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Noise spectroscopy of a quantum-classical environment with a diamond qubit
摘要： Knowing a quantum system’s environment is critical for its practical use as a quantum device. Qubit sensors can reconstruct the noise spectral density of a classical bath, provided long enough coherence time. Here, we present a protocol that can unravel the characteristics of a more complex environment, comprising both unknown coherently coupled quantum systems, and a larger quantum bath that can be modeled as a classical stochastic field. We exploit the rich environment of a nitrogen-vacancy center in diamond, tuning the environment behavior with a bias magnetic field, to experimentally demonstrate our method. We show how to reconstruct the noise spectral density even when limited by relatively short coherence times, and identify the local spin environment. Importantly, we demonstrate that the reconstructed model can have predictive power, describing the spin qubit dynamics under control sequences not used for noise spectroscopy, a feature critical for building robust quantum devices. At lower bias fields, where the effects of the quantum nature of the bath are more pronounced, we find that more than a single classical noise model are needed to properly describe the spin coherence under different controls, due to the back action of the qubit onto the bath.
关键词： nitrogen-vacancy center,diamond qubit,noise spectroscopy,dynamical decoupling,quantum-classical environment
更新于2025-09-09 09:28:46
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[IEEE 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz2018) - Nagoya, Japan (2018.9.9-2018.9.14)] 2018 43rd International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Terahertz (THz) Direct Detectors based on Superconducting HEBs with Thermal, Microwave and THz Biasing
摘要： Terahertz (THz) direct detectors based on superconducting niobium nitride (NbN) hot electron bolometers (HEBs) with thermal, microwave (MW) and THz biasing have been studied at 0.65 THz and 4.2 K in detail. The current responsivity and noise equivalent power (NEP) have been measured and compared respectively. The detectors with the MW and THz biasing have about one order higher current responsivity than that of the thermal one. With the MW biasing, an NEP at the order of pW/√Hz is obtained by choosing the MW frequency and power appropriately.
关键词： Terahertz,direct detectors,microwave biasing,niobium nitride,current responsivity,hot electron bolometers,superconducting,THz biasing,thermal biasing,noise equivalent power
更新于2025-09-09 09:28:46
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[IEEE 2018 International Conference on Microwave and Millimeter Wave Technology (ICMMT) - Chengdu, China (2018.5.7-2018.5.11)] 2018 International Conference on Microwave and Millimeter Wave Technology (ICMMT) - Dependence of Noise Temperature of Superconducting HEB Mixers on Frequency and Bath Temperature
摘要： A log-spiral antenna coupled 0.1-1.5 THz NbN superconducting HEB mixer has been characterized by measuring its double sideband (DSB) receiver noise temperature (Trec) from 0.22 THz to 1.44 THz and at 4 K-7 K bath temperatures. The measured uncorrected Trec is 800 K, 800 K, 750 K and 850 K at 0.22 THz, 0.55 THz, 0.85 THz and 1.44 THz respectively. The optimal bias voltage seems independent to the frequency and bath temperature. The bath-temperature dependence of noise temperature has also been investigated, the bath temperature has limited effect on the noise temperature when it is operated below its transition temperature. A similar frequency response of corrected mixer noise temperature has been observed at 4 K and 7 K bath temperature, which indicates the RF coupling efficiency of planar spiral antenna of HEB mixer.
关键词： frequency dependence,receiver noise temperature,bath temperature dependence,Superconducting HEB mixer
更新于2025-09-09 09:28:46
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Noise Behavior and Implementation of Interferometer-Based Broadband VNA
摘要： This paper analyzes and accurately models the complex noise behavior of vector network analyzers (VNAs) when measuring large-mismatch devices and subsequently shows how the VNA measurement noise performance is enhanced through implementation of a high-speed, broadband, active RF interferometer module. The presented VNA noise model provides a solid framework, benchmarked by measurement data, to analyze existing RF interferometer approaches. The performance improvement of the proposed interferometer implementation is then benchmarked in terms of magnitude and phase stability of the renormalized impedance level. A test bench employing the novel add-on RF interferometer module is presented and demonstrated to achieve high-speed cancellation of the scattered wave over a broad frequency band. The first experiment shows ultralow noise in a 1–18 GHz broadband measurement of co-planar waveguide 0.5-Ω and 5-kΩ impedance standards. Employing the proposed hardware setup improves the noise uncertainty for the 5-kΩ impedance standard by a factor of 8 and 20 at 1 and 18 GHz, respectively. In the second experiment, a factor of 2 height-resolution enhancement is achieved in a scanning microwave microscope when the RF interferometer module is added to the instrument.
关键词： vector network analyzer (VNA),impedance mismatch,noise,Extreme impedance measurement,microwave interferometry,nanoelectronics,nanostructures
更新于2025-09-09 09:28:46
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Ultra-low Noise Balanced Detectors for Optical Time Domain Measurements
摘要： Two ultra-low noise balanced detectors used for optical time domain measurements are presented in this paper. Both simultaneously achieve high bandwidth and low noise that is extremely difficult to realize in commercial detectors. Two-stage amplification circuits based on transimpedance amplifiers (TIAs) were used for these detectors, with special modifications implemented for different applications. To further suppress noise, a low noise junction field effect transistor (JFET) is connected between the photodiode and TIA to reduce the impact of amplifier leakage current in one of the detectors. Benefiting from this design, a 70 MHz sensitive detector with a gain of 3.2E5 V/W and low noise equivalent power density (NEP) of 2.2 pW/rtHz was implemented. For another balanced detector used in higher bandwidth applications, the differential transimpedance amplifier circuit is used, with the detector achieving a 250 MHz bandwidth with a gain of 5E4 V/W, equivalent to NEP of 6.2 pW/rtHz. Due to the difficulty of achieving high bandwidth with low noise, we perform theoretical analysis and simulations for our designs to ensure that these two design goals are realized simultaneously. The performance of the detectors is consistent with our analysis. In addition, a simplified optical testing system was built to test and calculate the performance of the detectors in their respective applications. The results show that both detectors are well balanced and achieve a common mode rejection ratio (CMRR) greater than 50 dB.
关键词： Balanced detectors,optoelectronic devices,time domain measurements,circuit simulations,noise measurements
更新于2025-09-09 09:28:46
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Floquet topological transition by unpolarized light
摘要： We study Floquet topological transition in irradiated graphene when the polarization of incident light changes randomly with time. We numerically confirm that the noise-averaged time-evolution operator approaches a steady value in the limit of exact Trotter decomposition of the whole period during which incident light has a different polarization at each interval of the decomposition. This steady limit is found to coincide with the time-evolution operator calculated from the noise-averaged Hamiltonian. We observe that at the six corners (Dirac K point) of the hexagonal Brillouin zone of graphene random Gaussian noise strongly modifies the phase band structure induced by circularly polarized light, whereas in the zone center ((cid:2) point) even a strong noise is not able to do the same. This can be understood by analyzing the deterministic noise-averaged Hamiltonian, which has a different Fourier structure as well as a lower number of symmetries compared to the noise-free one. In one-dimensional systems noise is found to renormalize only the drive amplitude.
关键词： unpolarized light,noise-averaged Hamiltonian,Floquet topological transition,irradiated graphene,phase band structure
更新于2025-09-09 09:28:46
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[IEEE 2018 24th International Conference on Pattern Recognition (ICPR) - Beijing, China (2018.8.20-2018.8.24)] 2018 24th International Conference on Pattern Recognition (ICPR) - Neighborhood-Based Recovery of Phase Unwrapping Faults
摘要： Among several structured light approaches, phase shift is the most widely adopted in real-world 3D reconstruction devices. This is mainly due to its high accuracy, strong resilience to noise and straightforward implementation. However, Phase shift also exhibits an inherent weakness, that is the spatial ambiguity resulting from the periodicity of the sinusoidal wave adopted. Of course many phase unwrapping methods have been proposed to solve such ambiguity. One of the most promising methods exploits additional signals of mutually prime periods, in order to observe a distinct combination of phases for each spatial point. Unfortunately, for such combination to be properly recognized, a very high accuracy in phase recovery must be attained for each signal. In fact, even modest errors could lead to unwrapping faults, making the overall approach much less resilient to noise than plain phase shift. With this paper we introduce a feasible and effective fault recovery method that can be directly applied to multi-period phase shift. The combined pipeline offers an optimal accuracy and coverage even with high noise conditions, overcoming the setbacks of the original method. The performance of such pipeline is established by means of an in depth set of experimental evaluations and comparison, both with real and synthetically generated data.
关键词： structured light,noise resilience,3D reconstruction,phase unwrapping,phase shift
更新于2025-09-09 09:28:46
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A Low-rank Tensor Model for Hyperspectral Image Sparse Noise Removal
摘要： Hyperspectral image (HSI) has been widely used in target detection and classification. However, various kinds of noise in HSIs affect the applications of HSIs. In this paper, we propose a low-rank (LR) tensor recovery model to remove noise. Considering that the HSI is a 3-D HSI data, and the underlying LR tensor property is used in the model. Then, according to the similarity of adjacent bands images, the regularization on the difference of adjacent bands images is considered. The experiments of removing noise from different noisy HSIs show that our method can achieve better performance on removing sparse noise, especially for strips removal.
关键词： low-rank,Hyperspectral image,tensor,sparse noise removal
更新于2025-09-09 09:28:46
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Weak convergence rates for stochastic evolution equations and applications to nonlinear stochastic wave, HJMM, stochastic Schr?dinger and linearized stochastic Korteweg–de Vries equations
摘要： We establish weak convergence rates for noise discretizations of a wide class of stochastic evolution equations with non-regularizing semigroups and additive or multiplicative noise. This class covers the nonlinear stochastic wave, HJMM, stochastic Schr¨odinger and linearized stochastic Korteweg–de Vries equation. For several important equations, including the stochastic wave equation, previous methods give only suboptimal rates, whereas our rates are essentially sharp.
关键词： stochastic evolution equations,multiplicative noise,additive noise,linearized stochastic Korteweg–de Vries equation,stochastic Schr¨odinger,non-regularizing semigroups,weak convergence rates,HJMM,stochastic wave equation
更新于2025-09-04 15:30:14
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Voltage Noise and Jitter Analysis for Swept Source Optical Coherence Tomography using KTa1-xNbxO3 Deflector
摘要： This paper describes voltage noise and jitter analysis for the depth deviation of a point spread function in a swept source optical coherence tomography system using a KTa1-xNbxO3 deflector. An interference waveform with voltage noise and jitter was simulated according to a previous report. Typical values for the voltage noise ΔVTYP and jitter ΔtTYP were also obtained from a previous report and experiment. It was determined that the depth deviation is limited by the ΔtTYP of the system. Therefore, the quality of the tomographic image can be efficiently improved by reducing jitter.
关键词： Interference waveform,Jitter,Simulation,Swept source optical coherence tomography,Signal-to-noise ratio,Voltage noise
更新于2025-09-04 15:30:14