Science & Technology Module

Quantum Computing & Quantum Technologies

Quantum computing leverages quantum mechanical principles—specifically superposition, entanglement, and quantum tunneling—to process information exponentially faster than classical binary computers for specific algorithmic tasks. While classical computers rely on binary bits (0 or 1), quantum processors utilize quantum bits (qubits), which can exist in linear combinations of states ( $|0\\\\rangle$ and $|1\\\\rangle$ ). Major physical implementations include superconducting transmon qubits, trapped-ion systems, and photonic circuits. In April 2023, India's Union Cabinet approved the National Quantum Mission (NQM) with a budgetary outlay of over ₹6,000 crore, aimed at developing intermediate-scale quantum computers with 50 to 1,000 physical qubits, secure quantum key distribution (QKD), and quantum sensors.

Practice Topic MCQs All Category Topics

Key Concepts & Examination Highlights

India approved the National Quantum Mission (NQM) in April 2023 to advance quantum computing, communications, and sensing technologies.
Quantum superposition enables a qubit to exist simultaneously in states $|0\rangle$ , $|1\rangle$ , or linear combinations thereof until measured.
Quantum Key Distribution (QKD) utilizes quantum mechanics to encrypt communications such that any eavesdropping immediately perturbs the transmission.
Quantum entanglement is a physical phenomenon where pairs of qubits interact in ways such that the quantum state of each particle cannot be described independently of the state of the others, regardless of distance.
Shor's algorithm, formulated by Peter Shor in 1994, is a quantum algorithm capable of finding prime factors of large integers in polynomial time, posing a cryptographic threat to classical RSA encryption.
Grover's algorithm provides a quadratic speedup for searching unsorted databases, reducing computational complexity from $O(N)$ to $O(\sqrt{N})$ .
Quantum supremacy (or quantum advantage) refers to the milestone where a programmable quantum device solves a computational problem that is infeasible for the world's most powerful classical supercomputers.
Major physical modalities for building qubits include superconducting circuits (transmons), trapped ions, optical photons, topological qubits, and silicon spin qubits.
The BB84 protocol, developed by Charles Bennett and Gilles Brassard in 1984, was the first proposed quantum key distribution scheme based on the no-cloning theorem.
Quantum decoherence occurs when a quantum system interacts with its external environment, causing the loss of quantum phase information and introducing computational errors.
The National Quantum Mission in India is implemented by the Department of Science and Technology (DST) with four thematic hubs (T-Hubs) focusing on quantum computation, communication, sensing, and materials.
Qubits (quantum bits) exploit the quantum principles of superposition and entanglement to represent and process states between $|0\rangle$ and $|1\rangle$ simultaneously.
Quantum superposition allows a qubit state to be expressed as a linear combination $|\psi\rangle = \alpha|0\rangle + \beta|1\rangle$ , where $|\alpha|^2 + |\beta|^2 = 1$ .
Quantum entanglement describes a non-local correlation between qubits such that the quantum state of one instantaneously determines the state of another, irrespective of physical distance.
Shor's algorithm, formulated by Peter Shor in 1994, is a quantum algorithm that factors large integers in polynomial time, posing a cryptographic challenge to classical RSA encryption.
Grover's algorithm, developed by Lov Grover in 1996, provides a quadratic speedup for searching unsorted databases of $N$ entries in $O(\sqrt{N})$ time.
Quantum key distribution (QKD), notably the BB84 protocol developed by Charles Bennett and Gilles Brassard, uses single-photon polarization to exchange provably secure cryptographic keys.
Quantum supremacy (quantum advantage) refers to a quantum computer solving a mathematically defined problem that is infeasible for the world's most powerful classical supercomputers.
Superconducting transmon qubits, used by IBM and Google, operate at cryogenic temperatures near absolute zero (approximately 15 millikelvin) inside dilution refrigerators.
Trapped-ion quantum computers, developed by companies like IonQ and Quantinuum, trap ionized atoms using electromagnetic fields and manipulate qubit states with precision lasers.
Topological quantum computing aims to protect quantum information natively against decoherence by braiding non-Abelian anyons in exotic two-dimensional semiconductor-superconductor systems.
Quantum decoherence is the loss of quantum coherence caused by environmental thermal and electromagnetic noise, posing the primary challenge to scalable fault-tolerant quantum computing.
Quantum error correction (QEC) spreads quantum information across multiple physical qubits using surface codes to detect and correct bit-flip and phase-flip errors without measuring the state.
India launched the National Quantum Mission (NQM) in 2023 with a budget of Rs 6,003 crore to develop intermediate-scale quantum computers with 50-1000 physical qubits over eight years.
Post-quantum cryptography (PQC) involves classical cryptographic algorithms (such as lattice-based cryptography) standardized by NIST to resist attacks from future fault-tolerant quantum computers.
A bloch sphere is a geometrical representation of the pure state space of a two-level quantum mechanical system (qubit).
The no-cloning theorem, proven by Wootters, Zurek, and Dieks in 1982, states that it is impossible to create an identical copy of an arbitrary unknown quantum state.
The quantum teleportation protocol transfers an unknown quantum state from a sender to a receiver across classical channels using shared entanglement and Bell state measurement.
Quantum volume is a single-number metric developed by IBM to measure the computational power, gate fidelity, and error mitigation of a quantum processor.
A Hadamard gate ( $H$ ) transforms the standard computational basis states $|0\rangle$ and $|1\rangle$ into equal superpositions $\frac{|0\rangle + |1\rangle}{\sqrt{2}}$ and $\frac{|0\rangle - |1\rangle}{\sqrt{2}}$ .
The CNOT (Controlled-NOT) gate is a fundamental two-qubit entangling gate that flips the state of the target qubit if and only if the control qubit is in state $|1\rangle$ .
The four Bell states ( $|\Phi^+\rangle, |\Phi^-\rangle, |\Psi^+\rangle, |\Psi^-\rangle$ ) are maximally entangled two-qubit quantum states forming an orthonormal basis.
Variational Quantum Eigensolvers (VQE) are hybrid quantum-classical algorithms designed to calculate molecular ground-state energies and solve quantum chemistry problems on NISQ devices.
Noisy Intermediate-Scale Quantum (NISQ) era describes current quantum processors containing 50 to a few thousand non-fault-tolerant qubits subject to environmental noise.
The Quantum Approximate Optimization Algorithm (QAOA) is a hybrid quantum-classical algorithm developed by Edward Farhi et al. to solve combinatorial optimization problems.
Quantum annealing, implemented commercially by D-Wave systems, uses quantum fluctuations to find the global minimum of complex objective optimization functions.
Surface codes are the leading topological quantum error-correcting codes requiring nearest-neighbor 2D qubit connectivity with a fault-tolerance threshold around 1%.
The Deutsch-Jozsa algorithm, formulated in 1992, was among the first quantum algorithms demonstrating an exponential separation in query complexity over classical deterministic algorithms.
The Simon algorithm provides an exponential quantum speedup for finding hidden periodicities in boolean functions, serving as the direct inspiration for Shor's factoring algorithm.
Quantum sensing exploits quantum entanglement and squeezed light states to achieve measurement sensitivities surpassing the standard quantum limit (Heisenberg limit).
Nitrogen-vacancy (NV) centers in synthetic diamonds function as atomic-scale quantum sensors capable of measuring magnetic fields, electric fields, and temperatures at nanometer resolution.
Quantum Key Distribution via satellite was demonstrated by China's Micius (Mozi) quantum satellite in 2017, establishing intercontinental entangled QKD links over 1,200 km.
Post-quantum cryptographic algorithms standardized by NIST in 2024 include ML-KEM (Kyber) for key encapsulation and ML-DSA (Dilithium) and SLH-DSA (SPHINCS+) for digital signatures.
Quantum Zeno effect is a phenomenon where frequent, continuous quantum measurements inhibit the natural time evolution of a quantum state, effectively 'freezing' it.
Quantum random number generators (QRNGs) generate truly unpredictable random numbers derived from the fundamental indeterminism of quantum measurement events.
Rabi oscillations are the periodic oscillations of atomic or qubit populations between two quantum energy levels under the influence of an oscillating electromagnetic driving field.
T1 relaxation time (longitudinal relaxation) measures the time it takes for a qubit to lose energy to its environment and decay from $|1\rangle$ to ground state $|0\rangle$ .
T2 dephasing time (transverse relaxation) measures the coherence time over which a qubit maintains its quantum phase relationship before phase errors destroy superposition.
Photonic quantum computing uses single photons as qubits, manipulating states with linear optical elements (beam splitters, phase shifters) and waveguide circuits at room temperature.
Silicon spin qubits confine individual electron or hole spins inside semiconductor quantum dots, leveraging existing commercial semiconductor manufacturing fabrication lines.

Curriculum & Reference Sources: Department of Science and Technology (DST), National Quantum Mission Guidelines, IEEE Quantum

Sample Solved Questions & Concept Explanations

8 Verified Concept Questions

Q1.EASY

What fundamental unit of quantum information is used in quantum computing instead of a classical binary bit?

Q2.MEDIUM

Which quantum physics principle asserts that two entangled particles remain interconnected such that measuring one instantly determines the state of the other regardless of distance?

Q3.MEDIUM

What is 'Quantum Supremacy' (Quantum Advantage) in computational science?

Q4.MEDIUM

What is 'Shor's Algorithm' in quantum computing, formulated by Peter Shor in 1994?

Q5.MEDIUM

What is 'Grover's Algorithm' in quantum computing, formulated by Lov Grover in 1996?

Q6.MEDIUM

What is 'Quantum Teleportation' in quantum information science?

Q7.HARD

In quantum error correction, what is the 'Surface Code' lattice architecture designed to achieve?

Q8.HARD

What is the 'No-Cloning Theorem' in quantum mechanics, proved by Wootters, Zurek, and Dieks in 1982?