arXiv subjects

K. Muhammed Shafi

Publications and source records attributed to K. Muhammed Shafi.

11 recordsLinked to original sources

arXiv2024

Experimental realization of universal quantum gates and six-qubit entangled state using photonic quantum walk

For quantum computation using photons, performing deterministic quantum gate operations is a challenge due to the probabilistic nature of the photon-photon interaction. Encoding qubits in multiple degrees-of-freedom of photons and controlling operations between them is one of the promising ways to navigate the probabilistic behavior. Using single-photon discrete-time quantum walk in combination with polarization and path degrees-of-freedom, we experimentally demonstrate the realization of a universal set of quantum gates with high fidelity at room temperature. The deterministic realization of quantum gates through photonic quantum walk are characterized via quantum state tomography. For a three-qubit system using a single photon, the first qubit is encoded using polarization information, and the other two qubits are encoded using path information, closely resembling a Galton-board setup. To generate a six-qubit Greenberger-Horne-Zeilinger state, entangled photon pairs are used to entangle the two three-qubit modules on which gate operations are performed. We also provide insights into the mapping of photonic quantum walk operations to quantum circuits and propose methods to resourcefully scale. This demonstration marks a significant progress towards using quantum walks for quantum computing and provides a framework for using fewer photons in combination with different degrees-of-freedom of photon to scale the number of qubits.

quant-ph↗

arXiv2024

Quantum illumination using polarization-entangled photon pairs for enhanced object detection

Entangled light sources for illuminating objects offer advantages over conventional illumination methods by enhancing the detection sensitivity of reflecting objects. The core of the quantum advantage lies in effectively exploiting quantum correlations to isolate noise and detect objects with low reflectivity. This work experimentally demonstrates the benefits of using polarization-entangled photon pairs for quantum illumination and shows that the quantum correlation measure, using CHSH value and normalized CHSH value, is robust against losses, noise, and depolarization. We report the detection of objects with reflectivity ($\eta$) as low as 0.05 and an object submerged in noise with a signal-to-noise ratio of 0.003 using quantum correlation and residual quantum correlation measures, surpassing previous results. Additionally, we demonstrate that the normalized CHSH value aids in estimating the reflectivity of the detected object. Furthermore, we analyze the robustness of the correlation measure under photon attenuation in atmospheric conditions to show the practical feasibility of real-time applications.

quant-ph↗

arXiv2023

Multi-bit quantum random number generator from path-entangled single photons

Measurement outcomes on quantum systems exhibit inherent randomness and are fundamentally nondeterministic. This has enabled quantum physics to set new standards for the generation of true randomness with significant applications in the fields of cryptography, statistical simulations, and modeling of the nondeterministic behavior in various other fields. In this work, we present a scheme for the generation of multi-bit random numbers using path-entangled single photons. Without losing their intrinsic randomness, the protocol allows us to engineer the distribution from which we sample random numbers. For the experimental demonstration, we use single photons generated using spontaneous parametric down-conversion (SPDC), and assign a multi-bit commitment along the path. One-bit and two-bit random numbers are then generated from measuring entangled states in the path basis. In addition to passing the NIST tests for randomness, we also demonstrate the certification of quantumness and self-certification of quantum random number generator (QRNG) using Clauser, Horne, Shimony and Holt (CHSH) inequality violation. The path-entangled states can generate higher bitrates compared to heralded single photon or entangled photon schemes which are limited by the coincidence counts. The scheme involves distribution of photons along multiple paths resulting in multiple bits from one photon and avoids the limitation imposed by the detection dead time of one detector. We demonstrate this by generating a high rate of about 80 Mbps when the single photon detector saturates at around 28 Mcps.

quant-ph↗

arXiv2023

Quantum illumination using polarization-path entangled single photons for low reflectivity object detection in noisy background

Detecting object with low reflectivity embedded within a noisy background is a challenging task. Quantum correlations between pairs of quantum states of light, though are highly sensitive to background noise and losses, offer advantages over traditional illumination methods. Instead of using correlated photon pairs which are sensitive, we experimentally demonstrate the advantage of using heralded single-photons entangled in polarization and path degree of freedom for quantum illumination. In the study, the object of different reflectivity is placed along the path of the signal in a variable thermal background before taking the joint measurements and calculating the quantum correlations. We show the significant advantage of using non-interferometric measurements along the multiple paths for single photon to isolate the signal from the background noise and outperform in detecting and ranging the low reflectivity objects even when the signal-to-noise ratio is as low as 0.03. Decrease in visibility of polarization along the signal path also results in similar observations. This will have direct relevance to the development of single-photon based quantum LiDAR and quantum imaging.

quant-ph↗

arXiv2023

Bell-inequality in path-entangled single photon and purity of single photon state

Different degrees of freedom of single photons have been entangled and are used as a resource for various quantum technology applications. We present a simple scheme to perform Bell's test and show the violation of CHSH inequality in a path-entangled single photon state using interferometric and its equivalent non-interferometric approach in beam splitter setting. We demonstrate this experimentally by generating and controlling path-entangled state using both, heralded and un-heralded single photons from spontaneous parametric down-conversion. The experimental results we present show the transition to violation of CHSH inequality when the purity of single photons state visibility increase above 70\% , $\mathcal{P} > 0.7$. Our procedure using single beam splitter and two detector module for un-heralded single photon source allows a simple way to test for purity of any single photon source and to study quantum correlations on systems driven by dynamics where single particle entanglement with position space is prominent.

quant-ph↗

arXiv2022

Second-order correlations and purity of unheralded single photons from spontaneous parametric down-conversion

Various quantum technology applications require high-purity single photons with high generation rate. Although different methods are employed to generate such photons, heralded single photons from spontaneous parametric down-conversion (SPDC) is the most commonly used approach. Photon generation rate from the heralded single-photon sources are limited by the efficiency of the detectors to record coincidence detection of the photon pairs which are lower than the single-photon counts recorded separately on each detector. In this paper we present a revised expression to calculate second-order temporal correlation function, $g^{(2)}$ for any fixed time window (bin) and report the experimental characterization of purity of unheralded and heralded single photons from the SPDC process. With an appropriate choice of time bin for a given pump power, without heralding we show that higher rate of single photons with $g^{(2)}(0) = 0$ can be generated with very high probability.

quant-ph↗

arXiv2022

Bright and polarized fiber in-line single photon source based on plasmon-enhanced emission into nanofiber guided modes

We demonstrate a bright and polarized fiber in-line single photon source based on plasmon-enhanced emission of colloidal single quantum dots into an optical nanofiber. We show that emission properties of single quantum dots can be strongly enhanced in the presence of single gold nanorods leading to a bright and strongly polarized single photon emission. The single photons are efficiently coupled to guided modes of the nanofiber and eventually to a single mode optical fiber. The brightness (fiber-coupled photon count rate) of the single photon source is estimated to be 12.2(0.6) MHz, with high single photon purity (g2(0) = 0.20(0.04)) and degree of polarization as high as 94-97%. The present device can be integrated into fiber networks paving the way for potential applications in quantum networks.

quant-ph↗

arXiv2022

Integration of silicon-vacancy centers in nanodiamonds with an optical nanofiber

We experimentally demonstrate the integration of silicon-vacancy centers in nanodiamonds (SiV-NDs) with an optical nanofiber (ONF). We grow SiV-NDs on seed NDs dispersed on a quartz substrate using a microwave plasma-assisted chemical vapor deposition method. First, we search and characterize SiV-NDs on a quartz substrate using an inverted confocal microscope and an atomic force microscope (AFM). Subsequently, we pick up SiV-NDs from the quartz substrate and deposit them on the surface of a free-standing ONF using the AFM tip. The fluorescence emission spectrum, photon count rate, and intensity correlations for SiV-NDs are systematically measured.

quant-ph↗

arXiv2022

One-sided composite cavity on an optical nanofiber for cavity QED

We demonstrate a one-sided cavity on an optical nanofiber (ONF) using a composite method. The one-sided composite cavity is created by mounting an asymmetric defect mode grating on an ONF. We design the one-sided composite cavity on an ONF to enhance channeling efficiency into one side of ONF while operating from under- to critical- and over-coupling regimes using numerical simulations. Experimentally, we demonstrate coupling characteristics of the one-sided composite cavity, showing good correspondence with simulation results.

quant-ph↗

arXiv2020

Occurrence control of charged exciton for a single CdSe quantum dot at cryogenic temperatures on an optical nanofiber

We discuss photo-luminescence characteristics of CdSe core/shell quantum dots at cryogenic temperatures using a hybrid system of a single quantum dot and an optical nanofiber. The key point is to control the emission species of quantum dot to charged excitons, known as trions, which have superior characteristics to neutral excitons. We investigate the photocharging behavior for the quantum dots by varying the wavelength and intensity of irradiating laser light, and establish a method to create a permanently charged situation which lasts as long as the cryogenic temperature is maintained. The present photocharging method may open a new route to applying the CdSe quantum dots in quantum photonics, and the hybrid system of photocharged quantum-dot and optical nanofiber may readily be applicable to a fiber-in-line single-photon generator.

cond-mat.mes-hall↗

arXiv2020

Efficient fiber in-line single photon source based on colloidal single quantum dots on an optical nanofiber

We demonstrate a fiber in-line single photon source based on a hybrid system of colloidal single quantum dots deposited on an optical nanofiber and cooled down to cryogenic temperature (3.7 K). We show that a charged state (trion) of the single quantum dot exhibits a photo-stable emission of single photons with high quantum efficiency, narrow linewidth (3 meV FWHM) and fast decay time ($10.0\pm0.5$ ns). The single photons are efficiently coupled to the guided modes of the nanofiber and eventually to a single mode optical fiber. The brightness (efficiency) of the single photon source is estimated to be $16\pm2\%$ with a maximum photon count rate of $1.6\pm0.2$ MHz and a high single photon purity ($g^2(0)=0.11\pm0.02$). The device can be easily integrated to the fiber networks paving the way for potential applications in quantum networks.

physics.optics↗