arXiv subjects

Naresh Sharma

Publications and source records attributed to Naresh Sharma.

At least 19 recordsLinked to original sources

arXiv2026

Luminosity-Dependent Variations in the Secondary Maximum of Type Ia Supernovae and Their Connection to Host Galaxy Morphology

Type Ia supernovae (SNe Ia) are considered standardizable candles and are therefore important probes of the universe's expansion history and cosmic distances. In comparison to the optical and IR photometric observations, NIR light curves of SNe Ia are more uniform and are less affected by dust extinction; hence, they can provide more precise distance estimates. This study examines the relationship between the luminosity-dependent behavior of the NIR secondary maximum ($t_2$) and the decline rate parameter ($\Delta m_{15}$) in the B Band. We analyzed 54 SNe Ia using linear, piecewise linear regression, and non-linear models along with non-parametric statistical techniques to examine the correlation between $t_2$ and $\Delta m_{15}$. Our results show that the secondary maximum timing varies among SNe Ia but exhibits a luminosity-dependent structure, with significant differences between SNe hosted in late and early-type galaxies. Two separate groups belonging to different host morphologies have been identified through our analysis, one containing brighter SNe and the other containing fainter SNe. These findings have important implications for improving the calibration of SNe Ia for cosmological applications.

astro-ph.CO↗

arXiv2025

Heterogeneous integration of silicon nitride and amorphous silicon carbide photonics

Amorphous silicon carbide (a-SiC) has emerged as a compelling candidate for applications in integrated photonics, known for its high refractive index, high optical quality, high thermo-optic coefficient, and strong third-order nonlinearities. Furthermore, a-SiC can be easily deposited via CMOS-compatible chemical vapor deposition (CVD) techniques, allowing for precise thickness control and adjustable material properties on arbitrary substrates. Silicon nitride (SiN) is an industrial well-established and well-matured platform, which exhibits ultra-low propagation loss, but it is suboptimal for high-density reconfigurable photonics due to the large minimum bending radius and constrained tunability. In this work, we monolithically combine a-SiC with SiN photonics, leveraging the merits of both platforms, and achieve the a-SiC/SiN heterogeneous integration with an on-chip interconnection loss of 0.32$\pm$0.10 dB, and integration density increment exceeding 4,444-fold. By implementing active devices on a-SiC, we achieve 27 times higher thermo-optic tuning efficiency, with respect to the SiN photonic platform. In addition, the a-SiC/SiN platform gives the flexibility to choose the optimal fiber-to-chip coupling strategy depending on the interfacing platform, with efficient side-coupling on SiN and grating-coupling on a-SiC platform. The proposed a-SiC/SiN photonic platform can foster versatile applications in programmable and quantum photonics, nonlinear optics, and beyond.

physics.optics↗

arXiv2024

How accurate are current $^{56}$Ni mass estimates in Type Ia Supernovae?

The diversity of type Ia supernovae (SNe Ia) has become increasingly apparent with the rapid growth in observational data. Understanding the explosion mechanism of SNe Ia is crucial for their cosmological calibration and for advancing our knowledge of stellar physics. The estimation of $^{56}$Ni mass produced in these events is key to elucidating their explosion mechanism. This study compares two methods of $^{56}$Ni mass estimation. We first examine the relationship between peak luminosity and the second maximum in near-infrared (NIR) bands using observations of 18 nearby SNe Ia. Based on this relationship, we estimate the Ni mass for a set of nine well-observed SNe Ia using the Arnett rule. Additionally, we estimate the $^{56}$Ni mass using bolometric light curves of these SNe through energy conservation arguments. A comparison of these two estimation methods using Student's t-test reveals no statistically significant differences between the estimates. This finding suggests that both methods provide robust estimates of Ni mass in SNe Ia.

astro-ph.HE↗

arXiv2024

Heterogeneous integration of amorphous silicon carbide on thin film lithium niobate

In the past decade, lithium niobate (LiNbO3 or LN) photonics, thanks to its heat-free and fast electro-optical modulation, second-order non-linearities and low loss, has been extensively investigated. Despite numerous demonstrations of high-performance LN photonics, processing lithium niobate remains challenging and suffers from incompatibilities with standard complementary metal-oxide semiconductor (CMOS) fabrication lines, limiting its scalability. Silicon carbide (SiC) is an emerging material platform with a high refractive index, a large non-linear Kerr coefficient, and a promising candidate for heterogeneous integration with LN photonics. Current approaches of SiC/LN integration require transfer-bonding techniques, which are time-consuming, expensive, and lack precision in layer thickness. Here we show that amorphous silicon carbide (a-SiC), deposited using inductively coupled plasma enhanced chemical vapor deposition (ICPCVD) at low temperatures (< 165 C), can be conveniently integrated with LiNbO3 and processed to form high-performance photonics. Most importantly, the fabrication only involves a standard, silicon-compatible, reactive ion etching step and leaves the LiNbO3 intact, hence its compatibility with standard foundry processes. As a proof-of-principle, we fabricated waveguides and ring resonators on the developed a-SiC/LN platform and achieved intrinsic quality factors higher than 106,000 and resonance electro-optic tunability of 3.4 pm/V with 3 mm tuning length. We showcase the possibility of dense integration by fabricating and testing ring resonators with 40um radius without a noticeable loss penalty. Our platform offers a CMOS-compatible and scalable approach for implementation of future fast electro-optic modulators and reconfigurable photonic circuits as well as nonlinear processes which can benefit from involving both second and third-order nonlinearities.

physics.optics↗

arXiv2024

Magic silicon dioxide for widely tunable integrated photonics

Integrated photonic circuits have transformed data communication, biosensing, and light detection and ranging, and hold wide-ranging potential for optical computing, optical imaging and signal processing. These applications often require tunable and reconfigurable photonic components, most commonly accomplished through the thermo-optic effect. However, the resulting tuning window is limited for standard optical materials such as silicon dioxide and silicon nitride. Most importantly, bidirectional thermal tuning on a single platform has not been realized. For the first time, we show that by tuning and optimizing the deposition conditions in inductively-coupled plasma chemical vapor deposition (ICPCVD) of silicon dioxide, this material can be used to deterministically tune the thermo-optic properties of optical devices without introducing significant losses. We demonstrate that we can deterministically integrate positive and negative wavelength shifts on a single chip, validated on amorphous silicon carbide (a-SiC), silicon nitride (SiN) and silicon-on-insulator (SOI) platforms. We observe up to a 10-fold improvement of the thermo-optic tunability and, in addition, demonstrate athermal ring resonators with shifts as low as 1.5 pm/{\deg}C. This enables the fabrication of a novel tunable coupled ring optical waveguide (CROW) requiring only a single heater. In addition, the low-temperature deposition of our silicon dioxide cladding can be combined with lift-off to isolate the optical devices resulting in a decrease in thermal crosstalk by at least two orders of magnitude. Our method paves the way for novel photonic architectures incorporating bidirectional thermo-optic tunability.

physics.optics↗

arXiv2023

Real-Time Measurements of Photonic Microchips with Femtometer-Scale Spectral Precision and Ultra-High Sensitivity

Photonic integrated circuits (PICs) are enabling major breakthroughs in a number of areas, including quantum computing, neuromorphic processors, wearable devices, and more. Nevertheless, existing PIC measurement methods lack the spectral precision, speed, and sensitivity required for refining current applications and exploring new frontiers such as point-of-care or wearable biosensors. Here, we present the Sweeping Optical Frequency Mixing Method (SOHO), surpassing traditional PIC measurement methods with real-time operation, 30 dB higher sensitivity, and over 100 times better spectral resolution. Leveraging the frequency mixing process with a sweeping laser and custom control software, SOHO excels in simplicity, eliminating the need for advanced optical components and additional calibration procedures. We showcase its superior performance on ultrahigh-quality factor (Q) fiber-loop resonators (Q = 46M) as well as microresonators realized on a new optical waveguide platform. An experimental spectral resolution of 19.1 femtometers is demonstrated using an 85-meter-long unbalanced fiber Mach Zehnder Interferometer, constrained by noise resulting from the extended fiber length, while the theoretical resolution is calculated to be 6.2 femtometers, limited by the linewidth of the reference laser. With its excellent performance metrics, SOHO has the potential to become a vital measurement tool in photonics, excelling in high-speed and high-resolution measurements of weak optical signals.

physics.optics↗

arXiv2023

High-quality amorphous Silicon Carbide for hybrid photonic integration at low temperature

Integrated photonic platforms have proliferated in recent years, each demonstrating its own unique strengths and shortcomings. However, given the processing incompatibilities of different platforms, a formidable challenge in the field of integrated photonics still remains for combining the strength of different optical materials in one hybrid integrated platform. Silicon carbide is a material of great interest because of its high refractive index, strong second and third-order non-linearities and broad transparecy window in the visible and near infrared. However, integrating SiC has been difficult, and current approaches rely on transfer bonding techniques, that are time consuming, expensive and lacking precision in layer thickness. Here, we demonstrate high index Amorphous Silicon Carbide (a-SiC) films deposited at 150$^{\circ}$C and verify the high performance of the platform by fabricating standard photonic waveguides and ring resonators. The intrinsic quality factors of single-mode ring resonators were in the range of $Q_{int} = (4.7-5.7)\times10^5$ corresponding to optical losses between 0.78-1.06 dB/cm. We then demonstrate the potential of this platform for future heterogeneous integration with ultralow loss thin SiN and LiNbO$_3$ platforms.

physics.optics↗

arXiv2021

Reconstructive Spectrometer using Photonic Crystal Cavity

Optical spectrometers have propelled scientific and technological advancements in a wide range of fields. While sophisticated systems with excellent performance metrics are serving well in controlled laboratory environments, many applications require systems that are portable, economical, and robust to optical misalignment. Here, we propose and demonstrate a spectrometer that uses a planar one-dimensional photonic crystal cavity as a dispersive element and a reconstructive computational algorithm to extract spectral information from spatial patterns. The simple fabrication and planar architecture of the photonic crystal cavity render our spectrometry platform economical and robust to optical misalignment. The reconstructive algorithm allows miniaturization and portability. The intensity transmitted by the photonic crystal cavity has a wavelength-dependent spatial profile. We generate the spatial transmittance function of the system using finite-difference time-domain method and also estimate the dispersion relation. The transmittance function serves as a transfer function in our reconstructive algorithm. We show accurate estimation of various kinds of input spectra. We also show that the spectral resolution of the system depends on the cavity linewidth that can be improved by increasing the number of periodic layers in distributed Bragg mirrors. Finally, we experimentally estimate the center wavelength and linewidth of the spectrum of an unknown light emitting diode. The estimated values are in good agreement with the values measured using a commercial spectrometer.

physics.optics↗

arXiv2020

Translationally Invariant Generation of Annular Beams using Thin Films

Thin film optical elements exhibiting translational invariance, and thus robustness to optical misalignment, are crucial for rapid development of compact and integrated optical devices. In this letter, we experimentally demonstrate a beam-shaping element that generates an annular beam by spatially filtering the fundamental Gaussian mode of a laser beam. The element comprises of a one-dimensional photonic crystal cavity fabricated using sputtered thin films. The planar architecture and in-plane symmetry of the element render our beam-shaping technique translationally invariant. The generated annular beam is sensitive to the polarization direction and the wavelength of the incident laser beam. Using this property of the annular beam, we show simultaneous generation of concentric annular beams of different wavelengths. Our experimental observations show an excellent agreement with simulation results performed using finite-difference time-domain method. Such a beam-shaping element has applications in areas ranging from microscopy and medicine to semiconductor lithography and manufacturing in microelectronics industry.

physics.optics↗

arXiv2019

Light emission from the layered metal 2H-TaSe$_2$ and its potential applications

Conventional metals, in general, do not exhibit strong photoluminescence. 2H-TaSe$_2$ is a layered transition metal dichalcogenide that possesses metallic property with charge density wave characteristics. Here we show that 2H-TaSe$_2$ exhibits a surprisingly strong optical absorption and photoluminescence resulting from inter-band transitions. We use this perfect combination of electrical and optical properties in several optoelectronic applications. We show a seven-fold enhancement in the photoluminescence intensity of otherwise weakly luminescent multi-layer MoS$_2$ through non-radiative resonant energy transfer from TaSe$_2$ transition dipoles. Using a combination of scanning photocurrent and time-resolved photoluminescence measurements, we also show that the hot electrons generated by light absorption in TaSe$_2$ have a rather long lifetime unlike conventional metals, making TaSe$_2$ an excellent hot electron injector. Finally, we show a vertical TaSe$_2$/MoS$_2$/graphene photodetector demonstrating a responsivity of $>10$ AW$^{-1}$ at $0.1$ MHz - one of the fastest reported photodetectors using MoS$_2$.

cond-mat.mes-hall↗

arXiv2019

Comment on "Conditional Decoupling of Quantum Information"

Berta et al [Phys. Rev. Lett., 121, 040504 (2018)] claim that their result provides a conceptually new extension of the decoupling approach to quantum information theory. We provide an alternate proof using the plain-vanilla decoupling approach for the achievable rates of their main result and hence, their claim is unwarranted, and the title can be misleading when taken in conjunction with the claim.

quant-ph↗

arXiv2015

More on a trace inequality in quantum information theory

It is known that for a completely positive and trace preserving (cptp) map ${\cal N}$, $\text{Tr}$ $\exp$$\{ \log \sigma$ $+$ ${\cal N}^\dagger [\log {\cal N}(\rho)$ $-\log {\cal N}(\sigma)] \}$ $\leqslant$ $\text{Tr}$ $\rho$ when $\rho$, $\sigma$, ${\cal N}(\rho)$, and ${\cal N}(\sigma)$ are strictly positive. We state and prove a relevant version of this inequality for the hitherto unaddressed case of these matrices being nonnegative. Our treatment also provides an alternate proof for the strictly positive case.

quant-ph↗

arXiv2015

Random coding exponents galore via decoupling

A missing piece in quantum information theory, with very few exceptions, has been to provide the random coding exponents for quantum information-processing protocols. We remedy the situation by providing these exponents for a variety of protocols including those at the top of the family tree of protocols. Our line of attack is to provide an exponential bound on the decoupling error for a restricted class of completely positive maps where a key term in the exponent is in terms of a R\'enyi \alpha-information-theoretic quantity for any \alpha $\in$ (1,2]. Among the protocols covered are fully quantum Slepian-Wolf, quantum state merging, quantum state redistribution, quantum/classical communication across channels with side information at the transmitter with or without entanglement assistance, and quantum communication across broadcast channels.

quant-ph↗

arXiv2014

A strong converse for the quantum state merging protocol

The Polyanskiy-Verdú paradigm provides an elegant way of using generalized-divergences to obtain strong converses and thus far has remained confined to protocols involving channels (classical or quantum). In this paper, drawing inspirations from it, we provide strong converses for protocols involving LOCC (local operations and classical communication). The key quantity that we work with is the Rényi relative entropy of entanglement. We provide a strong converse for the quantum state merging protocol that gives an exponential decay of the fidelity of the protocol for rates below the optimum with the number of copies of the state and are provided both for entanglement rate with LOCC as well as for classical communication with one-way LOCC. As an aside, the developments also yield short strong converses for the entanglement-concentration of pure states and the Schumacher compression.

quant-ph↗

arXiv2013

A gambling interpretation of some quantum information-theoretic quantities

It is known that repeated gambling over the outcomes of independent and identically distributed (i.i.d.) random variables gives rise to alternate operational meaning of entropies in the classical case in terms of the doubling rates. We give a quantum extension of this approach for gambling over the measurement outcomes of tensor product states. Under certain parameters of the gambling setup, one can give operational meaning of von Neumann entropies. We discuss two variants of gambling when a helper is available and it is shown that the difference in their doubling rates is the quantum discord. Lastly, a quantum extension of Kelly's gambling setup in the classical case gives a doubling rate that is upper bounded by the Holevo information.

quant-ph↗

arXiv2013

Non-asymptotic information theoretic bound for some multi-party scenarios

In the last few years, there has been a great interest in extending the information-theoretic scenario for the non-asymptotic or one-shot case, i.e., where the channel is used only once. We provide the one-shot rate region for the distributed source-coding (Slepian-Wolf) and the multiple-access channel. Our results are based on defining a novel one-shot typical set based on smooth entropies that yields the one-shot achievable rate regions while leveraging the results from the asymptotic analysis. Our results are asymptotically optimal, i.e., for the distributed source coding they yield the same rate region as the Slepian-Wolf in the limit of unlimited independent and identically distributed (i.i.d.) copies. Similarly for the multiple-access channel the asymptotic analysis of our approach yields the rate region which is equal to the rate region of the memoryless multiple-access channel in the limit of large number of channel uses.

cs.IT↗

arXiv2012

On the strong converses for the quantum channel capacity theorems

A unified approach to prove the converses for the quantum channel capacity theorems is presented. These converses include the strong converse theorems for classical or quantum information transfer with error exponents and novel explicit upper bounds on the fidelity measures reminiscent of the Wolfowitz strong converse for the classical channel capacity theorems. We provide a new proof for the error exponents for the classical information transfer. A long standing problem in quantum information theory has been to find out the strong converse for the channel capacity theorem when quantum information is sent across the channel. We give the quantum error exponent thereby giving a one-shot exponential upper bound on the fidelity. We then apply our results to show that the strong converse holds for the quantum information transfer across an erasure channel for maximally entangled channel inputs.

quant-ph↗

arXiv2011

On some special cases of the Entropy Photon-Number Inequality

We show that the Entropy Photon-Number Inequality (EPnI) holds where one of the input states is the vacuum state and for several candidates of the other input state that includes the cases when the state has the eigenvectors as the number states and either has only two non-zero eigenvalues or has arbitrary number of non-zero eigenvalues but is a high entropy state. We also discuss the conditions, which if satisfied, would lead to an extension of these results.

quant-ph↗