Quantum Communication Underwater using hBN Single Photon Emitters Challenges in Underwater Communication Acoustic waves: work over long distances but low data rates, insecure, omni-directional Electromagnetic waves (Radio, Infrared) cannot propagate underwater Optical wavelengths mostly absorbed → communication limited to few meters Current Optical Communication Issues Blue/green light (~417 nm) reduces absorption Attenuated lasers used for underwater communication Probabilistic photon generation → not ideal for high-security applications Need for reliable, on-demand quantum light sources Hexagonal Boron Nitride (hBN) Single Photon Emitters B-centres in hBN emit at 436 nm Engineered using electron beam Photostable and reliable Emission near water absorption minimum Suitable for underwater quantum communication T...

Quantum Key Distribution (QKD): An Intuitive Explanation This explanation rebuilds the ideas behind Quantum Key Distribution (QKD) from the ground up, focusing on intuition first and math second. Big Picture Quantum Key Distribution is a way for two parties (Alice and Bob) to: Create a shared random secret key Detect if anyone (Eve) tried to eavesdrop The core idea: measuring a quantum system changes it . Everything else in QKD follows from this rule. 1. What Are Quantum “States”? A photon can be polarized in different directions: Horizontal (↔) Vertical (↕) Diagonal (↗) Other diagonal (↘) We label these using symbols: |0⟩ = horizontal |1⟩ = vertical These form one basis (a way of asking questions). ...

Quantum Computing Fundamentals Understanding qubits, basis, Hadamard transform, and quantum probability 1. Qubit (quantum bit) A qubit is a unit vector in a 2-dimensional complex Hilbert space: \[ |\psi\rangle = \alpha |0\rangle + \beta |1\rangle \] where \[ \alpha, \beta \in \mathbb{C}, \quad |\alpha|^2 + |\beta|^2 = 1 \] \(|0\rangle, |1\rangle\) are basis states \(|\alpha|^2\) = probability of measuring 0 \(|\beta|^2\) = probability of measuring 1 2. Basis (measurement basis) A basis is a set of orthonormal vectors used to describe or measure a qubit. (a) Computational (Z) basis \[ |0\rangle = \begin{pmatrix} 1 \\ 0 \end{pmatrix...

Quantum vs Classical Communication The difference between having only 10–12 qubits in quantum computers and kbps–Gbps speeds in conventional communication can be confusing. This difference exists because quantum and classical systems work in fundamentally different ways. 1. Qubits and Quantum Superposition Qubits are the basic units of quantum computing. Unlike classical bits (which are either 0 or 1), a qubit can exist in a superposition of both 0 and 1 at the same time. This means that even a small number of qubits can represent a very large number of possible states. The computing power grows exponentially as more qubits are added. Qubit (quantum bit) A qubit is a unit vector in a 2-dimensional complex Hilbert space: \[ |\psi\rangle = \alpha |0\rangle + \beta |1\rangle \] where ...