Loaded Quality Factor Research Articles

Calibration of Superconducting Radio-Frequency cavity forward and reflected channels based on stored energy dynamics

Modern superconducting radio-frequency linear accelerators require the cavity bandwidth and detuning to be within a specified range to maximize the efficiency of the machine. To correctly estimate these states during operation, the measured RF signals should be calibrated. Due to the finite isolation of the waveguide directional couplers, cross-coupling effects in the forward and reflected channels complicate the calibration of the RF signals in Low-Level RF control systems. Past work proposed a compensation method employing least-squares optimization. This method requires the directivity of the directional couplers to be much higher than one. Additionally, the algorithm requires a tuning parameter to optimize the calculated calibration. However, for some accelerating systems, finding an acceptable value for such a parameter is challenging and time-consuming. Other methods strongly depend on the forward-reflected ratio during the field decay phase. This, in some circumstances, may decrease the accuracy due to noise or systematic errors. In this paper, we present a way to overcome these limitations by performing a global nonlinear least square optimization constrained by energy conservation laws. The method is tested with L-band superconducting resonators at loaded quality factors of 4.6⋅106 and 2.8⋅107.

Deepest sensitivity to wavelike dark photon dark matter with superconducting radio frequency cavities

Wavelike, bosonic dark matter candidates like axions and dark photons can be detected using microwave cavities known as haloscopes. Traditionally, haloscopes consist of tunable copper cavities operating in the TM010 mode, but ohmic losses have limited their performance. In contrast, superconducting radio frequency (SRF) cavities can achieve quality factors of ∼1010, perhaps 5 orders of magnitude better than copper cavities, leading to more sensitive dark matter detectors. In this paper, we first derive that the scan rate of a haloscope experiment is proportional to the loaded quality factor QL, even if the cavity bandwidth is much narrower than the dark matter halo line shape. We then present a proof-of-concept search for dark photon dark matter using a nontunable ultrahigh-quality SRF cavity. We exclude dark photon dark matter with kinetic mixing strengths of χ>1.5×10−16 for a dark photon mass of mA′=5.35 μeV, achieving the deepest exclusion to wavelike dark photons by almost an order of magnitude. Published by the American Physical Society 2024

Phase-Slip Based SQUID Used as a Photon Switch in Superconducting Quantum Computation Architectures

The photon storage time in a superconducting coplanar waveguide (CPW) resonator is contingent on the loaded quality factor, primarily dictated by the input and output capacitance of the resonator. The phase-slip based superconducting quantum interference device (PS-SQUID) comprises two phase-slip (PS) junctions connected in series with a superconducting island in between. The PS-SQUID can manifest nonlinear capacitance behavior, with the capacitance finetuned by the gate voltage to minimize the impact of magnetic field noise as much as possible. By substituting the coupling capacitance of the CPW resonator with the PS-SQUID, the loaded quality factor of the resonator can be changed by three orders, thus, we get a microwave photon switch in superconducting quantum computation architectures. Furthermore, by regulating the loaded quality factors, the coupling strength between the CPW and superconducting quantum circuits can be controlled, enabling the ability to manipulate stationary qubits and flying qubits.

Near-quantum-limited haloscope search for dark-photon dark matter enhanced by a high- Q superconducting cavity

We report new experimental results on the search for dark photons based on a near-quantum-limited haloscope equipped with a superconducting cavity. The loaded quality factor of the superconducting cavity is 6×105, so that the expected signal from dark-photon dark matter can be enhanced by more than one order compared to a copper cavity. A Josephson parametric amplifier with a near-quantum-limited noise temperature has been utilized to minimize the noise during the search. Furthermore, a digital acquisition card based on field programmable gate arrays has been utilized to maximize data collection efficiency with a duty cycle being 100%. This work has established the most stringent constraints on dark photons at around 26.965 μeV. In the future, our apparatus can be extended to search for other dark matter candidates, such as axions and axionlike particles, and scrutinize new physics beyond the Standard Model. Published by the American Physical Society 2024

Calibration of the cryogenic measurement system of a resonant haloscope cavity* *Measurements were performed at Hunan Normal University in Changsha. This work was supported in part by the Scientific Instrument Developing Project of the Chinese Academy of Sciences (YJKYYQ20190049), the International Partnership Program of Chinese Academy of Sciences for Grand Challenges (112311KYSB20210012), the National Natural Science Foundation of China (12074117,

Possible light bosonic dark matter interactions with the Standard Model photon have been searched using microwave resonant cavities. In this paper, we describe the cryogenic readout system calibration of a 7.138 GHz copper cavity with a loaded quality factor whose operation at a temperature of 22 mK is based on a dilution refrigerator. Our readout system consists of High Electron Mobility Transistors working as cryogenic amplifiers at 4 K, plus room-temperature amplifiers and a spectrum analyzer for signal power detection. We tested the system with a superconducting two-level system based on a single-photon source in the microwave frequency regime. We obtained an overall 95.6 dB system gain and –71.4 dB attenuation in the cavity's input channel. The effective noise temperature of the measurement system is 7.5 K.

Multimodule microwave assembly for fast readout and charge-noise characterization of silicon quantum dots

Fast measurements of quantum devices is useful in areas such as quantum sensing, quantum computing, and nanodevice quality analysis. Here, we develop a superconductor-semiconductor multimodule microwave assembly to demonstrate charge-state readout at the state of the art. The assembly consist of a superconducting readout resonator interfaced to a silicon-on-insulator (SOI) chiplet containing quantum dots (QDs) in a high-κ nanowire transistor. The superconducting chiplet contains resonant and coupling elements as well as LC filters that, when interfaced with the silicon chip, result in a resonant frequency f=2.12 GHz, a loaded quality factor Q=850, and a resonator impedance Z=470Ω. Combined with the large gate lever arms of SOI technology, we achieve a minimum integration time for single and double QD transitions of 2.77 and 13.5 ns, respectively. We utilize the assembly to measure charge noise over 9 decades of frequency up to 500 kHz and find a 1/f dependence across the whole frequency spectrum as well as a charge-noise level of 4μeV/Hz at 1 Hz. The modular microwave circuitry presented here can be directly utilized in conjunction with other quantum devices to improve the readout performance as well as enable large bandwidth noise spectroscopy, all without the complexity of superconductor-semiconductor monolithic fabrication. Published by the American Physical Society 2024

Retracted: Calibration of superconducting radio-frequency cavity forward and reflected channels based on stored energy dynamics

Modern superconducting radio-frequency linear accelerators require the cavity bandwidth and detuning to be within a specified range to maximize the efficiency of the machine. To correctly estimate these states during operation, the measured RF signals should be calibrated. Due to the finite isolation of the waveguide directional couplers, cross-coupling effects in the forward and reflected channels complicate the calibration of the RF signals in Low-Level RF control systems. Past work proposed a compensation method employing least-squares optimization. This method requires the directivity of the directional couplers to be much higher than one. Additionally, the algorithm requires a tuning parameter to optimize the calculated calibration. However, for some accelerating systems, finding an acceptable value for such a parameter is challenging and time-consuming. In this paper, we present a way to overcome these limitations by performing a nonlinear least square optimization constrained by energy conservation laws. The method is tested with L-band superconducting resonators at loaded quality factors of 4.6⋅106 and 2.8⋅107.

Capacitive crosstalk in gate-based dispersive sensing of spin qubits

In gate-based dispersive sensing, the response of a resonator attached to a quantum dot gate is detected by a reflected radio frequency signal. This enables fast readout of spin qubits and tune up of arrays of quantum dots but comes at the expense of increased susceptibility to crosstalk, as the resonator can amplify spurious signals and induce fluctuations in the quantum dot potential. We attach tank circuits with superconducting NbN inductors and internal quality factors Qi>1000 to the interdot barrier gate of silicon double quantum dot devices. Measuring the interdot transition in transport, we quantify radio frequency crosstalk that results in a ring-up of the resonator when neighboring plunger gates are driven with frequency components matching the resonator frequency. This effect complicates qubit operation and scales with the loaded quality factor of the resonator, the mutual capacitance between device gate electrodes, and with the inverse of the parasitic capacitance to ground. Setting qubit frequencies below the resonator frequency is expected to substantially suppress this type of crosstalk.

On-chip electro-optically tunable Fabry-Perot cavity laser on erbium doped thin film lithium niobate

We demonstrate an on-chip electro-optically tunable Fabry-Perot (FP) cavity laser on Er3+-doped thin film lithium niobate (Er: TFLN). The FP cavity consists of two Sagnac loop reflectors at the two ends with a loaded quality factor of 1.3 × 105 and a free spectral range of 68 pm. The fabricated Er: TFLN FP laser structure is integrated with microelectrodes designed for electro-optically tuning, and a continuous laser wavelength tuning with 24 pm around 1544 nm is achieved by applying a driving voltage from −6 V to 6 V.

Feedforward resonance control for the European X-ray free electron laser high duty cycle upgrade

The High Duty Cycle (HDC) upgrade is a proposed improvement to the existing European X-ray Free Electron Laser (EuXFEL) to extend the pulsed RF duty factor from the actual value of around 1% to more than 5% up to Continuous Wave (CW). To implement this upgrade, the loaded quality factor (QL) of the superconducting cavities will increase by more than one order of magnitude. This will result in shrinking the cavity bandwidth to values as low as a few Hertz. Since the Lorentz Force Detuning (LFD) experienced during the accelerating field buildup is of hundreds of Hertz, the Low-Level RF (LLRF) system has to accurately track and control the cavity resonance frequency to obtain the desired accelerating gradient. Moreover, ponderomotive instabilities have to be suppressed to achieve stability during beam acceleration. Since LFD is a repetitive disturbance in cavity frequency, the correction to its effects can be implemented as a feedforward compensation on the piezoelectric tuners of the cavity. Initial results on the simulation of feedforward resonance control in the HDC regime are discussed in this proceeding.

Simulation framework for microwave SQUID multiplexer optimization

So far, performance prediction and optimization of microwave SQUID multiplexers have largely been based on simple approximate analytical models and experimental results. This is caused by the complexity of the underlying physics and the intricacy of operation and readout parameters. As a simplified description can never account for all potential effects occurring in a real device, we have developed a software framework to simulate the characteristics and performance of a microwave SQUID multiplexer. Our simulation framework is a powerful tool to guide understanding and optimization of microwave SQUID multiplexers and other related devices. It includes common readout schemes such as open-loop or flux ramp-modulated readout as well as the nonlinear behavior of Josephson tunnel junctions. Moreover, it accounts for the non-zero response time of superconducting microwave resonators with high loaded quality factors as well as the most significant noise contributions such as amplifier noise, resonator noise, as well as SQUID noise. This ultimately leads to a prediction of device performance that is significantly better compared to simple analytical methods. Using the simulation framework, we discuss first steps toward full microwave SQUID multiplexer optimization and highlight some other applications for which our simulation framework can be used.

Electro-mechanical tuning of high-Q bulk acoustic phonon modes at cryogenic temperatures

We investigate the electromechanical properties of quartz bulk acoustic wave resonators at extreme cryogenic temperatures. By applying a DC bias voltage, we demonstrate broad frequency tuning of high-Q phonon modes in a quartz bulk acoustic wave cavity at cryogenic temperatures of 4 K and 20 mK. More than 100 line-widths of tuning of the resonance peak without any degradation in loaded quality factor, which are as high as 1.73×109, is seen for high order overtone modes. For all modes and temperatures, the observed coefficient of frequency tuning is ≈ 3.5 mHz/V per overtone number n corresponding to a maximum of 255.5 mHz/V for the n = 73 overtone mode. No degradation in the quality factor is observed for any value of an applied biasing field.

Small-sized x-band open resonator for wide-range permittivity measurements of solid-state dielectrics

A study using computer simulation of a compact two-mirror symmetric open resonator for use in the X band for measurements of the complex permittivity of flat samples was carried out. The possibilities of minimizing the dimensions of an open resonator with a loaded quality factor of about 104 are investigated. Comparative studies of various coupling elements of an open resonator with a waveguide are carried out. It is shown that coupling elements in the form of a slot on the mirror, which smoothly passes into a standard waveguide, have advantages for use in open resonator for permittivity measurements, compared with coupling elements in the form of a hole in the diaphragm at the end of waveguide on the mirror surface. It is shown that slot coupling elements make it possible to achieve in open resonators almost twice as much field magnitude than coupling elements in the form of holes.

Exploration of a PBG-based cavity structure for a multiple-beam extended interaction klystron

The feasibility of a photonic band-gap (PBG)-based interaction structure was analytically explored for a multiple-beam extended interaction klystron amplifier. This configuration accrues the advantages of the multiple-defect PBG-based extended interaction structure and multiple-beam operation. The mode configurations were analysed through 3D electromagnetic simulation and the applicability of the photonic band-gap cavity was studied for the multiple-beam operation of an extended interaction klystron amplifier. A typical six-defect cavity operating at around 83 GHz was designed for electron–wave interaction at 2π mode with 6 electron beams each carrying 300 mA current at the accelerating potential of 16.5 kV. A particle-in-cell simulation shows that an output power of ∼2 kW is possible with electronic efficiency of around 6.7%. A frequency-scaled-down interaction structure at Ku-band was fabricated and cold measurements were carried out to ascertain the feasibility. The measured values of the frequency for various modes, loaded quality factor and 3 dB bandwidth were found to be within 0.36%, 5.3% and 4.07%, respectively, against those from the simulation.

Al0.78Sc0.22N Lamb Wave Contour Mode Resonators.

This article presents the lamb wave contour mode resonators (CMRs) based on 22% aluminum scandium nitride (AlScN) thin film with λ of 12-24 [Formula: see text], and operating in [Formula: see text] mode. We report the design, fabrication, and characterization of 500 nm-thick AlScN CMRs, which take advantage of optimized stress control of co-sputtered AlScN thin films and vertical inductively coupled plasma (ICP) etching profile. The experimental results are compared to theoretical predictions by finite element analysis (FEA). All Al 0.78 Sc [Formula: see text] devices show excellent agreement with simulations in piezoelectric coupling using modified AlScN film parameters. The best Al 0.78 Sc [Formula: see text] CMR has achieved an electromechanical coupling coefficient ( kt2) of 5.24% and loaded quality factor ( Q ) of 1219 with an operating frequency at approximately 300 MHz, which exhibits a high Figure-of-Merit (FoM) of 63.88 in piezoelectric microelectromechanical system (MEMS) lamb wave CMR. This article also presents the co-sputtering characteristics of the AlScN thin films under [Formula: see text] gas to achieve low-stress and high-quality piezoelectric materials, and the etching optimization of high concentration Sc doping aluminum nitride (AlN) thin films under Cl2/BCl3/Ar chemistry to obtain record profile angle of 77°, high selectivity of 1:1 with SiO2 hard mask.

Efficient acousto-optic modulation using a microring resonator on a thin-film lithium niobate-chalcogenide hybrid platform.

This Letter presents the first, to the best of our knowledge, thin-film lithium niobate-chalcogenide based microring acousto-optic modulator where an interdigital transducer and a chalcogenide strip waveguide are integrated on X-cut thin-film lithium niobate. The microring resonator exhibits a high loaded quality factor of 5 × 105. The developed hybrid acousto-optic modulator with an interaction length of 120 µm demonstrates an effective half-wave voltage of only 1.74 V, which corresponds to a voltage-length product of 0.02 V•cm. The performance of the acousto-optic modulator demonstrated on the unsuspended thin-film lithium niobate-chalcogenide waveguide platform is on par with that obtained from an acoustic cavity assisted homogeneous lithium niobate counterpart.

Design and Testing of an Ultralow Q CBPM

High repetition rates are considered essential to meet the anticipated new demands of the free-electron laser (FEL) facility. To offer precise beam handling for high-repetition-rate FEL facilities operating in a multi-bunch mode, an ultralow quality factor ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> ) cavity beam position monitor (CBPM) is studied to distinguish nanosecond spaced electron bunches, enabling the independent position measurement of each bunch and reducing the contamination between bunch signals. The low- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\!Q$ </tex-math></inline-formula> CBPM consists of two cavities: a reference cavity and a position cavity. The reference cavity is mainly used for bunch charge normalization, and the position cavity can measure the beam position vertically and horizontally. This article studies the method to attain a low loaded quality factor for the CBPM and presents the design and preliminary test results. The test results show that both the loaded quality factors of the reference cavity and the position cavity can reach 13, which enables bunch position monitoring for those high repetition rate FEL facilities.

Al0.7Sc0.3N butterfly-shaped laterally vibrating resonator with a figure-of-merit (kt2·Qm) over 146

This work presents the laterally vibrating Lamb wave resonators (LVRs) based on a 30% aluminum scandium nitride (Al0.7Sc0.3N) thin film with three interdigited transducer pairs operating in the S0 mode. In order to reduce the anchor loss, perfect matched layer-based finite element analysis simulations are utilized to design and optimize the device. Thanks to the high quality AlScN using magnetron sputtering with a single alloy target, vertical etching profile, and designed device structure, 1-μm-thick Al0.7Sc0.3N-based LVRs with high performance are fabricated. The resonator equivalent electric parameters are extracted utilizing the modified Butterworth–Van Dyke model. The best Al0.7Sc0.3N LVR achieves an electromechanical coupling coefficient (kt2) of 9.7% and a loaded quality factor (Qr) of 1141.5 operating at approximately 305 MHz. The same resonator shows a motional quality factor (Qm) of 1507.2, resulting in a high figure-of-merit (FoM = kt2 · Qm) of 146.2. A 1.8 MHz tuning range is measured for an Al0.7Sc0.3N LVR by applying DC voltage in the range of −40 to 40 V due to the ferroelectric property of high Sc doping in Al0.7Sc0.3N. With the high FoM, Qr, Qm, and low motional resistance (Rm), the Al0.7Sc0.3N-based LVRs show strong potential in applications of radio frequency communications and piezoelectric transducers.

Study of Thin Film LiNbO3 Laterally Excited Bulk Acoustic Resonators

This work presents an in-depth study of simulation and measurement results of laterally excited shear bulk acoustic resonators (XBAR) in Lithium Niobate, at 5 GHz with high electromechanical coupling factor (<inline-formula> <tex-math notation="LaTeX">$k_{t}^{2}$ </tex-math></inline-formula>) as high as 25&#x0025;, and with impedances at resonance close to <inline-formula> <tex-math notation="LaTeX">$2~\Omega $ </tex-math></inline-formula>. Loaded Quality factors of up to 340 and 150 are obtained at resonance and anti-resonance, respectively. Experimental00 dispersion behaviors of main mode and spurious are presented. Several geometric parameters affecting resonator performance are studied in order to improve figure of merits (FoM) of the device for 5G filter applications. The modified fabrication process presented shows a high yield of over 90&#x0025; of devices which can be scalable for mass production of high frequency, sub-6 GHz, wide band filters. [2021-0202]

Polysilicon micro-heaters for resonance tuning in CMOS photonics.

A new, to the best of our knowledge, device platform for tuning the resonance wavelength of integrated photonic resonators based on polysilicon-based micro-heaters for complementary metal-oxide semiconductor (CMOS)-foundry-based active Si photonics is demonstrated. The miniaturized micro-heater can be placed directly on the active Si layer, with a pedestal providing the optical and electrical isolation needed for the implementation of ultrafast active photonic devices such as modulators. The demonstrated devices do not require any additional modifications to the standard CMOS foundry processes. Experiments demonstrate a tuning efficiency of 0.25 nm/mW (or 42 GHz/mW) for a 5-µm-radius microdisk resonator with a loaded quality factor (Q) > 35,000. This polysilicon-based heater demonstrates a tunability of 42 GHz/mW with an average switching time of 60 µs. The proposed compact heater architecture enables it to be kept near to the optical mode, thereby providing efficient and high-speed wavelength tuning for resonant devices.