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Science and Technology Class 02

Previous Class Topic

  • Supercomputers and their role in material science simulations

Government of India’s National Quantum Mission

  • Announced in 2023 with a significant budget by the Department of Science and Technology
  • Focuses on Quantum Computing, Quantum Communication, Quantum Sensing, Metrology, and Quantum Materials
  • Timeline set from 2023 to 2031
  • Aims to develop powerful quantum technologies, align current research, and build capacities in quantum-related fields

Foundational Concepts of Quantum Mechanics

Limitations of Classical Physics

  • Classical physics (Newtonian Mechanics) effectively explains macroscale phenomena
  • At microscopic scales (atoms, molecules, subatomic particles), classical laws fail to predict experimental outcomes
  • A shift is required to understand behaviors at quantum scales, leading to the advent of quantum mechanics

Emergence of Modern Physics and the Nature of Light

  • Historically, light was debated to be a particle (Newton) or a wave (Huygens)
  • Ether theory was discarded after Maxwell’s electromagnetic theory explained light traveling without a medium
  • Experiments revealed the photoelectric effect, showing that light can behave as discrete packets of energy (photons) and supporting wave-particle duality

Photoelectric Effect & Wave-Particle Duality

  • Certain metals emit electrons when exposed to light of particular frequencies
  • Classical wave theory did not explain the immediate electron emission
  • Einstein proposed photons as quantized energy packets, earning him the 1921 Nobel Prize
  • Demonstrated that light can exhibit both wave and particle properties
  • Introduced energy quantization: E ∝ frequency with no continuous intermediate values

Uncertainty Principle & Quantum Collapse

  • Heisenberg’s Uncertainty Principle: Position and momentum of a particle cannot be measured precisely at the same time
  • This limitation stems from fundamental quantum behavior rather than instrument deficiency
  • Observing one property inevitably disturbs the other
  • Quantum Collapse: Upon measurement, a quantum system in superposition collapses into a single outcome
  • This remains a central mystery in quantum mechanics with ongoing philosophical debates on whether observation shapes reality

Superposition & Entanglement

  • Superposition: A system can exist in multiple states simultaneously until measured
    • Electrons, photons, and other particles exhibit this phenomenon
    • Double-slit experiments confirm wave-like interference patterns
  • Entanglement: Two or more particles become correlated such that a change in one immediately affects the other
    • Einstein described it as “spooky action at a distance”
    • Experiments verified these correlations do not violate relativity since no information travels faster than light
    • It is central to quantum computing, enabling powerful parallel processing

Quantum Computing

Qubits vs. Classical Bits

  • Classical computers use bits in a binary system (0 or 1)
  • Qubits exploit quantum phenomena: they can be 0, 1, or a superposition of both
  • This property allows for simultaneous exploration of multiple computational paths
  • Implemented using superconductors, electron spin states, and other quantum phenomena

Key Challenges in Quantum Computing

Decoherence & Error Correction

  • Decoherence: Loss of quantum information due to interaction with the environment
  • Qubits are extremely sensitive; stray radiation, temperature fluctuations, or cosmic particles can disrupt them
  • Maintaining qubits near absolute zero prevents unwanted interactions but is expensive and technically complex
  • Current coherent times can be under 10 seconds, limiting practical calculations
  • Error correction strategies involve additional qubits to detect and correct errors, increasing system complexity

Scalability & Cost

  • Practical applications require large-scale quantum computers (hundreds of thousands to millions of qubits)
  • Increasing the number of qubits amplifies decoherence risks and infrastructure demands
  • Facilities must combine specialized chip design, extreme cooling, and advanced error-correction technologies
  • The high cost is driven by cryogenic cooling, specialized hardware, and the need for expertise in quantum physics

Need for New Algorithms and Skills

  • Traditional algorithms built on logical operations with bits do not directly translate to qubit operations
  • Quantum algorithms require deep physics knowledge to harness superposition and entanglement
  • New programming languages, operating systems, and developer skills must incorporate quantum principles

Cryptography & Shor’s Algorithm

  • Modern encryption relies on mathematical problems that are easy to perform but hard to reverse, such as factoring large numbers
  • Shor’s Algorithm (1997): Theoretically demonstrates how a quantum computer can factor large integers exponentially faster
  • This ability threatens widely used encryption schemes, prompting global competition in quantum computing
  • Leads to heightened strategic interest due to potential risks to banking, government, and private data
  • Post-Quantum Cryptography seeks new encryption schemes that are resistant to quantum attacks

Applications in Molecular Simulations

  • Quantum chemistry often requires simulating atomic and molecular interactions governed by quantum laws
  • Classical supercomputers face exponential complexity as the number of particles increases
  • Quantum computers can potentially handle these simulations more efficiently
  • Benefits include advancements in drug discovery, new medicine design, improved fertilizers and pesticides, and the development of novel materials like superconductors

Superconductors & the Meissner Effect

  • Superconductivity: Zero electrical resistance and expulsion of magnetic fields below a material’s critical temperature
  • Explained by quantum mechanics as electrons move without energy loss
  • Meissner Effect: Superconductors repel external magnetic fields, enabling magnetic levitation and frictionless transport (e.g., Maglev trains)
  • Uses include MRI machines, particle accelerators, and other high-field applications
  • Major research challenge: Most superconductors require extremely low temperatures (near -270°C), spurring research into room-temperature superconductors

Additional Developments in Quantum Hardware

Willow Chip

  • Developed by Google to enhance quantum error correction capabilities exponentially
  • Aims to make quantum computations more reliable by quickly detecting and correcting errors
  • Part of ongoing efforts to reduce decoherence and stabilize qubits

Topological Superconducting Qubit with Majorana Zero Modes

  • Majorana particles are theorized to be their own antiparticles
  • A topological state may protect qubit information from environmental disturbances
  • Microsoft’s recent claim of detecting Majorana zero modes suggests a new method to combat decoherence
  • However, subsequent research has questioned the validity of these findings
  • This reflects the rapid pace and occasional controversy in quantum hardware development

Quantum Communication

Quantum Key Distribution (QKD)

  • Uses quantum properties such as superposition and entanglement to securely exchange encryption keys
  • Qubits exchanged over fiber or satellite networks serve as the key material
  • Any interception by an eavesdropper disturbs the system, alerting the communicators
  • QKD remains robust against both classical and advanced quantum attacks under ideal conditions
  • Current limitations include photon loss over long distances and atmospheric interference
  • Ongoing research aims to extend QKD networks from a few hundred kilometers to thousands

Quantum Teleportation

  • Involves transferring the quantum state of a particle from one location to another without physical movement
  • Requires entangled qubits between sender and receiver, along with classical communication
  • Does not allow faster-than-light information transfer; complies with relativistic constraints
  • Promotes the development of highly secure communication protocols and distributed quantum computing architectures

Quantum Sensing & Metrology

Importance of Precision Measurement

  • Measurement is fundamental to scientific validation and technological applications
  • Quantum sensors can detect minute changes in magnetic, electric, or gravitational fields
  • Enhanced sensitivity is achieved through the use of entanglement and superposition

Atomic Clocks

  • Rely on electron oscillations in atoms such as cesium or rubidium
  • Provide highly stable time standards crucial for GPS accuracy, astronomical observations, and global synchronization

High-Precision Detection

  • Quantum Magnetometers measure very small magnetic fields, benefiting healthcare (e.g., MRI) and geological prospecting
  • Gravitational Field Sensors hold potential for more accurate earthquake predictions and underground resource mapping
  • Quantum-based sensors represent some of the most mature quantum technologies with practical applications

Topic to be Discussed in the Next Class

  • Artificial Intelligence