Tunable Microwave Cavity Research Articles

Feedback Stabilization of the Resonant Frequency in a Tunable Microwave Cavity with Single-Photon Occupancy

We successfully demonstrate low-frequency noise suppression in the resonant-frequency fluctuations of a cavity-embedded Cooper-pair transistor (cCPT) driven at single-photon occupancy. In particular, we report a reduction in the resonant-frequency fluctuations caused by the internal charge noise over a bandwidth of approximately $1.4\phantom{\rule{0.2em}{0ex}}\text{kHz}$ when the cavity is driven at an average photon number $n=10$ and a bandwidth of 11 Hz for an average $n=1$. The gate-dependent tunability of the cCPT allows us to implement a feedback scheme derived from the Pound-Drever-Hall locking technique. This reduces fluctuations due to intrinsic charge noise, which otherwise interfere with the operation of the cCPT as a near quantum-limited electrometer. Our technique can be generalized to achieve frequency stabilization in tunable microwave resonators that play a vital role in today's quantum computing architectures, thereby moderating the limitations in detection caused by the intrinsic $1/f$ noise on such circuit devices. The work discusses the various aspects relating to the operation of a fully functional feedback loop down to the single-photon level.

Search for 70 μeV Dark Photon Dark Matter with a Dielectrically Loaded Multiwavelength Microwave Cavity.

Microwave cavities have been deployed to search for bosonic dark matter candidates with masses of a few μeV. However, the sensitivity of these cavity detectors is limited by their volume, and the traditionally employed half-wavelength cavities suffer from a significant volume reduction at higher masses. Axion dark matter experiment (ADMX)-Orpheus mitigates this issue by operating a tunable, dielectrically loaded cavity at a higher-order mode, which allows the detection volume to remain large. The ADMX-Orpheus inaugural run excludes dark photon dark matter with kinetic mixing angle χ>10^{-13} between 65.5 μeV (15.8 GHz) and 69.3 μeV (16.8 GHz), marking the highest-frequency tunable microwave cavity dark matter search to date.

A symmetric multi-rod tunable microwave cavity for a microwave cavity dark matter axion search.

The microwave cavity technique is currently the most sensitive way of looking for dark matter axions in the 0.1 GHz-10 GHz range, corresponding to masses of 0.41 µeV-41 µeV. A particular challenge for frequencies greater than 5 GHz is designing a cavity with a large volume that contains a resonant mode that shows high coupling to dark matter axions, a high quality factor, is broadly tunable, and is free from intruder modes. For the Haloscope at Yale Sensitive to Axion Cold dark matter, we have designed and constructed an optimized high frequency cavity with a tuning mechanism that preserves a high degree of rotational symmetry, critical to maximizing its figure of merit. This cavity covers an important frequency range according to recent theoretical estimates for the axion mass, 5.5 GHz-7.4 GHz, and the design appears extendable to higher frequencies as well. This paper will discuss key design and construction details of the cavity, present a summary of the design evolution, and alert practitioners of potentially unfruitful avenues for future work.

Automated wide-ranged finely tunable microwave cavity for narrowband phase noise filtering.

Narrowband microwave filters have wide ranging applications, including the reduction in phase noise of microwave sources within a given frequency band. The prospect of developing an automated filter that tunes itself to an arbitrary desired frequency at maximum extinction promises many experimental advantages such as an enhanced efficiency in performing fine frequency detuning scans and saving time and effort as compared to manual tuning. We design, construct, and program such an automated system and present its hardware and software for reproducibility. It consists of a cylindrical cavity filter and two motors, which change the cavity length and the coupling strength of the microwave field into the cavity, respectively. By measuring the cavity response, an algorithm implemented in Python optimizes these two parameters to achieve the tuning of the filter cavity to the desired frequency with a precision of around 20 kHz, which is significantly better than the cavity linewidth (∼1 MHz). We also demonstrate the suppression of phase noise at the desired frequency by more than 10 dB.

Noise Temperature Measurements for Axion Haloscope Experiments at IBS/CAPP

The axion was first introduced as a consequence of the Peccei-Quinn mechanism to solve the CP problem in strong interactions of particle physics and is a well motivated cold dark matter candidate. This particle is expected to interact extremely weakly with matter and its mass is expected to lie in $\mu$eV range with the corresponding frequency roughly in GHz range. In 1983 P. Sikivie proposed a detection scheme, so called axion haloscope, where axions resonantly convert to photons in a tunable microwave cavity permeated by a strong magnetic field. A major source of the experimental noise is attributed to added noise by RF amplifiers, and thus precise understandings of amplifiers' noise is of importance. We present the measurements of noise temperatures of various low noise amplifiers broadly used for axion dark matter searches.

Ferromagnetic resonance, magnetic susceptibility, and transformation of domain structure in CoFeB film with growth induced anisotropy

Field dependence of magnetic susceptibility in nanocrystalline CoFeB film was studied in a wide frequency range from 500 kHz to 15 GHz. Anomalies of the susceptibility were detected exciting CoFeB film with a solenoidal coil, microwave strip line, in the tunable microwave cavity as well as employing magneto-optical domains imaging. Critical spin fluctuations in the form of “soft” modes were observed in a whole range of orientations of magnetic field perpendicular to the “easy” magnetic axis. A sequence of domain structure transformations was extensively examined in a “hard” direction in in-plane magnetic field reduced below the field of uniaxial anisotropy Hp = 535 Oe. At first, uniformly magnetized state in CoFeB film transforms to stripe domains separated by low angle Néel domain walls (DWs) parallel to the “hard”-axis. Then, at critical field Hcr = 232 Oe, Néel DWs gradually convert to the“easy”-axis oriented Bloch DWs loaded with vertical Bloch lines (VBLs). After field reversal at H = −Hcr, backward conversion of VBL-loaded Bloch DWs to Néel DWs results in instantaneous energy release and sharp anomaly of magnetic susceptibility. Appearance of critical spin fluctuations accomplishes domains transformation to the uniformly magnetized state at H = −535 Oe.

High-$Q$ Tunable Microwave Cavity Resonators and Filters Using SOI-Based RF MEMS Tuners

This paper presents the modeling, design, fabrication, and measurement of microelectromechanical systems-enabled continuously tunable evanescent-mode electromagnetic cavity resonators and filters with very high unloaded quality factors (Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> ). Integrated electrostatically actuated thin diaphragms are used, for the first time, for tuning the frequency of the resonators/filters. An example tunable resonator with 2.6:1 (5.0-1.9 GHz) tuning ratio and Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> of 300-650 is presented. A continuously tunable two-pole filter from 3.04 to 4.71 GHz with 0.7% bandwidth and insertion loss of 3.55-2.38 dB is also shown as a technology demonstrator. Mechanical stability measurements show that the tunable resonators/filters exhibit very low frequency drift (less than 0.5% for 3 h) under constant bias voltage. This paper significantly expands upon previously reported tunable resonators.

10.1007/s11487-008-3006-y

It is found that, in a gapped-post-adjacent-plunger system, reflection of microwave radiation occurs. This reflection is dependent on the magnitude and direction of the magnetic field. It is indicated that this phenomenon can be used for the development of tunable microwave cavities.

Magnetic-field controlled resonances in a gapped-post-adjacent-plunger system

It is found that, in a gapped-post-adjacent-plunger system, reflection of microwave radiation occurs. This reflection is dependent on the magnitude and direction of the magnetic field. It is indicated that this phenomenon can be used for the development of tunable microwave cavities.

Cryogenic tunable microwave cavity at 13GHz for hyperfine spectroscopy of antiprotonic helium

For the precise measurement of the hyperfine structure of antiprotonic helium, microwave radiation of 12.9 GHz frequency is needed, tunable over ±100MHz. A cylindrical microwave cavity is used whose front and rear faces are meshed to allow the antiprotons and laser beams to enter. The cavity is embedded in a cryogenic helium gas target. Frequency tuning of ∼300MHz with Q values of 2700–3000 was achieved using over-coupling and an external triple stub tuner. We also present Monte-Carlo simulations of the stopping distribution of antiprotons in the low-density helium gas using the GEANT4 package with modified energy loss routines.

Cryogenic tunable microwave cavity at 13 GHz for hyperfine spectroscopy of antiprotonic helium

For the precise measurement of the hyperfine structure of antiprotonic helium, microwave radiation of 12.9GHz frequency is needed, tunable over ±100MHz. A cylindrical microwave cavity is used whose front and rear faces are meshed to allow the antiprotons and laser beams to enter. The cavity is embedded in a cryogenic helium gas target. Frequency tuning of ∼300MHz with Q values of 2700–3000 was achieved using over-coupling and an external triple stub tuner. We also present Monte-Carlo simulations of the stopping distribution of antiprotons in the low-density helium gas using the GEANT4 package with modified energy loss routines.

Microwave cavity searches for dark-matter axions

Recent determinations of cosmological parameters point to a flat Universe, whose total energy density is composed of about two-thirds vacuum energy and one-third matter. Ordinary baryonic matter is relegated to a small fraction of the latter, within which the luminous part is an order of magnitude smaller yet. Particle dark matter, i.e., one or more relic particle species from the big bang, is thus strongly suggested as the dominant component of matter in the Universe. The axion, a hypothetical elementary pseudoscalar arising from the Peccei-Quinn solution to the strong-$\mathrm{CP}$ problem, is a well-motivated candidate. If the axion exists, it must be extremely light, in the mass range of ${10}^{\ensuremath{-}6}--{10}^{\ensuremath{-}3}\mathrm{eV},$ and possess extraordinarily feeble couplings to matter and radiation. Nevertheless, as proposed by Sikivie in 1983, the axion's two-photon coupling lends itself to a feasible search strategy with currently available technology. In this scheme, axions resonantly convert to single microwave photons by a Primakoff interaction, in a tunable microwave cavity permeated by a strong magnetic field. Present experiments utilizing heterostructure transistor microwave amplifiers have achieved total system noise temperatures of $\ensuremath{\sim}3\mathrm{K}$ and represent the world's quietest spectral radio receivers. Exclusion regions have already been published well into the band of realistic axion model couplings, within the lowest decade of mass range. Recent breakthroughs in the development of near-quantum-limited superconducting quantum interference device amplifiers should reduce the system noise temperature to $\ensuremath{\sim}100\mathrm{mK}$ or less. Ongoing research into using Rydberg-atom single-quantum detectors as the detector in a microwave cavity experiment could further reduce the effective noise temperature. In parallel with improvements in amplifier technology, promising concepts for higher-frequency cavity resonators are being explored to open up the higher decades in mass range. Definitive experiments to find or exclude the axion may therefore be at hand in the next few years. As the microwave cavity technique measures the total energy of the axion, a positive discovery could well reveal fine structure of the signal due to flows of nonthermalized axions. Manifesting diurnal and sidereal modulation, such detailed features would contain a wealth of information about the history, structure, and dynamics of our Milky Way galaxy.

Initiation of microwave-induced electrical breakdown of high-pressure gases

Measurements of microwave-induced electrical breakdown at 2.45 GHz in Ar, Kr, and Xe have been made in a tunable microwave cavity. The influence of UV illumination on gas breakdown at pressures up to 300 torr, and data on fiber initiator-induced breakdown above atmospheric pressure are presented. A marked decrease in the statistical spread in breakdown was observed with UV illumination, but the maximum pressures at which breakdown occurred with available microwave power, with and without UV illumination, were the same. To initiate breakdown in gases above 1 atm, a conducting fiber was used to enhance the applied macroscopic electric field at the fiber tip. Using 8-/spl mu/m diameter SiC fibers coated with 0.2-/spl mu/m-thick Pt, breakdown was obtained with pulses as short as 0.25 ms in the pressure range 1-3 atm for Ar, Kr, and Xe. The required microwave electric field at 2280 torr with one fiber was less than that at 200 torr without a fiber. The increase of the breakdown field with pressure was much slower than linear. The effect of fiber length, diameter, orientation, and conductivity, and of the number of fibers, on the required breakdown electric field, and fiber initiation in Cl/sub 2/ mixture gases, were also investigated.

The Consolidation and Processing of Graphite Fiber/Polymer Composites by Controlled Mode Microwaves

ABSTRACTComposite laminates have been cured under pressure in a tunable microwave cavity. A 7-in. diam cavity with a sliding short was tuned to produce single mode or controlled hybrid mode standing waves at 2.45 GHz. Graphite/epoxy laminates were processed with power inputs as low as 2 W/g.A low loss press was designed and built to operate inside the cavity. The press can apply 100 psi pressure on a 9-in. square laminate. An empirical approach has been used to develop processing conditions for high quality laminates. Graphite/epoxy composites were cured in 90 min or less. A simple on-off temperature control loop modulated power input to the cavity with a coaxial switch.Mechanical testing and differential scanning calorimetry have been used to evaluate the composites. The material properties have been related to processing conditions.

Ferrite-Tunable Microwave Cavities and the Introduction of a New Reflectionless, Tunable Microwave Filter

Large ferrite samples are placed in microwave cavities with the object of achieving tunable microwave cavities. Experimental data, at X band frequencies, on ferrite tuning of conventional band-pass and band elimination cavities are presented. Curves of applied dc magnetic field vs cavity resonant frequency, bandwidth, loss, cavity Q, and window coupling coefficients are included. Of particular interest are the results obtained with a new type cavity filter. With a single circularly polarized cavity, a reflectionless filter is achieved which couples nearly 100 per cent of the energy from the main waveguide at the cavity resonant frequency. Experimental results, on the ferrite loading of these circularly polarized cavities, are presented, and a number of practical microwave applications are discussed.