arXiv subjects

Bohnishikha Ghosh

Publications and source records attributed to Bohnishikha Ghosh.

6 recordsLinked to original sources

arXiv2026

Robust One-Sided Device-Independent Quantum Key Distribution via High-Dimensional Steering

Quantum key distribution (QKD) brings the promise of communication with information-theoretic security but is limited in practice due to its susceptibility to noise, losses, and device imperfections. To address these challenges, we propose a robust high-dimensional (HD) one-sided device-independent QKD (1sDI-QKD) protocol and present a proof-of-principle experimental implementation using photons entangled in the transverse-spatial degree-of-freedom. We develop a systematic security analysis of HD 1sDI-QKD protocols, leveraging quantum steering to certify security, and evaluate achievable secret key rates for different measurement configurations and system dimensions using reverse reconciliation. Our analysis shows that increasing the dimension enhances robustness against both noise and loss. We then demonstrate the key experimental building blocks required for implementing the protocol: (a) a high-quality source of high-dimensional photonic entanglement, and (b) a fully programmable, high-dimensional multi-outcome measurement device operating in up to dimension 11. Using these components, we obtain positive key rates for all investigated dimensions under the fair-sampling assumption, with the highest key rates achieved for dimension d=7. Finally, we discuss the steps required for a practical, loophole-free implementation of 1sDI-QKD in realistic regimes of loss and noise.

quant-ph↗

arXiv2025

Quantum Information Processing with Spatially Structured Light

Qudits have proven to be a powerful resource for quantum information processing, offering enhanced channel capacities, improved robustness to noise, and highly efficient implementations of quantum algorithms. The encoding of photonic qudits in transverse-spatial degrees of freedom has emerged as a versatile tool for quantum information processing, allowing access to a vast information capacity within a single photon. In this review, we examine recent advances in quantum optical circuits with spatially structured light, focusing particularly on top-down approaches that employ complex mode-mixing transformations in free-space and fibers. In this context, we highlight circuits based on platforms such as multi-plane light conversion, complex scattering media, multimode and multi-core fibers. We discuss their applications for the manipulation and measurement of multi-dimensional and multi-mode quantum states. Furthermore, we discuss how these circuits have been employed to perform multi-party operations and multi-outcome measurements, thereby opening new avenues for scalable photonic quantum information processing.

quant-ph↗

arXiv2024

Canonical and Poynting currents in propagation and diffraction of structured light: tutorial

Local propagation and energy flux in structured optical fields is often associated with the Poynting vector. However, the local phase gradient (i.e., local wavevector) in monochromatic fields in free space is described by another fundamental quantity: the canonical momentum density. The distributions of the Poynting and canonical momentum densities can differ significantly from each other in structured fields. We examine the role of these quantities in the propagation and diffraction of structured optical fields, exemplified by various circularly-polarized vortex beams carrying orbital angular momentum. We describe the canonical and Poynting momentum distributions in such beams, experimentally measure the local transverse momentum density by Shack-Hartmann wavefront sensor, and investigate fine features of the diffraction of various vortex beams on a knife-edge aperture. In all cases, the measured local momentum density and local beam evolution are consistent with the canonical momentum distribution rather than the Poynting vector. Furthermore, we introduce the local angular velocity in vortex beams and determine the universal integral $π$ angle of azimuthal rotation in an arbitrary (yet circularly-symmetric) propagating and diffracting vortex beam. Finally, we discuss the "supermomentum" and "backflow" effects; both of these phenomena are examples of superoscillations and are related to the properties of the canonical momentum. Our results reveal the profound role of the canonical momentum in the evolution of light and demonstrate the importance of distinguishing between it and the Poynting vector in structured light.

physics.optics↗

arXiv2023

Azimuthal backflow in light carrying orbital angular momentum

M.V. Berry's work [J. Phys. A: Math. Theor. 43, 415302 (2010)] highlighted the correspondence between backflow in quantum mechanics and superoscillations in waves. Superoscillations refer to situations where the local oscillation of a superposition is faster than its fastest Fourier component. This concept has been used to demonstrate backflow in transverse linear momentum for optical waves. In this work, we examine the interference of classical light carrying only negative orbital angular momentum and observe in the dark fringes of such an interference, positive local orbital angular momentum. This finding may have implications for the studies of light-matter interaction and represents a step towards observing quantum backflow in two dimensions.

physics.optics↗

arXiv2022

Demonstrating backflow in classical two beams' interference

The well-known interference pattern of bright and dark fringes was first observed for light beams back in 1801 by Thomas Young. The maximum visibility fringes occur when the irradiance of the two beams is equal, and as the ratio of the beam intensities deviates from unity, fringe visibility decreases. An interesting outcome that might not be entirely intuitive, however, is that the wavefront of such unequal amplitude beams' superposition will exhibit a wavy behavior. In this work, we experimentally observe the backflow phenomenon within this wavy wavefront. Backflow appears in both optics (retro-propagating light) and in quantum mechanics where a local phase gradient is not present within the spectrum of the system. It has become an interesting subject for applications as it is closely related to superoscillations whose features are used in super resolution imaging and in a particle's path manipulations. The first successful attempt to observe backflow was made only recently in an assembly of optical fields, by synthesizing their wavefront in a complex manner. Yet, backflow is perceived as hard to detect. Here, by utilizing interference in its most basic form, we reveal that backflow in optical fields is robust and surprisingly common, more than it was previously thought to be.

physics.optics↗

arXiv2019

Advantage in two-way communication using non-classical states of light

The advantage of using a single-photon two-mode entangled state in two-way communication via maximal violation of an inequality associated with the `Guess Your Neighbour's Input' (GYNI) game has been theoretically [Phys. Rev. Lett. 120, 060503 (2018)] as well as experimentally [CLEO FID.4 (OSA, 2018)] established quite recently. We show that such an advantage can also be obtained using any single-mode pure non-classical state embedded in a two-mode pure entangled state, wherein the other mode is the vacuum (henceforth referred to as a generalized NOON state), regardless of the average photon number of the single mode state. For the special cases of the even-coherent, odd-coherent, and squeezed vacuum NOON states, we establish that the advantage is also maximal. We show that the usage of the even-coherent NOON states can provide an advantage under noisy apparatuses (beam splitters and photo detectors). As an aside, we study how some of these states fare in terms of violation of a reference-frame independent Bell-type inequality.

quant-ph↗