain boundary angle.

Josephson parametric circulator with same-frequency signal ports, 200 MHz bandwidth, and high dynamic range

We demonstrate a 3-port Josephson parametric circulator matched to 50 Ω using second order Chebyshev networks. The device notably operates with two of its signal ports at the same frequency and uses only two out-of-phase pumps at a single frequency. As a consequence, when operated as an isolator, it does not require phase coherence between the pumps and the signal, thus simplifying the requirements for its integration into standard dispersive qubit readout setups. The device utilizes parametric couplers based on a balanced bridge of rf-superconducting quantum interference device arrays, which offer purely parametric coupling and high dynamic range. We characterize the device by measuring its full 3 × 3 S-matrix as a function of frequency and the relative phase between the two pumps. We find up to 15 dB nonreciprocity over a 200 MHz signal band, port match better than 10 dB, low insertion loss of 0.6 dB, and saturation power exceeding −80 dBm.

Preparation of high-quality factor dielectric resonators for low-noise YBa[formula omitted]Cu[formula omitted]O[formula omitted] radio frequency superconducting quantum interference devices

Tank circuit (resonator) is essential for the operation of the radio frequency (rf) superconducting quantum interference device (SQUID) and the quality factor of the tank circuit has significant impact on the sensitivity of the rf SQUID. For high transition temperature (high-Tc) rf SQUID, dielectric resonator is presently one of the most practical tank circuits. By growing YBa2Cu3O7−δ (YBCO) superconducting thin film on (100) SrTiO3 substrate with a pulsed-laser deposition technique and then patterning the YBCO thin film into flux concentrator with a washer structure, a series of dielectric resonators with unloaded quality factor Q0 ranging from 200 to 6000 has been prepared. Surface morphology and electrical transport measurements have been carried out to investigate the dependence of Q0 on the property of the YBCO thin film, which suggests that it is effective to boost the Q0 of the resonator through improvements in both the crystalline quality and the superconductivity of the thin film. By integrating the resonators with the same SQUID chip, a set of YBCO rf SQUIDs has been assembled to explore the influence of Q0 of the resonator on the performance of the rf SQUID. It is observed that the white noise of the device decreases substantially with the increase of Q0, in accordance with the theoretical suggestion. Moreover, as Q0 rises, the low frequency noise of the device is shown to reduce as well, revealing the importance of the high-Q0 resonator in depressing the noise of the high-Tc rf SQUID over the entire frequency range. With the resonator of Q0=6000, the YBCO rf SQUID at 77 K exhibits a field sensitivity of 50 fT/Hz1/2 in the white noise region, 58 fT/Hz1/2 and 110 fT/Hz1/2 at 10 Hz and 1 Hz respectively, suggesting its potential in applications such as magnetoencephalography in biomagnetism which have critical requirements on field sensitivity of the high-Tc SQUID especially at low frequencies.

Tuning of strong nonlinearity in radio-frequency superconducting-quantum-interference-device meta-atoms.

Strong nonlinearity of a self-resonant radio-frequency (rf) superconducting-quantum-interference-device (SQUID) meta-atom is explored via intermodulation (IM) measurements. Previous work in zero dc magnetic flux showed a sharp onset of IM response as the frequency sweeps through the resonance. A second onset at higher frequency was also observed, creating a prominent gap in the IM response. By extending those measurements to nonzero dc flux, different dynamics are revealed, including dc flux tunability of the aforementioned gaps and enhanced IM response near geometric resonance of the rf SQUID. These features observed experimentally are understood and analyzed theoretically through a combination of a steady-state analytical modeling and a full numerical treatment of the rf SQUID dynamics. The latter in addition predicts the presence of chaos in narrow parameter regimes. The understanding of intermodulation in rf SQUID metamaterials is important for producing low-noise amplification of microwave signals and tunable filters.

Ultrastrong Tunable Coupler Between Superconducting LC Resonators

We investigate the ultrastrong tunable coupler for coupling of superconducting resonators. The obtained coupling constant exceeds 1 GHz, and the wide-range tunability is achieved for both antiferromagnetics and ferromagnetics from $\ensuremath{-}1086$ to 604 MHz. The ultrastrong coupler is composed of a rf superconducting quantum interference device (SQUID) and dc SQUID as tunable junctions, which connect to resonators via shared aluminum thin-film meander lines enabling such a huge coupling constant. The spectrum of the coupler obviously shows the breaking of the rotating-wave approximation, and our circuit model treating the Josephson junction as a tunable inductance reproduces the experimental results well. The ultrastrong coupler is expected to be utilized in quantum annealing circuits and/or noisy intermediate-scale quantum devices with dense connections between qubits.

High-Tc rf SQUIDs with Large Flux Focusing

The high-Tc rf SQUID (superconducting quantum interference device) sensor, in which the rf SQUID was placed face to face with superconductor flux concentrator/dielectric resonator, was designed and fabricated. The SQUID sensor was made up of a SQUID washer (with an area of 9.6 mm2 and an inductance of 150 pH) and a flux focusing/dielectric resonator (with an area of 100 mm2 and an resonant frequency varied from 430 to 650 MHz). The author conducted a test to prove that with a white flux noise spectral density of SΦ 1/2=3×10-5Φ0/ Hz1/2 and field sensitivity of BN100 fT/Hz1/2, this flux focusing/dielectric resonator-type rf SQUID sensor can work stably where electromagnetic interference is smaller.

Development of Metallic Contaminant Inspection System Using High-Tc rf-SQUID for Li-ion Battery Liquid Components

The use of a high-Tc (HTS) rf-superconducting quantum interference device (SQUID) for inspecting the liquid component of lithium-ion (Li-ion) batteries is proposed. It is possible that a small amount of metal can become mixed in with components of Li-ion batteries during the manufacturing process and contaminate them, with a resultant fire risk, Thus, the development of a highly sensitive inspection system is required. In this article we describe a test system, we developed using a single channel HTS rf-SQUID consisting of a cryostat, a polyethylene tube, and a permanent magnet. The SQUID needs to be installed as close to the battery liquid as possible to obtain more sensitive readings. Therefore, we designed a microscope-type SQUID cryostat in which the SQUID can approach the target as close as 1 mm. In the system, the liquid was not flowed through the polyethylene tube, but a small metallic sample stack on a fishing line was moved by a motor. A stainless steel cut wire with a nominal size of φ 50 μm was prepared. After magnetizing the sample, the stray magnetic field of the sample was measured by the SQUID. The peak-to-peak signal scaled inversely with the cube of the stand-off distance. It was found that a signal of the sample with φ 50 μm at a distance of 26 mm could be detected if the signal-to-noise ratio ( SNR ) > 3 was supposed as the threshold of the inspection. The dependence on the sample size was also investigated, using stainless steel samples with different sizes (φ 50–φ 160 μm). The peak-to-peak signal scaled with the cube of the diameter.

Superconducting Quantum Annealing Architecture with LC Resonators

We propose a novel architecture for superconducting circuits to improve the efficiency of a quantum annealing system. To increase the capability of a circuit, it is desirable for a qubit to be coupled not only with adjacent qubits but also with other qubits located far away. We introduce a circuit that uses a lumped element resonator coupled each with one qubit. The resonator-qubit pairs are coupled by rf-superconducting quantum interference device (SQUID) based couplers. These pairs make a large quantum system for quantum annealer. This system could prepare the problem Hamiltonian and tune the parameters for quantum annealing procedure.

The step-edge type HTS rf SQUID coupling with a LC circuit in ultra-low field NMR system

The step-edge type high temperature superconductor (HTS) radio frequency (rf) superconducting quantum interference devices (SQUIDs) were fabricated from YBa2Cu3O7−δ thin films with a field sensitivity of 66 fT/Hz1/2. Even though the sensitivity of the rf SQUID sensor used in the experiments was degraded to 77 fT/Hz1/2 in the magnetic shielded room (MSR), the performance of the rf SQUID sensor was good enough for the ultra-low field (ULF) nuclear magnetic resonance (NMR) experiments at a measurement field of 61.5 μT. With the help of a strictly controlled fast switching circuit and a coupled LC circuit which acted as flux transformer, the signal-to-noise ratio (SNR) of the rf SQUID-based ULF NMR system with different operating points was measured. The optimum SNR was 40 dB which increased significantly by coupling an input coil closely beneath the rf SQUID sensor. The extracted 1/T1 value for pure water sample at 23 ∘C showed the rf SQUID based ULF NMR was an effective system for ULF NMR researches. All above, the direct coupled method and the control circuit show a great potential in the future rf SQUID-based ULF NMR &MRI system.

Hybrid rf SQUID qubit based on high kinetic inductance

We report development and microwave characterization of rf SQUID (Superconducting QUantum Interference Device) qubits, consisting of an aluminium-based Josephson junction embedded in a superconducting loop patterned from a thin film of TiN with high kinetic inductance. Here we demonstrate that the systems can offer small physical size, high anharmonicity, and small scatter of device parameters. The work constitutes a non-tunable prototype realization of an rf SQUID qubit built on the kinetic inductance of a superconducting nanowire, proposed in Phys. Rev. Lett. 104, 027002 (2010). The hybrid devices can be utilized as tools to shed further light onto the origin of film dissipation and decoherence in phase-slip nanowire qubits, patterned entirely from disordered superconducting films.

Detection of magnetic nanoparticles with a large scale AC superconducting susceptometer

Magnetic nanoparticles (MNPs) are being used in several applications in medicine such as hyperthermia, magnetic particle imaging, in vitro and in vivo bioassay, and still there are many other possibilities for use of these particles to come as research progress in this field. One crucial step of its use is the detection of these particles when present in a certain tissue. For in vitro bioassay, the sample can be harvested and placed inside the detector in optimal conditions to favor sensitivity. However, for in vivo human measurements the system must be noninvasive and conform to the anatomic restrictions requiring sensitive detectors and dedicated setups. In this study, we detect nanoparticles with an AC biosusceptometer having an excitation homogeneous magnetic field with 145 μT, provided by a set of rectangular large Rubens coils driven at 10 Hz. The magnetization induced in the sample was detected by a second-order axial gradiometer (20 mm in diameter and 40 mm of baseline) coupled to an RF Superconducting Quantum Interference Device (SQUID) model 330X (BTi). The MNPs used were manganese ferrite-based surface-coated with citric acid dissolved in water at various concentrations. The colloid is stable at physiological conditions. X-ray diffraction confirmed the spinel structure and using Scherrer’s relation revealed a particle size of 17.3 nm. The magnetization curve showed a typical superparamagnetic behavior with a specific saturation magnetization of 51.2 emu g−1. The stock solution of nanoparticles had a concentration of 23.17 mg ml−1, corresponding to 1.7 × 1015 NPs ml−1. Measurements were made in a volume of 30 ml with 20 × 103–100 × 103 dilutions of the stock solution of nanoparticles and performed at distances of 1.1, 1.5 and 2.5 cm from the top of the sample vial to the closest coil of the gradiometer. The limits of detection were 8.1 × 109 NP ml−1, 9.5 × 109 NP ml−1 and 11.0 × 109 NP ml−1 for the distances above. These values suggest that the technique might have interesting applications in the real-time in vivo detection of nanoparticles after systemic injections. The present setup can be improved by using more sensitive SQUID sensors and less noisy cryostats.

Giant spin splitting and 0−π Josephson transitions from the Edelstein effect in quantum spin Hall insulators

Hybrid structures of quantum spin-Hall insulators (QSHIs) and superconductors (Ss) present a unique opportunity to access dissipationless topological states of matter, which, however, is frequently hindered by the lack of control over the spin polarization in QSHIs. We propose a very efficient spin-polarization mechanism based on the magnetoelectric (Edelstein) effect in superconducting QSHI structures. It acts akin to the Zeeman splitting in an external magnetic field, but with an effective $g$-factor of order of 1000, resulting in an unprecedented spin-splitting effect. It allows a magnetic control of the QSHI/S hybrids without destroying superconductivity. As an example, we demonstrate a recurrent crossover from $\Phi_0$ - to $\Phi_0/2$ - periodic oscillations of the Josephson current in an rf superconducting quantum interference device ($\Phi_0=h/2e$ is the magnetic flux quantum). The predicted period halving is a striking manifestation of $0-\pi$ Josephson transitions with a superharmonic $\pi$-periodic current-phase relationship at the transition. Such controllable $0-\pi$ transitions may offer new perspectives for dissipationless spintronics and engineering flux qubits.

Coherent oscillations of driven rf SQUID metamaterials.

Through experiments and numerical simulations we explore the behavior of rf SQUID (radio frequency superconducting quantum interference device) metamaterials, which show extreme tunability and nonlinearity. The emergent electromagnetic properties of this metamaterial are sensitive to the degree of coherent response of the driven interacting SQUIDs. Coherence suffers in the presence of disorder, which is experimentally found to be mainly due to a dc flux gradient. We demonstrate methods to recover the coherence, specifically by varying the coupling between the SQUID meta-atoms and increasing the temperature or the amplitude of the applied rf flux.

Homoclinic chaos in coupled SQUIDs

An rf superconducting quantum interference device (SQUID) consists of a superconducting ring interrupted by a Josephson junction (JJ). The induced supercurrents around the ring are determined by the JJ through the celebrated Josephson relations. We study the dynamics of a pair of parametrically-driven coupled SQUIDs lying on the same plane with their axes in parallel. The drive is through the alternating critical current of the JJs. This system exhibits rich nonlinear behavior, including chaotic effects. We take advantage of the weak damping that characterizes these systems to perform a multiple-scales analysis and obtain amplitude equations, describing the slow dynamics of the system. This picture allows us to expose the existence of homoclinic orbits in the dynamics of the integrable part of the slow equations of motion. Using high-dimensional Melnikov theory, we are able to obtain explicit parameter values for which these orbits persist in the full system, consisting of both Hamiltonian and non-Hamiltonian perturbations, to form so called Shilnikov orbits, indicating a loss of integrability and the existence of chaos.

Chimera states and synchronization in magnetically driven SQUID metamaterials

Superconducting QUantum Interference Device (SQUID) metamaterials are superconducting artificial media whose function relies both on their geometry and the extraordinary properties of superconductivity and the Josephson effect. Recent experiments on one- and two-dimensional radio-frequency (rf) SQUID metamaterials have revealed their wide-band tuneability, significantly reduced losses, dynamic multistability, and tunable broadband transparency. The simplest version of an rf SQUID involves a superconducting ring interrupted by a Josephson junction; this device is a highly nonlinear resonator with a strong response to applied magnetic fields. SQUID metamaterials exhibit peculiar magnetic properties such as negative diamagnetic permeability, predicted both for the quantum and the classical regime. The applied alternating fields induce (super)currents in the SQUID rings, which are therefore coupled through dipole-dipole magnetic forces. This interaction is weak due to its magnetic nature. However, it couples the SQUIDs non-locally since it falls-off as the inverse cube of their center-to-center distance.

Self-heterodyne detection of thein situphase of an atomic superconducting quantum interference device

We present theoretical and experimental analysis of an interferometric measurement of the {\it in-situ} phase drop across and current flow through a rotating barrier in a toroidal Bose-Einstein condensate (BEC). This experiment is the atomic analog of the rf-superconducting quantum interference device (SQUID). The phase drop is extracted from a spiral-shaped density profile created by the spatial interference of the expanding toroidal BEC and a reference BEC after release from all trapping potentials. We characterize the interferometer when it contains a single particle, which is initially in a coherent superposition of a torus and reference state, as well as when it contains a many-body state in the mean-field approximation. The single-particle picture is sufficient to explain the origin of the spirals, to relate the phase-drop across the barrier to the geometry of a spiral, and to bound the expansion times for which the {\it in-situ} phase can be accurately determined. Mean-field estimates and numerical simulations show that the inter-atomic interactions shorten the expansion time scales compared to the single-particle case. Finally, we compare the mean-field simulations with our experimental data and confirm that the interferometer indeed accurately measures the {\it in-situ} phase drop.

Noise-Induced Hopping in an RF SQUID

An RF superconducting quantum interference device (RF SQUID), which is an important bistable system, has attracted much attention for its important applications in nonlinear fields. With different potential shapes at 20 mK, we perform detailed research on the relationship between the probability of the phase particle in the left potential well (P L ) of an RF SQUID and the external noise intensity (D), which provides a method to identify the symmetry of any tunable bistable systems. A qualitative model is proposed to understand the physical process, and the numerical results are well consistent with the experimental results.

Development of Metallic Contaminant Detection System Using RF High-Tc SQUIDs for Food Inspection

In this study, we developed a practical magnetic metallic contaminant detector using three high-Tc RF superconducting quantum interference devices (SQUIDs) for food inspection. Finding small metallic contaminants is important for food safety. When contamination occurs, the manufacturer of the product suffers a great loss to recall the tainted products. Therefore we developed a practical food contaminant detection system based on high-Tc RF SQUIDs. The system was covered with waterproof stainless steel plates, and the outer dimensions of the system were 2450 mm (W) × 714 mm (D) × 1555 mm (H). An acceptable inspected object size was 150 mm (W) × 100 mm (H), which is sufficiently large for practical food inspection. A digital filtering technique has been newly introduced to reduce noise. As a result, the signal-to-noise ratio (SNR) was dramatically improved, and we were able to robustly detect a steel ball as small as 0.3 mm in diameter.

Homoclinic chaos in a pair of parametrically-driven coupled SQUIDs

An rf superconducting quantum interference device (SQUID) consists of a superconducting ring interrupted by a Josephson junction (JJ). When driven by an alternating magnetic field, the induced supercurrents around the ring are determined by the JJ through the celebrated Josephson relations. This system exhibits rich nonlinear behavior, including chaotic effects. We study the dynamics of a pair of parametrically-driven coupled SQUIDs arranged in series. We take advantage of the weak damping that characterizes these systems to perform a multiple-scales analysis and obtain amplitude equations, describing the slow dynamics of the system. This picture allows us to expose the existence of homoclinic orbits in the dynamics of the integrable part of the slow equations of motion. Using high-dimensional Melnikov theory, we are able to obtain explicit parameter values for which these orbits persist in the full system, consisting of both Hamiltonian and non-Hamiltonian perturbations, to form so-called Silnikov orbits, indicating a loss of integrability and the existence of chaos.