Exotic Spin-dependent Energy-level Shift Noise Induced by Thermal Motion

Searching for exotic spin-dependent interactions that beyond the standard model has been of interest for past decades and is crucial for unraveling the mysteries of the universe. Previous laboratory searches primarily focus on searching for either static or modulated energy-level shifts caused by exotic spin-dependent interactions. Here, we introduce a theoretical model based on thermal motion of particles, providing another efficient way to search for exotic spin-dependent interactions. The theoretical model indicates that as the exotic spin-dependent interactions are related with the relative displacements and velocities of atoms, atoms undergoing thermal motion would experience a fluctuating energy-level shift induced by the exotic interactions. Moreover, the resulting exotic energy-level shift noise could be sensed by high-sensitivity instruments. By using the model and taking the high-sensitivity atomic magnetometer as an example, we set the most stringent laboratory experiment constraints on eight different kinds of exotic spin- and velocity-dependent interactions, with five of which at the force range below 1 cm have not been covered previously. Furthermore, this theoretical model can be easily applied in other fields of quantum sensing, such as atomic clocks, atom interferometers and NV-diamond sensors, to further improve the laboratory constraints on exotic spin-dependent interactions

Ultimate parameters of an all-optical MX resonance in Cs in ultra-weak magnetic field

We present the results of studying the parameters of the magnetic MX resonance in an all-optical sensor built according to the two-beam Bell-Bloom scheme in nonzero ultra-weak magnetic fields in which the effects of spin-exchange broadening suppression are partially manifested. We report on the features of the resonance under these conditions. We also optimize the resonance parameters to achieve maximum sensitivity in magnetoencephalographic sensors. We demonstrate an improvement in the ultimate achievable sensitivity of an all-optical MX sensor by a factor of four or more, which in our experiment corresponds to a decrease from 13 to 3 fT/Hz1/2 in a volume of 0.13 cm3. We also report the effect of incomplete suppression of spin-exchange broadening under conditions of strong transverse modulated optical pumping, and propose a semi-empirical model to describe it

10-Hertz quantum light source generation on the cesium D2 line using single photon modulation

Generation of quantum light source is a promising technique to overcome the standard quantum limit in precision measurement. Here, we demonstrate an experimental generation of quadrature squeezing resonating on the cesium D2 line down to 10 Hz for the first time. The maximum squeezing in audio frequency band is 5.57 dB. Moreover, we have presented a single-photon modulation locking to control the squeezing angle, while effectively suppressing the influence of laser noise on low-frequency squeezing. The whole system operates steadily for hours. The generated low-frequency quantum light source can be applied in quantum metrology,light-matter interaction investigation and quantum memory in the audio frequency band and even below

Squeezed-ligh-enhanced magnetometry in a high density atomic vapor

(English) This thesis describes experiments that employ squeezed light to improve the performance of a sensitive optically-pumped magnetometer (OPM). The squeezed light source employs parametric amplification of vacuum fluctuations to produce squeezed vacuum and polarization-squeezed light tunable around the Rb D1 line. The OPM employs Bell-Bloom optical pumping of a high density vapor (with atom number density 10^{13}) and paramagnetic Faraday rotation, also on the Rb D1 line. The setup allows convenient switching from probing with laser light to probing with polarization-squeezed light, to study the use of the latter in atomic magnetometry. The magnetometer shows sub-pT/Hz^{1/2} sensitivity, limited by quantum noise; spin projection noise at low frequencies (<100Hz) and photon shot noise at high frequencies. Probing with polarization squeezed light suppresses the photon shot noise by 2dB, limited by the available squeezing and optical losses in passing through the vapor. This shot-noise suppression improves the high-frequency sensitivity and increases the measurement bandwidth, with no observed loss of sensitivity at any frequency. This result confirms experimentally the expected evasion of measurement back-action noise in the Bell-Bloom magnetometer. The thesis also develops a physical model to explain the observed spin dynamics of the Bell-Bloom magnetometer. The model describes the combined spin and optical polarization dynamics using Bloch equations with stochastic drive and detection noise terms. A perturbative approach and Fourier methods are then used to obtain analytic expressions for the magnetometer's frequency response, spin projection noise and photon shot noise. The role of measurement back-action emerges from a study of this model. As polarization squeezing reduces optical noise in the detected Stokes parameter, the accompanying ellipticity anti-squeezing is shunted into the unmeasured spin component. The thesis also reports a study of squeezed-light-enhanced magnetometry at a range of atomic densities, from 2.18 10^{12} atoms/cm3 to 1.13 10^{13} atoms/cm3 . Operating with fixed conditions of optical pumping, the signal amplitude, instrument noise spectrum and magnetic resonance width are measured as a function of atomic number density, for both laser- and squeezed-light probing. The equivalent magnetic noise spectra are then calculated. In the photon-shot-noise-limited portion of the spectrum, the squeezed light probing improves the magnetometer's sensitivity and measurement bandwidth for the full range of atomic density values. In particular, the laser-probed magnetometer shows a sensitivity optimum at n ~ 6 10 ^{12} atoms/cm3, and the squeezed-light-probed magnetometer surpasses this sensitivity. The thesis concludes with a discussion of the potential of stronger optical squeezing to enhance the instrument's sensitivity in different portions of the spectrum. Using the theory model we estimate the enhancement of the equivalent magnetic noise spectrum for 2 dB , 5.6 dB and perfect squeezing (zero noise in the detected polarization component) at the input to the atomic medium.(Català) Aqueta tesi descriu la millora d’un magnetòmetre de bombeig òptic (OPM) mitjançant l’ús d’estats de llum amb incertesa comprimida (squeezed states). S’usa amplificació paramètrica per a comprimir la incertesa de la font de llum. En concret, es comprimeix la incertesa de l’estat de buit quàntic, com també de la polarització òptica, amb la possibilitar d’ajustar la longitud d’ona al voltant de la transició atòmica D1 de 87Rb. L’OPM usa bombeig òptic Bell-Bloom de vapors d’alta densitat (amb densitats atòmiques properes a 1013) i rotació de Faraday, també al voltant de la transició atòmica D1 de 87Rb. L’aparell experimental permet canviar de mostreig amb llum coherent làser a mostreig amb llum de polarització comprimida, amb la finalitat d’avaluar el seu impacte en la sensitivitat del magnetòmetre. El magnetòmetre té una sensitivitat de sub-pT{ ?Hz , principalment limitada per soroll quàntic; soroll de projecció de spin a baixes freqüències (À 100 Hz) i soroll de quantització fotònica a altes freqüències. L’ús d’estats de llum amb polarització comprimida permet reduir el soroll fotònic en „ 2 dB, limitat per la compressió disponible i les pèrdues en travessar el vapor atòmic. La supressió del soroll fotònic augmenta l’amplada de banda del sistema amb l’avantatge de no perdre sensitivitat a cap banda de freqüència. Els resultats experimentals confirmen l’esperada supressió de retroalimentació de soroll en magnetòmetres de Bell-Bloom. La tesi també estudia el model teòric darrere les dinàmiques de spin en un magnetòmetre de tipus Bell-Bloom. El model descriu la combinació de les dinàmiques de spin i de la polarització òptica mitjançant equacions de Bloch forcades estocàsticament i amb termes de soroll de detecció. Es treballa en el límit pertorbatiu on mitjançant mètodes de Fourier s’obtenen expressions analítiques de la resposta en freqüència del magnetòmetre, dels sorolls de projecció de spin i del soroll de quantització fotònica. El rol de la retroalimentació de soroll també s’extrau d’aquest model. En concret, s’observa que la compressió en polarització redueix el soroll en els paràmetres de Stokes detectats, mentre els paràmetres de spin no mesurats experimenten una expansió de la seva incertesa (anti-squeezing). La tesi estudia magnetòmetres òptics de llum amb incertesa comprimida per a densitats entre 2.18 ˆ 1012 atoms{cm3 i 1.13 ˆ 1013 atoms{cm3. Es mesuren l’amplitud de senyal, l’espectre de soroll i l’amplada de la ressonància magnètica en funció de la densitat atòmica, per a un bombeig òptic constant i per a ambdós tipus de mostreig òptic (llum coherent i llum de polarització comprimida). A continuació, es calculen els espectres de soroll equivalents. En la part d’espectre on domina el soroll de quantització fotònica, s’observa que l’ús de llum de polarització comprimida millora la sensitivitat del magnetòmetre al llarg de tot el rang de densitats atòmics. En concret, la sensitivitat del magnetòmetre amb mostreig coherent és òptima per a n « 6ˆ1012 atoms{cm3 i es demostra una millora amb l’ús de mostreig amb llum comprimida. Es conclou amb una discussió sobre l’efecte de compressions més severes en la sensitivitat del magnetòmetre. Mitjançant el model teòric s’estima la millora en la sensitivitat per a compressions de 2 dB, 5.6 dB i “compressió perfecta” a l’entrada del medi atòmicPostprint (published version

Gravitational wave detection with optical lattice atomic clocks

We propose a space-based gravitational wave (GW) detector consisting of two spatially separated, drag-free satellites sharing ultrastable optical laser light over a single baseline. Each satellite contains an optical lattice atomic clock, which serves as a sensitive, narrowband detector of the local frequency of the shared laser light. A synchronized two-clock comparison between the satellites will be sensitive to the effective Doppler shifts induced by incident GWs at a level competitive with other proposed space-based GW detectors, while providing complementary features. The detected signal is a differential frequency shift of the shared laser light due to the relative velocity of the satellites, and the detection window can be tuned through the control sequence applied to the atoms’ internal states. This scheme enables the detection of GWs from continuous, spectrally narrow sources, such as compact binary inspirals, with frequencies ranging fromPhysic

Optomechanics with a hybrid carbon nanotube resonator

© 2018 The Author(s). In just 20 years of history, the field of optomechanics has achieved impressive progress, stepping into the quantum regime just 5 years ago. Such remarkable advance relies on the technological revolution of nano-optomechanical systems, whose sensitivity towards thermal decoherence is strongly limited due to their ultra-low mass. Here we report a hybrid approach pushing nano-optomechanics to even lower scales. The concept relies on synthesising an efficient optical scatterer at the tip of singly clamped carbon nanotube resonators. We demonstrate high signal-to-noise motion readout and record force sensitivity, two orders of magnitude below the state of the art. Our work opens the perspective to extend quantum experiments and applications at room temperature

Photodetectors

In this book some recent advances in development of photodetectors and photodetection systems for specific applications are included. In the first section of the book nine different types of photodetectors and their characteristics are presented. Next, some theoretical aspects and simulations are discussed. The last eight chapters are devoted to the development of photodetection systems for imaging, particle size analysis, transfers of time, measurement of vibrations, magnetic field, polarization of light, and particle energy. The book is addressed to students, engineers, and researchers working in the field of photonics and advanced technologies

Error-corrected quantum metrology

Quantum metrology, which studies parameter estimation in quantum systems, has many applications in science and technology ranging from frequency spectroscopy to gravitational wave detection. Quantum mechanics imposes a fundamental limit on the estimation precision, called the Heisenberg limit (HL), which bears a quadratic enhancement over the standard quantum limit (SQL) determined by classical statistics. The HL is achievable in ideal quantum devices, but is not always achievable in presence of noise. Quantum error correction (QEC), as a standard tool in quantum information science to combat the effect of noise, was considered as a candidate to enhance quantum metrology in noisy environment. This thesis studies metrological limits in noisy quantum systems and proposes QEC protocols to achieve these limits. First, we consider Hamiltonian estimation under Markovian noise and obtain a necessary and sufficient condition called the ``Hamiltonian-not-in-Lindblad-span\u27\u27 condition to achieve the HL. When it holds, we provide ancilla-assisted QEC protocols achieving the HL; when it fails, the SQL is inevitable even using arbitrary quantum controls, but approximate QEC protocols can achieve the optimal SQL coefficient. We generalize the results to parameter estimation in quantum channels, where we obtain the ``Hamiltonian-not-in-Kraus-span\u27\u27 condition and find explicit formulas for asymptotic estimation precision by showing attainability of previously established bounds using QEC protocols. All QEC protocols are optimized via semidefinite programming. Finally, we show that reversely, metrological bounds also restrict the performance of error-correcting codes by deriving a powerful bound in covariant QEC

Magnetic DNA detection sensor for point-of-care diagnostics

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University LondonThis thesis focuses on inductive base sensor design at MHz range frequency. The background theory, design, experiments and results for a new magnetic particles sensor is presented. A new magnetic sensor based on a planar coil was investigated for DNA pathogen detection. Change in inductance of the planar coil due to the presence of magnetic particles with varying mass was measured. The experimental set-up consisted of different sized planar coil with associated electronics for inductance measurements. The best sensor performance was accomplished using two different inductors while oscillating at frequencies 2.4MHz using 9.5μH inductor and 7.2MHz with 85μH inductor. The sensor has very large signal to noise ratio (580×103), while the average amount of frequency drift was 0.58. This sensor was tested with various types of magnetic particles. In addition, iron-oxide nanoparticles were synthesized through water in oil microemulsion method and with an average size of 25nm. The best sensitivity achieved for detection of 50μg iron-oxide particles was with the bead size of 10nm. 81Hz frequency shift was attained in regard to that amount of particles. This research shows that increasing the resonance frequency to 7.2MHz can cause the larger output signal difference (frequency shift) in the presence of magnetic particles; however, the sensor stability is the most important factor for determining the detection resolution and sensitivity. The sensitivity is better if the sensor can detect smaller amount of magnetic sample. The results of this research demonstrate that while the sample consists of smaller size particles, the sensor can detect the lower amount of sample. This is due to the heating effect of nanoparticles. On the other hand the sample distance from the sensor has a major impact on the sensitivity too; the shorter the distance, the higher the sensitivity. This technique can potentially be extended to detect several different types of bacterial pathogens and can be modified for multiplex quantitative detection. This sensing technique will be incorporated into a handheld, disposable microfluidic chip for point-of-care diagnostics for sexually transmitted diseases. Key words: Point of care diagnostics, Magnetic particle Detection, Molecular detection, Inductive sensin