We present a study of the Rydberg spectrum in 39 K for nS and nD 3/2 series connected to 5 2 P 1/... more We present a study of the Rydberg spectrum in 39 K for nS and nD 3/2 series connected to 5 2 P 1/2 using two-photon spectroscopy based on EIT in a heated vapor cell. We observed some 80 transitions from 5P 1/2 to Rydberg states with principal quantum numbers n ∼ 50 − 90, and determined their transition frequencies and state energies with sub-GHz precision. Our spectroscopy results lay the groundwork for using Rydberg atoms as sensitive microwave photon detectors in searches for dark matter axions in the ∼ 40 − 200 µeV mass range, which is a prime range for future axion searches suggested by theory studies.
Dark photon exclusions for unpolarized dark photons converted from axion measurements in a .mat f... more Dark photon exclusions for unpolarized dark photons converted from axion measurements in a .mat file. Keys for the data are 'RBF_ueV', 'RBF_chi', 'UF_ueV', 'UF_chi', 'HAYSTAC_ueV', 'HAYSTAC_chi', 'ADMX_ueV', 'ADMX_chi', 'CAPP_ueV', and 'CAPP_chi' to obtain exclusions for unpolarized dark photons for each of these experiments. In order to obtain the n% confidence exclusions for the polarized case, multiply the "chi" arrays by 3 then divide by (1-n); for example, to obtain the filled-in exclusions in Figure 1 of the related arxiv manuscript where n=95%, multiply the "chi" arrays by 3/0.05. To use this file format in Python, use a script like the following: <pre>import matplotlib.pyplot as plt from scipy.io import loadmat mat_file = loadmat('haloscope_exclusions_unpolarized.mat') masses_in_ueV = mat_file['HAYSTAC_ueV'] chi_exclusion = mat_file['HAYSTAC_chi']...
We demonstrate optical levitation of SiO_2 spheres with masses ranging from 0.1 to 30 nanograms. ... more We demonstrate optical levitation of SiO_2 spheres with masses ranging from 0.1 to 30 nanograms. In high vacuum, we observe that the measured acceleration sensitivity improves for larger masses and obtain a sensitivity of 0.4 × 10^-6 g/√(Hz) for a 12 ng sphere, more than an order of magnitude better than previously reported for optically levitated masses. In addition, these techniques permit long integration times and a mean acceleration of (-0.7±2.4 [stat] ± 0.2 [syst])× 10^-9 g is measured in 1.4× 10^4 s. Spheres larger than 10 ng are found to lose mass in high vacuum where heating due to absorption of the trapping laser dominates radiative cooling. This absorption constrains the maximum size of spheres that can be levitated and allows a measurement of the absorption of the trapping light for the commercially available spheres tested here. Spheres consisting of material with lower absorption may allow larger objects to be optically levitated in high vacuum.
A single vertical laser beam is used to trap SiO2 and vaterite spheres with diameters ranging fro... more A single vertical laser beam is used to trap SiO2 and vaterite spheres with diameters ranging from 5 to 32um. The center of mass acceleration sensitivity for the SiO2 spheres is as low as 4 × 10−7 g/Hz−1/2 for the largest spheres. This system also allows high-bandwidth modulation of the polarization of the trapping beam, enabling control of the rotation of the microspheres. The maximum rotation speeds exceed a few MHz for both types of spheres, while the damping time exceeds several hours at 2 × 10−7 mbar. This setup can be used to measure forces and torques acting on the microspheres
In a resource constrained future, localised energy generation is likely to be a critical pathway ... more In a resource constrained future, localised energy generation is likely to be a critical pathway to fulfill future energy demand. This paper presents how existing low, medium and high density residential developments with respective dwelling typologies could be retrofitted effectively with renewable energy infrastructure provisions. Localised energy infrastructure in this paper includes provision of photovoltaic modules (PV), solar hot water panels (SHW) and small wind turbines (SWT). This research initially reviews international and national pioneering residential projects applying renewable energy generation techniques. Key approaches and mechanisms are identified considering: residential densities; dwelling typologies; levels of distributed infrastructure provisions; energy outputs and funding, management and implementation methods. Using aerial photographs, GIS and census data, potential for localised energy infrastructure in three low, medium and high density case studies are d...
The dark (or hidden) photon is a massive U(1) gauge boson theorized as a dark force mediator. Dar... more The dark (or hidden) photon is a massive U(1) gauge boson theorized as a dark force mediator. Dark photons can be detected with axion cavity haloscopes by probing for a power excess caused by the dark photon's kinetic mixing with Standard Model photons. Haloscope axion exclusion limits may therefore be converted into competitive dark photon parameter limits via the calculation of a corresponding dark photon to photon coupling factor. This calculation allows for an improvement in sensitivity of around four orders of magnitude relative to other dark photon exclusions and may be attained using existing data. We present how one converts haloscope axion search limits and a summary of relevant experimental parameter from published searches. Finally, we present limits on the kinetic mixing coefficient between dark photons and the Standard Model photons based on existing haloscope axion searches.
Millicharged particles (mCPs) are hypothesized particles possessing an electric charge that is a ... more Millicharged particles (mCPs) are hypothesized particles possessing an electric charge that is a fraction of the charge of the electron. We report a search for mCPs with charges > ∼ 10 −4 e that improves sensitivity to their abundance in matter by roughly two orders of magnitude relative to previous searches. This search is sensitive to such particles over a wide range of masses and charges for which they can form stable bound states with matter, corresponding to a gap in parameter space that is beyond the reach of previous searches from accelerators, colliders, cosmic-ray experiments, and cosmological constraints.
Optical Trapping and Optical Micromanipulation XVI, 2019
A single beam optical trapping system is used to trap and rotate silica and vaterite microspheres... more A single beam optical trapping system is used to trap and rotate silica and vaterite microspheres in high vacuum. Large vaterite microspheres with diameters up to 15 μm are fabricated with multi-stage precipitation reactions and are rotated in the trap through the transfer of spin angular momentum from the photons in the trapping beam to the spheres. An electro-optic modulator is used to vary the polarization of the trapping beam, allowing for control over the rotation with damping times on the order of a day and with rotation frequencies up to 10 MHz for 10 μm diameter spheres. While highly birefringent spheres are successfully trapped at moderate vacuum pressures (⪆10−2 mbar), poor reproducibility is observed for trapping spheres in high vacuum. This trapping behavior is found to be independent of the morphology, birefringence, and monodispercity of the spheres.
In dark matter axion searches, quantum uncertainty manifests as a fundamental noise source, limit... more In dark matter axion searches, quantum uncertainty manifests as a fundamental noise source, limiting the measurement of the quadrature observables used for detection. We use vacuum squeezing to circumvent the quantum limit in a search for a new particle. By preparing a microwave-frequency electromagnetic field in a squeezed state and near-noiselessly reading out only the squeezed quadrature [1], we double the search rate for axions over a mass range favored by recent theoretical projections [2, 3]. We observe no signature of dark matter axions in the combined 16.96-17.12 and 17.14-17.28 µeV/c 2 mass window for axion-photon couplings above gγ = 1.38 × g KSVZ γ , reporting exclusion at the 90% level.
Abstract Urban agriculture in home gardens builds resilience, improves health and food security, ... more Abstract Urban agriculture in home gardens builds resilience, improves health and food security, provides ecological and environmental benefits and connects people back to nature. This research estimated total available productive land and urban agriculture potential of home gardens in ‘general residential’ and ‘low-density residential’ land use zones using a case study of a regional City of Dubbo in Australia. All the plots in six selected categories ranging from 300 m2 to 1200 m2 were spatially analysed using Census and ortho-imagery data and spatial analysis (GIS and remote sensing) methods. 601–750 m2 and 751–900 m2 subdivision categories cover nearly 40% of all residential land use zones in the City of Dubbo. Four productive land utilisation scenarios (90%, 75%, 50% and 25%) were modelled to evaluate the extent to which urban agriculture in home gardens could supply the share of resident households' annual dietary energy demand. The high utilisation scenario could support 84.3%, while the lowest utilisation scenario could meet 23.4% of the residents’ annual dietary vegetable demand. The plots in the 751–900 m2 category, with the highest productive land cover, could produce up to 1443 metric tons of vegetables annually under the lowest utilisation scenario. The potential of home gardens to grow food depends on plot sizes and configuration, onsite land cover patterns and available productive land, morphologies urban/suburban forms, and related social, cultural and economic factors. Appropriate planning policy support and considering a long term planning horizon, grants and incentives, horticulture training and skill development could immensely help in the uptake of urban agriculture in residential land uses. If productive land in millions of residential gardens put to urban agricultural uses, it could work cumulatively as an alternative local food production network.
A circularly polarized laser beam is used to levitate and control the rotation of microspheres in... more A circularly polarized laser beam is used to levitate and control the rotation of microspheres in high vacuum. At low pressure, rotation frequencies as high as 6 MHz are observed for birefringent vaterite spheres, limited by centrifugal stresses. Due to the extremely low damping in high vacuum, controlled optical rotation of amorphous SiO2 spheres is also observed at rates above several MHz. At 10 −7 mbar, a damping time of 6×10 4 s is measured for a 10 µm diameter SiO2 sphere. No additional damping mechanisms are observed above gas damping, indicating that even longer damping times may be possible with operation at lower pressure. The controlled optical rotation of microspheres at MHz frequencies with low damping, including for materials that are not intrinsically birefringent, provides a new tool for performing precision measurements using optically levitated systems.
We demonstrate optical levitation of SiO2 spheres with masses ranging from 0.1 to 30 nanograms. I... more We demonstrate optical levitation of SiO2 spheres with masses ranging from 0.1 to 30 nanograms. In high vacuum, we observe that the measured acceleration sensitivity improves for larger masses and obtain a sensitivity of 0.4 × 10 −6 g/ √ Hz for a 12 ng sphere, more than an order of magnitude better than previously reported for optically levitated masses. In addition, these techniques permit long integration times and a mean acceleration of (−0.7 ± 2.4 [stat] ± 0.2 [syst]) × 10 −9 g is measured in 1.4 × 10 4 s. Spheres larger than 10 ng are found to lose mass in high vacuum where heating due to absorption of the trapping laser dominates radiative cooling. This absorption constrains the maximum size of spheres that can be levitated and allows a measurement of the absorption of the trapping light for the commercially available spheres tested here. Spheres consisting of material with lower absorption may allow larger objects to be optically levitated in high vacuum.
This article gives an overview of the role of the London Foreign Exchange Joint Standing Committe... more This article gives an overview of the role of the London Foreign Exchange Joint Standing Committee, and reviews the work undertaken by the Committee during 2000.
We present a study of the Rydberg spectrum in 39 K for nS and nD 3/2 series connected to 5 2 P 1/... more We present a study of the Rydberg spectrum in 39 K for nS and nD 3/2 series connected to 5 2 P 1/2 using two-photon spectroscopy based on EIT in a heated vapor cell. We observed some 80 transitions from 5P 1/2 to Rydberg states with principal quantum numbers n ∼ 50 − 90, and determined their transition frequencies and state energies with sub-GHz precision. Our spectroscopy results lay the groundwork for using Rydberg atoms as sensitive microwave photon detectors in searches for dark matter axions in the ∼ 40 − 200 µeV mass range, which is a prime range for future axion searches suggested by theory studies.
Dark photon exclusions for unpolarized dark photons converted from axion measurements in a .mat f... more Dark photon exclusions for unpolarized dark photons converted from axion measurements in a .mat file. Keys for the data are 'RBF_ueV', 'RBF_chi', 'UF_ueV', 'UF_chi', 'HAYSTAC_ueV', 'HAYSTAC_chi', 'ADMX_ueV', 'ADMX_chi', 'CAPP_ueV', and 'CAPP_chi' to obtain exclusions for unpolarized dark photons for each of these experiments. In order to obtain the n% confidence exclusions for the polarized case, multiply the "chi" arrays by 3 then divide by (1-n); for example, to obtain the filled-in exclusions in Figure 1 of the related arxiv manuscript where n=95%, multiply the "chi" arrays by 3/0.05. To use this file format in Python, use a script like the following: <pre>import matplotlib.pyplot as plt from scipy.io import loadmat mat_file = loadmat('haloscope_exclusions_unpolarized.mat') masses_in_ueV = mat_file['HAYSTAC_ueV'] chi_exclusion = mat_file['HAYSTAC_chi']...
We demonstrate optical levitation of SiO_2 spheres with masses ranging from 0.1 to 30 nanograms. ... more We demonstrate optical levitation of SiO_2 spheres with masses ranging from 0.1 to 30 nanograms. In high vacuum, we observe that the measured acceleration sensitivity improves for larger masses and obtain a sensitivity of 0.4 × 10^-6 g/√(Hz) for a 12 ng sphere, more than an order of magnitude better than previously reported for optically levitated masses. In addition, these techniques permit long integration times and a mean acceleration of (-0.7±2.4 [stat] ± 0.2 [syst])× 10^-9 g is measured in 1.4× 10^4 s. Spheres larger than 10 ng are found to lose mass in high vacuum where heating due to absorption of the trapping laser dominates radiative cooling. This absorption constrains the maximum size of spheres that can be levitated and allows a measurement of the absorption of the trapping light for the commercially available spheres tested here. Spheres consisting of material with lower absorption may allow larger objects to be optically levitated in high vacuum.
A single vertical laser beam is used to trap SiO2 and vaterite spheres with diameters ranging fro... more A single vertical laser beam is used to trap SiO2 and vaterite spheres with diameters ranging from 5 to 32um. The center of mass acceleration sensitivity for the SiO2 spheres is as low as 4 × 10−7 g/Hz−1/2 for the largest spheres. This system also allows high-bandwidth modulation of the polarization of the trapping beam, enabling control of the rotation of the microspheres. The maximum rotation speeds exceed a few MHz for both types of spheres, while the damping time exceeds several hours at 2 × 10−7 mbar. This setup can be used to measure forces and torques acting on the microspheres
In a resource constrained future, localised energy generation is likely to be a critical pathway ... more In a resource constrained future, localised energy generation is likely to be a critical pathway to fulfill future energy demand. This paper presents how existing low, medium and high density residential developments with respective dwelling typologies could be retrofitted effectively with renewable energy infrastructure provisions. Localised energy infrastructure in this paper includes provision of photovoltaic modules (PV), solar hot water panels (SHW) and small wind turbines (SWT). This research initially reviews international and national pioneering residential projects applying renewable energy generation techniques. Key approaches and mechanisms are identified considering: residential densities; dwelling typologies; levels of distributed infrastructure provisions; energy outputs and funding, management and implementation methods. Using aerial photographs, GIS and census data, potential for localised energy infrastructure in three low, medium and high density case studies are d...
The dark (or hidden) photon is a massive U(1) gauge boson theorized as a dark force mediator. Dar... more The dark (or hidden) photon is a massive U(1) gauge boson theorized as a dark force mediator. Dark photons can be detected with axion cavity haloscopes by probing for a power excess caused by the dark photon's kinetic mixing with Standard Model photons. Haloscope axion exclusion limits may therefore be converted into competitive dark photon parameter limits via the calculation of a corresponding dark photon to photon coupling factor. This calculation allows for an improvement in sensitivity of around four orders of magnitude relative to other dark photon exclusions and may be attained using existing data. We present how one converts haloscope axion search limits and a summary of relevant experimental parameter from published searches. Finally, we present limits on the kinetic mixing coefficient between dark photons and the Standard Model photons based on existing haloscope axion searches.
Millicharged particles (mCPs) are hypothesized particles possessing an electric charge that is a ... more Millicharged particles (mCPs) are hypothesized particles possessing an electric charge that is a fraction of the charge of the electron. We report a search for mCPs with charges > ∼ 10 −4 e that improves sensitivity to their abundance in matter by roughly two orders of magnitude relative to previous searches. This search is sensitive to such particles over a wide range of masses and charges for which they can form stable bound states with matter, corresponding to a gap in parameter space that is beyond the reach of previous searches from accelerators, colliders, cosmic-ray experiments, and cosmological constraints.
Optical Trapping and Optical Micromanipulation XVI, 2019
A single beam optical trapping system is used to trap and rotate silica and vaterite microspheres... more A single beam optical trapping system is used to trap and rotate silica and vaterite microspheres in high vacuum. Large vaterite microspheres with diameters up to 15 μm are fabricated with multi-stage precipitation reactions and are rotated in the trap through the transfer of spin angular momentum from the photons in the trapping beam to the spheres. An electro-optic modulator is used to vary the polarization of the trapping beam, allowing for control over the rotation with damping times on the order of a day and with rotation frequencies up to 10 MHz for 10 μm diameter spheres. While highly birefringent spheres are successfully trapped at moderate vacuum pressures (⪆10−2 mbar), poor reproducibility is observed for trapping spheres in high vacuum. This trapping behavior is found to be independent of the morphology, birefringence, and monodispercity of the spheres.
In dark matter axion searches, quantum uncertainty manifests as a fundamental noise source, limit... more In dark matter axion searches, quantum uncertainty manifests as a fundamental noise source, limiting the measurement of the quadrature observables used for detection. We use vacuum squeezing to circumvent the quantum limit in a search for a new particle. By preparing a microwave-frequency electromagnetic field in a squeezed state and near-noiselessly reading out only the squeezed quadrature [1], we double the search rate for axions over a mass range favored by recent theoretical projections [2, 3]. We observe no signature of dark matter axions in the combined 16.96-17.12 and 17.14-17.28 µeV/c 2 mass window for axion-photon couplings above gγ = 1.38 × g KSVZ γ , reporting exclusion at the 90% level.
Abstract Urban agriculture in home gardens builds resilience, improves health and food security, ... more Abstract Urban agriculture in home gardens builds resilience, improves health and food security, provides ecological and environmental benefits and connects people back to nature. This research estimated total available productive land and urban agriculture potential of home gardens in ‘general residential’ and ‘low-density residential’ land use zones using a case study of a regional City of Dubbo in Australia. All the plots in six selected categories ranging from 300 m2 to 1200 m2 were spatially analysed using Census and ortho-imagery data and spatial analysis (GIS and remote sensing) methods. 601–750 m2 and 751–900 m2 subdivision categories cover nearly 40% of all residential land use zones in the City of Dubbo. Four productive land utilisation scenarios (90%, 75%, 50% and 25%) were modelled to evaluate the extent to which urban agriculture in home gardens could supply the share of resident households' annual dietary energy demand. The high utilisation scenario could support 84.3%, while the lowest utilisation scenario could meet 23.4% of the residents’ annual dietary vegetable demand. The plots in the 751–900 m2 category, with the highest productive land cover, could produce up to 1443 metric tons of vegetables annually under the lowest utilisation scenario. The potential of home gardens to grow food depends on plot sizes and configuration, onsite land cover patterns and available productive land, morphologies urban/suburban forms, and related social, cultural and economic factors. Appropriate planning policy support and considering a long term planning horizon, grants and incentives, horticulture training and skill development could immensely help in the uptake of urban agriculture in residential land uses. If productive land in millions of residential gardens put to urban agricultural uses, it could work cumulatively as an alternative local food production network.
A circularly polarized laser beam is used to levitate and control the rotation of microspheres in... more A circularly polarized laser beam is used to levitate and control the rotation of microspheres in high vacuum. At low pressure, rotation frequencies as high as 6 MHz are observed for birefringent vaterite spheres, limited by centrifugal stresses. Due to the extremely low damping in high vacuum, controlled optical rotation of amorphous SiO2 spheres is also observed at rates above several MHz. At 10 −7 mbar, a damping time of 6×10 4 s is measured for a 10 µm diameter SiO2 sphere. No additional damping mechanisms are observed above gas damping, indicating that even longer damping times may be possible with operation at lower pressure. The controlled optical rotation of microspheres at MHz frequencies with low damping, including for materials that are not intrinsically birefringent, provides a new tool for performing precision measurements using optically levitated systems.
We demonstrate optical levitation of SiO2 spheres with masses ranging from 0.1 to 30 nanograms. I... more We demonstrate optical levitation of SiO2 spheres with masses ranging from 0.1 to 30 nanograms. In high vacuum, we observe that the measured acceleration sensitivity improves for larger masses and obtain a sensitivity of 0.4 × 10 −6 g/ √ Hz for a 12 ng sphere, more than an order of magnitude better than previously reported for optically levitated masses. In addition, these techniques permit long integration times and a mean acceleration of (−0.7 ± 2.4 [stat] ± 0.2 [syst]) × 10 −9 g is measured in 1.4 × 10 4 s. Spheres larger than 10 ng are found to lose mass in high vacuum where heating due to absorption of the trapping laser dominates radiative cooling. This absorption constrains the maximum size of spheres that can be levitated and allows a measurement of the absorption of the trapping light for the commercially available spheres tested here. Spheres consisting of material with lower absorption may allow larger objects to be optically levitated in high vacuum.
This article gives an overview of the role of the London Foreign Exchange Joint Standing Committe... more This article gives an overview of the role of the London Foreign Exchange Joint Standing Committee, and reviews the work undertaken by the Committee during 2000.
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Papers by sumita Ghosh