arXiv subjects

M. S. Tame

Publications and source records attributed to M. S. Tame.

At least 19 recordsLinked to original sources

arXiv2026

Experimental plasmonic sensing of malaria using an aluminum metasurface

A wide range of methods currently exist for testing the presence of malaria, each with its own advantages and disadvantages. New technologies are urgently needed to develop more effective diagnosis tools to fight and eradicate malaria. Optical biosensors that employ surface plasmon resonance (SPR) techniques are a promising category of devices for detecting malaria biomarkers. One such biomarker is plasmodium lactate dehydrogenase (pLDH), a protein produced during the life cycle of the malaria parasite, which is a metabolic enzyme found in all plasmodium species, including the most widespread falciparum. This work reports on the design, probing, and experimental performance of an optical biosensor for detecting pLDH based on SPR and extraordinary optical transmission. The biosensor is composed of an aluminum metasurface made from an array of nanoholes. The sensor operates in the visible spectral region and achieves label-free sensing of plasmodium falciparum LDH (pfLDH) spiked in phosphate-buffered saline. The sensor has a spectral sensitivity of 360 nm/RIU and an LOD of 1.3 nM, equivalent to 45.6 ng/mL of pfLDH. This type of optical biosensor may offer a cost-effective and high sensitivity method for active infection diagnosis.

physics.med-ph↗

arXiv2026

Weighted graph states as a resource for quantum metrology

Quantum metrology exploits quantum mechanical effects to increase the precision of measurements of physical quantities. A wide variety of applications are currently being developed for scientific and technological purposes, however, most research relies on the use of highly entangled resource states that are challenging to generate and control in a given physical system. Here, we study the use of weighted graph states as more accessible resources for quantum metrology, which yield a favorable precision beyond the classical limit, approaching the Heisenberg limit. We find a notable robustness to variation in weights and less challenging weight requirements compared to standard graph states, which require a maximal weight at all edges. Both of these aspects reduce the practical demands in a physical setup, with the latter implying significantly less entanglement is required to gain a quantum advantage in metrology. We study the quantum Fisher information and optimized estimator variance of two identified sub classes of weighted graph states for an arbitrary number of N qubits, providing analytical forms and investigating their scaling. Our work opens up opportunities for using weakly entangled states in quantum-enhanced metrology.

quant-ph↗

arXiv2026

An effective microscopic model for plasmonic sensing of malaria

Malaria remains a major health threat in low-resource regions and rapid diagnostic tests often lack the sensitivity required for early detection. To address this and help establish more sensitive testing devices, we develop a predictive microscopic model for plasmonic biosensing using metasurfaces. Specifically, we consider the detection of plasmodium lactate dehydrogenase (pLDH), a well-known malaria biomarker. An example metasurface is studied to showcase the effective microscopic model - it consists of a gold nanohole array (150nm film; 150nm diameter; 400nm period) and the biochemistry above it is modelled as stacks of closely packed adlayers. Using Maxwell Garnett effective medium theory we link the refractive index of the pLDH biomarker adsorbed layer on top of the metasurface to the bulk concentration of pLDH in the buffer. This effective microscopic model accounts for the combined optical properties of the biochemistry matrix, bound pLDH and the buffer medium. By simulating the sensor using the finite element method and an approximate analytical method, we show that the effective model allows one to determine the sensor response, predict binding interactions, and quantify concentration changes on the sensor surface. We then calculate the sensor sensitivity for our example metasurface and its theoretical limit of detection (LOD). The lowest LOD calculated based on the model is 0.02nM of pLDH, equivalent to 0.7ng/mL, which is a 30 times improvement over current rapid diagnostic tests. While this improvement in performance is highly promising, further work on transferring the ideal theory developed here to field-tested empirical performance will be required. The effective microscopic model we introduce is quite general and the framework developed offers a broadly applicable tool for the design and optimization of other types of highly sensitive plasmonic biosensors.

physics.optics↗

arXiv2025

Verification of single-photon path entanglement using a nitrogen vacancy center

Path entanglement is an essential resource for photonic quantum information processing, including in quantum computing, quantum communication and quantum sensing. In this work, we experimentally study the generation and verification of bipartite path-entangled states using single photons produced by a nitrogen-vacancy center within a nanodiamond. We perform a range of measurements to characterize the photons being generated and verify the presence of path entanglement. The experiment is performed using continuous-wave laser excitation and a novel state generation 'time-window' method. This approach to path entanglement verification is different to previous work as it does not make use of a pulsed laser excitation source.

quant-ph↗

arXiv2025

Quantum plasmonics model of refractive index sensing using photon correlations

The interaction between the electric dipole moments of a quantum emitter and a metal nanoparticle gives rise to unique optical properties, such as interference-induced photon correlations, that could be useful for enhanced intensity-based sensing. Using the quantum theory of photodetection, we propose a nanosensor system comprising a quantum emitter and a metal nanoparticle that explores the possibility of utilizing higher-order photon correlations for refractive index sensing. Both the refractive index sensitivity and resolution of the nanosensor, whose scattering spectrum lies within the visible region, are predicted. The sensor is supported by a substrate and driven weakly by a coherent field. By calculating the mean photocount and its second factorial moment resulting from the scattered field of the system, the sensing performance of the intensity and intensity-intensity correlation, are compared at optimal driving wavelengths. The mean photocount was found to be inherently low, inhibiting the role of interference-induced photon antibunching in minimizing the sensor's intensity shot noise. However, a regime in which the noise could be reduced below the shot noise limit is identified, leading to a quantum enhancement in the sensing performance.

quant-ph↗

arXiv2025

Tunable negative permeability in a quantum plasmonic metamaterial

We consider the integration of quantum emitters into a negative permeability metamaterial design in order to introduce tunability as well as nonlinear behavior. The unit cell of our metamaterial is a ring of metamolecules, each consisting of a metal nanoparticle and a two-level semiconductor quantum dot (QD). Without the QDs, the ring of the unit cell is known to act as an artificial optical magnetic resonator. By adding the QDs we show that a Fano interference profile is introduced into the magnetic field scattered from the ring. This induced interference is shown to cause an appreciable effect in the collective magnetic resonance of the unit cell. We find that the interference provides a means to tune the response of the negative permeability metamaterial. The exploitation of the QD's inherent nonlinearity is proposed to modulate the metamaterial's magnetic response with a separate control field.

quant-ph↗

arXiv2024

Electrostatic dipole polarizability and plasmon resonances of multilayer nanoshells

We propose a generalized formula for calculating the dipole polarizability of spherical multilayer nanoshells (MNSs) within the long-wavelength approximation (LWA). Given a MNS with a finite number of concentric layers, radii, and dielectric properties, embedded in a dielectric medium, in the presence of a uniform electric field, we show that its frequency-dependent and complex dipole polarizability can be expressed in terms of the dipole polarizability of the preceding MNS. This approach is different from previous more involved methods where the LWA polarizability of a MNS is usually derived from scattering coefficients. Using both finite-element method- and Mie theory-based simulations, we show that our proposed formula reproduces the usual LWA results, when it is used to predict absorption spectra, by comparing the results to simulated spectra obtained from MNSs with $n$ number of layers up to $n = 6$ layers. An iterative algorithm for calculating the dipole polarizability of a MNS based on the generalized formula is presented. A Fröhlich function whose zeroes correspond to the dipolar localized surface plasmon resonances (LSPRs) supported by the MNS is proposed. We identify a pairing behaviour by some LSPRs in the Fröhlich function that might also be useful for mode characterization.

physics.optics↗

arXiv2024

Robustness of the projected squeezed state protocol

Projected squeezed (PS) states are multipartite entangled states generated by unitary spin squeezing, followed by a collective quantum measurement and post-selection. They can lead to an appreciable decrease in the state preparation time of the maximally entangled N-qubit Greenberger-Horne-Zeilinger (GHZ) state when compared to deterministic preparation by unitary transformations in physical systems where spin squeezing can be realized, such as ion, neutral atom, and superconducting qubits. Here we simulate the generation of PS states in non-ideal experimental conditions with relevant decoherence channels. By employing the Kraus operator method, and quantum trajectory method to reduce the computational complexity, we assess the quantum Fisher information and overlap fidelity with an ideal GHZ state. Our findings highlight PS states as useful metrological resources, demonstrating a robustness against environmental effects with increasing qubit number N.

quant-ph↗

arXiv2024

Quantum random number generation using an on-chip nanowire plasmonic waveguide

Quantum random number generators employ the inherent randomness of quantum mechanics to generate truly unpredictable random numbers, which are essential in cryptographic applications. While a great variety of quantum random number generators have been realised using photonics, few exploit the high-field confinement offered by plasmonics, which enables device footprints an order of magnitude smaller in size. Here we integrate an on-chip nanowire plasmonic waveguide into an optical time-of-arrival based quantum random number generation setup. Despite loss, we achieve a random number generation rate of 14.4 Mbits/s using low light intensity, with the generated bits passing industry standard tests without post-processing. By increasing the light intensity, we were then able to increase the generation rate to 41.4 Mbits/s, with the resulting bits only requiring a shuffle to pass all tests. This is an order of magnitude increase in the generation rate and decrease in the device size compared to previous work. Our experiment demonstrates the successful integration of an on-chip nanoscale plasmonic component into a quantum random number generation setup. This may lead to new opportunities in compact and scalable quantum random number generation.

quant-ph↗

arXiv2022

Measurement of binding kinetics using quantum plasmonic resonance sensing applied to HIV-1

The work done in this paper is an extension of the work done by Mpofu et al in [1]. The motivation for this paper is to show the potential of quantum bio-sensing techniques in applications to complex viruses like the human immunodeficiency virus (HIV) and to show it's potential in binding reactions where the signal is small and can potentially be buried in noise. In this paper we show theoretically that using quantum states of light such as the Fock state improves the precision in the estimation of kinetic parameters measured from the sensorgrams produced by the Kretschmann conguration. Though the Fock state is not the only quantum state in this study we look only at the Fock state because it has been shown to be the state which offers the best enhancement [1]. We show here that the Fock state allows us to measure the parameters more accurately in comparison to the classical (Coherent) state of light. We consider in this paper a binding reaction involving HIV type 1 (HIV-1). Specifically we look at the binding reaction between a variant of HIV-1 protease and nelnavir which is an inhibitor. Such a study is also offers value for drug discovery research as it points to the development of new technologies which can be applied to testing the efficacy of new drugs. Quantum technologies can prove to be useful in the fight against the HIV pandemic and assist in the continual research towards the development of treatments and a cure.

quant-ph↗

arXiv2022

Measuring kinetic parameters using quantum plasmonic sensing

The measurement of parameters that describe kinetic processes is important in the study of molecular interactions. It enables a deeper understanding of the physical mechanisms underlying how different biological entities interact with each other, such as viruses with cells, vaccines with antibodies, or new drugs with specific diseases. In this work, we study theoretically the use of quantum sensing techniques for measuring the kinetic parameters of molecular interactions. The sensor we consider is a plasmonic resonance sensor -- a label-free photonic sensor that is one of the most widely used in research and industry. The first type of interaction we study is the antigen BSA interacting with antibody IgG1, which provides a large sensor response. The second type is the enzyme carbonic anhydrase interacting with the tumor growth inhibitor benzenesulfonamide, which produces a small sensor response. For both types of interaction we consider the use of two-mode Fock states, squeezed vacuum states and squeezed displaced states. We find that these quantum states offer an enhancement in the measurement precision of kinetic parameters when compared to that obtained with classical light. The results may help in the design of more precise quantum-based sensors for studying kinetics in the life sciences.

quant-ph↗

arXiv2022

Experimental measurement of kinetic parameters using quantum plasmonic sensing

Kinetic models are essential for describing how molecules interact in a variety of biochemical processes. The estimation of a model's kinetic parameters by experiment enables researchers to understand how pathogens, such as viruses, interact with other entities like antibodies and trial drugs. In this work, we report a simple proof-of-principle experiment that uses quantum sensing techniques to give a more precise estimation of kinetic parameters than is possible with a classical approach. The interaction we study is that of bovine serum albumin (BSA) binding to gold via an electrostatic mechanism. BSA is an important protein in biochemical research as it can be conjugated with other proteins and peptides to create sensors with a wide range of specificity. We use single photons generated via parametric down-conversion to probe the BSA-gold interaction in a plasmonic resonance sensor. We find that sub-shot-noise level fluctuations in the sensor signal allow us to achieve an improvement in the precision of up to 31.8% for the values of the kinetic parameters. This enhancement can in principle be further increased in the setup. Our work highlights the potential use of quantum states of light for sensing in biochemical research.

quant-ph↗

arXiv2020

Photon-added coherent states using the continuous-mode formalism

The addition of a photon into the same mode as a coherent state produces a nonclassical state that has interesting features, including quadrature squeezing and a sub-Poissonian photon-number distribution. The squeezed nature of photon-added coherent (PAC) states potentially offers an advantage in quantum sensing applications. Previous theoretical works have employed a single-mode treatment of PAC states. Here, we use a continuous-mode approach that allows us to model PAC state pulses. We study the properties of a single-photon and coherent state wavepacket superimposed with variable temporal and spectral overlap. We show that, even without perfect overlap, the state exhibits a sub-Poissonian number distribution, second-order quantum correlations and quadrature squeezing for a weak coherent state. We also include propagation loss in waveguides and study how the fidelity and other properties of PAC state pulses are affected.

quant-ph↗

arXiv2020

Experimental investigation of Markovian and non-Markovian channel addition

The study of memory effects in quantum channels helps in developing characterization methods for open quantum systems and strategies for quantum error correction. Two main sets of channels exist, corresponding to system dynamics with no memory (Markovian) and with memory (non-Markovian). Interestingly, these sets have a non-convex geometry, allowing one to form a channel with memory from the addition of memoryless channels and vice-versa. Here, we experimentally investigate this non-convexity in a photonic setup by subjecting a single qubit to a convex combination of Markovian and non-Markovian channels. We use both divisibility and distinguishability as criteria for the classification of memory effects, with associated measures. Our results highlight some practical considerations that may need to be taken into account when using memory criteria to study system dynamics given by the addition of Markovian and non-Markovian channels in experiments.

quant-ph↗

arXiv2018

Active control of a plasmonic metamaterial for quantum state engineering

We experimentally demonstrate the active control of a plasmonic metamaterial operating in the quantum regime. A two-dimensional metamaterial consisting of unit cells made from gold nanorods is investigated. Using an external laser we control the temperature of the metamaterial and carry out quantum process tomography on single-photon polarization-encoded qubits sent through, characterizing the metamaterial as a variable quantum channel. The overall polarization response can be tuned by up to 33% for particular nanorod dimensions. To explain the results, we develop a theoretical model and find that the experimental results match the predicted behavior well. This work goes beyond the use of simple passive quantum plasmonic systems and shows that external control of plasmonic elements enables a flexible device that can be used for quantum state engineering.

physics.app-ph↗

arXiv2018

Experimental demonstration of a measurement-based realisation of a quantum channel

We introduce and experimentally demonstrate a method for realising a quantum channel using the measurement-based model. Using a photonic setup and modifying the bases of single-qubit measurements on a four-qubit entangled cluster state, representative channels are realised for the case of a single qubit in the form of amplitude and phase damping channels. The experimental results match the theoretical model well, demonstrating the successful performance of the channels. We also show how other types of quantum channels can be realised using our approach. This work highlights the potential of the measurement-based model for realising quantum channels which may serve as building blocks for simulations of realistic open quantum systems.

quant-ph↗

arXiv2018

Probing decoherence in plasmonic waveguides in the quantum regime

We experimentally investigate the decoherence of single surface plasmon polaritons in metal stripe waveguides. In our study we use a Mach-Zehnder configuration previously considered for measuring decoherence in atomic, electronic and photonic systems. By placing waveguides of different length in one arm we are able to measure the amplitude damping time T_1 = 1.90 +/- 0.01 x 10^-14 s, pure phase damping time T_2^* = 11.19 +/- 4.89 x 10^-14 s and total phase damping time T_2 = 2.83 +/- 0.32 x 10^-14 s. We find that decoherence is mainly due to amplitude damping and thus loss arising from inelastic electron and photon scattering plays the most important role in the decoherence of plasmonic waveguides in the quantum regime. However, pure phase damping is not completely negligible. The results will be useful in the design of plasmonic waveguide systems for carrying out phase-sensitive quantum applications, such as quantum sensing. The probing techniques developed may also be applied to other plasmonic nanostructures, such as those used as nanoantennas, as unit cells in metamaterials and as nanotraps for cold atoms.

quant-ph↗

arXiv2017

Experimental verification of entanglement generated in a plasmonic system

A core process in many quantum tasks is the generation of entanglement. It is being actively studied in a variety of physical settings - from simple bipartite systems to complex multipartite systems. In this work we experimentally study the generation of bipartite entanglement in a nanophotonic system. Entanglement is generated via the quantum interference of two surface plasmon polaritons in a beamsplitter structure, i.e. utilising the Hong-Ou-Mandel (HOM) effect, and its presence is verified using quantum state tomography. The amount of entanglement is quantified by the concurrence and we find values of up to 0.77 +/- 0.04. Verifying entanglement in the output state from HOM interference is a nontrivial task and cannot be inferred from the visibility alone. The techniques we use to verify entanglement could be applied to other types of photonic system and therefore may be useful for the characterisation of a range of different nanophotonic quantum devices.

quant-ph↗