Quantum Noise Reduction Research Articles

Generation of squeezed vacuum state in the millihertz frequency band

The detection of gravitational waves has ushered in a new era of observing the universe. Quantum resource advantages offer significant enhancements to the sensitivity of gravitational wave observatories. While squeezed states for ground-based gravitational wave detection have received marked attention, the generation of squeezed states suitable for mid-to-low-frequency detection has remained unexplored. To address the gap in squeezed state optical fields at ultra-low frequencies, we report on the first direct observation of a squeezed vacuum field until Fourier frequency of 4 millihertz with the quantum noise reduction of up to 8.0 dB, by the employment of a multiple noise suppression scheme. Our work provides quantum resources for future gravitational wave observatories, facilitating the development of quantum precision measurement.

Pushing the boundaries of gravitational wave detection

Broadband reduction of quantum noise should accelerate discovery

Weak Force Sensing Based on Optical Parametric Amplification in a Cavity Optomechanical System Coupled in Series with Two Oscillators

AbstractIn the realm weak force sensing, an important issue is to suppress fundamental noise (quantum noise and thermal noise), as they limit the accuracy of force measurement. In this study, a weak force sensing scheme that combines a degenerate optical parametric amplifier (OPA) and an auxiliary mechanical oscillator into a cavity optomechanical system to reduce quantum noise is investigated. It is demonstrated that the noise reduction of two coupled oscillators depends on their norm mode splitting. and provide a classic analogy and quantum perspective for further clarification. Besides, the noise reduction mechanism of OPA is to reduce the fluctuation of photon number and enhance the squeezing of the cavity field. A specific design is proposed that aimed at enhancing the joint effect of both, beyond what can be achieved using OPA alone or two series coupled oscillators. This scheme provides a new perspective for deeper understanding of cavity field squeezing and auxiliary oscillator in force sensing.

A CNN-based denoising method trained with images acquired with electron density phantoms for thin-sliced coronary artery calcium scans.

This work proposed a convolutional neural network (CNN)-based method trained with images acquired with electron density phantoms to reduce quantum noise for coronary artery calcium (CAC) scans reconstructed with slice thickness less than 3mm. A DenseNet model was used to estimate quantum noise for CAC scans reconstructed with slice thickness of 0.5, 1.0 and 1.5mm. Training data was acquired using electron density phantoms in three different sizes. The label images of the CNN model were real noise maps, while the input images of the CNN model were pseudo noise maps. Image denoising was conducted by subtracting the CNN output images from thin-sliced CAC scans. The efficacy of the proposed method was verified through both phantom study and patient study. By means of phantom study, the proposed method was proven effective in reducing quantum noise in CAC scans reconstructed with 1.5-mm slice thickness without causing significant texture change or variation in HU values. With regard to patient study, calcifications were more clear on the denoised CAC scans reconstructed with slice thickness of 0.5, 1.0 and 1.5mm than on 3-mm slice images, while over-smooth changes were not observed in the denoised CAC scans reconstructed with 1.5-mm slice thickness. Our results demonstrated that the electron density phantoms can be used to generate training data for the proposed CNN-based denoising method to reduce quantum noise for CAC scans reconstructed with 1.5-mm slice thickness. Because anthropomorphic phantom is not a necessity, our method could make image denoising more practical in routine clinical practice.

Optimization of Quantum Noise in Space Gravitational-Wave Antenna DECIGO with Optical-Spring Quantum Locking Considering Mixture of Vacuum Fluctuations in Homodyne Detection

Quantum locking using optical spring and homodyne detection has been devised to reduce the quantum noise that limits the sensitivity of the DECIGO, a space-based gravitational-wave antenna in the frequency band around 0.1 Hz for the detection of primordial gravitational waves. The reduction in the upper limit of energy density ΩGW from 2×10−15 to 1×10−16, as inferred from recent observations, necessitates improved sensitivity in the DECIGO to meet its primary science goals. To accurately evaluate the effectiveness of this method, this paper considers a detection mechanism that takes into account the influence of vacuum fluctuations on homodyne detection. In addition, an advanced signal processing method is devised to efficiently utilize signals from each photodetector, and design parameters for this configuration are optimized for the quantum noise. Our results show that this method is effective in reducing quantum noise, despite the detrimental impact of vacuum fluctuations on its sensitivity.

Acoustic frequency atomic spin oscillator in the quantum regime

Quantum noise reduction and entanglement-enhanced sensing in the acoustic frequency range is an outstanding challenge relevant for a number of applications including magnetometry and broadband noise reduction in gravitational wave detectors. Here we experimentally demonstrate quantum behavior of a macroscopic atomic spin oscillator in the acoustic frequency range. Quantum back-action of the spin measurement, ponderomotive squeezing of light, and virtual spring softening are observed at oscillation frequencies down to the sub-kHz range. Quantum noise sources characteristic of spin oscillators operating in the near-DC frequency range are identified and means for their mitigation are presented.

Frequency-Dependent Squeezed Vacuum Source for the Advanced Virgo Gravitational-Wave Detector.

In this Letter, we present the design and performance of the frequency-dependent squeezed vacuum source that will be used for the broadband quantum noise reduction of the Advanced Virgo Plus gravitational-wave detector in the upcoming observation run. The frequency-dependent squeezed field is generated by a phase rotation of a frequency-independent squeezed state through a 285m long, high-finesse, near-detuned optical resonator. With about 8.5dB of generated squeezing, up to 5.6dB of quantum noise suppression has been measured at high frequency while close to the filter cavity resonance frequency, the intracavity losses limit this value to about 2dB. Frequency-dependent squeezing is produced with a rotation frequency stability of about 6Hz rms, which is maintained over the long term. The achieved results fulfill the frequency dependent squeezed vacuum source requirements for Advanced Virgo Plus. With the current squeezing source, considering also the estimated squeezing degradation induced by the interferometer, we expect a reduction of the quantum shot noise and radiation pressure noise of up to 4.5dB and 2dB, respectively.

Exceptional-point sensing with a quantum interferometer

Recently, multiple studies have suggested that exceptional points (EPs) in lossless nonlinear optical systems can minimize quantum noise arising from the material gain and loss in conventional non-Hermitian systems, offering the possibility of quantum EP sensing. Meanwhile, nonlinear SU(1,1) interferometers have been established as useful in sensing due to their reduced quantum noise. In this work, we demonstrate the existence of EPs in a dual-beam SU(1,1) interferometer with two nonlinear parametric amplifiers. Our analysis of the input-output matrix in terms of joint quadrature amplitudes shows that EPs can be linked to both high signal, through a zero matrix element, and low noise, through noise preservation, in sensing by selecting an appropriate operation gauge of the quadrature amplitudes. Additionally, for a multistage SU(1,1) interferometer, EPs of the overall input-output matrix form multiple bands of high signal-to-noise ratio (SNR) which further separate into two phases indicated by the EPs of the transfer matrix of a repeating unit. Our investigations demonstrate the significance of quantum EPs in quantum interferometer sensing and broaden the operating regimes from diabolical points in some of the conventional SU(1,1) interferometers to EPs while still maintaining a high SNR.

Broadband squeezed microwaves and amplification with a Josephson travelling-wave parametric amplifier

Squeezing of the electromagnetic vacuum is an essential metrological technique used to reduce quantum noise in applications spanning gravitational wave detection, biological microscopy, and quantum information science. In superconducting circuits, the resonator-based Josephson-junction parametric amplifiers conventionally used to generate squeezed microwaves are constrained by a narrow bandwidth and low dynamic range. In this work, we develop a dual-pump, broadband Josephson traveling-wave parametric amplifier that combines a phase-sensitive extinction ratio of 56 dB with single-mode squeezing on par with the best resonator-based squeezers. We also demonstrate two-mode squeezing at microwave frequencies with bandwidth in the gigahertz range that is almost two orders of magnitude wider than that of contemporary resonator-based squeezers. Our amplifier is capable of simultaneously creating entangled microwave photon pairs with large frequency separation, with potential applications including high-fidelity qubit readout, quantum illumination and teleportation.

The Advanced Virgo+ status

The gravitational wave detector Advanced Virgo+ is currently in the commissioning phase in view of the fourth Observing Run (O4).The major upgrades with respect to the Advanced Virgo configuration are the implementation of an additional recycling cavity, the Signal Recycling cavity (SRC), at the output of the interferometer to broaden the sensitivity band and the Frequency Dependent Squeezing (FDS) to reduce quantum noise at all frequencies.The main difference of the Advanced Virgo + detector with respect to the LIGO detectors is the presence of marginally stable recycling cavities, with respect to the stable recycling cavities present in the LIGO detectors, which increases the difficulties in controlling the interferometer in presence of defects (both thermal and cold defects).This work will focus on the interferometer commissioning, highlighting the control challenges to maintain the detector in the working point which maximizes the sensitivity and the duty cycle for scientific data taking.

Phase space nonclassicality and sub-Poissonianity of deformed photon-added nonlinear cat states: algebraic and group theoretical approach.

In this Letter, we introduce four distinct classes of f-deformed photon-added nonlinear cat state. This would be achieved by recalling a nonlinear coherent states approach, as well as a particular class of Gilmore-Perelomov-type of SU(1,1) coherent state and a class of SU(2) coherent state. We then examine the role of photon addition and nonlinearity functions in the phase space structure and sub-Poissonianity of even, odd, and Yurke-Stoler nonlinear cat states. The effect of photon addition, which results in a π phase shift at the origin of the Wigner function toward negativity, interestingly enhances the nonclassicality by means of the Wigner function and Mandel parameter. Furthermore, owing to photon addition, we can observe a deformation in the Gaussian shape of the Wigner function, which may be found to be potentially useful in quantum noise reduction. Moreover, the deformation function shows a remarkable role in revealing the nonclassical behavior and can increase the depth and the domain of nonclassicality.

Demonstration of length control for a filter cavity with coherent control sidebands

For broadband quantum noise reduction of gravitational-wave detectors, a frequency-dependent squeezed vacuum field realized using a filter cavity is the most promising technique and will be implemented in Advanced LIGO and Advanced Virgo in the fourth observing run. To obtain the benefit of frequency-dependent squeezing, the length and alignment of the filter cavity with respect to the squeezed vacuum field must be accurately controlled. To this purpose, a new length and alignment control scheme for a filter cavity, using coherent control sidebands, was suggested [Phys. Rev. D 102, 042003 (2020)]. The coherent control sidebands are already used to control the squeezing angle in squeezed vacuum sources for gravitational-wave detectors. As both the squeezed vacuum field and coherent control sidebands have the same mode-matching conditions and almost the same frequency, the length and alignment of the filter cavity with respect to the squeezed vacuum field can be accurately controlled with this scheme. In this paper, we experimentally demonstrate the new control scheme for a filter cavity with coherent control sidebands. In addition to the conventional filter cavity control with the green field, we succeed in controlling the length of a 300-m filter cavity with coherent control sidebands and reduce the filter cavity length noise (rms) from 6.8 to 2.1 pm.

Squeezing microwaves by magnetostriction.

Squeezed light finds many important applications in quantum information science and quantum metrology, and has been produced in a variety of physical systems involving optical non-linear processes. Here, we show how a non-linear magnetostrictive interaction in a ferrimagnet in cavity magnomechanics can be used to reduce quantum noise of the electromagnetic field. We show optimal parameter regimes where a substantial and stationary squeezing of the microwave output field can be achieved. Realization of the scheme is within reach of current technology in cavity electromagnonics and magnomechanics. Our work provides a new and practicable approach for producing squeezed vacuum states of electromagnetic fields, and may find promising applications in quantum information processing and quantum metrology.

PHSOR05 Presentation Time: 12:50 PM: The Effect of Quantum Noise on a Novel Multilateration-Based Brachytherapy Source Localization Approach

<h3>Purpose</h3> Multilateration, a mathematical technique for localizing a point source in 3D based on measurements related to its location, can be adapted to single-source (i.e. high-dose-rate or pulsed-dose-rate) brachytherapy applications using measurement information provided by particle detector camera(s). Multilateration could be used as a safety measure to locate and monitor the source position, or as an enabler of novel applications such as reconstruction of the delivered radiation dose. However, the accuracy of this method is limited by quantum noise, a dominant source of noise in planar images from photon-counting systems. This work studies the impact of quantum noise on the accuracy of multilateration for a variety of source strengths, source positions, and photon-counting camera system setups. <h3>Materials and Methods</h3> The effect of quantum noise on the accuracy of multilateration was examined systematically for a variety of source strengths, source positions, and camera system set-ups. Quantum noise was simulated by sampling from the Poisson distribution at each image pixel, with the distribution means based on the expected image flux per pixel derived from physics principles. Source strength was fixed at 40700 U (10 Ci), and acquisition times varied from 0.03 s, chosen to represent real-time planar image acquisition at 30 frames/sec, to 10 s. Image size varied from 32 × 32 pixels² to 256 × 256 pixels², and pixel size varied from 0.05 × 0.05 mm² to 5 × 5 mm². Source-to-camera distances (SCD) varied from 100 mm to 1000 mm, and off-axis displacement varied from 0 mm to 100 mm. These parameter ranges were used to perform multilateration on simulated single- and dual-camera system acquisitions, with further optimization of the dual-camera systems for camera-to-camera orientation and spacing. To improve consistency, each configuration was simulated using different random number generator seeds for quantum noise generation, and the resulting errors were averaged. <h3>Results</h3> The effect of quantum noise on multilateration accuracy depended on source strength, acquisition time, SCD, off-axis displacement, and camera system set-up. Figure 1 shows the achievable resolution as a function of SCD for acquisition times of 0.03, 0.1, 1, and 10 s, recorded with a single-camera with 256 × 256 pixels² (0.5 × 0.5 mm² pixel size), with errors averaged across the range of off-axis displacements. At large SCDs, simulated multilateration accuracy was approximately a cubic function of SCD, which agrees with the results of error propagation theory applied to this system. At SCDs up to 1000 mm, single-camera systems produced sub-mm precision in some realistic acquisition parameter ranges, and dual-camera systems had greater source positioning accuracy. The improvement due to the addition of a second camera was smaller when the source was close to the central axis of the first camera, and the improvement's magnitude depended on the camera system setup. For systems with camera sizes of 256 × 256 pixels² (0.5 × 0.5 mm² pixel size), the second camera improved the accuracy by about 7% on-axis and about 15% off-axis, averaging over the range of simulated SCDs. There was a tradeoff between reducing quantum noise and decreasing intra-pixel averaging which discouraged very small or very large pixel sizes. <h3>Conclusions</h3> Multilateration has the potential to provide sub-mm precision for source localization in single-source brachytherapy, even with the limits imposed by quantum noise. This technique could be implemented for general safety measures and for applications such as dose reconstruction. We note that this analysis was strictly intended for photon-counting systems, where quantum noise was the dominant source of planar image noise. The results may help evaluate existing cameras and guide future camera system set-up for multilateration applications, a subject of our future study.

ETpathfinder: a cryogenic testbed for interferometric gravitational-wave detectors

The third-generation (3G) of gravitational wave observatories, such as the Einstein Telescope (ET) and Cosmic Explorer, aim for an improvement in sensitivity of at least a factor of ten over a wide frequency range compared to the current advanced detectors. In order to inform the design of the 3G detectors and to develop and qualify their subsystems, dedicated test facilities are required. ETpathfinder prototype uses full interferometer configurations and aims to provide a high sensitivity facility in a similar environment as ET. Along with the interferometry at 1550 nm and silicon test masses, ETpathfinder will focus on cryogenic technologies, lasers and optics at 2090 nm and advanced quantum-noise reduction schemes. This paper analyses the underpinning noise contributions and combines them into full noise budgets of the two initially targeted configurations: (1) operating with 1550 nm laser light and at a temperature of 18 K and (2) operating at 2090 nm wavelength and a temperature of 123 K.

Squeezed States of Light for Future Gravitational Wave Detectors at a Wavelength of 1550nm.

The generation of strongly squeezed vacuum states of light is a key technology for future ground-based gravitational wave detectors (GWDs) to reach sensitivities beyond their quantum noise limit. For some proposed observatory designs, an operating laser wavelength of 1550nm or around 2 μm is required to enable the use of cryogenically cooled silicon test masses for thermal noise reduction. Here, we present for the first time the direct measurement of up to 11.5dB squeezing at 1550nm over the complete detection bandwidth of future ground-based GWDs ranging from 10kHz down to below 1Hz. Furthermore, we directly observe a quantum shot-noise reduction of up to (13.5±0.1) dB at megahertz frequencies. This allows us to derive a precise constraint on the absolute quantum efficiency of the photodiode used for balanced homodyne detection. These results hold important insight regarding the quantum noise reduction efficiency in future GWDs, as well as for quantum information and cryptography, where low decoherence of nonclassical states of light is also of high relevance.

Characterization of different reconstruction techniques on computer-aided system for detection of pulmonary nodules in lung from low-dose CT protocol

In this study, we aim to investigate the effect of different reconstruction techniques on computer-aided system (CAD) pulmonary nodules in low-dose CT. A prospective collection of 380 patients with low-dose chest CT pulmonary nodules was performed. Filtered back projection, quantum noise reduction, 3D adaptive iteration, and cloud iterative techniques were used to reconstruct the original data. The average signal-to-noise ratio (SNR) of each technique was measured. Compared with the contrast-to-noise ratio (CNR), we analyzed the sensitivity and false-positive number of the lung nodules by CAD in each group of techniques. The SNR and CNR are sequentially improved according to the filtered back projection, quantum noise reduction, three-dimensional adaptive iteration, and cloud iterative technique (P < 0.05). The sensitivity increased with the improvement of the objective image quality, while the false positive rate decreases. There are differences in the sensitivity of various nature nodules under different reconstruction techniques (P < 0.05). Although the CAD has good performance in detecting various lung nodules under different reconstruction techniques, there are some differences in energy efficiency under different reconstruction techniques. Therefore, the robustness of CAD still needs to be further solved. Multi-center large sample validation is still required to evaluate the energy efficiency of pulmonary nodule CAD.

10dB Quantum-Enhanced Michelson Interferometer with Balanced Homodyne Detection.

Future generations of gravitational-wave detectors (GWD) are targeting an effective quantum noise reduction of 10dB via the application of squeezed states of light. In the last joint observation run O3, the advanced large-scale GWDs LIGO and Virgo already used the squeezing technology, albeit with a moderate efficiency. Here, we report on the first successful 10dB sensitivity enhancement of a shot-noise limited tabletop Michelson interferometer via squeezed light in the fundamental Gaussian laser mode, where we also implement the balanced homodyne detection scheme that is planned for the third GWD generation. In addition, we achieved a similarly strong quantum noise reduction when the interferometer was operated in higher-order Hermite-Gaussian modes, which are discussed for the GWD thermal noise mitigation. Our results are an important step toward the targeted quantum noise level in future GWDs and, moreover, represent significant progress in the application of nonclassical states in higher-order modes for interferometry, increased spatial resolution, and multichannel sensing.

Thermally controlled optical resonator for vacuum squeezed states separation.

Future gravitational-wave detectors will use frequency-dependent squeezed vacuum states to obtain broadband reduction of quantum noise. Quantum noise is one of the major limitations to the sensitivity of these detectors. Advanced LIGO+, Advanced Virgo+, and KAGRA plan to generate frequency-dependent squeezed states by coupling a frequency-independent squeezed light state with a filter cavity. An alternative technique is under consideration, based on conditional squeezing with quantum entanglement: Einstein-Podolsky-Rosen (EPR) squeezing. In the EPR scheme, two vacuum entangled states, the signal field at ω0 and the idler field at ω0+Δ, must be spatially separated with an optical resonator and sent to two separate homodyne detectors. In this framework, we have designed and tested a solid Fabry-Perot etalon, to be used in an EPR table-top experiment prototype, thermally controlled without the use of a control probe optical beam. This device can also be used in optical experiments where the use of a bright beam to control an optical resonator is not possible, or where a simpler optical device is preferred.

Enhancing the precision limits of interferometric satellite geodesy missions.

Satellite geodesy uses the measurement of the motion of one or more satellites to infer precise information about the Earth’s gravitational field. In this work, we consider the achievable precision limits on such measurements by examining approximate models for the three main noise sources in the measurement process of the current Gravitational Recovery and Climate Experiment (GRACE) Follow-On mission: laser phase noise, accelerometer noise and quantum noise. We show that, through time-delay interferometry, it is possible to remove the laser phase noise from the measurement, allowing for almost three orders of magnitude improvement in the signal-to-noise ratio. Several differential mass satellite formations are presented which can further enhance the signal-to-noise ratio through the removal of accelerometer noise. Finally, techniques from quantum optics have been studied, and found to have great promise for reducing quantum noise in other alternative mission configurations. We model the spectral noise performance using an intuitive 1D model and verify that our proposals have the potential to greatly enhance the performance of near-future satellite geodesy missions.