arXiv subjects

Ayan Majumder

Publications and source records attributed to Ayan Majumder.

8 recordsLinked to original sources

arXiv2026

Towards Quantum Limited Spatial Resolution of NV-Diamond Magnetometry

Optically addressable ensembles of solid-state defects, such as nitrogen vacancy (NV) centers, are a leading modality for imaging-based magnetometry, thermometry and strain sensing. However, monitoring the fluorescence of individual defects within a sub-diffraction ensemble remains an outstanding challenge that currently limits access to atomic-scale features and dynamics. For compact clusters of NVs, we formulate imaging-based atomic sensing as a low-dimensional multiparameter estimation task in which one seeks to localize each defect and quantify the field strength in its immediate vicinity. In this work, we employ optical spatial mode demultiplexing (SPADE) to enhance localization and brightness estimation accuracy at sub-diffraction scales. Specifically, we develop a two-stage sensing protocol that augments direct imaging by projecting the incoming optical field onto point spread function (PSF)-adapted, i.e., PAD spatial modes and Yuen-Kennedy-Lax (YKL) spatial modes enabling efficient extraction of emitter positions and brightnesses. The YKL-SPADE measurement employed for brightness estimation is shown to be quantum-optimal in the case of two emitters and establishes a new connection between quantum detection and estimation theories. We numerically evaluate the statistical performance of our protocol for sub-diffraction optically detected magnetic resonance (ODMR) and Rabi sensing experiments. Compared to conventional focal plane intensity measurements, our protocol improves emitter localization accuracy by 6$\times$ and brightness estimation accuracy by 2$\times$ for tightly confined ensembles, residing well below the diffraction limit.

quant-ph↗

arXiv2026

Quantum Networks Using Color Defects in Diamond: Principles, Progress, and Perspectives

Large-scale quantum networks will enable entirely new applications of quantum information science in fields such as quantum communication, distributed quantum computing, sensing, and metrology. To build nodes of such networks, diamond color defects are one of the promising candidates. Their excellent optical properties, fast spin-qubit control, and long spin coherence times make them well-suited for quantum information processing and quantum memory applications. Additionally, recent advances in the heterogeneous integration of diamond nanophotonic structures with photonic integrated circuits have made these systems more efficient and well-suited for scalable quantum processor architectures. In this comprehensive review, we discuss the optical and spin properties of these systems, recent progress in the building blocks of quantum networks, and demonstrations of metropolitan-scale quantum networks, as well as the challenges associated with these systems at both the fundamental and experimental levels, along with potential solutions.

quant-ph↗

arXiv2026

Observation of Shear Strain in Ion-Implanted Diamond Substrate and Diamond Nanophotonic Structures

Negatively charged nitrogen-vacancy (NV) centers and other color centers in diamonds have emerged as promising platforms for quantum communication, quantum information processing, and nanoscale sensing, owing to their long spin coherence times, fast spin control, and efficient photon coupling. Deterministic placement of individual color centers into nanophotonic structures is critical for scalable device integration, and ion implantation is the most viable technique. Nanofabrication processes, including diamond etching, are essential to realize these structures but can introduce crystal strain through lattice damage. In this work, we investigate the impact of ion implantation and nanofabrication-induced strain on the electronic spin levels of NV-centers. We demonstrate that the zero-field continuous-wave optically detected magnetic resonance (CW-ODMR) spectroscopy serves as a sensitive probe of local crystal strain. We report the presence of a shear strain feature in diamond substrates arising from the ion-implantation and nanofabrication processes, as evidenced by the asymmetric splitting black observed in the zero-field CW-ODMR spectrum of NV-centers.

quant-ph↗

arXiv2023

Ultrafast Green Single Photon Emission from an InGaN Quantum Dot-in-a-GaN Nanowire at Room Temperature

In recent years, there has been a growing demand for room-temperature visible single-photon emission from InGaN nanowire-quantum-dots (NWQDs) due to its potential in developing quantum computing, sensing, and communication technologies. Despite various approaches explored for growing InGaN quantum dots on top of nanowires (NWs), achieving the emission of a single photon at room temperature with sensible efficiency remains a challenge. This challenge is primarily attributed to difficulties in accomplishing the radial confinement limit and the inherent giant built-in potential of the NWQD. In this report, we have employed a novel Plasma Assisted Molecular Beam Epitaxy (PAMBE) growth approach to reduce the diameter of the QD to the excitonic Bohr radius of InGaN, thereby achieving strong lateral confinement. Additionally, we have successfully suppressed the strong built-in potential by reducing the QD diameter. Toward the end of the report, we have demonstrated single-photon emission ($λ$ = 561 nm) at room-temperature from the NWQD and measured the second-order correlation function $g^{2}(0)$ as 0.11, which is notably low compared to other reported findings. Furthermore, the lifetime of carriers in the QD is determined to be 775 ps, inferring a high operational speed of the devices.

cond-mat.mes-hall↗

arXiv2023

Opto-thermoelectric trapping of Fluorescent Nanodiamonds on Plasmonic Nanostructures

Deterministic optical manipulation of fluorescent nanodiamonds (FNDs) in fluids has emerged as an experimental challenge in multimodal biological imaging. Designing and developing nano-optical trapping strategies to serve this purpose is an important task. In this letter, we show how chemically-prepared gold nanoparticles and silver nanowires can facilitate Opto-thermoelectric force to trap individual entities of FNDs using a long working distance lens, low power-density illumination (532 nm laser, 12 $μW/μm^2$). Our trapping configuration combines the thermoplasmonic fields generated by individual plasmonic nanoparticles and the opto-thermoelectric effect facilitated by the surfactant to realise a nano-optical trap down to a single FND 120 nm in diameter. We utilise the same trapping excitation source to capture the spectral signatures of single FNDs and track their position. By tracking the FND, we observe the differences in the dynamics of FND around different plasmonic structures. We envisage that our drop-casting platform can be extrapolated to perform targeted, low-power trapping, manipulation, and multimodal imaging of FNDs inside biological systems such as cells.

physics.optics↗

arXiv2020

Low cost passive pH sensor fabricated on scotch tape

We report the fabrication and characterization results of a simple and low-cost pH sensor fabricated using a graphite pencil to define a working electrode and silver paste to define a reference electrode on scotch tape. The sensor operation is based on potentiometric measurement and thereby insensitive to fabrication variations in shape of the electrode unlike amperometric and chemiresistive measurement techniques. The substrate of the disposable sensor is prepared by pasting scotch tape atop a piece of chart paper, and two types of sensors fabricated with 6B and 2B graphite pencils are tested with three solutions with different pH values. The sensor functions as a passive sensing tag without requiring any external power or stimulus, and the measured sensitivities of the pH sensors fabricated using 2B and 6B pencil carbon electrodes (PCEs) are $-4.54mV/pH$ and $-4.09mV/pH$ respectively.

physics.app-ph↗

arXiv2018

Experimental Demonstration of Non-Destructive Discrimination of Arbitrary Set of Orthogonal Quantum States Using 5-qubit IBM Quantum Computer on Cloud

A protocol for non-destructive descrimination of arbitrary set of orthogonal quantum states was proposed by V. S. Manu et al., using an algorithm based on quantum phase estimation. IBM Corporation has released a superconductivity based 5-qubit (5-qubit transmon bowtie chip 3 and IBM 5-qubit real processor) quantum computer named Quantum Experience and placed it on cloud. In this paper we take advantage of the online availability of those real quantum processors(ibmqx2 amd ibmqx4) and carry out the above protocol that has experimentally demonstrated earlier using NMR quantum processor. Here, we set up experiments for arbitrary one-qubit and two-qubit orthogonal quantum states. The experiment confirmed that the arbitrary orthogonal quantum states can be discriminate in a nondestructive manner with a high fidelity. We compare the outcomes of those experiments which are done by ibmqx2 and ibmqx4 processors. Here, we also show the state tomography for the single qubit experiments.

quant-ph↗

arXiv2017

Experimental Realization of Secure Multiparty Quantum Summation Using Five-Qubit IBM Quantum Computer on Cloud

A scheme for secure multiparty quantum summation was proposed by Run-hau Shi et al.,(SCIENTIFIC REPORTS, 6:19655, DOI:10.1038/srep19655). IBM Corporation has released a superconductivity based 5-qubit quantum computer named "Quantum Experience" and placed it on "cloud". In this paper we take advantage of the online availability of this real quantum processor(ibmqx2) and carry out the above protocol that has never been experimentally demonstrated earlier. Here, we set up experiments for secure quantum summation of one-qubit secret states . Besides, we propose a protocol for square and cubic summation and also simulate the proposed protocol for both cases. Experimental implementation of secure multiparty quantum summation protocol for two or more qubit secret state and the proposed protocol for square(and cubic) summation are not possible using the available 5-qubit quantum processor(ibmqx2). IBM has recently placed a 16-qubit quantum processor(ibmqx3) on the cloud but it is still not accessible for all users. We describe a simulation for two and three qubit secret state and proposed protocol for square(and cubic) summation using a simulator(Custom Topology) which is provided by IBM Corporation.

quant-ph↗