Total System Noise Research Articles

Extensive Search for Axion Dark Matter over 1 GHz with CAPP’S Main Axion Experiment

We report an extensive high-sensitivity search for axion dark matter above 1 GHz at the Center for Axion and Precision Physics Research (CAPP). The cavity resonant search, exploiting the coupling between axions and photons, explored the frequency (mass) range of 1.025 GHz (4.24 μeV) to 1.185 GHz (4.91 μeV). We have introduced a number of innovations in this field, demonstrating the practical approach of optimizing all the relevant parameters of axion haloscopes, extending presently available technology. The CAPP 12 T magnet with an aperture of 320 mm made of Nb3Sn and NbTi superconductors surrounding a 37 l ultralight-weight copper cavity is expected to convert Dine-Fischler-Srednicki-Zhitnitsky axions into approximately 102 microwave photons per second. A powerful dilution refrigerator, capable of keeping the core system below 40 mK, combined with quantum-noise-limited readout electronics, achieved a total system noise of about 200 mK or below, which corresponds to a background of roughly 4×103 photons per second within the axion bandwidth. The combination of all those improvements provides unprecedented search performance, imposing the most stringent exclusion limits on axion-photon coupling in this frequency range to date. These results also suggest an experimental capability suitable for highly sensitive searches for axion dark matter above 1 GHz. Published by the American Physical Society 2024

Single-detector double-beam modulation for high-sensitivity infrared spectroscopy

Balanced detection based on double beams is widely used to reduce common-mode noises, such as laser intensity fluctuation and irregular wavelength scanning, in absorption spectroscopy. However, employing an additional detector can increase the total system noise due to added non-negligible thermal noise of the detector, particularly with mid-infrared (IR) detectors. Herein, we demonstrate a new optical method based on double-beam modulation (DBM) that uses a single-element detector but keeps the advantage of double-beam balanced detection. The sample and reference path beams were modulated out-of-phase with each other at a high frequency, and their average and difference signals were measured by two lock-in amplifiers and converted into absorbance. DBM was coupled with our previously reported solvent absorption compensation (SAC) method to eliminate the IR absorption contribution of water in aqueous solutions. The DBM-SAC method enabled us to acquire IR absorption spectra of bovine serum albumin solutions down to 0.02 mg/mL. We investigated the noise characteristics of DBM measurements when the wavelength was either fixed or scanned. The results demonstrate that DBM can lower the limit of detection by ten times compared to the non-modulation method.

Extended Axion Dark Matter Search Using the CAPP18T Haloscope.

We report an extended search for the axion dark matter using the CAPP18T haloscope. The CAPP18T experiment adopts innovative technologies of a high-temperature superconducting magnet and a Josephson parametric converter. The CAPP18T detector was reconstructed after an unexpected incident of the high-temperature superconducting magnet quenching. The system reconstruction includes rebuilding the magnet, improving the impedance matching in the microwave chain, and mechanically readjusting the tuning rod to the cavity for improved thermal contact. The total system noise temperature is ∼0.6 K. The coupling between the cavity and the strong antenna is maintained at β≃2 to enhance the axion search scanning speed. The scan frequency range is from 4.8077 to 4.8181GHz. No significant indication of the axion dark matter signature is observed. The results set the best upper bound of the axion-photon-photon coupling (g_{aγγ}) in the mass ranges of 19.883 to 19.926 μeV at ∼0.7×|g_{aγγ}^{KSVZ}| or ∼1.9×|g_{aγγ}^{DFSZ}| with 90%confidence level. The results demonstrate that a reliable search of the high-mass dark matter axions can be achieved beyond the benchmark models using the technology adopted in CAPP18T.

Very Low-Noise Figure HTSC RF Front-End

A very low noise figure radio frequency (RF) front-end for the cellular realm is presented. The front-end is composed of two planar YBCO high critical temperature superconductor (HTSC) bandpass filters (BPFs) and a low temperature, low noise amplifier. Using advanced HTSC growth techniques, 8-pole hairpin BPFs are implemented in a YBCO thin film grown on both sides of a sapphire substrate. The front-end is designed and implemented based on the optimal configuration of the filters derived from advanced electromagnetic simulations. Measured performance at 77 K shows a high-frequency response and very low losses, with an insertion loss of 0.15 dB and a rejection ratio of −93 dBc. The integration of HTSC filters with the low noise amplifier results in a system with superior performance, with a low noise figure of around 0.5 dB. Low insertion loss and the compact dimensions of the filter, along with low total system noise, make the designed superconducting RF front-end highly attractive for radio receivers.

Ultraprecision quantum sensing and measurement based on nonlinear hybrid optomechanical systems containing ultracold atoms or atomic Bose–Einstein condensate

In this review, the authors study how a hybrid optomechanical system (OMS), in which a quantum micro- or nano-mechanical oscillator is coupled to the electromagnetic radiation pressure, consisting of an ensemble of ultracold atoms or an atomic Bose–Einstein condensate, can be used as an ultraprecision quantum sensor for measuring very weak signals. As is well-known in any precise quantum measurement, the competition between the shot noise and the backaction noise of measurement executes a limitation on the measurement precision which is the so-called standard quantum limit (SQL). In the case where the intensity of the signal is even lower than the SQL, one needs to perform an ultraprecision quantum sensing to beat the SQL. For this purpose, the authors review three important methods for surpassing the SQL in a hybrid OMS: (i) the backaction evading measurement of a quantum nondemolition variable of the system, (ii) the coherent quantum backaction noise cancelation, and (iii) the so-called parametric sensing, the simultaneous signal amplification, and added noise suppression below the SQL. Furthermore, the authors have shown in this article for the first time how the classical fluctuation of the driving laser phase, the so-called laser phase noise, affects the power spectrum of the output optical field in a standard OMS and induces an additional impression noise which makes the total system noise increase above the SQL. Also, for the first time in this review it has been shown that in the standard OMSs, it is impossible to amplify the signal while suppressing the noise below the SQL simultaneously.

Wide-band parametric amplifier readout and resolution of optical microwave kinetic inductance detectors

The energy resolution of a single photon counting microwave kinetic inductance detector can be degraded by noise coming from the primary low temperature amplifier in the detector's readout system. Until recently, quantum limited amplifiers have been incompatible with these detectors due to the dynamic range, power, and bandwidth constraints. However, we show that a kinetic inductance based traveling-wave parametric amplifier can be used for this application and reaches the quantum limit. The total system noise for this readout scheme was equal to ∼2.1 in units of quanta. For incident photons in the 800–1300 nm range, the amplifier increased the average resolving power of the detector from ∼6.7 to 9.3 at which point the resolution becomes limited by noise on the pulse height of the signal. Noise measurements suggest that a resolving power of up to 25 is possible if the redesigned detectors can remove this additional noise source.

Mitigation strategies against radiation-induced background for space astronomy missions

The Advanced Telescope for High ENergy Astrophysics (ATHENA) mission is a major upcoming space-based X-ray observatory due to be launched in 2028 by ESA, with the purpose of mapping the early universe and observing black holes. Background radiation is expected to constitute a large fraction of the total system noise in the Wide Field Imager (WFI) instrument on ATHENA, and designing an effective system to reduce the background radiation impacting the WFI will be crucial for maximising its sensitivity. Significant background sources are expected to include high energy protons, X-ray fluorescence lines, 'knock-on' electrons and Compton electrons. Due to the variety of the different background sources, multiple shielding methods may be required to achieve maximum sensitivity in the WFI. These techniques may also be of great interest for use in future space-based X-ray experiments. Simulations have been developed to model the effect of a graded-Z shield on the X-ray fluorescence background. In addition the effect of a 90nm optical blocking filter on the secondary electron background has been investigated and shown to modify the requirements of any secondary electron shielding that is to be used.

Soft‐output MMSE MIMO detector under different channel estimation models

This study considers the effect of channel estimation error (CEE) on the soft-output bit log-likelihood ratio (LLR) in a multiple-input–multiple-output detection system which the source sends their quadrature amplitude modulation to the detector through Rayleigh fading channels. The new expressions of LLR with maximum-likelihood CE for deterministic channel model and minimum mean square error (MMSE) CE for random channel model are obtained separately for linear MMSE receiver using known pilot-symbol-aided CE. Meanwhile, the optimal power allocation between training and data transmissions for these two different LLR expressions, which attends to get the maximum ratio of signal and interference plus noise ratio, are obtained under the total transmitting power constraints. Numerical results show that the power allocation ratio sets to be ∼0.5 is optimal for two new different LLRs at the same total power and system noise. Moreover, the derived LLR expressions match the simulation result and outperform the conventional system without the consideration of CEE and optimal power allocation. Meanwhile, the system performance is better than the existing research with the consideration of CE.

Optimizing noise for defect analysis with through-focus scanning optical microscopy.

Through-focus scanning optical microscopy (TSOM) shows promise for patterned defect analysis, but it is important to minimize total system noise. TSOM is a three-dimensional shape metrology method that can achieve sub-nanometer measurement sensitivity by analyzing sets of images acquired through-focus using a conventional optical microscope. Here we present a systematic noise-analysis study for optimizing data collection and data processing parameters for TSOM and then demonstrate how the optimized parameters affect defect analysis. We show that the best balance between signal-to-noise performance and acquisition time can be achieved by judicious spatial averaging. Correct background-signal subtraction of the imaging-system inhomogeneities is also critical, as well as careful alignment of the constituent images used in differential TSOM analysis.

Cryogenic Ka-Band 180$^{\circ}$ Phase Switch Based on Schottky Diodes

A Ka-band hybrid 0/180 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$^{\circ}$</tex> </formula> phase switch working at cryogenic temperature is presented. The circuit is designed on an alumina substrate using uniplanar hybrid technology, combining air-bridged coplanar waveguides and slotlines. Schottky diodes are used as switching elements, taking advantage of their cryogenic behavior, with low equivalent series resistance and low capacitance. Cryogenic performance at 15 K shows a phase difference response of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$177 \pm 2^{\circ}$</tex></formula> , average insertion losses of 1 dB and amplitude imbalance of less than 0.2 dB between states in the frequency range from 24 to 37 GHz (40% relative bandwidth) with a low-power consumption of 10.5 mW. The low insertion loss and small phase error make the designed phase switch suitable to be used on radioastronomy receivers (QUIJOTE experiment 26–36 GHz band) minimizing the total system noise temperature.

Effect of four-wave mixing in WDM optical fibre systems

Wavelength division multiplexing (WDM) can both significantly enhance transmission capacity and provide more flexibility in optical network design. Through the use of erbium-doped fibre amplifiers (EDFAs), it is possible to build long-distance transparent optical transmission links without electrical regenerators. In such systems, fibre nonlinearities are likely to impose a transmission limit due to increased total interaction length. There are a number of optical nonlinear effects in optical fibres, such as stimulated Raman scattering (SRS), stimulated Brillouin scattering (SBS), carrier-induced phase modulation and four-wave mixing (FWM). Out of these SRS and FWM are the dominant effects. In this paper, an algorithm has been suggested to study the effect of FWM in the total system noise considering the combined effect of SRS and FWM in the presence of amplified spontaneous noise (ASE). It has been found from the study that to maximize the signal-to-noise ratio of the transmitted signal in a WDM system FWM noise needs to be reduced as this is the dominant noise factor.

Compound semiconductor radiation detectors

We discuss the potential benefits of using compound semiconductors for the detection of X- and γ-ray radiation. While Si and Ge have become detection standards for energy dispersive spectroscopy in the laboratory, their use for an increasing range of applications is becoming marginalized by one or more of their physical limitations; namely the need for ancillary cooling systems or bulky cryogenics, their modest stopping powers and radiation intolerance. Compound semiconductors encompass such a wide range of physical properties that it is technically feasible to engineer a material to any application. Wide band-gap compounds offer the ability to operate in a wide range of thermal and radiation environments, whilst still maintaining sub-keV spectral resolution at hard X-ray wavelengths. Narrow band-gap materials, on the other hand, offer the potential of exceeding the spectral resolution of both Si and Ge, by as much as a factor of 3. Assuming that the total system noise can be reduced to a level commensurate with Fano noise, spectroscopic detectors could work in the XUV, effectively bridging the gap between the ultraviolet and soft X-ray wavebands. Thus, in principle, compound semiconductor detectors can provide continuous spectroscopic coverage from the far infrared through to γ-ray wavelengths. However, while they are routinely used at infrared and optical wavelengths, in other bands, their development has been plagued by material and fabrication problems. This is particularly true at hard X- and γ-ray wavelengths, where only a few compounds (e.g., GaAs, CdZnTe and HgI2) have evolved sufficiently to produce working detection systems. In this paper, we examine the current status of research in compound semiconductors and by a careful examination of material properties and future requirements, recommend a number of compounds for further development. In the longer term, when material problems are sufficiently under control, we believe the future lies in the development of heterostructures and inserted interface layers to overcome contacting problems and quantum heterostructures and superlattices to facilitate low-noise readout.

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.

A diode laser based gas monitor suitable for measurement of trace gas exchange using micrometeorological techniques

A fast response, sensitive, field-worthy trace gas analyzer (TGA), based on the principle of diode laser absorption spectroscopy has been developed. The TGA is suitable for in situ trace gas flux measurements using micrometeorological techniques, and is capable of achieving total system noise levels of less than 1, 2, or 4 part per billion by volume (ppbv) rms for N 2O, NH 3, and CH 4, respectively, for a 5-s integration period, and less than 50 pptv for 1-h averaging periods. This sensitivity is accomplished using a unique approach to digital signal processing and a single-path sample absorption cell, both of which reduce noise due to optical fringes. The instrument is also capable of rapid sampling rates (10 samples/s) sufficient for eddy correlation (EC) measurements when used with the appropriate flow system design. The TGA software and electronics have been designed to interface directly with micrometeorological instrumentation such as sonic anemometers, facilitating the use with the eddy correlation and gradient techniques. The operation, characteristics, and practical aspects of employing the TGA with micrometeorological techniques are reviewed. Gradient flux data for N 2O and CH 4 from field study measurements is from two plots are presented. The results demonstrate the capabilities of the TGA to make sensitive, continuous measurements of trace gas fluxes using micrometeorological techniques, allowing the assessment of the immediate and long-term impact of treatments or perturbations to natural and agricultural systems.

LaCoste &amp; Romberg gravity meter: System analysis and instrumental errors

Although the LaCoste &amp; Romberg (L&amp;R) gravity sensor can be used with great care to collect 1-μGal data, the sensor has a thermodynamic noise limit of 0.012 μGal—about two orders of magnitude below the present measurement precision. Hence, thermodynamic noise is not the limiting factor, and there is significant room for improvement by bringing the other perturbing influences under adequate control. We do not see any fundamental instrumental limitations to substantially improving measurement accuracy at least down to 0.1 μGal. We have improved the noise level, stability, and reliability of the L&amp;R borehole gravity meter sensor, with the goal of reducing the total system noise to below 1 μGal. In the process of these improvements, we made several fundamental observations about noise sources within the L&amp;R sensor, particularly related to thermal noise, electronic noise, sources of mechanical and electrical rectification errors, temporal mass variations, and instrument tares and drift. It has always been assumed that the effective proof mass of the L&amp;R sensor did not change over the time scale of a gravity survey. From our experiments we conclude that this assumption is incorrect below about 10 μGal. Large instrumental errors are produced by temporal proof‐mass variations over time scales of a survey, resulting from contamination and migration of dust, oil, and other volatiles inside the sensor. The results are drift and tares, for it takes only 0.01 μg of dust or oil transferred to the proof mass to offset the gravity reading by 1 μGal.

Noise characteristics of double relaxation oscillation superconducting quantum interference devices with reference junction

We fabricated double relaxation oscillation SQUIDs (DROSs) with a reference junction and investigated their noise characteristics. Because of the large flux-to-voltage transfer of 1-3 mV/0, the room-temperature dc preamplifier could readout SQUID output voltage directly and the contribution of the preamplifier input noise to the total system noise was negligible. The flux noise of the DROS planar gradiometer is about 4 µ0 Hz-1/2 at 100 Hz, corresponding to a field gradient noise of 1 fT cm-1 Hz-1/2, when operated inside a moderately shielded room. Because of the large modulation voltage of about 100 µV, stable flux-locked-loop operation was possible against drift in the input offset voltage.

System Noise in the NESDIS TOVS Forward Model. Part II: Consequences

Abstract To utilize satellite radiance sounding data, in either explicit or implicit retrieval algorithms, a proper understanding of the noise in the measurements is required. Conventionally, to define the expected accuracy of atmospheric profiles inferred from sounder data, instrument noise equivalent temperature difference (NEΔT) noise specifications have been used to simulate spacecraft data. Here it is demonstrated that NEΔT noise specifications are inappropriate for this purpose. Instead, total system noise estimates should be employed since use of sounding data in any type of physical retrieval algorithm implies application of a radiative transfer model, which in turn must be “calibrated” against in situ and satellite data. It is demonstrated that the accuracy of atmospheric retrievals inferred from the TIROS Operational Vertical Sounder radiometers is limited by the total system noise rather than NEΔT noise, and that modeled radiance temperatures perturbed by Gaussian total system noise very nearly...

System Noise in the NESDIS TOVS Forward Model. Part I: Specification

Abstract The National Environmental Satellite Data and Information Service (NESDIS) collocation data archive of satellite and radiosonde measurements is used to investigate errors in in situ radiosonde data and a NESDIS-like radiative transfer forward model. It is shown that the radiative transfer model errors have a strong airmass dependence and that these errors are not primarily due to nonrepresentativeness or radiosonde errors. However, errors in the in situ data do exist. For example, the National Meteorological Center radiosonde radiation adjustment algorithm in use during the period of data collection (1989–90) does not appear to provide adjustments of uniform quality across radiosonde sounding systems. The total system noise appropriate for use in retrieval algorithms is shown to vary from values close to the radiometer noise equivalent temperature difference (NEΔT) specifications for stratospheric channels to several times the NEΔT values for lower-tropospheric channels. Because of the significan...

Optimum design of optical storage media for drive compatibility

Interchangeability standards for writable optical data storage media allow considerable range in the design of media and optical devices. Naturally, the most reliable system performance occurs when the media design is made fully compatible with the particular characteristics of the drive. This paper treats design of the thin film structure of magneto-optical media for optimum readout compatibility with the drive. The methodology centers on maximization of system signal-to-noise ratio (SNR) under general conditions of system noise composition. We present simple models for the behavior of the various noise components in optical disk drives-medium, laser, shot, electronic. The total system noise model is supplied with relative component weights derived from experimental noise decomposition measurements on the physical system (drive or tester). By changing the relative weights of system noise components, one can readily identity optimum medium designs under different conditions of noise dominance.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analysis of electron image detection efficiency of slow-scan CCD cameras

We develop a stochastic model of electron image detection by slow-scan CCD cameras, and employ the model to investigate the performance of the cameras. The model takes full account of the channel mixing effect in multi-channel detectors. We demonstrate that channel mixing may result in an apparent detective quantum efficiency (DQE) greater than the theoretical limit of one, and that taking the channel mixing into account corrects this deficiency. We then determine the DQE of an actual slow-scan camera (Gatan model 679) from stochastic measurements, and show that its DQE closely approaches the ideal performance over a wide range of input intensities. The principal factors responsible for the good performance of the camera are shown to be: (i) high gain factor of the camera; (ii) low total system noise; and (iii) ability to correct gain variation of the camera by dividing by a gain reference image.