arXiv subjects

Hamim Mahmud Rivy

Publications and source records attributed to Hamim Mahmud Rivy.

9 recordsLinked to original sources

arXiv2026

Rapid multi-mode trapped-ion laser cooling in a phase-stable standing wave

Laser cooling is fundamental to quantum computing and metrology using atomic systems. Precise control often requires cooling atoms' motional degrees of freedom to the quantum ground state, imposing operation time and architectural limitations particularly in large-scale systems. Here we demonstrate how the integrated optical control of interest for scaling trapped-ion systems additionally enables laser cooling that bypasses limitations of conventional schemes. Leveraging multi-channel integrated delivery of ultraviolet to infrared wavelengths for calcium ion control including in passively phase-stable ultraviolet standing waves (SWs), we experimentally verify a long-standing prediction by Cirac et al., realizing Doppler cooling to below the conventional Doppler limit at a SW node. We also present the first realization of ground-state cooling via electromagnetically induced transparency (EIT) using a ``probe" beam delivered as a SW with atoms positioned at a node, predicted to enable multi-mode sub-recoil-limit laser cooling. We demonstrate cooling of motional modes spanning an approximately 5 MHz bandwidth from the Doppler temperature to near the ground state within 150~\textmu s, reaching $\bar n \approx 0.05$ phonon number occupancies for the target mode. Direct evaluation against the comparable running-wave (RW) scheme shows the SW implementation's simultaneous advantage in cooling rate, motional mode bandwidth, and final phonon number, as previously theoretically predicted. Our work leverages capabilities enabled by integrated optical delivery to demonstrate fast cooling of multiple modes to the quantum ground state, and more broadly how scalable approaches to optical control can enable enhancements in fundamental atomic functionalities.

physics.atom-ph↗

arXiv2025

HfO$_2$-based platform for high-index-contrast visible/UV integrated photonics

Ultraviolet and visible integrated photonics are enabling for applications in quantum information, sensing, and spectroscopy, among others. Few materials support low-loss photonics into the UV, and the relatively low refractive index of known depositable materials limits the achievable functionality. Here we present a high-index integrated photonics platform based on HfO$_2$ and Al$_2$O$_3$ composites deposited via Atomic Layer Deposition (ALD) with low loss in the visible and near-UV. We show that Al$_2$O$_3$ incorporation dramatically decreases bulk loss compared to pure HfO$_2$, consistent with inhibited crystallization due to the admixture of Al$_2$O$_3$. Composites exhibit refractive index $n$ following the average of that of HfO$_2$ and Al$_2$O$_3$, weighted by the HfO$_2$ fractional composition $x$. At $λ=375$ nm, composites with $x=0.67$ exhibit $n=2.08$ preserving most of HfO$_2$'s significantly higher index, and $3.8(7) $ dB/cm material loss. We further present fully etched and cladded waveguides, grating couplers, and ring resonators, realizing single-mode waveguide loss of $0.25(2)$ dB/cm inferred from resonators of 2.6 million intrinsic quality factor at $λ=729$ nm, $2.6(2)$ dB/cm at $λ=405$ nm, and $7.7(6)$ dB/cm at $λ=375$ nm. We measure the composite's thermo-optic coefficient (TOC) to be $2.44(3) \times 10^{-5}$ RIU/$^\circ$C near $λ=397$ nm. This work establishes (HfO$_2$)$_x$(Al$_2$O$_3$)$_{1-x}$ composites as a platform amenable to integration for low-loss, high-index photonics spanning the UV to NIR.

physics.optics↗

arXiv2024

Atomic fluorescence collection into planar photonic devices

Fluorescence collection from individual emitters plays a key role in state detection and remote entanglement generation, fundamental functionalities in many quantum platforms. Planar photonics have been demonstrated for robust and scalable addressing of trapped-ion systems, motivating consideration of similar elements for the complementary challenge of photon collection. Here, using an argument from the reciprocity principle, we show that far-field photon collection efficiency can be simply expressed in terms of the fields associated with the collection optic at the emitter position alone. We calculate collection efficiencies into ideal paraxial and fully vectorial focused Gaussian modes parameterized in terms of focal waist, and further quantify the modest enhancements possible with more general beam profiles, establishing design requirements for efficient collection. Towards practical implementation, we design, fabricate, and characterize two diffractive collection elements operating at $λ=397$ nm; a forward emitting design is predicted to offer 0.25% collection efficiency into a single waveguide mode, while a more efficient reverse-emitting design offers $1.14\%$ collection efficiency, albeit with more demanding fabrication requirements. Close agreement between simulated and measured emission for both designs indicates practicality of these collection efficiencies, and we indicate avenues to improved devices approaching the limits predicted for ideal beams. We point out a particularly simple integrated waveguide configuration for polarization-based remote entanglement generation enabled by integrated collection.

physics.optics↗

arXiv2023

Single atom in a superoscillatory optical trap

Optical tweezers have become essential tools to manipulate atoms or molecules at a single particle level. However, using standard diffracted-limited optical systems, the transverse size of the trap is lower bounded by the optical wavelength, limiting the application range of optical tweezers. Here we report trapping of single ultracold atom in an optical trap that can be continuously tuned from a standard Airy focus to a subwavelength hotspot smaller than the usual Abbe's diffraction limit. The hotspot was generated using the effect of superoscillations, by the precise interference of multiple free-space coherent waves. We argue that superoscillatory trapping and continuous potential tuning offer not only a way to generate compact and tenable ensembles of trapped atoms for quantum simulators but will also be useful in single molecule quantum chemistry and the study of cooperative atom-photon interaction within subwavelength arrays of quantum emitters.

physics.atom-ph↗

arXiv2020

On the Modified Einstein-Laub and Modified Chu Optical Force Formulations

In several experiments involving material background, it has been observed that the Chu, Einstein-Laub and Ampere formulations of optical force lead to either different optical forces or wrong total optical force. In order to identify the exact reason behind such significant disagreements, we investigate the optical force in a number of tractor beam and lateral force experiments. We demonstrate that the modified Einstein-Laub or modified Chu formulations, obtained from two mathematical consistency conditions of force calculation, give the time-averaged force that agrees with the experiments. We consider both the chiral and achiral objects embedded in complex material backgrounds. Though the distinct formulations of optical force have been made mathematically equivalent in this work; the aspect of physical consistency of these distinct optical force formulations have also been investigated. It is known that the theory of Minkowski suggests zero bulk force inside a lossless object for which we still do not have any experimental verification. In contrast, both modified Einstein-Laub and modified Chu force formulations suggest non-zero bulk force inside a lossless object. Hence, for a future resolution of this discrepancy, we also suggest a possible experiment to investigate the bulk force and to check the validity of these distinct formulations.

physics.optics↗

arXiv2018

Chiral standing waves and its trapping force on chiral particles

Up to now, in the literature of optical manipulation, optical force due to chirality usually coexists with the non-chiral force and the chiral force usually takes a very small portion of the total force. In this work, we investigate a case where the optical force exerted on an object is purely due to the chirality while there is zero force on non-chiral object. We find that a trapping force arises on chiral particles when it is placed in a field consisted of two orthogonally polarized counter-propagating plane waves. We have revealed the underlying physics of this force by modeling the particle as a chiral diploe and analytically study the optical force. We find besides chirality; the trapping force is also closely related to the dual electric-magnetic symmetry of field and dual asymmetry of material. We also demonstrate that the proposed idea is not restricted to dipolar chiral objects only. Chiral Mie objects can also be trapped based on the technique proposed in this article. Notably, such chiral trapping forces have been found robust by varying several parameters throughout the investigation. This trapping force may find applications in identifying object's chirality and the selective trapping of chiral objects.

physics.optics↗

arXiv2018

Determining the Increase or Decrease of Photon Momentum: Dielectric or Plasmonic Mie Object at Air-Liquid Interface

Though the interfacial tractor beam experiment supports the increase of photon momentum (i.e., Minkowski momentum), it is still a matter of investigation whether, inside matter, the photon momentum always increases. Considering the inhomogeneous or heterogeneous background, we have demonstrated that if the background and the half-immersed object are both non-absorbing, the transferred photon momentum to the object can be considered as the one of Minkowski exactly at the interface. In contrast, the presence of loss inside matter, either in the half-immersed object (i.e., plasmonic or lossy dielectric) or in the background, changes the whole situation. For such cases, our several demonstrations and proposed thought experiments have strongly supported the decrease of photon momentum instead of the usual perception of its increase. Although almost all the major radiation pressure experiments have so far supported the linear increase of photon momentum, our proposed simple experimental set-ups may introduce a novel way to observe and verify the exactly opposite proposal: the Abraham momentum of photon. Finally, as an interesting sidewalk, based on several parameters, a machine learning based system has been developed to predict the transferred momentum of photon within a very short time avoiding time-consuming full simulation.

physics.optics↗

arXiv2018

A General Way to Control the Reversal of Near Field Optical Binding Force between Plasmonic or Dielectric Dimers

Controlling the near field optical binding force can be a key factor for particle clustering, aggregation and localized surface plasmon sensors. So far there is no generic way to reverse the near field optical binding force for plasmonic or dielectric nano-dimers of distinct shapes (cube, cylinder, ring, sphere). In this article, for both plasmonic and dielectric objects, we have demonstrated a general way to control the reversal of near field binding force for different shaped dimer sets. The force reversal is achieved by simple breaking of symmetry, considering the nano particles are half or less than half immersed in an inhomogeneous dielectric background, i.e. at air-water interface. Such reversals have been explained based on Fano resonance, interference fields, unusual behavior of optical Lorentz force and image charge theory. However, if the dimer set is placed over a dielectric interface or fully inside a homogeneous medium, the sign of binding force does not reverse. Our proposed configuration provides a generic mechanism of archiving binding force reversal for both plasmonic and dielectric objects, which can be verified by very simple experimental set-up.

physics.optics↗

arXiv2017

Spherical Plasmonic Heterodimers: Reversal of Optical Binding Force as the Effect of Symmetry Breaking

The stimulating connection between the reversal of near field plasmonic binding force and the role of symmetry breaking has not been investigated in detail in literature. As both bonding and anti-bonding modes are present in the visible spectra of well-known spherical plasmonic heterodimer sets, binding force reversal is commonly believed to occur for all such heterodimers. But our work suggests a very different proposal. We demonstrate that for the symmetry broken heterodimer configurations: reversal of lateral (for on-axis heterodimers) and longitudinal (for off-axis heterodimers: end-fire and nearly end-fire configurations) near field binding force follow fully distinct mechanisms; i.e. later one on relative orientation and constructive dipole-quadrupole resonance but the former one on light polarization and the induced electric resonance. Interestingly, the reversal of longitudinal near field binding force can be easily controlled just by changing the direction of light propagation or just their relative orientation. Though it is commonly believed that plasmonic forces mostly arise from the surface force and Fano resonance can be a promising way to achieve binding force reversal; our study based on Lorentz force dynamics suggests notably opposite proposals (for both instances) for the case of plasmonic spherical heterodimers. Observations of this article can be very useful for improved sensors, particle clustering and aggregation.

physics.optics↗